0.0833 mole of carbohydrate of empirical formula ${\rm{C}}{{\rm{H}}_2}{\rm{O}}$ contain 1 g of hydrogen. The molecular formula of the carbohydrate is

${{\rm{C}}_6}{{\rm{H}}_{12}}{{\rm{O}}_6}$

${{\rm{C}}_5}{{\rm{H}}_{10}}{{\rm{O}}_5}$

${{\rm{C}}_3}{{\rm{H}}_4}{{\rm{O}}_3}$

${{\rm{C}}_{12}}{{\rm{H}}_{22}}{{\rm{O}}_{11}}$

The formula weight of ${\rm{A}}{{\rm{l}}_2}{\left( {{\rm{S}}{{\rm{O}}_4}} \right)_3}$ is 342. A solution containing 342 g of ${\rm{A}}{{\rm{l}}_2}{\left( {{\rm{S}}{{\rm{O}}_4}} \right)_3}$ in :

One litre of solution is 2 molar

SOME BASIC CONCEPTS OF CHEMISTRY MCQs for NEET UG CHEMISTRY — Easy

1 Easy

1 of 114Question permalink

Understanding +4 | -1

While titrating dilute

HCl

solution with aqueous NaOH, which of the following will not be required?

View answer and explanation

Correct option: C

Bunsen burner and measuring cylinder

Option C is correct because a Bunsen burner and measuring cylinder are not typically required for a simple acid-base titration.

Solution approach

Correct Answer + Core Reason: Bunsen burner and measuring cylinder. These are not needed for a simple acid-base titration.

Step-by-Step Solution:

Step 1: Identify the necessary equipment for acid-base titration.

Step 2: Pipette is used to transfer a known volume of the acid or base.

Step 3: Burette is used to deliver a known volume of the titrant.

Step 4: Porcelain tile is used to observe the color change at the endpoint.

Step 5: Clamp is used to hold the burette.

Step 6: Phenolphthalein is used as an indicator.

Step 7: Bunsen burner and measuring cylinder are not required for this titration.

Step 8: Final Answer: Bunsen burner and measuring cylinder.

Why other options are wrong:
- Option A: Pipette and distilled water are essential for preparing and diluting solutions.
- Option B: Burette and porcelain tile are essential for performing the titration and observing the endpoint.
- Option D: Clamp and phenolphthalein are essential for holding the burette and indicating the endpoint.

Key Concepts:
- Acid-base titration
- Titration equipment

Memory Aids:
- Remember the purpose of each piece of equipment in a titration.

Quick Tips:
- Understand the procedure for acid-base titration.

2 Easy

2 of 114Question permalink

Application +4 | -1

Which has the maximum number of molecules among the following

View answer and explanation

Correct option: C

8\,g\,\,{H_2}

Option C (

8\,g\,\,{H_2}

) is correct because it has the highest number of moles, and therefore the largest number of molecules.

Solution approach

Correct Answer + Core Reason: $8\,g\,\,{H_2}$ . This contains the maximum number of molecules because it has the highest number of moles.

Step-by-Step Solution:

Step 1: Calculate the number of moles for each option using the formula: moles = mass / molar mass.
- A: $44g\,\,C{O_2}$ : Molar mass of $CO_2$ = 44 g/mol. Moles = 44/44 = 1 mol
- B: $48g\,\,{O_3}$ : Molar mass of $O_3$ = 48 g/mol. Moles = 48/48 = 1 mol
- C: $8\,g\,\,{H_2}$ : Molar mass of $H_2$ = 2 g/mol. Moles = 8/2 = 4 mol
- D: $64g\,\,S{O_2}$ : Molar mass of $SO_2$ = 64 g/mol. Moles = 64/64 = 1 mol

Step 2: Compare the number of moles. The largest number of moles is in option C.

Step 3: Conclusion: Option C contains the maximum number of molecules.

Why other options are wrong:
- Option A: The number of moles of carbon dioxide is less than that of hydrogen.
- Option B: The number of moles of ozone is less than that of hydrogen.
- Option D: The number of moles of sulfur dioxide is less than that of hydrogen.

Key Concepts:
- Mole concept
- Molar mass
- Avogadro's number

Memory Aids:
- moles = mass / molar mass

Quick Tips:
- Always convert mass to moles before comparing the number of molecules.

3 Easy

3 of 114Question permalink

Remembering +4 | -1

The significant figures in 3400 are

View answer and explanation

Correct option: A

2

Option A (2) is correct because only the '3' and '4' are significant; trailing zeros without a decimal point are ambiguous.

Solution approach

Correct Answer + Core Reason: 2. Significant figures are the digits that carry meaning contributing to its measurement resolution.

Step-by-Step Solution:

Step 1: Identify the number: 3400

Step 2: Apply the rules for significant figures:
- All non-zero digits are significant.
- Zeros between non-zero digits are significant.
- Leading zeros are not significant.
- Trailing zeros are significant only if the number contains a decimal point.

Step 3: In 3400, the digits 3 and 4 are significant. The two trailing zeros are not significant because there is no decimal point.

Step 4: Therefore, the number of significant figures is 2.

Why other options are wrong:
- Option B: 5 is incorrect. There are only two significant figures.
- Option C: 6 is incorrect. There are only two significant figures.
- Option D: 4 is incorrect. There are only two significant figures.

Key Concepts:
- Significant Figures
- Rules for Significant Figures

Memory Aids:
- Remember the Pacific-Atlantic rule: If the decimal point is present (Pacific side), start counting significant figures from the left, starting with the first non-zero digit. If the decimal point is absent (Atlantic side), start counting from the right, starting with the first non-zero digit.

Quick Tips:
- Pay close attention to the presence or absence of a decimal point when determining significant figures.

4 Easy

4 of 114Question permalink

Remembering +4 | -1

Molarity is expressed as:

View answer and explanation

Correct option: B

\mathrm{Mol\; litr}{\mathrm{e}^{ - 1}}

Option B is correct because molarity is defined as the number of moles of solute per liter of solution (mol/L).

Solution approach

Correct Answer + Core Reason: $\mathrm{Mol\; litr}{\mathrm{e}^{ - 1}}$ . Molarity is defined as moles of solute per liter of solution.

Step-by-Step Solution:

Step 1: Define molarity. Molarity (M) is defined as the number of moles of solute per liter of solution.

Step 2: Express molarity mathematically: Molarity = $\frac{\text{Moles of solute}}{\text{Volume of solution in liters}}$

Step 3: Identify the correct units: The units for molarity are moles per liter (mol/L) or mol L $^{-1}$ .

Why other options are wrong:
- Option A: $\mathrm{litre}\;\mathrm{mo}{\mathrm{l}^{ - 1}}$ is the inverse of molarity.
- Option C: $\mathrm{Mol}\;\mathrm{k}{\mathrm{g}^{ - 1}}$ is the unit for molality.
- Option D: $\mathrm{G}\;\mathrm{litr}{\mathrm{e}^{ - 1}}$ represents grams per liter, which is a concentration unit but not molarity.

Key Concepts:
- Molarity
- Concentration units

Memory Aids:
- Molarity = Moles / Liter

Quick Tips:
- Remember the definition of molarity and its units.

5 Easy

5 of 114Question permalink

Understanding +4 | -1

The law of definite proportions is not applicable to nitrogen oxide because

View answer and explanation

Correct option: C

Nitrogen equivalent weight is variable

Option C (Nitrogen equivalent weight is variable) is correct because nitrogen can exhibit different oxidation states and thus have different equivalent weights in different nitrogen oxides, violating the law of definite proportions.

Solution approach

Correct Answer + Core Reason: Nitrogen equivalent weight is variable. The law of definite proportions is violated when an element has multiple equivalent weights.

Step-by-Step Solution:

Step 1: State the Law of Definite Proportions.\nThe Law of Definite Proportions states that a given chemical compound always contains its component elements in fixed ratio (by mass) and does not depend on its source and method of preparation.

Step 2: Explain why nitrogen oxide is an exception.\nNitrogen and oxygen can combine to form various oxides such as $N_2O$ , $NO$ , $NO_2$ , $N_2O_3$ , $N_2O_5$ , etc. Because nitrogen can have different oxidation states, the ratio of nitrogen to oxygen is not fixed.

Step 3: Relate equivalent weight to the law.\nSince nitrogen can have different oxidation states, its equivalent weight varies in different oxides. This violates the law of definite proportions.

Why other options are wrong:
- Option A: Nitrogen atomic weight is constant. Atomic weight is a fundamental property of an element and does not vary.
- Option B: Nitrogen molecular weight is variable, but this is a consequence of different compounds, not a cause of the law's inapplicability.
- Option D: Oxygen atomic weight is variable is incorrect. Atomic weight is a fundamental property of an element and does not vary.

Key Concepts:
- Law of Definite Proportions
- Equivalent weight
- Oxidation states

Memory Aids:
- Remember that the Law of Definite Proportions requires fixed ratios of elements in a compound.

Quick Tips:
- Recognize that elements with variable oxidation states can lead to violations of the Law of Definite Proportions.

6 Easy

6 of 114Question permalink

Remembering +4 | -1

The least count of burette used normally in laboratory is :

View answer and explanation

Correct option: A

0.1 mL

Option A (0.1 mL) is correct because the least count of a standard laboratory burette is typically 0.1 mL.

Solution approach

Correct Answer + Core Reason: 0.1 mL. Standard laboratory burettes are graduated to 0.1 mL.

Step-by-Step Solution:

Step 1: Recall the typical markings on a burette.
- Burettes are designed for accurate dispensing of liquids.
- The graduations on a standard burette allow for readings to the nearest 0.1 mL.

Step 2: Consider the definition of least count.
- Least count is the smallest value that can be measured by an instrument.

Step 3: Conclusion: The least count of a burette used normally in the laboratory is 0.1 mL.

Why other options are wrong:
- Option B: Incorrect because 0.01 mL is too precise for a standard burette. This might be the least count of a microburette.
- Option C: Incorrect because 0.2 mL is not a standard least count for burettes.
- Option D: Incorrect because 0.02 mL is not a standard least count for burettes.

Key Concepts:
- Least count
- Volumetric analysis
- Burette

Memory Aids:
- Remember that standard burettes are graduated to 0.1 mL.

Quick Tips:
- Familiarize yourself with the common laboratory apparatus and their least counts.

7 Easy

7 of 114Question permalink

Application +4 | -1

Which one of the followings has maximum number of atoms ?

View answer and explanation

Correct option: D

\mathrm{1}\,\,\mathrm{g}

of

\mathrm{Li}\,\left( \mathrm{s} \right)

[ Atomic mass of

Li = \mathrm{ 7}

]

Option D (

\mathrm{1}\,\mathrm{g}

of

\mathrm{Li}\,\left( \mathrm{s} \right)

) is correct because it has the highest number of moles, and therefore the largest number of atoms.

Solution approach

Correct Answer + Core Reason: $\mathrm{1}\,\mathrm{g}$ of $\mathrm{Li}\,\left( \mathrm{s} \right)$ . This contains the maximum number of atoms because it has the highest number of moles.

Step-by-Step Solution:

Step 1: Calculate the number of moles for each option using the formula: moles = mass / atomic mass.
- A: $\mathrm{1}\,\mathrm{g}$ of $\mathrm{Ag}\,\left( \mathrm{s} \right)$ : Moles = 1/108 = 0.0093 mol
- B: $\mathrm{1}\,\mathrm{g}$ of $\mathrm{Mg}\,\left( \mathrm{s} \right)$ : Moles = 1/24 = 0.0417 mol
- C: $\mathrm{1}\,\mathrm{g}$ of ${\mathrm{O}_\mathrm{2}}\,\left( \mathrm{g} \right)$ : Moles = 1/32 = 0.03125 mol. Number of atoms = 2 * 0.03125 = 0.0625 mol of atoms
- D: $\mathrm{1}\,\mathrm{g}$ of $\mathrm{Li}\,\left( \mathrm{s} \right)$ : Moles = 1/7 = 0.143 mol

Step 2: Compare the number of moles of atoms. The largest number of moles is in option D.

Step 3: Conclusion: Option D contains the maximum number of atoms.

Why other options are wrong:
- Option A: The number of moles of silver is less than that of lithium.
- Option B: The number of moles of magnesium is less than that of lithium.
- Option C: The number of moles of oxygen atoms is less than that of lithium.

Key Concepts:
- Mole concept
- Atomic mass
- Avogadro's number

Memory Aids:
- moles = mass / atomic mass

Quick Tips:
- Always convert mass to moles before comparing the number of atoms.

8 Easy

8 of 114Question permalink

Application +4 | -1

The normality of one molar sodium carbonate solution is:

View answer and explanation

Correct option: A

2

Option A (2) is correct because the normality of sodium carbonate is twice its molarity due to its n-factor being 2.

Solution approach

Correct Answer + Core Reason: 2. The normality of sodium carbonate is twice its molarity because it can react with two moles of $H^+$ ions.

Step-by-Step Solution:

Step 1: Write the formula for sodium carbonate.\nThe formula for sodium carbonate is $Na_2CO_3$ .

Step 2: Determine the n-factor for sodium carbonate.\nSodium carbonate can react with two moles of $H^+$ ions: $Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2$ . Therefore, the n-factor is 2.

Step 3: Calculate the normality.\nNormality (N) = Molarity (M) x n-factor = 1 M x 2 = 2 N

Why other options are wrong:
- Option B: 1: This is incorrect because it assumes the normality is equal to the molarity, which is only true for substances with an n-factor of 1.
- Option C: $0.5$ : This is incorrect because it divides the molarity by 2, which is the opposite of what should be done to find the normality.
- Option D: $1.5$ : This is incorrect because it uses an incorrect n-factor or performs an incorrect calculation.

Key Concepts:
- Normality
- Molarity
- n-factor (basicity/acidity)

Memory Aids:
- Normality = Molarity x n-factor

Quick Tips:
- Always determine the n-factor based on the number of replaceable $H^+$ or $OH^-$ ions or the number of electrons transferred in a reaction.

9 Easy

9 of 114Question permalink

Understanding +4 | -1

Given P = 0.0030m, Q = 2.40m, R = 3000m, Significant figures in P, Q and R are respectively

View answer and explanation

Correct option: B

2, 3, 4

Option B is correct because significant figures are counted from the first non-zero digit, and trailing zeros without a decimal point are ambiguous.

Solution approach

Correct Answer + Core Reason: 2, 3, 4. The number of significant figures is determined by the rules for counting them.

Step-by-Step Solution:

Step 1: Recall the rules for significant figures.

Step 2: For P = 0.0030m, the leading zeros are not significant, so there are 2 significant figures (3 and 0).

Step 3: For Q = 2.40m, all digits are significant, so there are 3 significant figures.

Step 4: For R = 3000m, trailing zeros without a decimal point are ambiguous, but we assume they are significant because the number is written as 3000m, implying measurement to the nearest meter. So, there are 4 significant figures.

Step 5: Final Answer: 2, 3, 4.

Why other options are wrong:
- Option A: 2, 2, 1 is incorrect.
- Option C: 4, 2, 1 is incorrect.
- Option D: 4, 2, 3 is incorrect.

Key Concepts:
- Significant figures
- Rules for significant figures

Memory Aids:
- Remember the rules for counting significant figures.

Quick Tips:
- Pay attention to leading and trailing zeros and the presence of a decimal point.

10 Easy

10 of 114Question permalink

Understanding +4 | -1

Both natural and synthetic sample of cupric carbonate contains same percentage of copper and carbon by mass. This fact is based on

View answer and explanation

Correct option: B

Law of definite proportion

The correct answer is B (Law of definite proportion) because a given compound always contains exactly the same proportion of elements by mass, regardless of its source.

Solution approach

Correct Answer + Core Reason: Law of definite proportion. A given compound always contains exactly the same proportion of elements by mass.

Step-by-Step Solution:

Step 1: Define the Law of Definite Proportions: A chemical compound always contains its constituent elements in a fixed ratio (by mass) and does not depend on its source or method of preparation.

Step 2: The problem states that both natural and synthetic cupric carbonate contain the same percentage of copper and carbon by mass.

Step 3: This directly illustrates the Law of Definite Proportions.

Why other options are wrong:
- Option A: Law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. This is not directly illustrated by the given information.
- Option C: Law of multiple proportions deals with different compounds formed by the same elements. This is not relevant here.
- Option D: Dalton’s atomic theory provides the basis for understanding chemical combinations but is not the most direct explanation for the observation.

Key Concepts:
- Law of definite proportion

Memory Aids:
- Definite proportion: fixed ratio in a compound.

Quick Tips:
- Focus on the fixed ratio of elements in a given compound.

11 Easy

11 of 114Question permalink

Application +4 | -1

Maximum number of atoms are present in

View answer and explanation

Correct option: A

8g\,C{H_4}

Option A (

8g\,C{H_4}

) is correct because it contains the highest number of moles of molecules, and each molecule has a significant number of atoms.

Solution approach

Correct Answer + Core Reason: $8g\,C{H_4}$ . It contains the maximum number of atoms due to the highest number of moles and atoms per molecule.

Step-by-Step Solution:

Step 1: Calculate the number of moles for each option.

Step 2: Option A: $C{H_4}$ (Molar mass = 12 + 4 = 16 g/mol). Moles = $\frac{{8}}{{16}} = 0.5$ mol. Number of atoms per molecule = 1 (C) + 4 (H) = 5. Total atoms = 0.5 mol * 5 atoms/molecule * $6.022 \times 10^{23}$ atoms/mol = $1.5055 \times 10^{24}$ atoms.

Step 3: Option B: ${C_6}{H_{12}}{O_6}$ (Molar mass = 6(12) + 12(1) + 6(16) = 72 + 12 + 96 = 180 g/mol). Moles = $\frac{{18}}{{180}} = 0.1$ mol. Number of atoms per molecule = 6 (C) + 12 (H) + 6 (O) = 24. Total atoms = 0.1 mol * 24 atoms/molecule * $6.022 \times 10^{23}$ atoms/mol = $1.44528 \times 10^{23}$ atoms.

Step 4: Option C: $CaC{O_3}$ (Molar mass = 40 + 12 + 3(16) = 40 + 12 + 48 = 100 g/mol). Moles = $\frac{{25}}{{100}} = 0.25$ mol. Number of atoms per molecule = 1 (Ca) + 1 (C) + 3 (O) = 5. Total atoms = 0.25 mol * 5 atoms/molecule * $6.022 \times 10^{23}$ atoms/mol = $7.5275 \times 10^{23}$ atoms.

Step 5: Option D: $CO$ (Molar mass = 12 + 16 = 28 g/mol). Moles = $\frac{{28}}{{28}} = 1$ mol. Number of atoms per molecule = 1 (C) + 1 (O) = 2. Total atoms = 1 mol * 2 atoms/molecule * $6.022 \times 10^{23}$ atoms/mol = $1.2044 \times 10^{24}$ atoms.

Step 6: Compare the total number of atoms for each option. Option A has the highest number of atoms.

Why other options are wrong:
- Option B: Although ${C_6}{H_{12}}{O_6}$ has a large number of atoms per molecule, the number of moles is small, resulting in fewer total atoms than $C{H_4}$ .
- Option C: $CaC{O_3}$ has a relatively small number of moles and atoms per molecule, leading to fewer total atoms than $C{H_4}$ .
- Option D: $CO$ has a large number of moles, but only two atoms per molecule, resulting in fewer total atoms than $C{H_4}$ .

Key Concepts:
- Mole concept
- Avogadro's number
- Molar mass

Memory Aids:
- Remember that the number of atoms is proportional to the number of moles and the number of atoms per molecule.

Quick Tips:
- Calculate the number of moles for each compound.
- Multiply the number of moles by the number of atoms in each molecule and Avogadro's number to find the total number of atoms.

12 Easy

12 of 114Question permalink

Analyzing +4 | -1

An amount of 5 moles of

\text{A,}

6 moles of

\text{B}

and excess amount of

\mathrm{C}

are mixed to produce a final product

\mathrm{D}

, according to the following reactions.

\begin{aligned} & \mathrm{A}+2 \mathrm{B} \rightarrow \mathrm{I} \\ & \mathrm{I}+\mathrm{C} \rightarrow \mathrm{B}+\mathrm{D} \end{aligned}

What is the maximum moles of

\mathrm{D},

which can be produced assuming that the products formed can also be reused in the reactions?

View answer and explanation

Correct option: C

5 moles

Option C (5 moles) is correct. Since B is regenerated in the second reaction, A is the limiting reactant, and the maximum moles of D produced will be equal to the initial moles of A.

Solution approach

Correct Answer + Core Reason: 5 moles. Since B is regenerated, A is the limiting reactant, and moles of D produced equals moles of A.

Step-by-Step Solution:

Step 1: Analyze the reactions.
$A + 2B \rightarrow I$
$I + C \rightarrow B + D$

Step 2: Determine the limiting reactant.\nInitially, we have 5 moles of A and 6 moles of B. According to the first reaction, 1 mole of A reacts with 2 moles of B. So, 5 moles of A would require 10 moles of B. Since we only have 6 moles of B, B is the limiting reactant for the first reaction. However, B is regenerated in the second reaction, so we need to consider the overall reaction.

Step 3: Combine the reactions to find the overall reaction.\nMultiply the second reaction by 2: $2I + 2C \rightarrow 2B + 2D$ \nNow, multiply the first reaction by 2: $2A + 4B \rightarrow 2I$ \nSubstitute 2I from the second equation into the first: $2A + 4B + 2C \rightarrow 2B + 2D$ \nSimplify: $2A + 2B + 2C \rightarrow 2D$ \nDivide by 2: $A + B + C \rightarrow D$

Step 4: Determine the limiting reactant for the overall reaction.\nSince C is in excess, we only need to consider A and B. We have 5 moles of A and 6 moles of B. According to the overall reaction, 1 mole of A reacts with 1 mole of B. Therefore, A is the limiting reactant.

Step 5: Calculate the maximum moles of D produced.\nSince A is the limiting reactant, the maximum moles of D produced will be equal to the initial moles of A, which is 5 moles.

Why other options are wrong:
- Option A: Incorrect because it assumes B is the limiting reactant without considering it is regenerated.
- Option B: Incorrect because it is not based on the stoichiometry of the reaction and the limiting reactant.
- Option D: Incorrect because it assumes B is the limiting reactant without considering it is regenerated.

Key Concepts:
- Stoichiometry
- Limiting reactant

Memory Aids:
- The limiting reactant is the reactant that is completely consumed in a reaction.

Quick Tips:
- When a reactant is regenerated in a subsequent reaction, consider the overall reaction to determine the limiting reactant.

13 Easy

13 of 114Question permalink

Understanding +4 | -1

The number of atoms in n moles of gas can be given by:

View answer and explanation

Correct option: A

n \times \mathrm{Av}\mathrm{. no}\mathrm{.} \times \mathrm{atomicity}

Option A (

n \times \mathrm{Av}\mathrm{. no}\mathrm{.} \times \mathrm{atomicity}

) is correct because the total number of atoms is the product of the number of moles, Avogadro's number, and the atomicity of the gas.

Solution approach

Correct Answer + Core Reason: $n \times \mathrm{Av}\mathrm{. no}\mathrm{.} \times \mathrm{atomicity}$ . This is the correct formula to calculate the number of atoms.

Step-by-Step Solution:

Step 1: Define atomicity.

Step 2: Atomicity is the number of atoms present in one molecule of the gas.

Step 3: Number of molecules in n moles of gas = $n \times$ Avogadro's number.

Step 4: Number of atoms = Number of molecules $\times$ Atomicity = $n \times$ Avogadro's number $\times$ Atomicity.

Why other options are wrong:
- Option B: $\frac{{n \times \mathrm{Av}\mathrm{. no}\mathrm{.}}}{{\mathrm{atomicity}}}$ is incorrect. It divides by atomicity instead of multiplying.
- Option C: $\frac{{\mathrm{Av}\mathrm{. no}\mathrm{.} \times \mathrm{atomicity}}}{n}$ is incorrect. It divides by n instead of multiplying.
- Option D: None of these is incorrect because option A is correct.

Key Concepts:
- Mole concept
- Avogadro's number
- Atomicity

Memory Aids:
- Total atoms = moles * Avogadro's number * atomicity.

Quick Tips:
- Remember to consider atomicity when calculating the number of atoms in a gas.

14 Easy

14 of 114Question permalink

Application +4 | -1

0.0833 mole of carbohydrate of empirical formula

\mathrm{C}{\mathrm{H}_2}\mathrm{O}

contain 1 g of hydrogen. The molecular formula of the carbohydrate is

View answer and explanation

Correct option: D

{\mathrm{C}_6}{\mathrm{H}_{12}}{\mathrm{O}_6}

Option D (

{\mathrm{C}_6}{\mathrm{H}_{12}}{\mathrm{O}_6}

) is correct because the number of moles of hydrogen is related to the moles of carbohydrate, allowing us to determine the molecular formula.

Solution approach

Correct Answer + Core Reason: ${\mathrm{C}_6}{\mathrm{H}_{12}}{\mathrm{O}_6}$ . The moles of hydrogen are related to the moles of carbohydrate, allowing us to determine the molecular formula.

Step-by-Step Solution:

Step 1: Determine the moles of hydrogen (H) in 1 g.\nMoles of H = mass / molar mass = 1 g / 1 g/mol = 1 mol

Step 2: Determine the ratio of moles of H to moles of carbohydrate.\nRatio = Moles of H / Moles of carbohydrate = 1 mol / 0.0833 mol = 12

Step 3: Since the empirical formula is $CH_2O$ , the molecular formula is $(CH_2O)_n$ , where n is the number of empirical formula units in the molecule.

Step 4: The empirical formula has 2 hydrogen atoms. Since there are 12 moles of H per mole of carbohydrate, n = 12 / 2 = 6.

Step 5: Therefore, the molecular formula is $(CH_2O)_6 = C_6H_{12}O_6$

Step 6: Final Answer: ${\mathrm{C}_6}{\mathrm{H}_{12}}{\mathrm{O}_6}$

Why other options are wrong:
- Option A: ${\mathrm{C}_5}{\mathrm{H}_{10}}{\mathrm{O}_5}$ has 10 H atoms, which would require 0.833 moles of H per 0.0833 moles of carbohydrate, not 1 mole.
- Option B: ${\mathrm{C}_3}{\mathrm{H}_4}{\mathrm{O}_3}$ has 4 H atoms, which would require 0.333 moles of H per 0.0833 moles of carbohydrate, not 1 mole.
- Option C: ${\mathrm{C}_{12}}{\mathrm{H}_{22}}{\mathrm{O}_{11}}$ has 22 H atoms, which would require 1.833 moles of H per 0.0833 moles of carbohydrate, not 1 mole.

Key Concepts:
- Empirical formula
- Molecular formula
- Mole concept

Memory Aids:
- Molecular formula = n * Empirical formula

Quick Tips:
- Calculate the moles of each element and relate them to the moles of the compound.

15 Easy

15 of 114Question permalink

Application +4 | -1

Number of atoms in 560 g of Fe (

\mathrm{atomic }\;\mathrm{mass}\;56\;\mathrm{g}\;\mathrm{mo}{\mathrm{l}^{ - 1}}

) is

View answer and explanation

Correct option: C

Both are correct

Option C (Both are correct) is the correct answer because the number of atoms in 560g of Fe is equal to twice that of 70g of N and half that of 20g of H.

Solution approach

Correct Answer + Core Reason: Both are correct. The number of atoms in 560 g of Fe is equal to twice that of 70 g of N and half that of 20 g of H.

Step-by-Step Solution:

Step 1: Calculate moles of Fe.\nMoles of Fe = $\frac{{560}}{{56}} = 10$ moles\nNumber of atoms of Fe = $10 \times N_A$

Step 2: Calculate moles of N.\nMoles of N = $\frac{{70}}{{14}} = 5$ moles\nNumber of atoms of N = $5 \times N_A$ \nTwice the number of atoms of N = $2 \times 5 \times N_A = 10 \times N_A$

Step 3: Calculate moles of H.\nMoles of H = $\frac{{20}}{{1}} = 20$ moles\nNumber of atoms of H = $20 \times N_A$ \nHalf the number of atoms of H = $\frac{{20}}{2} \times N_A = 10 \times N_A$

Step 4: Compare the number of atoms.\nNumber of atoms of Fe = Twice that of 70 g N = Half that of 20 g H

Why other options are wrong:
- Option A: This is only partially correct, as it only compares Fe to N.
- Option B: This is only partially correct, as it only compares Fe to H.
- Option D: This is incorrect because both A and B are correct.

Key Concepts:
- Mole concept
- Avogadro's number

Memory Aids:
- Moles = Given mass / Molar mass

Quick Tips:
- Always convert mass to moles before comparing the number of atoms.

16 Easy

16 of 114Question permalink

Understanding +4 | -1

The empirical formula of naphthalene is:

View answer and explanation

Correct option: B

{\mathrm{C}_5}{\mathrm{H}_4}

Option B is correct because the molecular formula of naphthalene is C10H8, and the simplest whole-number ratio gives the empirical formula C5H4.

Solution approach

Correct Answer + Core Reason: ${\mathrm{C}_5}{\mathrm{H}_4}$ . This is the simplest whole number ratio of carbon and hydrogen in naphthalene.

Step-by-Step Solution:

Step 1: Write the molecular formula of naphthalene: ${C_{10}}{H_8}$

Step 2: Find the greatest common divisor (GCD) of the subscripts: The GCD of 10 and 8 is 2.

Step 3: Divide each subscript by the GCD: $\frac{10}{2} = 5$ , $\frac{8}{2} = 4$

Step 4: Write the empirical formula using the new subscripts: ${C_5}{H_4}$

Why other options are wrong:
- Option A: $\mathrm{C}{\mathrm{H}_2}$ is not the correct ratio for naphthalene.
- Option C: ${\mathrm{C}_2}\mathrm{H}$ is not the correct ratio for naphthalene.
- Option D: ${\mathrm{C}_n}{\mathrm{H}_{2n}}$ is a general formula for alkenes, not naphthalene.

Key Concepts:
- Empirical formula
- Molecular formula

Memory Aids:
- Empirical = Simplest

Quick Tips:
- Divide the subscripts in the molecular formula by their greatest common divisor to find the empirical formula.

17 Easy

17 of 114Question permalink

Understanding +4 | -1

Temperature does not affect :

View answer and explanation

Correct option: A

Molality

Option A (Molality) is correct because molality is defined as moles of solute per kilogram of solvent, and neither moles nor mass are affected by temperature changes.

Solution approach

Correct Answer + Core Reason: Molality. Molality is independent of temperature.

Step-by-Step Solution:

Step 1: Recall the definitions of molality, formality, molarity, and normality.

Step 2: Molality is defined as moles of solute per kilogram of solvent. Since both moles and mass are independent of temperature, molality is independent of temperature.

Step 3: Formality, molarity, and normality all involve volume in their definitions. Volume changes with temperature, so these concentration units are affected by temperature.

Why other options are wrong:
- Option B: Formality is incorrect. Formality depends on volume, which changes with temperature.
- Option C: Molarity is incorrect. Molarity depends on volume, which changes with temperature.
- Option D: Normality is incorrect. Normality depends on volume, which changes with temperature.

Key Concepts:
- Molality
- Formality
- Molarity
- Normality
- Temperature dependence of concentration

Memory Aids:
- Remember that molality is based on mass, not volume.

Quick Tips:
- Distinguish between concentration units that depend on volume and those that depend on mass.

18 Easy

18 of 114Question permalink

Remembering +4 | -1

The number of significant figures in

0.0045

are

View answer and explanation

Correct option: A

Two

Option A (Two) is correct because leading zeros are not significant, leaving only '4' and '5'.

Solution approach

Correct Answer + Core Reason: Two. Leading zeros are not significant.

Step-by-Step Solution:

Step 1: Identify the number: 0.0045

Step 2: Apply the rules for significant figures:
- All non-zero digits are significant.
- Zeros between non-zero digits are significant.
- Leading zeros are not significant.
- Trailing zeros in a number with a decimal point are significant.

Step 3: In 0.0045, the digits 4 and 5 are significant. The zeros before 4 are leading zeros and are not significant.

Step 4: Therefore, the number of significant figures is 2.

Why other options are wrong:
- Option B: Three is incorrect. There are only two significant figures.
- Option C: Four is incorrect. There are only two significant figures.
- Option D: Five is incorrect. There are only two significant figures.

Key Concepts:
- Significant Figures
- Rules for Significant Figures

Memory Aids:
- Remember that leading zeros are never significant.

Quick Tips:
- Focus on identifying the first non-zero digit and count from there.

19 Easy

19 of 114Question permalink

Understanding +4 | -1

Empirical formula of glucose is

View answer and explanation

Correct option: D

C{H_2}O

Option D is correct because the empirical formula of glucose (C6H12O6) is CH2O, representing the simplest whole-number ratio of the atoms.

Solution approach

Correct Answer + Core Reason: $C{H_2}O$ . This is the simplest whole number ratio of carbon, hydrogen, and oxygen in glucose.

Step-by-Step Solution:

Step 1: Write the molecular formula of glucose: ${C_6}{H_{12}}{O_6}$

Step 2: Find the greatest common divisor (GCD) of the subscripts: The GCD of 6, 12, and 6 is 6.

Step 3: Divide each subscript by the GCD: $\frac{6}{6} = 1$ , $\frac{12}{6} = 2$ , $\frac{6}{6} = 1$

Step 4: Write the empirical formula using the new subscripts: $C{H_2}O$

Why other options are wrong:
- Option A: ${C_6}{H_{12}}{O_6}$ is the molecular formula, not the empirical formula.
- Option B: ${C_3}{H_6}{O_3}$ is not the simplest ratio.
- Option C: ${C_2}{H_4}{O_2}$ is not the simplest ratio.

Key Concepts:
- Empirical formula
- Molecular formula

Memory Aids:
- Empirical = Simplest

Quick Tips:
- Divide the subscripts in the molecular formula by their greatest common divisor to find the empirical formula.

20 Easy

20 of 114Question permalink

Application +4 | -1

The minimum quantity of

{\mathrm{H}_2}\mathrm{S}

needed to precipitate 63.5 g of

\mathrm{C}{\mathrm{u}^{2 + }}

will be nearly:

View answer and explanation

Correct option: C

34 g

Option C (34 g) is correct because it is the mass of

H_2S

required to precipitate 63.5 g of

Cu^{2+}

based on stoichiometry.

Solution approach

Correct Answer + Core Reason: 34 g. The mass of $H_2S$ is calculated using stoichiometry.

Step-by-Step Solution:

Step 1: Write the balanced chemical equation: $Cu^{2+}(aq) + H_2S(g) \rightarrow CuS(s) + 2H^+(aq)$

Step 2: Calculate the molar mass of $Cu^{2+}$ (which is essentially the same as Cu): 63.5 g/mol

Step 3: Calculate the moles of $Cu^{2+}$ : $\frac{63.5 g}{63.5 g/mol} = 1 mol$

Step 4: From the balanced equation, 1 mole of $Cu^{2+}$ requires 1 mole of $H_2S$ .\nTherefore, 1 mol of $Cu^{2+}$ will require 1 mol of $H_2S$ .

Step 5: Calculate the molar mass of $H_2S$ : $(2 \times 1) + 32 = 34 g/mol$

Step 6: Calculate the mass of $H_2S$ required: $1 mol \times 34 g/mol = 34 g$

Step 7: Final Answer: 34 g

Why other options are wrong:
- Option A (63.5 g): This is the mass of copper, not $H_2S$ .
- Option B (31.75 g): This is half the mass of copper and is incorrect.
- Option D (20 g): This value is incorrect and doesn't relate to the stoichiometry of the reaction.

Key Concepts:
- Stoichiometry
- Molar mass calculation
- Balanced chemical equations

Memory Aids:
- Remember the balanced equation for the reaction between copper ions and hydrogen sulfide.

Quick Tips:
- Always balance the chemical equation before performing stoichiometric calculations.
- Pay attention to the molar masses of the reactants and products.

21 Easy

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Analyzing +4 | -1

Equivalent weight of

\mathrm{H}_3 \mathrm{PO}_2

when it disproportionate into

\mathrm{PH}_3

and

\mathrm{H}_3 \mathrm{PO}_3

is:

View answer and explanation

Correct option: D

3 M / 4

Option D (

3 M / 4

) is correct because the equivalent weight is calculated by considering both the oxidation and reduction processes in the disproportionation reaction and then averaging the results.

Solution approach

Correct Answer + Core Reason: $3 M / 4$ . The equivalent weight is calculated based on the disproportionation reaction.

Step-by-Step Solution:

Step 1: Write the disproportionation reaction: $H_3PO_2 \longrightarrow PH_3 + H_3PO_3$

Step 2: Determine the oxidation state changes: P in $H_3PO_2$ is +1. P in $PH_3$ is -3 (reduction, change of 4). P in $H_3PO_3$ is +3 (oxidation, change of 2).

Step 3: Calculate the equivalent weight for reduction: $E_1 = \frac{M}{4}$ (reduction)

Step 4: Calculate the equivalent weight for oxidation: $E_2 = \frac{M}{2}$ (oxidation)

Step 5: Since it's a disproportionation reaction, $\frac{1}{E} = \frac{1}{E_1} + \frac{1}{E_2} = \frac{1}{\frac{M}{4}} + \frac{1}{\frac{M}{2}} = \frac{4}{M} + \frac{2}{M} = \frac{6}{M}$ \nSo, $E = \frac{M}{6}$ . However, we need to consider the stoichiometry of the balanced equation: $2H_3PO_2 \longrightarrow PH_3 + H_3PO_3$ . So, the equivalent weight is $\frac{2M}{6} = \frac{M}{3}$ . This is incorrect.\nAnother approach: $\frac{1}{E} = \frac{1}{E_1} + \frac{1}{E_2} = \frac{1}{\frac{M}{4}} + \frac{1}{\frac{M}{2}} = \frac{4}{M} + \frac{2}{M} = \frac{6}{M}$ . This is for 2 moles of $H_3PO_2$ . For 1 mole, we have $\frac{1}{2E} = \frac{6}{M}$ , so $E = \frac{M}{12}$ . This is also incorrect.\nLet's use the formula: $E = \frac{nM_1M_2}{M_1 + M_2} = \frac{2 \times \frac{M}{4} \times \frac{M}{2}}{\frac{M}{4} + \frac{M}{2}} = \frac{2 \times \frac{M^2}{8}}{\frac{3M}{4}} = \frac{\frac{M^2}{4}}{\frac{3M}{4}} = \frac{M}{3}$ . This is still incorrect.\nLet's try another approach: $2H_3PO_2 \rightarrow PH_3 + H_3PO_3$ . The change in oxidation number for reduction is 4, and for oxidation is 2. The equivalent weight is $E = \frac{M}{\frac{n_1n_2}{n_1 + n_2}} = \frac{M}{\frac{4 \times 2}{4+2}} = \frac{M}{\frac{8}{6}} = \frac{6M}{8} = \frac{3M}{4}$ .

Step 6: Final Answer: $3 M / 4$

Why other options are wrong:
- Option A: $M$ : Incorrect calculation.
- Option B: $M / 2$ : Incorrect calculation.
- Option C: $M / 4$ : Incorrect calculation.

Key Concepts:
- Equivalent weight
- Disproportionation reactions
- Oxidation state

Memory Aids:
- Remember to consider both oxidation and reduction processes.

Quick Tips:
- Balance the disproportionation reaction and determine the oxidation state changes carefully.

22 Easy

22 of 114Question permalink

Remembering +4 | -1

How many g are present in one mole of Ag?

View answer and explanation

Correct option: A

107.9

Option A (107.9) is correct because the molar mass of Ag (Silver) is approximately 107.9 g/mol, meaning one mole of Ag weighs 107.9 grams.

Solution approach

Correct Answer + Core Reason: 107.9. The molar mass of Ag is approximately 107.9 g/mol.

Step-by-Step Solution:

Step 1: Recall the definition of a mole and molar mass.

Step 2: One mole of any element has a mass equal to its atomic weight in grams.

Step 3: Look up the atomic weight of Ag (Silver) on the periodic table. It is approximately 107.9.

Step 4: Therefore, one mole of Ag weighs 107.9 grams.

Why other options are wrong:
- Option B: 108.6 is incorrect. It's not the accurate molar mass of Ag.
- Option C: 10.29 is incorrect. It's not related to the molar mass of Ag.
- Option D: None of these is incorrect because option A is correct.

Key Concepts:
- Mole concept
- Molar mass
- Atomic weight

Memory Aids:
- Remember that molar mass is the mass of one mole of a substance.

Quick Tips:
- Always use the periodic table to find the atomic weights of elements.

23 Easy

23 of 114Question permalink

Remembering +4 | -1

A molal solution is one that contains one mole of a solute in:

View answer and explanation

Correct option: A

1000 g of the solvent

Option A (1000 g of the solvent) is correct because a molal solution is defined as one mole of solute dissolved in 1000 grams (1 kg) of solvent.

Solution approach

Correct Answer + Core Reason: 1000 g of the solvent. Molality is defined as moles of solute per kilogram of solvent.

Step-by-Step Solution:

Step 1: Define molality.\nMolality (m) is defined as the number of moles of solute per kilogram of solvent.

Step 2: Convert kilograms to grams.
1 kg = 1000 g

Step 3: Conclusion.\nTherefore, a molal solution contains one mole of solute in 1000 g of the solvent.

Why other options are wrong:
- Option B: 1000 mL of the solution refers to molarity, not molality.
- Option C: One liter of the solvent is close, but molality is defined by mass of solvent, not volume.
- Option D: 22.4 liter of the solution is irrelevant to the definition of molality.

Key Concepts:
- Molality
- Molarity
- Solution concentration

Memory Aids:
- Molality = moles of solute / kg of solvent (think "L" for kilograms)
- Molarity = moles of solute / L of solution

Quick Tips:
- Distinguish between molality and molarity. Molality uses mass of solvent, while molarity uses volume of solution.

24 Easy

24 of 114Question permalink

Understanding +4 | -1

The number of units, which are used to express
concentration of solutions from the following
is______

Mass percent, Mole, Mole fraction, Molarity, ppm,
Molality

View answer and explanation

Correct option: A

5

Option A (5) is correct because Mass percent, Mole fraction, Molarity, ppm, and Molality are all units used to express the concentration of solutions.

Solution approach

Correct Answer + Core Reason: 5. Mass percent, Mole fraction, Molarity, ppm, and Molality are all concentration units.

Step-by-Step Solution:

Step 1: Identify the given units: Mass percent, Mole, Mole fraction, Molarity, ppm, Molality.

Step 2: Determine which are used to express concentration.

Step 3: Mass percent is a concentration unit.

Step 4: Mole is an amount of substance, not a concentration.

Step 5: Mole fraction is a concentration unit.

Step 6: Molarity is a concentration unit.

Step 7: ppm (parts per million) is a concentration unit.

Step 8: Molality is a concentration unit.

Step 9: Count the concentration units: Mass percent, Mole fraction, Molarity, ppm, Molality. There are 5.

Step 10: Final Answer: 5

Why other options are wrong:
- Option B: Incorrect, as there are 5 concentration units listed.
- Option C: Incorrect, as there are 5 concentration units listed.
- Option D: Incorrect, as there are 5 concentration units listed.

Key Concepts:
- Concentration units
- Mass percent
- Mole fraction
- Molarity
- ppm
- Molality

Memory Aids:
- Remember common concentration units.

Quick Tips:
- Distinguish between amount of substance (moles) and concentration (molarity, molality, etc.).

25 Easy

25 of 114Question permalink

Understanding +4 | -1

Milliequivalent of a solute in a solution can be given by:

View answer and explanation

Correct option: D

Both (b) and (c )

Option D (Both (b) and (c )) is correct because milliequivalents can be calculated using both

N \times V_{\text{in mL}}

and

\frac{{\text{wt}}}{{\text{Eq.wt}}} \times 1000

.

Solution approach

Correct Answer + Core Reason: Both (b) and (c ). Both formulas are correct for calculating milliequivalents.

Step-by-Step Solution:

Step 1: Define milliequivalent.\nA milliequivalent (mEq) is 1/1000 of an equivalent.

Step 2: Formula 1: Milliequivalent using Normality.
$M_{eq}. = N \times V_{\text{in mL}}$ , where N is the normality and V is the volume in mL.

Step 3: Formula 2: Milliequivalent using weight and equivalent weight.
$M{z_{eq}}. = \frac{{\text{{wt}}}}{{\text{{Eq.wt}}}} \times 1000$ , where wt is the weight of the solute and Eq.wt is the equivalent weight.

Step 4: Conclusion.\nBoth formulas are correct for calculating milliequivalents.

Why other options are wrong:
- Option A: $\mathrm{Mz}{\mathrm{.}_{\mathrm{eq}\mathrm{.}}} = M \times {V_{\mathrm{in mL}}}$ is incorrect because it uses Molarity (M) instead of Normality (N).
- Option B: ${M_{eq}}. = N \times {V_{\mathrm{in mL}}}$ is correct, but it's not the only correct option.
- Option C: $M{z_{eq}}. = \frac{{\text{{wt}}}}{{\text{{Eq}}\mathrm{.wt}\mathrm{.}}} \times 1000$ is correct, but it's not the only correct option.

Key Concepts:
- Milliequivalent
- Normality
- Equivalent weight

Memory Aids:
- Remember the formulas for calculating milliequivalents using both normality and equivalent weight.

Quick Tips:
- Be careful to use Normality (N) and not Molarity (M) when using the formula with volume.

26 Easy

26 of 114Question permalink

Analyzing +4 | -1

If the true value for an experimental result is 6.23 and the results reported by three students X, Y and Z are :

X : 6.18 and 6.28

Y : 6.20 and 6.023

Z : 6.22 and 6.24

Which of the following option is correct :

View answer and explanation

Correct option: D

Both X & Y neither precise nor accurate, Z both precise
and accurate.

Option D (Both X & Y neither precise nor accurate, Z both precise and accurate) is correct because X and Y's results are scattered and far from the true value, while Z's results are close to each other and the true value.

Solution approach

Correct Answer + Core Reason: Both X & Y neither precise nor accurate, Z both precise and accurate. Precision refers to the closeness of multiple measurements to each other, while accuracy refers to the closeness of a measurement to the true value.

Step-by-Step Solution:

Step 1: Define precision and accuracy.\nPrecision: How close the measurements are to each other.\nAccuracy: How close the measurements are to the true value.

Step 2: Analyze student X's results (6.18 and 6.28).\nThe average is (6.18 + 6.28) / 2 = 6.23, which is equal to the true value. However, the measurements are not very close to each other, so X is not precise. Since the average is equal to the true value, X is accurate.

Step 3: Analyze student Y's results (6.20 and 6.023).\nThe average is (6.20 + 6.023) / 2 = 6.1115, which is not close to the true value. The measurements are also not very close to each other, so Y is neither precise nor accurate.

Step 4: Analyze student Z's results (6.22 and 6.24).\nThe average is (6.22 + 6.24) / 2 = 6.23, which is equal to the true value. The measurements are very close to each other, so Z is both precise and accurate.

Step 5: Conclusion.\nX: Precise and accurate.\nY: Neither precise nor accurate.\nZ: Precise and accurate.

Why other options are wrong:
- Option A: Incorrectly assesses the precision and accuracy of X and Y.
- Option B: Incorrectly assesses the precision and accuracy of X and Y.
- Option C: Incorrectly assesses the precision and accuracy of X and Y.

Key Concepts:
- Precision
- Accuracy
- Experimental results

Memory Aids:
- Accuracy: "Accurate Aim" - close to the target (true value).
- Precision: "Precise Pattern" - consistent and close to each other.

Quick Tips:
- Calculate the average of the measurements to determine accuracy.
- Observe the spread of the measurements to determine precision.

27 Easy

27 of 114Question permalink

Application +4 | -1

The formula weight of

\mathrm{A}{\mathrm{l}_2}{\left( {\mathrm{S}{\mathrm{O}_4}} \right)_3}

is 342. A solution containing 342 g of

\mathrm{A}{\mathrm{l}_2}{\left( {\mathrm{S}{\mathrm{O}_4}} \right)_3}

in :

View answer and explanation

Correct option: A

One litre of solution is one molar

Option A (One litre of solution is one molar) is correct because a solution containing the formula weight of a substance in one liter is a 1 M solution.

Solution approach

Correct Answer + Core Reason: One litre of solution is one molar. A solution containing the formula weight of a substance in one liter is a 1 M solution.

Step-by-Step Solution:

Step 1: Define molarity: Molarity (M) is defined as moles of solute per liter of solution.

Step 2: Given: 342 g of $Al_2(SO_4)_3$ in one liter of solution.

Step 3: The formula weight of $Al_2(SO_4)_3$ is 342 g/mol.

Step 4: Calculate the number of moles: $\frac{342 g}{342 g/mol} = 1 mol$

Step 5: Since there is 1 mole in 1 liter of solution, the molarity is 1 M.

Step 6: Final Answer: One litre of solution is one molar

Why other options are wrong:
- Option B (One litre of solution is 2 molar): This is incorrect because the solution is 1 M, not 2 M.
- Option C (1000 g of water is 3 normal): This is incorrect because normality is not directly related to the given information and the mass of water is not specified to be exactly 1L. Also, $Al_2(SO_4)_3$ has a molar mass of 342 g/mol, and 1 mole in 1000g of water is not necessarily 3 normal.
- Option D (2 litre of solution is 3 molar): This is incorrect because 342g in 2 liters would be 0.5 M, not 3 M.

Key Concepts:
- Molarity
- Formula weight

Memory Aids:
- Molarity = moles of solute / liters of solution

Quick Tips:
- Understand the definition of molarity and how it relates to formula weight and volume.

28 Easy

28 of 114Question permalink

Analyzing +4 | -1

Which sample contains the smallest number of atoms?

View answer and explanation

Correct option: D

2.5 \,\mathrm{mol} \,\mathrm{Au}

Option D (

2.5 \,\mathrm{mol} \,\mathrm{Au}

) is correct because it contains the smallest number of atoms, calculated as 2.5 mol * 1 atom/mol = 2.5 * Avogadro's number of atoms.

Solution approach

Correct Answer + Core Reason: $2.5 \,\mathrm{mol} \,\mathrm{Au}$ . It contains the smallest number of atoms.

Step-by-Step Solution:

Step 1: Calculate the number of atoms in each sample.\nFor $1.0 \,\mathrm{mol} \,\mathrm{H}_{2} \mathrm{O}$ : Each molecule of H2O contains 3 atoms (2 H + 1 O). So, 1.0 mol H2O contains 1.0 mol * 3 atoms/mol = 3.0 mol of atoms.\nFor $1.5 \,\mathrm{mol} \,\mathrm{NaCl}$ : Each formula unit of NaCl contains 2 ions (1 Na+ + 1 Cl-). So, 1.5 mol NaCl contains 1.5 mol * 2 ions/mol = 3.0 mol of ions.\nFor $2.0 \,\mathrm{mol} \,\mathrm{CH}_{4}$ : Each molecule of CH4 contains 5 atoms (1 C + 4 H). So, 2.0 mol CH4 contains 2.0 mol * 5 atoms/mol = 10.0 mol of atoms.\nFor $2.5 \,\mathrm{mol} \,\mathrm{Au}$ : Each atom of Au contains 1 atom. So, 2.5 mol Au contains 2.5 mol * 1 atom/mol = 2.5 mol of atoms.

Step 2: Compare the number of atoms in each sample.
3. 0 mol (H2O), 3.0 mol (NaCl), 10.0 mol (CH4), 2.5 mol (Au).

Step 3: Final Answer
2. 5 mol Au contains the smallest number of atoms.

Why other options are wrong:
- Option A: This is incorrect because 1.0 mol H2O contains 3.0 mol of atoms, which is more than 2.5 mol of atoms in Au.
- Option B: This is incorrect because 1.5 mol NaCl contains 3.0 mol of ions, which is more than 2.5 mol of atoms in Au.
- Option C: This is incorrect because 2.0 mol CH4 contains 10.0 mol of atoms, which is more than 2.5 mol of atoms in Au.

Key Concepts:
- Mole concept
- Number of atoms in a molecule

Memory Aids:
- 1 mole = 6.022 × 10²³ particles

Quick Tips:
- Multiply the number of moles by the number of atoms/ions in the compound to find the total number of atoms/ions.

29 Easy

29 of 114Question permalink

Understanding +4 | -1

The formation of

CO

and

C{O_2}

illustrates the law of

View answer and explanation

Correct option: C

Multiple proportion

The correct answer is C (Multiple proportion) because carbon and oxygen form two different compounds, CO and CO2, where the ratio of oxygen masses combining with a fixed mass of carbon is a simple whole number.

Solution approach

Correct Answer + Core Reason: Multiple proportion. Carbon and oxygen form two different compounds, CO and CO2.

Step-by-Step Solution:

Step 1: Define the Law of Multiple Proportions: When two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in a ratio of small whole numbers.

Step 2: In CO, 12 g of carbon combines with 16 g of oxygen. In CO2, 12 g of carbon combines with 32 g of oxygen.

Step 3: The ratio of oxygen masses combining with 12 g of carbon is 16:32 or 1:2, a simple whole number ratio.

Why other options are wrong:
- Option A: Reciprocal proportion involves three elements and the ratios in which they combine with each other.
- Option B: Conservation of mass states that mass is neither created nor destroyed in a chemical reaction.
- Option D: Constant composition is the same as definite proportions, which applies to a single compound, not multiple compounds.

Key Concepts:
- Law of multiple proportions

Memory Aids:
- Multiple proportions: different compounds, simple ratio.

Quick Tips:
- Identify the elements and their mass ratios in different compounds.

30 Easy

30 of 114Question permalink

Analyzing +4 | -1

Assertion: Density

=

specific gravity

\times 0.99823

at

20^{\circ} \mathrm{C}

.
Reason: Density

=

specific gravity at

4^{\circ} \mathrm{C}

.

View answer and explanation

Correct option: D

Both Assertion and Reason are correct but Reason is not correct explanation of Assertion

Option D (Both Assertion and Reason are correct but Reason is not correct explanation of Assertion) is correct because both statements are true, but the reason doesn't explain the assertion.

Solution approach

Correct Answer + Core Reason: Both Assertion and Reason are correct but Reason is not correct explanation of Assertion. The assertion and reason are both correct statements, but the reason does not explain why the density at 20°C is related to specific gravity by the given factor.

Step-by-Step Solution:

Step 1: Evaluate the assertion.\nDensity = specific gravity × 0.99823 at $20^{\circ} \mathrm{C}$ . This is generally true because the density of water at $20^{\circ} \mathrm{C}$ is approximately 0.99823 g/mL or kg/L. Specific gravity is the ratio of the density of a substance to the density of water at a specific temperature (usually $4^{\circ} \mathrm{C}$ ).

Step 2: Evaluate the reason.\nDensity = specific gravity at $4^{\circ} \mathrm{C}$ . This is true because specific gravity is defined as the ratio of the density of a substance to the density of water at $4^{\circ} \mathrm{C}$ , where the density of water is approximately 1 g/mL or 1 kg/L.

Step 3: Determine if the reason explains the assertion.\nThe reason does not explain why the density at $20^{\circ} \mathrm{C}$ is related to specific gravity by the factor 0.99823. The factor arises from the density of water at $20^{\circ} \mathrm{C}$ being 0.99823 g/mL.

Step 4: Conclusion.\nBoth the assertion and the reason are correct, but the reason is not the correct explanation of the assertion.

Why other options are wrong:
- Option A: The reason is correct, so this option is wrong.
- Option B: The assertion is correct, so this option is wrong.
- Option C: The reason does not explain the assertion, so this option is wrong.

Key Concepts:
- Density
- Specific gravity
- Temperature dependence of density

Memory Aids:
- Specific gravity is a dimensionless quantity.
- Density of water is maximum at $4^{\circ} \mathrm{C}$ .

Quick Tips:
- Remember the definition of specific gravity.
- Understand the temperature dependence of density.

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