NEET UG CHEMISTRY MCQ: PRACTICAL CHEMISTRY

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The principal reason that solid sodium hydroxide is not used as a primary standard for acid-base titrations is that it

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Correct option: A

Absorbs water from air

The correct answer is A (Absorbs water from air) because solid sodium hydroxide is hygroscopic and readily absorbs moisture and carbon dioxide from the air, making it difficult to obtain a precise weight.

More Questions from PRACTICAL CHEMISTRY

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A pale green crystalline inorganic salt (A) dissolves freely in water. It gives a brown precipitate on addition of aqueous

\mathrm{NaOH}.

The solution of (A) also gives a black precipitate on bubbling

\mathrm{H}_2 \mathrm{S}

in alkaline medium. An aqueous solution of the (A) decolorizes the pink colour of the permanganate solution. The metal in the salt solution is

100 \mathrm{~ml}

\mathrm{NaHC}_2 \mathrm{O}_4

required

50 \mathrm{~ml}

0.1 \mathrm{~M} \, \mathrm{KMnO}_4

solution in acidic medium. Volume of

0.1 \mathrm{~M} \mathrm{~NaOH}

required by

100 \mathrm{~ml}

\mathrm{NaHC}_2 \mathrm{O}_4

is The ion that cannot be precipitated by both

{HCl}

and

{H}_2 {S}

is The rapid change of pH near the stoichiometric point of an acid-base titration in the basis of indicator detection. pH of the solution is related to ratio of the concentrations of the conjugated acid

(HIn)

and the base

(In)

forms of the indicator by the expression. On heating colourless solid

A,

gas

B

(liquid at room temp.) and gas

C

are formed.

A

is decomposed by

\mathrm{NaOH}

on heating to form gas

D

giving white fumes with

\mathrm{HCl}.

Gas

{C}

occupies

800 \mathrm{~ml} / \mathrm{g}

at N.T.P. Hence

A

is Standard

HCl

solution is titrated to a pink phenolphthalein endpoint by adding a

\mathrm{NaOH}

solution while stirring. If a solution becomes pink throughout but loses its color upon standing for a short time, what should be done to restore the color?