The Lassaigne's extract is boiled with dil. HNO_ 3 before testing for halogens because

Correct answer: B. Na_ 2 S and NaCN are decomposed by HNO_ 3 Na_ 2 S and NaCN, formed during fusion with metallic sodium, must be removed before adding AgNO_ 3 , otherwise black ppt. due to Na_ 2 S or white precipitate due to AgCN will be formed and thus white precipitate of AgCl will not be identified easily. Na_ 2 S+2 AgNO_ 3 2 NaNO_ 3 + Black Ag_ 2 S +AgNO_ 3 NaNO_ 3 + White Ag CN +AgNO_ 3 NaNO_ 3 + White Ag Cl _ 2 S+2 HNO_ 3 boil 2 NaNO_ 3 +H_ 2 S +HNO_ 3 boil NaNO_ 3 +HCN

BITSAT 2020

Exam: BITSAT
Year: 2020
Subject: Chemistry
Chapter: General Organic Chemistry

BITSAT 2020 · Chemistry · General Organic Chemistry

The Lassaigne's extract is boiled with dil. HNO_ 3 before testing...

The Lassaigne's extract is boiled with dil.

\mathrm{HNO}_{3}

before testing for halogens because

Options

Asilver halides are soluble in $\mathrm{HNO}_{3}$
B $\mathrm{Na}_{2} \mathrm{ S}$ and $\mathrm{NaCN}$ are decomposed by $\mathrm{HNO}_{3}$
C $\mathrm{Ag}_{2} \mathrm{ S}$ is soluble in $\mathrm{HNO}_{3}$
D $\mathrm{AgCN}$ is soluble in $\mathrm{HNO}_{3}$

Correct answer

B. $\mathrm{Na}_{2} \mathrm{ S}$ and $\mathrm{NaCN}$ are decomposed by $\mathrm{HNO}_{3}$

Step-by-step solution

\mathrm{Na}_{2} \mathrm{ S}

and

\mathrm{NaCN},

formed during fusion with metallic sodium, must be removed before adding

\mathrm{AgNO}_{3},

otherwise black ppt. due to

\mathrm{Na}_{2} \mathrm{ S}

or white precipitate due to

\mathrm{AgCN}

will be formed and thus white precipitate of

\mathrm{AgCl}

will not be identified easily.

\mathrm{Na}_{2} \mathrm{ S}+2 \mathrm{AgNO}_{3} \longrightarrow 2 \mathrm{NaNO}_{3}+\underset{\text{ Black }}{\mathrm{Ag}_{2} \mathrm{ S}} \downarrow\mathrm{NaCN}+\mathrm{AgNO}_{3} \longrightarrow \mathrm{NaNO}_{3} + \underset{\text{ White }}{\mathrm{Ag} \mathrm{CN}} \downarrow\mathrm{NaCl}+\mathrm{AgNO}_{3} \longrightarrow \mathrm{NaNO}_{3}+\underset{\text{ White }}{\mathrm{Ag} \mathrm{Cl}} \downarrow\mathrm{Na}_{2} \mathrm{ S}+2 \mathrm{HNO}_{3} \stackrel{\text{ boil }}{\longrightarrow} 2 \mathrm{NaNO}_{3}+\mathrm{H}_{2} \mathrm{ S} \uparrow\mathrm{NaCN}+\mathrm{HNO}_{3} \stackrel{\text{ boil }}{\longrightarrow} \mathrm{NaNO}_{3}+\mathrm{HCN} \uparrow

Practice General Organic Chemistry on Quantrex Academy →

More from General Organic Chemistry

The number of geometrical isomers possible for the compound, CH_3 CH=CH-CH=CH_2 is BITSAT 2024 Correct order of stability of carbanion is BITSAT 2024 Which of the following is not correct about Grignard reagent? BITSAT 2024 The IUPAC name of the following molecule is BITSAT 2024 Choose the correct stability order of the given free radicals. BITSAT 2024 Which of the following is strongest Bronsted base? BITSAT 2024 Which of the following acts as the stationary phase in paper chromatography? BITSAT 2023 Which one of the following exhibits geometrical isomerism? BITSAT 2023 Full General Organic Chemistry list All BITSAT PYQs