2 mL each of concentrated $HCl, {HNO}_{3}$ and a mixture of concentrated $HCl$ and concentrated ${HNO}_{3}$ in the ratio of 3 : 1 were taken in test tubes labelled as A, B and C. A small piece of gold was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C respectively. Answer the following question.

Give reason why this observation was made.

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Solution

A 3:1 mixture of concentrated $H C l a n d {HNO}_{3}$ is known as aqua regia.

Aqua regia dissolves gold, though neither constituent acid will do so alone, because, in combination, each acid performs a different task and will actually dissolve a virtually undetectable amount of gold, forming gold ions.

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Q. Question 21
2 mL each of concentrated

HCl, {HNO}_{3}

and a mixture of concentrated

HCl

and concentrated

{HNO}_{3}

in the ratio of 3 : 1 were taken in test tubes labelled as A, B and C. A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C respectively. The metal could be
(a)

Al

(b)

Au

(c)

Cu

(d)

Pt

Q. 2 ml each of concentrated

H C l

H N O_{3}

and a mixture of concentrated

H C l

and concentrated

H N O_{3}

2 mL of ethanoic acid was taken in each of the 3 test tubes A, B and C. To these test tubes 2 mL, 4 mL and 8 mL of water was added respectively. Which test tube will give a clear solution?

Q. 2 ml of ethanoic acid was taken in each of the three test tubes A, B and C. To these test tubes 2 ml, 4 ml and 8 ml of water was added respectively. Which test tube should contain a clear solution?

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A 3:1 mixture of concentrated HCl and HNO3 is known as aqua regia. Aqua regia dissolves gold, though neither constituent acid will do so alone, because, in combination, each acid performs a different task and will actually dissolve a virtually undetectable amount of gold, forming gold ions.