Identification of ions and gases

When an acid, X, was added to a solution containing the nitrate of metal Y, a dense white substance was precipitated.

• acid X: nitric acid; metal Y: zinc

• acid X: sulfuric acid; metal Y: barium

• acid X: hydrochloric acid; metal Y: calcium

• acid X: nitiric acid; metal Y: silver

Answer explanation

When an acid, X, was added to a solution containing the nitrate of metal Y, a dense white substance was precipitated.

Barium nitrate + sulfuric acid

--> barium sulfate + nitric acid

Ba(NO₃)₂ (aq) + H₂SO₄ (aq)

--> BaSO₄ (s) + 2HNO₃(aq)

Silver nitrate + nitric acid --> No visible rxn
Unless it is
Silver nitrate + hydrochloric acid
--> silver chloride + nitric acid

AgNO₃ (aq) + HCl (aq)

--> AgCl (s) + HNO₃(aq)

When dilute acid was added to an unknown sample, effervescence was observed. Which anion is present?

• ammonium ion

• carbonate ion

• nitrate ion

• sulfate ion

Answer explanation

Acid + carbonate
--> Salt + carbon dioxide + water
(ACSCW)

As a gas was bubbled through limewater, this was observed. What is the identity of the gas?

• hydrogen

• ammonia

• oxygen

• carbon dioxide

Answer explanation

Limewater is used to test for carbon dioxide gas!

Gas produced gives white precipitate in limewater.

CO₂ (g) + Ca(OH)₂ (aq) --> CaCO₃ (s) + H₂O (l)

A colourless pungent gas turns damp red litmus paper blue. What is the identity of the gas?

• hydrogen

• ammonia

• oxygen

• carbon dioxide

Answer explanation

Ammonia is an alkaline gas that turns damp red litmus paper blue.

When dilute nitric acid, followed by silver nitrate solution was added to an unknown sample, a white precipitate was observed. What is the white precipitate formed?

• silver chloride

• silver carbonate

• silver nitrate

• silver sulfate

Answer explanation

When dilute nitric acid, followed by silver nitrate:
This is to test for chloride ions!

Ag⁺ (aq) + Cl^- (aq) --> AgCl (s) white ppt

When dilute nitric acid, followed by barium nitrate solution was added to an unknown sample, a white precipitate was observed. What is the white precipitate formed?

• barium chloride

• barium carbonate

• barium nitrate

• barium sulfate

As a gas was bubbled through limewater, this was observed. What is the correct way to describe it?

• white cloudy emulsion

• white chalky solution

• white milky solution

• white precipitate formed in limewater

This is the setup to test for which gas?

• hydrogen

• ammonia

• oxygen

• carbon dioxide

Which of the following chemicals can be used to test for cations?

• Aqueous ammonia

• Ammonium nitrate

• Sodium chloride

• Sodium hydroxide

Ammonium hydroxide is the same as

• aqueous ammonia

• ammonia solution

• NH₃ (aq)

• NH₄OH