(U1) Qualitative Tests

Question 1

What happens in a gas test with H₂

Answer 1

Gives a ‘pop’ with a burning splint

Question 2

What happens in a gas test with O₂

Answer 2

Relights a glowing splint

Question 3

What happens in a gas test with Cl₂

Answer 3

Bleaches damp litmus/ universal indicator paper

(after turning it red)

Question 4

What happens in a gas test with CO₂

Answer 4

Bubble through limewater, limewater turns milky

Question 5

What happens in a gas test with HCl (2)

Answer 5

• hot glass rod dipped in concentrated ammonia solution
• White smoke

Question 6

What happens in a gas test with NH₃ (4)

Answer 6

• hot glass rod dipped in concentrated Hydrochloric acid
• White smoke

Or

• Red litmus paper turns blue
• or damp ui paper turns blue

Question 7

What colour does a Li⁺ ion produce in a flame test?

Answer 7

Crimson

Question 8

What colour does a Na⁺ ion produce in a flame test?

Answer 8

Yellow / orange

Question 9

What colour does a K⁺ ion produce in a flame test?

What colour through cobalt glass?

Answer 9

1. Lilac
2. pink

Question 10

What colour does a Ca²⁺ ion produce in a flame test?

Answer 10

Brick red

Question 11

What colour does a Ba²⁺ ion produce in a flame test?

Answer 11

Apple green

Question 12

What colour does a Cu²⁺ ion produce in a flame test?

Answer 12

Green-blue

Question 13

Outline how to conduct a flame test (3)

Answer 13

• Dip a nichrome wire in concentrated hydrochloric acid.
• Dip the wire into the solid metal salt.
• Hold the wire in the blue Bunsen flame and note the colour of the flame.

Question 14

What colour precipitate does a Fe²⁺ ion cause when dissolved in sodium hydroxide/ammonia solution?

Answer 14

Green ppt

Question 15

What colour precipitate does a Fe³⁺ ion cause when dissolved and added to sodium hydroxide/ammonia solution?

Answer 15

Red-brown ppt

Question 16

What is the test for NH₄⁺ ions? (4)

Answer 16

• Warm with a solution of NaOH
• pungent smell observed
• damp ui paper turns blue
• or glass rod dipped in conc HCl produces white smoke

Question 17

What is the test for SO₄^2- ions? (3)

Answer 17

• dissolve salt in water
• add solution of barium chloride or barium nitrate
• white ppt

Question 18

What is the test for Cl^- ions? (4)

Answer 18

• add nitric acid
• add silver nitrate
• white ppt formed
• add dilute ammonia solution, ppt redissolves

Question 19

What is the test for Br^- ions? (5)

Answer 19

• add nitric acid
• add silver nitrate
• cream ppt formed
• add dilute ammonia solution, ppt doesnt redissolve
• add conc ammonia, ppt redissolves

Question 20

What is the test for I^- ions? (5)

Answer 20

• add nitric acid
• add silver nitrate
• yellow ppt formed
• add dilute ammonia solution, ppt doesnt redissolve
• add conc ammonia, ppt doesn’t redissolves

ppt is insoluble in all solutions of ammonia

Question 21

What is the test for CO₃^- and HCO₃^- ions? (4)

Answer 21

• add dilute acid
• bubble gas produced through limewater
• turns from colourless to milky white
• back to colourless when in excess

Question 22

What is the test for Iodine? (2)

Answer 22

• add a few drops of starch to the solution
• solution turns from yellow-brown to blue-black