2g) Chemical Tests

Question 1

Method for Cation flame test

Answer 1

1) sterilise a nichrome wire using concentrated acid / alcohol
2) Dip it into the compound to be tested to pick up a small amount of solid
3) Put the wire into a roaring blue Bunsen flame & record the colour

Question 2

Colour for K+ (flame test)

Answer 2

Lilac

Question 3

Colour for Na+ (flame test)

Answer 3

Yellow

Question 4

Colour for Li+ (flame test)

Answer 4

Red

Question 5

Colour for Ca ^2+ (flame test)

Answer 5

Orange-red

Question 6

Colour for Cu ^2+ (flame test)

Answer 6

Blue-green

Question 7

Test & result for ammonium ion (NH4 ^+)

Answer 7

Test: add sodium hydroxide (NaOH) to the solution/solid to be tested. Then test the gas given off with damp red litmus paper.

Result: damp red litmus turns blue

Question 8

Anion test for sulphate (SO4 ^2-) & result

Answer 8

• Add dilute hydrochloric acid to the solution to be tested (removes other anions)
• Add an equal volume of barium chloride solution (BaCl2)

White precipitate is produced (BaSO4)

Question 9

Anion test for Carbonate (CO3 ^2-) & result

Answer 9

• add dilute acid to the sample to be tested & look for fizzing
• test the gas evolved by bubbling it through limewater

Carbonate ion is present if limewater goes cloudy

Question 10

Anion test for chloride, Bromide and iodide ions

Answer 10

• add dilute nitric acid (HNO3) to the sample to be tested (removes other anions)
• add silver solution (AgNO3)

Forms a precipitate

Question 11

Colour for chloride ion precipitate

Answer 11

White

Question 12

Colour for bromide ion precipitate

Answer 12

Cream

Question 13

Colour for iodide ion precipitate

Answer 13

Yellow

Question 14

Cation test for copper and iron (II & III) ions. (Precipitation reaction)

Answer 14

Add a solution of the salt to be tested to the same volume of sodium hydroxide (NaOH)
Record observations

Question 15

Cu ^2+ precipitate colour

Answer 15

Blue

Question 16

Fe ^2+ precipitate colour

Answer 16

Green

Question 17

Fe ^3+ precipitate colour

Answer 17

Orange-brown

Question 18

Gas test for Hydrogen

Answer 18

Put a lit splint into sample

Gives a ‘squeaky pop’

Question 19

Gas test for Oxygen

Answer 19

Put a glowing splint into the sample

It re-lights

Question 20

Gas test for Carbon dioxide

Answer 20

Bubble gas through limewater

Limewater goes clowdy

Question 21

Gas test for chlorine (Cl2)

Answer 21

Put some damp litmus paper over the mouth of the gas jar

If chlorine present, it will be bleached

(If blue litmus paper used , it will go red first)

Question 22

Gas test for ammonia (NH3)

Answer 22

Damp red litmus paper over the mouth of test tube / gas jar

Red litmus paper turns blue (NH3 is an alkaline gas)

Question 23

Chemical test for water

Answer 23

Add anhydrous copper(II) sulphate (CuSO4)

It turns from white to blue

CuSO4 (white) + 5 H2O —> CuSO4 • 5H2O (blue)