Chemical Tests

Question 1

Test for NH4+

Answer 1

Method:
- Add sodium hydroxide, which produces ammonia gas, then test the gas using damp red litmus paper

Observation:
- Ammonia gas produced, which turns damp red litmus paper blue

Equation:

NH4+ + OH- → NH3 + H2O

Question 2

Test for Cu2+

Answer 2

Method:
- add sodium hydroxide

Observation:
- light blue precipitate formed

Equation:

Cu2+ + 2OH- → Cu(OH)2

Question 3

Test for Fe2+

Answer 3

Method:
- Add sodium hydroxide

Observation:
- Green precipitate formed

Equation:

Fe2+ + 2OH- → Fe(OH)2

Question 4

Test for Fe3+

Answer 4

Method:
- Add sodium hydroxide

Observation:
- Brown precipitate formed

Equation:

Fe3+ + 3OH- → Fe(OH)3

Question 5

Test for Cl-

Answer 5

Method:
- Acidify the sample with nitric acid to remove any rogue carbonate ions that are present, then add silver nitrate (AgNO3)

Observation:
- Forms a white precipitate

Equation:

Ag+ + Cl- → AgCl

Question 6

Test for Br-

Answer 6

Method:
- Acidify the sample with nitric acid to remove any rogue carbonate ions that are present, then add silver nitrate (AgNO3)

Observation:
- Forms a cream precipitate

Equation:

Ag+ + Br- → AgBr

Question 7

Test for I-

Answer 7

Method:
- Acidify the sample with nitric acid to remove any rogue carbonate ions that are present, then add silver nitrate (AgNO3)

Observation:
- Forms a yellow precipitate

Equation:

Ag+ + I- → AgI

Question 8

Test for SO42-

Answer 8

Method:
- Acidify the sample with dilute hydrochloric acid, then add a few drops of barium chloride solution

Observation:
- Forms a white precipitate of barium sulfate

Equation:
- Ba2+ + SO42- → BaSO4

Question 9

Test for CO32-

Answer 9

Method:
- Add dilute acid, then bubble any gas produced through limewater by using a delivery tube.

Observation:
- Limewater turns cloudy

Equation:

CO32- + 2H+ → CO2 + H2O
CO2 + Ca(OH)2 → CaCO3 + H2O

Question 10

Test for Li+ flame

Answer 10

Method:
- Dip a loop of nichrome/platinum wire into dilute acid; hold into the blue flame of a bunsen until there is no colour change; dip the loop into the sample and then hold into the edge of a blue bunsen flame.

Observation:
- Red flame

Question 11

Test for Na+ flame

Answer 11

Method:
- Dip a loop of nichrome/platinum wire into dilute acid; hold into the blue flame of a bunsen until there is no colour change; dip the loop into the sample and then hold into the edge of a blue bunsen flame.

Observation:
Yellow flame

Question 12

Test for K+ flame

Answer 12

Method:
- Dip a loop of nichrome/platinum wire into dilute acid; hold into the blue flame of a bunsen until there is no colour change; dip the loop into the sample and then hold into the edge of a blue bunsen flame.

Observation:
- Lilac flame

Question 13

Test for Ca2+ flame

Answer 13

Method:
- Dip a loop of nichrome/platinum wire into dilute acid; hold into the blue flame of a bunsen until there is no colour change; dip the loop into the sample and then hold into the edge of a blue bunsen flame.

Observation:
- Orange-red flame

Question 14

Test for Cu2+ flame

Answer 14

Method:
- Dip a loop of nichrome/platinum wire into dilute acid; hold into the blue flame of a bunsen until there is no colour change; dip the loop into the sample and then hold into the edge of a blue bunsen flame.

Observation:
- Blue-green flame

Question 15

Test for water

Answer 15

Method:
- Use anhydrous copper sulfate, or boil and measure the boiling point.

Observation:
- Copper sulfate turns from white to blue in the presence of water; boils at exactly 100oC.

Equation:

CuSO4 → CuSO4.5H2O