2g - chemical tests

Question 1

How do you test for hydrogen?

Answer 1

Method:

• collect gas in boiling tube
• Insert lit Splint inside the boiling tube

Result:
- If Hydrogen is present, the gas will burn with a ‘squeaky pop’

Question 2

How do you test for oxygen?

Answer 2

Method:

• Collect gas into a boiling tube
• Insert glowing splint

Result:
- If Oxygen is present, splint will relight

Question 3

How do you test for carbon dioxide?

Answer 3

Method:

• Bubble gas through limewater
• Observe colour change

Result:
- If Carbon Dioxide is present, limewater will turn milky and cloudy (form a white precipitate)

Question 4

How do you test for ammonia?

Answer 4

Method
- Lower damp red litmus paper into the test solution

Results:
- If Ammonia is present, damp red litmus paper turns Blue

Question 5

How do you test for chlorine?

Answer 5

Method:
- Lower damp blue litmus paper into test solution

Results:
- If Chlorine is present, damp litmus paper turns red then bleaches White

Question 6

How do you carry out a flame test and what is it?

Answer 6

FLAME TEST: Method to identify Metal Cations by the colour of flame they produce

METHOD:

• Platinum or Nichrome wire is cleaned by dipping it into Hydrochloric acid
• End of wire is dipped into fresh Hydrochloric acid and then into solid sample
• End of the wire with solid sample attached is placed into a non-luminous bunsen flame
• Colour of flame is observed and recorded

Question 7

What colour does the flame turn if lithium (Li⁺) is present?

Answer 7

bright red

Question 8

What colour does the flame turn if sodium (Na⁺) is present?

Answer 8

golden yellow

Question 9

What colour does the flame turn if potassium (K⁺) is present?

Answer 9

lilac

Question 10

What colour does the flame turn if calcium (Ca²⁺) is present?

Answer 10

orange-red

Question 11

What colour does the flame turn if copper (II) (Cu²⁺) is present?

Answer 11

Blue-Green

Question 12

Who do you test for chloride ions? What is the equation for the reaction?

Answer 12

Method:

• Add a small volume of Dilute Nitric Acid to react and remove Carbonate ions from sample solution
• Add a few drops of Silver Nitrate Solution
• Colour of precipitate is observed and recorded

Results:
- If a white precipitate is formed then chloride ions are present

Equation:
Ag+ + Cl- → AgCl

Question 13

Who do you test for bromide ions? What is the equation for the reaction?

Answer 13

Method:

• Add a small volume of Dilute Nitric Acid to react and remove Carbonate ions from sample solution
• Add a few drops of Silver Nitrate Solution
• Colour of precipitate is observed and recorded

Results:
- If bromide ions are present a cream precipitate will from

equation:
- Ag+ + Br- → AgNr

Question 14

Who do you test for iodide ions? What is the equation for the reaction?

Answer 14

Method:

• Add a small volume of Dilute Nitric Acid to react and remove Carbonate ions from sample solution
• Add a few drops of Silver Nitrate Solution
• Colour of precipitate is observed and recorded

Results:
- If iodide ions are present then a yellow precipitate will from

Equation:
- Ag+ + I- → Agl

Question 15

How do you test for sulphate ions?

Answer 15

Method:

• Add a small volume of Dilute Hydrochloric acid to react and remove Carbonate ions
• Add a few drops of Barium Chloride Solution
• Colour of precipitate is observed and recorded

result:
- If Sulfate ions are present, White precipitate will form (Barium Sulfate)

Question 16

How do you test for carbonate ions?

Answer 16

Method:

• Add Dilute Hydrochloric acid
• Gas produced is bubbled into limewater
• Colour of precipitate is observed and recorded

Result:

• fizzing will occur
• If Carbonate ions are present, limewater will turn milky

Question 17

How do you test for copper(II) ions?

Answer 17

Method:

• Add Aqueous Sodium Hydroxide
• Colour of precipitate is observed and recorded

Result:
- Blue Precipitate (solid)

Equation:
- Cu2+ + 2OH- → Cu(OH)2

Question 18

How do you test for iron(II) ion?

Answer 18

Method:

• Add Aqueous Sodium Hydroxide
• Colour of precipitate is observed and recorded

Result:
- Green Precipitate will form (solid)

Equation:
- Fe2+ + 2OH- → Fe(OH)2

Question 19

How do you test for iron(iii) ions?

Answer 19

Method:

• Add Aqueous Sodium Hydroxide
• Colour of precipitate is observed and recorded

Result:
- Brown precipitate will from (solid)

Equation:
- Fe3+ + 3OH- → Cu(OH)3

Question 20

How do you test for ammonium ions?

Answer 20

Method:

• Add Aqueous Sodium Hydroxide to the solid or solution and heat using bunsen burner (warm it)
• Lower damp red litmus paper into gas produced

Result:

• If Ammonium ions are present, pungent-smelling gas is produced
• Gas produced turns damp red litmus paper Blue

Question 21

How do you test for water?

Answer 21

Add anhydrous copper (II) sulfate (CuSO4) to a sample.

If water is present the anhydrous copper (II) sulfate will change from white to blue (into hydrated copper sulfate).

Question 22

describe a physical test to show whether a sample of water is pure:

Answer 22

METHOD 1:
Boil liquid and measure boiling point
Result: Boiling point of Water is 100°C

METHOD 2:
Freeze liquid and measure freezing point (same as melting point)
result: Freezing point (melting point) of Water is 0°C