RP 4 - Identification of cations and anions

Question 1

How do you test for group 2 metal cations?

Answer 1

1) Place 10 drops of a group 2 compound in a test tube
2) Add 10 drops of sodium hydroxide to the test tube and record any observations
3) Continue to add sodium hydroxide so it is in excess. Record any observations.
4) Repeat with other group 2 compounds

Question 2

What is the expected change when sodium hydroxide is added to barium chloride?

Answer 2

Initial = colourless solution
10 drops of sodium hydroxide = colourless solution
Excess sodium hydroxide = colourless solution

Question 3

What is the expected change when sodium hydroxide is added to calcium bromide?

Answer 3

Initial = colourless solution
10 drops of sodium hydroxide = slight white precipitate
Excess sodium hydroxide = slight white precipitate

Question 4

What is the expected change when sodium hydroxide is added to magnesium chloride?

Answer 4

Initial = colourless solution
10 drops of sodium hydroxide = slight white precipitate
Excess sodium hydroxide = white precipitate

Question 5

What is the expected change when sodium hydroxide is added to strontium chloride?

Answer 5

Initial = colourless solution
10 drops of sodium hydroxide = slight white precipitate
Excess sodium hydroxide = slight white precipitate

Question 6

How would you distinguish between calcium bromide and strontium chloride?

Answer 6

1) Place 10 drops of barium chloride in a test tube
2) Add 10 drops of sulphuric acid, record observations
3) Continue to add sulphuric acid until in excess
4) Repeat for other group 2 compounds

Question 7

What is the expected change when sulphuric acid is added to barium chloride?

Answer 7

Initial = colourless solution
10 drops of sulphuric acid = white precipitate
Excess sulphuric acid = white precipitate

Question 8

What is the expected change when sulphuric acid is added to calcium bromide?

Answer 8

Initial = colourless solution
10 drops of sulphuric acid = slight white precipitate
Excess sulphuric acid = slight white precipitate

Question 9

What is the expected change when sulphuric acid is added to magnesium chloride?

Answer 9

Initial = colourless solution
10 drops of sulphuric acid = slight white precipitate
Excess sulphuric acid = colourless solution

Question 10

What is the expected change when sulphuric acid is added to strontium chloride?

Answer 10

Initial = colourless solution
10 drops of sulphuric acid = white precipitate
Excess sulphuric acid = white precipitate

Question 11

How do you test for ammonium ions?

Answer 11

1) Place 10 drops of ammonium chloride into a test tube
2) Add 10 drops of sodium hydroxide solution and shake
3) Warm the solution in the test tube
4) Test the gas released with damp red litmus paper
5) If it goes blue ammonium ions are present

Question 12

How do you test a group 7/ halide ions?

Answer 12

1) To the compound being tested add nitric acid and silver nitrate. Record observations.
2) To samples of this solution a dilute and then concentrated ammonia

Question 13

What are the expected results when halide ions react with silver nitrate?

Answer 13

Cl- = white precipitate
Br- = cream precipitate
I- = yellow precipitate

Question 14

What are the expected results when halide ions react with dilute NH3?

Answer 14

Cl- = white precipitate disappears (solution is therefore colourless)
Br- = cream precipitate remains
I- = yellow precipitate remains

Question 15

What are the expected results when halide ions react with concentrated NH3?

Answer 15

Cl- = remains colourless
Br- = cream precipitate disappears (solution therefore colourless)
I- = yellow precipitate remains

Question 16

How do you test for hydroxide ions?

Answer 16

1) Test a 1 cm depth of solution in test tube with red litmus or universal indicator paper
2) Record your observations
3) Sodium hydroxide will turn damp red litmus paper blue

Question 17

How do you test for carbonate ions?

Answer 17

1) Put 2cm³ of calcium hydroxide into a test tube
2) 3 cm³ of sodium carbonate in another test tube then add an equal volume of dilute hydrochloric acid
3) Immediately put in a delivery tube with open and into the calcium hydroxide test tube
4) If calcium hydroxide goes cloudy carbonate ions were present in the other test tube

Question 18

How do you test for sulphate ions?

Answer 18

1) Add hydrochloric acid and barium chloride to the suspected sulphate solution
2) If sulphate irons are present a white precipitate of barium sulphate will form

Question 19

What is the order of testing ions?

Answer 19

Carbonate -> Sulfate -> Halide