Required practical 4

Question 1

Describe the test for halide ions

Answer 1

1. Add dilute HNO3 (to remove carbonate ions)
2. Add aqueous silver nitrate (AgNO3(aq))
   Confirmatory test:
3. Test solubility of precipitate in dilute/concentrated ammonia

Question 2

What are the observations if chloride ions are present

Answer 2

• White precipitate forms
• Precipitate is soluble in dilute aqueous ammonia

Question 3

What inferences can be made from the observations of chloride ions

Answer 3

• The precipitate is silver chloride (AgCl)
• Chloride ions are present

Question 4

What is the ionic equation for the test for chloride ions

Answer 4

Ag+(aq) + Cl-(aq) => AgCl(s)

Question 5

What are the observations if bromide ions are present

Answer 5

• Cream precipitate forms
• Precipitate is soluble in concentrated aqueous ammonia

Question 6

What inferences can be made from the observations of bromide ions

Answer 6

• The precipitate is silver bromide (AgBr)
• Bromide ions are present

Question 7

What is the ionic equation for the test for bromide ions

Answer 7

Ag+(aq) + Br-(aq) => AgBr(s)

Question 8

What are the observations if Iodide ions are present

Answer 8

• Yellow precipitate is formed
• Precipitate is insoluble in dilute and concentrated aqueous ammonia

Question 9

What inferences can be made from the observations of iodide ions

Answer 9

• The precipitate is silver iodide (AgI(s))
• There are I- ions present

Question 10

What is the ionic equation for the test for iodide ions

Answer 10

Ag+(aq) + I-(aq) => AgI(s)

Question 11

Describe the test for sulfate ions

Answer 11

1. Add dilute HCl (to remove carbonate ions)
2. Add aqueous barium chloride

Question 12

What are the observations for a positive test for sulfate ions

Answer 12

A white precipitate forms.

Question 13

What inferences can be made from the observations when testing for sulfate ions

Answer 13

• The precipitate is BaSO4(s)
• SO4(2-) ions are present

Question 14

What is the ionic equation for the test for sulfate ions

Answer 14

Ba2+(aq) + SO4(2-)(aq) => BaSO4(s)

Question 15

Describe the test for carbonate ions

Answer 15

Add dilute acid (e.g. HCl, HNO3 or H2SO4) to a compound or solution.

Question 16

What are the observations in the test for carbonate ions

Answer 16

• Effervesence giving colourless gas
• Gas turns lime water cloudy

Question 17

What inferences can be made from the observations in the test for carbonate ions

Answer 17

• Gas = CO2 (carbon dioxide)
• CO3(2-) or HCO3- ions present

Question 18

What is the ionic equation for the test for carbonate ions

Answer 18

• CO3(2-)(s/aq) + 2H+(aq) => CO2(g) + H2O(l)
• HCO3-(s/aq) + H+(aq) => CO2(g) + H2O(l)

Question 19

Describe the test for hydroxide ions

Answer 19

Test solution with red litmus/pH indicator.

Question 20

What are the observations in the test for hydroxide ions

Answer 20

• Red litmus paper turns blue
• pH indicator turns blue/purple

Question 21

What inferences can be made from the observations in the test for hydroxide ions

Answer 21

It’s alkali (and OH- ions present).

Question 22

Describe the test for ammonium ions

Answer 22

1. Add aqueous NaOH and warm mixture
2. Test the gas given off with litmus or pH paper

Question 23

What are the observations in the test for ammonium ions

Answer 23

• Gas evolved that turns damp red litmus paper blue
• Smells strongly of ammonia

Question 24

What inferences can be made from the observations in the test for ammonium ions

Answer 24

• Alkaline gas = ammonia
• NH4+ ions present

Question 25

What is the ionic equation for the test for ammonium ions

Answer 25

NH4+(s/aq) + OH-(aq) => NH3(g) + H2O(l)

Question 26

Describe the test for group 2 ions

Answer 26

Add aqueous NaOH to solution of compound.

Question 27

What are the observations for the test for group 2 ions

Answer 27

White ppt forms with Mg(2+) or Ca(2+).

Question 28

What inferences can be made from the observations in the test for group 2 ions

Answer 28

Precipitate forming = insoluble metal hydroxide, so either Mg(2+) ions or Ca(2+) ions present.

Question 29

What is the ionic equation for the test for group 2 ions

Answer 29

- Mg(2+)(aq) + 2OH-(aq) => Mg(OH)2(s) - Ca(2+)(aq) + 2OH-(aq) => Ca(OH)2(s)

Question 30

Describe the test for Ba(2+) ions or Sr(2+) ions

Answer 30

Add sulfuric acid (H2SO4) or any sulfate solution, e.g. Na2SO4

Question 31

What are the observations for the test for Ba(2+) ions or Sr(2+) ions

Answer 31

A white precipitate forms.

Question 32

What inferences can be made from the observations for the test for Ba(2+) ions or Sr(2+) ions

Answer 32

- Precipitate = BaSO4 - Ba(2+) or Sr(2+) ions present

Question 33

What is the ionic equation for the test for Ba(2+) ions or Sr(2+) ions

Answer 33

Ba(2+)(aq) + SO4(2-)(aq) => BaSO4(s)