Ch 11 Qualitative Analysis

Question 1

Solubility table: Solubility of nitrate salts?

Answer 1

All nitrates are soluble.

Question 2

Solubility table: Solubility of ammonium salts?

Answer 2

All ammonium salts are soluble.

Question 3

Solubility table: Solubility of group 1 salts?

Answer 3

All group 1 salts are soluble.

Question 4

Solubility table: Solubility of chloride, bromide and iodide salts?

Answer 4

All are soluble except lead (II) and silver.

Question 5

Solubility table: Solubility of sulfate salts?

Answer 5

All are soluble except lead (II), barium and calcium.

Question 6

Solubility table: Solubility of carbonate salts?

Answer 6

All group 1 and ammonium salts are soluble.

Question 7

Solubility table: Solubility of hydroxide salts?

Answer 7

All group 1 and ammonium salts are soluble. Calcium, barium and strontium are sparingly soluble. (Low solubility)

Question 8

Practical skills: What should you record if a gas is produced?

Answer 8

1. What you observed (effervescence, colour and odour)
2. How you tested for the gas and result
3. Identity of the gas

Example:
1. Effervescence produced, colourless and odourless gas liberated.
2. A gas that forms a white ppt with limewater is evolved.
3. The gas is carbon dioxide.

Question 9

What is a cation?

Answer 9

Positively-charged ion.

Question 10

What is an anion?

Answer 10

Negatively-charged ion.

Question 11

1. How can cations be identified? (Test for cation)
2. What must you record when writing down the results?

Answer 11

1. Add aqueous ammonia or aqueous sodium hydroxide. (Both provide OH- ions. Not stated in aqueous ammonia as it is a weak alkali.)
2. Colour of precipitate, whether the precipitate is soluble/insoluble in excess reagent, ammonia gas produced. (If any)

Question 12

1. How can anions be identified?
2. What must you record when writing down the results for anion tests?

Answer 12

1. By adding specific chemicals.
2. Colour of ppt, effervescence/gas produced. (If any)

Question 13

How can gases be identified?

Answer 13

By using specific tests.

Question 14

1. Test for carbonate anion
2. Positive result

Answer 14

1. Add dilute acid.
2. Effervescence, carbon dioxide produced.

Acid + Carbonate -> Salt + Water + Carbon dioxide

Question 15

1. Test for chloride anion
2. Positive result

Answer 15

1. Acidify with dilute nitric acid, then add aqueous silver nitrate.
2. White ppt (AgCl)

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

Question 16

1. Test for iodide anion
2. Positive result

Answer 16

1. Acidify with dilute nitric acid, then add aqueous silver nitrate/lead (II) nitrate.
2. Yellow ppt (AgI/PbI2)

Ag+ (aq) + I- (aq) -> AgI (s)
Pb2+ (aq) + I- (aq) -> PbI2 (s)

Question 17

1. Test for nitrate anion
2. Positive result

Answer 17

1. Add aqueous sodium hydroxide, then aluminium foil, warm carefully. (3 steps)
2. Ammonia produced

(Equation not in syllabus)

Question 18

1. Test for sulfate anion
2. Positive result

Answer 18

1. Acidify with dilute nitric acid, then add aqueous barium nitrate.
2. White ppt. (BaSO4)

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

Question 19

What is the identity of the precipitates produced during a test for aqueous cations?

Answer 19

Metal hydroxides.

Question 20

1. Test for aluminium cation
2. Positive result

Answer 20

Aqueous sodium hydroxide.
- White ppt, soluble in excess giving a colourless solution.

Aqueous ammonia.
- White ppt, insoluble in excess

White ppt: Al(OH)3

Question 21

1. Test for ammonium cation
2. Positive result

Answer 21

Aqueous sodium hydroxide.
- Ammonia produced on warming.

Aqueous ammonia.
- Ammonium salt + Alkali -> Salt + Water + Ammonia gas

Question 22

1. Test for calcium cation
2. Positive result

Answer 22

Aqueous sodium hydroxide.
- White ppt, insoluble in excess.

Aqueous ammonia.
- No ppt.

White ppt: Ca(OH)2

Question 23

1. Test for copper (II) cation
2. Positive result

Answer 23

Aqueous sodium hydroxide.
- Light blue ppt, insoluble in excess.

Aqueous ammonia.
- Light blue ppt, soluble in excess giving a dark blue solution.

Light blue ppt: Cu(OH)2

Question 24

1. Test for iron (II) cation
2. Positive result

Answer 24

Aqueous sodium hydroxide.
- Green ppt, insoluble in excess

Aqueous ammonia.
- Green ppt, insoluble in excess

Green ppt: Fe(OH)2

Question 25

1. Test for iron (III) cation 2. Positive result

Answer 25

Aqueous sodium hydroxide. - Red-brown ppt, insoluble in excess Aqueous ammonia. - Red-brown ppt, insoluble in excess Red-brown ppt: Fe(OH)3

Question 26

1. Test for zinc cation 2. Positive result

Answer 26

Aqueous sodium hydroxide. - White ppt, soluble in excess giving a colourless solution Aqueous ammonia. - White ppt, soluble in excess giving a colourless solution White ppt: ZN(OH))2

Question 27

1. Test for ammonia gas 2. Positive result

Answer 27

1. Place damp litmus paper at the mouth of the test tube 2. Turns damp red litmus paper blue

Question 28

1. Test for carbon dioxide gas 2. Positive result

Answer 28

1. Bubble gas into limewater 2. White ppt, soluble in excess CO2

Question 29

1. Test for chlorine gas 2. Positive result

Answer 29

1. Place damp litmus paper at the mouth of the test tube 2. Bleaches damp litmus paper

Question 30

1. Test for hydrogen gas 2. Positive result

Answer 30

1. Place a lighted splint at the mouth of the test tube 2. 'pops' with a lighted splint (explosive/flammable)

Question 31

1. Test for oxygen gas 2. Positive result

Answer 31

1. Insert a glowing splint into the test tube 2. Relights glowing splint (combustible)

Question 32

1. Test for sulfur dioxide gas 2. Positive result

Answer 32

1. Place filter paper dipped in purple aqueous acidified potassium manganate (VII) at the mouth of the test tube 2. Turns aqueous acidified potassium manganate (VII) from purple to colourless

Question 33

Acidic gases?

Answer 33

1. Carbon dioxide 2. Chlorine (also bleaching) 3. Sulfur dioxide

Question 34

Alkaline gases?

Answer 34

1. Ammonia

Question 35

Neutral gases?

Answer 35

1. Hydrogen 2. Oxygen