9 — salts

Question 1

Spectator ions

Answer 1

Spectator ions r substances that remain unchanged in their physical state or charge and do not take part in the reaction

Question 2

To evaporate to dryness vs to crystallise

Answer 2

D:
- crystals r anhydrous
C:
- crystals r hydrated

D:
- salt must be stable to heat
C:
- salt is decomposed by heat

D:
- solubility of salt does not vary much w hot tempt
C:
- solubility of salt s much greater in water at high temperature

Question 3

Acid + B.C. M. Procedure

Answer 3

1. Fill half a beaker with x acid. Add excess y carbonate and stir continuously until no more y carbonate will dissolve or when no more effervescence observed (metal/carbonate + acid)
2. Filter to remove excess y carbonate, collect the filtrate which is the YX solution
3. Heat the filtrate till a hot saturated solution is obtained, where mass of solution remains constant.
4. Leave saturated solution to cool and crystallise
5. Filter to collect the residue. Wash the crystals with distilled water to remove impurities. Dry the crystals betw a few sheets of filter paper.

Acid+ insoluble B.C.M.
- non group 1 or SPA but soluble
- acid containing anion and insoluble CO3 containing cation
- insoluble B.C.M.in excess to use up the acid, preventing contamination of salt w acid

Question 4

Titration apparatus

Answer 4

1. Burette
2. Pipette and pipette filler
3. Conical flasks
4. Appropriate indicator

Question 5

Titration procedure

Answer 5

1. Fill up a burette with dilute nitric acid. Note the initial burette reading (V1, cm3).
2. Pipette 25.0cm of dilute sodium hydroxide solution into a conical flask.
3. Add 2-3 drops of methyl orange (indicator) to the sodium hydroxide solution. The solution turns yellow.
4. While swirling the conical flask, add dilute nitric acid from the burette slowly until the solution just turns orange permanently. This is the end-point.
5. Record the final burette reading as V2 cm3.

Volume of acid required = (V2 - V1) cm^3

Reaction is repeated without the addition of an indicator as the indicator would cause the salt to be impure.

6. Pipette 25.0cm of sodium hydroxide solution into a conical flask.
7. Add (V2 - V1) c m of dilute nitric acid from the burette.
8. Heat the solution to evaporate the water until a hot saturated solution is obtained.
9. Allow the saturated solution to cool and crystallise.
10. Filter to collect the residue.
11. Wash crystals with cold distilled water to remove impurities.
12. Dry the crystals between sheets of filter paper.

Question 6

Precipitation

Answer 6

(Cation + NO3) + (SPA + anion)

1. Add and mix (SPA + anion) solution to (cation + NO3) solution and stir until no more precipitate forms
2. Filter to collect the residue
3. Wash the residue w small amount of distilled water to remove impurities
4. Allow precipitate to dry on a piece of filter paper