RP 4: Exam Questions

Question 1

A solution that is thought to contain chloride ions and iodide ions is tested.
1. Dilute nitric acid is added to the solution.
2. Aqueous silver nitrate is added to the solution.
3. A pale yellow precipitate forms.
4. Excess dilute aqueous ammonia is added to the mixture.
5. Some of the precipitate dissolves and a darker yellow precipitate remains.
Give a reason for the use of each reagent.
Explain the observations.
Give ionic equations for any reactions.

Answer 1

• HNO3 removes (hydroxide/carbonate) ions that may give other ppts
  with AgNO3
• AgNO3 produces ppts with halide ions.
• Ag+ + Cl- -> AgCl
• NH3 dissolves AgCl leaving yellow AgI
• AgCl(s) + 2NH3(aq) → Ag(NH3)2 (aq) + Cl− (aq)

Question 2

A student compares the rates of hydrolysis of 1-chlorobutane, 1-bromobutane and
1-iodobutane.
The suggested method is:
* add equal volumes of the three halogenoalkanes to separate test tubes
* add equal volumes of aqueous silver nitrate to each test tube
* record the time taken for a precipitate to appear in each test tube.
State and explain the order in which precipitates appear

Answer 2

Silver iodide then silver bromide then silver chloride
bond strength C−I < C−Br < C−Cl

Question 3

State what is observed when silver nitrate solution is added to sodium fluoride solution.

Answer 3

Colourless solution

Question 4

State one observation when NaCl is reacted with sulfuric acid. Give an equation and state the role of chloride ions.

Answer 4

Misty fumes
NaCl + H2SO4 → NaHSO4 + HCl
Proton acceptor

Question 5

Give an equation for the redox reaction between sodium bromide and concentrated H2SO4.

Answer 5

2NaBr + 2H2SO4 → Na2SO4 + Br2 + SO2 + 2 H2O

Question 6

State what is observed when aqueous chlorine is added to sodium bromide.
Give an ionic equation.

Answer 6

Yellow/orange solution
Cl2 + 2Br – → 2Cl– + Br2