(a) (i) Name three different methods for preparing salts. (ii) Give one example of a balanced equation for each of the methods named in (a)(i). (iii) State ...

(a) (i)  Name three different methods for preparing salts.
     (ii) Give one example of a balanced equation for each of the methods named in (a)(i).
     (iii) State two uses of sodium trioxocarbonate (IV). 

(b) If you were given some impure copper, describe how you would
obtain a specimen of the pure metal by electrolysis. 

(c) Given that sodium chloride has a solubility of 36.3 at 30  and 39.0 at
100  and that of silver nitrate is 297.0 at 30  and 952.0 at 100.

(i) Calculate the percentage of each substance in the saturated solution at 100  that is deposited on cooling to 30

(ii) Deduce which of the two salts can be purified more efficiently by crystallization.

Answer Details

a)

1. (i) Three different methods for preparing salts are precipitation, neutralization, and evaporation.
2. (ii) Examples of balanced equations for each method:
   • Precipitation: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
   • Neutralization: HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
   • Evaporation: NaCl(aq) → NaCl(s)
3. (iii) Two uses of sodium trioxocarbonate (IV) are:
   • As a cleaning agent: Sodium trioxocarbonate (IV) is used as a cleaning agent in many household and industrial cleaning products.
   • As a water softener: Sodium trioxocarbonate (IV) can be used to soften hard water by removing excess calcium and magnesium ions.

b)

1. To obtain a specimen of pure copper by electrolysis, you would need to follow these steps:
   • Obtain a supply of direct current (DC) and two electrodes (anode and cathode).
   • Place the impure copper in a solution that conducts electricity (such as copper sulfate solution).
   • Attach the impure copper to the anode and a pure copper plate to the cathode.
   • Turn on the DC and allow the copper ions to be attracted to the cathode, where they will deposit and form pure copper.

c)

To calculate the percentage of each substance in the saturated solution at 100 that is deposited on cooling to 30:

• For sodium chloride: (36.3/39.0) x 100 = 92.56%
• For silver nitrate: (297.0/952.0) x 100 = 31.22%

Based on the percentage of each substance that is deposited, sodium chloride can be purified more efficiently by crystallization.