Solutions to Mini-quiz #4 - 1999.02.05

1.a. Give the formula of a compound of one of the alkaline earth (group 2) elements that is insoluble in water.

MgF₂, Mg(OH)₂, Ca(OH)₂, CaCO₃, CaSO₄, BaSO₄

b. What is the anion present in the blue solution produced when sodium metal is dissolved in liquid ammonia?

It is the solvated (ammoniated) electron e^-(am). (The amide ion, NH₂^-, is only found after the sodium has reacted with the ammonia and the solution become colourless.)

2. Complete and balance TWO of the following equations:

a. 3Mg(s) + N₂(g) ---> Mg₃N₂(s) - (magnesium nitride)

b. CaO(s) + 3C(s) ---> CaC₂(s) + CO(g) - (calcium carbide or calcium acetylide)

c. 4KO₂(s) + 2CO₂(g) ---> 2K₂CO₃(s) + 3O₂(g) - (used to purify air in spacecraft etc.)

3. Sodium chloride and calcium carbonate are both mined in huge quantities. Give brief notes on how at least 3 products are obtained from ONE of them that are important in our everyday lives. (Include methods and uses.)

                     (reduce with C)   
  E.g. Fe2O3 -------------> Fe metal - useful structural
material.

These are just some of the uses you might have put down.

NaCl

• Essential dietary component (in small quantities.)
• Food preservation (e.g salt cod).
• To melt ice.

NaCl --(electrolyse molten)--> Na(s) + Cl₂(g)

Na:-

• Reducing agent esp. as amalgam or NH₃(l) solution.
• Used to make Ti metal from TiCl₄ - Ti used in aircraft.
• Used to make tetra-ethyl lead (TEL) for adding to gasolene.

Cl₂:-

• Used as a bleach itself and in sodium hydroxide solution as household "bleach", (Javex etc.)
• Used to make a wide range of other chemicals.

NaCl(aq) --(electrolyse in solution)--> NaOH + Cl₂ (see above) + H₂.

NaOH:-

• Widely used as a base in industry, the lab and the home (neutralisation of acids and e.g. drain cleaner.)

NaCl and CaCO₃

NaCl + CaCO₃ + energy --(Solvay process)--> Na₂CO₃ + CaCl_2.

(NaHCO₃ is also obtained by this process). CaCl₂:-

• "Liquid calcium" to reduce dust on dirt roads.
• Drying agent.

• Most used in glass manufacture.
• Cleaning agent ("washing soda").
• Mild base for neutralisation etc.

• Used in baking since it gives off CO₂ with weak acids or on heating ("baking soda").
• Also used to neutralise acids when a very weak base is required, e.g in medical situations for bee and nettle stings.

CaCO₃

• Limestone:-
  • as a building material.
  • to raise the pH of acid soil.
• Marble:- decorative use and statues etc.

CaCO₃ --(heat)--> CaO + CO₂

CaO (quicklime):-

• Once used in theatre spotlights - obsolete since electricity came into wide use!
• Used to make cement
• N.B. much too reactive for adding to soil!
• Used to make Ca(OH)₂ (slaked/builders lime) uses:-
  (CaO + H₂O ---> Ca(OH)₂)
• To make mortar in building.
• As a useful solid base for neutralisation.
• To detect CO₂ in the lab. (Saturated solution - lime water.)
• By fish poachers!

(C) H.J Clase 1999

---

| Top | 2210 Index | Problems Index |