How do you explain these occurrences using chemical and physical principles?

Question

Use chemical and physical principles to account for each of the following.

a) An aluminum container filled with an aqueous solution of CuSO4 eventually developed a leak. Include a chemical equation with your answer.

b) The inside of a metal container was cleaned with steam and immediately sealed. Later, the container imploded.

c) Skin feels cooler after rubbing alcohol has been applied to it.

d) The redness and itching of the skin caused by ant bites (injection of methanoic acid, HCO2H) can be relieved by applying a paste made from water and baking soda (solid sodium hydrogen carbonate). Include a chemical equation with your answer.

Answer 1

a)  Aluminum reacts with CuSO4 by displacing Copper in the solution:

2Al + 3CuSO4 = 3Cu + Al2(SO4)3

i.e. the CuSO4 is consuming the aluminum container.

b)  Cleaning the metal with steam would heat the metal considerably (the heat causes an expansion).  It was then sealed before it cooled.  Upon cooling, both the metal and the air inside the container cooled.  Cooling causes the pressure inside the container to drop and also the metal to shrink slightly thus causing the container to implode.  

c)  Rubbing alcohol evaporates quickly, the state change from liquid to gas requires energy, that energy being removed from the system by that physical reaction is felt as a drop in temperature.

d)  HCO2H is acidic, the redness and itching is a result of the acid.  Acids are neutralized by bases such as baking soda  (NaHCO3).

HCOOH + NaHCO3 --> H20 + CO2 + HCOONa