What does the process of froth flotation help to achieve? A. It makes the metal lighter.
B. It decreases the ratio of metal in the ore.
C. It crushes the ore to make contact with metallic compounds easier.
D. It increases the concentration of metal in the ore.

C. It crushes the ore to make contact with metallic compounds easier.

Explanation:

Let us assume that the solution has the same specific heat capacity as water, of 4.18 Joules per gram.

a) H = mCpΔT
Where m will be the mass of the solution. We do not incorporate the mass of Ca because it will dissolve and release some amount of Hydrogen gas; rendering its contribution negligible. Assuming solution density equal to water's 1 gram per cubic centimeter:
H = 50 x 4.18 x (71.4 - 25.2)
H = 9655.8 Joules are gained

b) Assuming no heat is lost to the surroundings,
Heat lost by reaction = Heat gained by soluton
Heat lost by reaction = 9655.8 Joules

c) Moles of Ca present = 0.5/40 = 0.0125
Heat of reaction is the energy released upon reaction of the quantities in the balanced equation of a reaction. In this case:
Ca + 2HCl → CaCl₂ + H₂
So 0.0125 moles produces 9655.8 Joules
1 mole will produce: 9655.8 / 0.0125
= 772.5 kJ