Question

Write the chemical equations showing the dissolution of sodium chloride, naphthalene C₁₀H₈, potassium phosphate, and calcium chloride. The first one has been done for you as an example.

          

NaCl    ^H2O      Na⁺ + Cl^-

    C10H8+H20--->10C-4 +8h+

    K3PO4+H2O--->(3K+)+1PO4-3

    CaCl2+H2O--->Ca(2+)+2Cl-

If an equal molar amount of each solute in the above was dissolved in 100 kg of water, which solute would cause the largest change in temperature? Explain your answer.

Answer 1

The balanced chemical equations for the dissolution of solute in water are as shown below.

Napthtalene is insoluble in water. In other words, it has very little solubility.

When equal molar amount of each solute in the above was dissolved in 100 kg of water, the molality m will be same for all the solutes and the solute that would cause the largest change in temperature will be the one which will have maximum value of the van't Hoff factor i.

The van't Hoff factor i will be maximum for the solute which will give maximum number of particles in the solution.

NaCl, naphthalene, potassium phosphate and calcium chloride on dissolution in water will give
2, 1, 7 and 5 particles respectively.

Since potassium phosphate gives maximum number of particles (7) on dissolution in water, it has maximum value of the van't Hoff factor i and the largest change in temperature.

Here, is the elevation in the boiling point, is the vant Hoff's factor, is the molality and is the molal elevation in the boiling point constant.