When 1 g of a salt is dissolved in 50.0 g of water, the temperature increases by 2.5ºC. Which of the following changes will cause the temperature to increase by about 5ºC?

Question

When 1 g of a salt is dissolved in 50.0 g of water, the temperature increases by 2.5ºC. Which of the following changes will cause the temperature to increase by about 5ºC?

a. Doubling the amount of salt to 2 g and doubling the amount of water to 100 g

b. Doubling the amount of water to 100 g for the same amount of salt

c. Halving the amount of salt to 0.5 g for the same amount of water

d. Doubling the amount of salt to 2 g for the same amount of water

Answer 1

First, if we are talking about table salt (NaCl), the solution will become colder as the process is endothermic. However, the problem may not be referring to table salt, so let's assume it is a salt that dissolves exothermically. Reason a will not work as although the amount of salt is doubled, the amount of water increases so that the extra heat evolved is used in heating the extra water and will not double the temperature.

Reason b won't work for essentially the same reason as in a.

Reason c won't work because there is less salt; therefore, the evolution of less heat.

Reason d is the correct answer as there is double the amount of salt in the same amount of water, so you would expect twice the heat evolved and an increase in the temperature of the water.