Question

Given the following, how do you calculate (a) the mass of water required to dissolve one hundred grams of sugar at 100°C and (b) the amount of sugar that remains in solution when the mixture in (a) is cooled to 20 C?

The solubility of sugar (sucrose) is 487 g/100 g water at 100°C and 204 g/100 g water at 20°C

Answer 1

(a) 20.5 g of water required; (b) 41.9 g of sugar remain in solution.

Explanation:

(a)

You know that 100 g water dissolve 487 g sugar.

∴ 100 g of sugar dissolve in

`100 color(red)(cancel(color(black)("g sugar"))) × "100 g water"/(487 color(red)(cancel(color(black)("g sugar")))) = "20.5 g water"`

So, 20.5 g of water contain 100 g of sugar at 100 °C.

(b)

At 20 °C, 20.5 g of water contain

`20.5 color(red)(cancel(color(black)("g water"))) × "204 g sugar"/(100 color(red)(cancel(color(black)("g water")))) = "41.9 g sugar"`