Task 2: Melting of ice cubes with various salt concentration

A day before the laboratory practical, the teacher prepares 3 differently concentrated solutions of table salt (sodium chloride). The first solution of table salt will be of 20 % that means that the teacher dissolves 200 grams of table salt in 800 ml of water and dyes it with food colouring.

The teacher then prepares the second solution of table salt of 10% that means the teacher dissolves 100 grams of table salt in 900 ml of water and again dyes the solution with food colouring, but this time he/she uses a different colour from the one he/she used for dying of the first solution.

The third solution will not contain any table salt. The teacher only dyes the water with the food colouring. He/she uses a different colour from those he/she used before. The teacher pours the prepared solutions into ice cubes moulds or ice bags and leaves them to freeze in the freezer until the next day.

On the day of the laboratory practical, the teacher prepares for the working group of pupils the following equipment: 3 beakers or bowls of the same size, a thermometer, time gauge (pupils can use their own devices for measuring the time, for example clocks, mobile phones).

Pupils fill all the containers with tap water of the same temperature. They measure the temperature with the prepared thermometer.

The teacher distributes three ice cubes of various colours to each working group. Pupils do not know that the ice cubes are not just clear frozen water. At the same time, they put one ice cube into each container and simultaneously start measuring the time it takes for each ice cube to dissolve.