"Heavy salt water" Return to list of pracs

Aim: This is an activity to begin a discussion about salt water.

Equipment: The equipment includes...  

• table salt;
• 4 plastic cups;
• paddle pop sticks;
• kitchen scales;
• measuring cup;
• water.

Method: Working in pairs, students fill each of their 2 cups with water. They then try to dissolve as much salt in one of their cups as possible. They can then taste both. Get them to then pour as accurately as possible 100mL into a 3rd (salt solution) and 4th cup (normal water) respectively. Place them both on a kitchen scale to note that one is heavier than the other.

Background knowledge: A discussion of taking into account the dissolved salt makes this solution heavier. Being heavier it allows objects in it to float higher that objects in normal water because there are more particles in the salt water colliding with the base of the object. For an object to float, the more dense the liquid (ie. the more particles in the water colliding with the base of the object) the higher it should float. Try it ... I hope this prac will work!