The difference between hard and soft water
Collect some hard water from a stream(or make some as defined in the next experiment). Also secure some soft water like as rain water or distilled water. Make some soap solution by dissolving soap shavings or powdered soap in a little warm water. Place equivalent amounts of hard and soft water in every of two bottles. Add soap solution to the soft water with a dropper, some drops at a time. Shake the bottle well after every addition. Count the number of drops of soap solution required to produce suds about 1 cm thick on the top.