This hydrometer experiment is designed to make a real chemist out of you. In the experiments in this book, but particularly this one, you will need to control all the variables. This means that all the materials and measurements will need to be the same. You will need to be patient here, too. It may take a little time to get your hydrometer and measurements adjusted, but you will succeed!
Things Required:
Your homemade hydrometer
A glass half-filled with tap water
2 rubber bands
2 tablespoonfuls salt
Directions:
Put one rubber band around the bottom of the glass of water and the other around the top. Carefully place the hydrometer in the water. Again, it should float freely straight up and should not touch the bottom of the glass. Push the hydrometer close to the side of the glass, being careful not to push the open end of it under the water, and let it float freely. Adjust the bottom rubber band around the glass so that it may mark the bottom of the clay ball on the hydrometer. This will measure how far your instrument drops in the water.
This Is What Happens:
In the salty water, the hydrometer floats higher and rises above the bottom rubber band. The water level of the salty water also rises above the top rubber band.
Science Behind It:
Salt water is denser or heavier than tap water, so fewer water molecules are displaced or forced out of position, by the weight of the hydrometer. So the straw sinks less in the salty water and rises above the rubber band.
