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This is a lesson on making a hydrometer




7, 8, 9  

Title – Making a hydrometer
By – Carol Frodge
Primary Subject – Science
Secondary Subjects –
Grade Level – 7-9
Lesson Plan: Making a Hydrometer
I use this hydrometer in a series of lessons including finding the relationship between density and salinity and density and temperature. This is an adaptation from Interaction of Earth and Time.
Problem: To make a hydrometer that works and test several solutions.

Test tube
One hole stopper
Glass tubing
Index card
Lead shot
Graduated cylinder

Part 1: Making the hydrometer
1.          Use a sharp pencil to carefully mark the long edge of an index card. Place a light mark every 2 millimeters. Make every fifth mark darker. Cut the marked edge to form a narrow strip that will fit inside the glass tubing.

2.          Place the marked strip inside the tubing. Hold the tubing and seal one end with a small amount of melted wax. The wax should form an airtight seal and also hold one end of the scale strip in place. Trim off any paper outside the wax seal.

3.          Moisten the outside of the unsealed end of the tubing with water. Carefully insert the moistened end into the stopper with the scale extending out the test tube .

4.          Place about 15 lead shot in the test tube and fit the stopper in place with the scale extending above the test tube.

5.          Obtain about 100 ml of water in a graduated cylinder. The density of water is 1.0 g/ml.

6.          Lower the hydrometer into the graduated cylinder. If the hydrometer sinks to the bottom, remove it and take out a few lead shot. If the hydrometer floats so that most of the scale is out of the water , add one or two lead shot to the test tube. Add or remove lead shot until the hydrometer floats with the second darkened line from waxed end of the tube at the water line. This marks 1.0 g/ml.

7.          Once you have calibrated the hydrometer (which means that it floats with the second darkened line from waxed end of the tube at the water line), don’t remove the stopper.

Part 2: Determining the densities of solutions A, B, and C.
(Solutions A,B, and C) can be made of different concentrations of salt or sugar.)

8.           Make a data chart in your lab book.

Solution          A          B          C
Trial 1                              
Trial 2                              
Trial 3                              

9.           Do one solution at a time. Pour about 90-100 ml of Solution A in your graduated cylinder. Place your hydrometer in the graduated cylinder. Read the density and record it in your chart.
Take your hydrometer out and repeat the process 2 more times. Return the solution A to the correct container.

10.           Repeat for solutions B and C.

11.           Record the solutions from least dense to most dense.

Least Dense          Middle Dense          Most Dense

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