How to Make a Concentration Tester for Salt Water

By Society & Culture & Entertainment Last updated Sunday, April/14/2024

Preparing the Hydrometer

1). Place a grape-size ball of clay onto one end of a straw.
2). Fill the graduated cylinder to the 100-mL mark with distilled water and place the end of the hydrometer containing the ball of clay into the water.
3). Tap the top of the straw one or two times to ensure that the submerged ball of clay is not sticking to the side of the cylinder.
4). Add or remove clay to the submerged end of the hydrometer such that only about 1 inch of the straw protrudes above the water level.

1). Prepare a standard solution by weighing out 3.2 g of sodium chloride, also known as table salt, and dissolving it in 96.8 mL of water measured with the graduated cylinder. This solution contains 3.2 percent salt by weight.
2). Measure the buoyancy of the solution by placing the hydrometer into the test solution and ensuring that it floats freely by tapping it with your finger. Then, using a metric ruler, measure the height of the straw (in millimeters) that extends above the water line in the hydrometer. Record both the percent salt of the solution and the height of the hydrometer above the water line.
3). Repeat twice the first two steps: in the first batch, combine 3.4 g of salt and 96.6 mL of distilled water; in the second batch, combine 3.6 g of salt and 96.4 mL of distilled water. Record all values with pen and paper for future reference.
4). Construct a calibration curve by plotting the height of hydrometer on the y-axis and percent salt on the x-axis. The percent salt is equal to the number of grams of salt in the test solutions: 3.2, 3.4 or 3.6.

1). Fill the graduated cylinder to 100 mL with the solution to be tested.
2). Place the hydrometer in the solution and record the height of the hydrometer that protrudes above the water level.
3). Refer to the calibration curve constructed previously. Find the height of the hydrometer on the y-axis, then find the x-value of the calibration curve for that particular y-value. The x-value represents the percent salt, by weight, in the sample.