Lab 7

Constructing & Calibrating a Simple Hydrometer

Objective

Determine the sugar concentration of a solution using a hydrometer.

Background

A hydrometer measures the specific gravity of a solution.

The higher the hydrometer floats, the more dense (concentrated) the solution is.

Specific gravity is a unitless ratio of the density of a liquid compared to water.

Experiment

Make a hydrometer.

Fill it about half-full with water and invert into 50 mL of pure water. Adjust weight of hydrometer until the stem floats about 2.5 cm above water level.

Pipet 50.0 mL of solution into a 50 mL grad. cyl.

Measure the height of the stem above the liquid level.

Repeat to complete the data table

Sugar Solution Height of Stem Above Water Level (cm)

Pure Water (0%)

2%

4%

6%

8%

Unknown

Analysis

1. Create a PROPER graph that displays the height of the hydrometer stem vs. sugar concentration. Connect the dots on this graph with a ‘best fit‘ line. This is your calibration curve.

2. Use your calibration curve to determine the approximate sugar concentration in the unknown.

Results:Your results statement should be under your graph and it should include what you believe the concentration of your unknown liquid is and how you determined it.

Questions

1. Why is it important that no water was lost or added to the hydrometer during this lab?

2. Name three sources of error in this experiment.

3. What is a hydrometer?

4. People claim that it is easier to float in the ocean that in a lake or pool, explain why.

5. Was it important to always use 50.0 mL of solution? Explain why or why not.