Density experiment

Density is defined as the mass (in grams) of 1 milliliter of a substance. If you were to drop a piece of aluminum into a glass of water, the aluminum would sink to the bottom. However, if you were to drop a piece of ice into a glass of water, the ice floats on the surface of the water. Both mass and volume are characteristics that can be easily measured in the laboratory. Instead of measuring the density of lumps of unknown metals, might it be interesting to measure the density of several popular soft drinks and fruit juices? Will they be heavier than water? Or lighter?

Mass = m Volume = V Density = D

D = m ÷ V or D = m/V

i Remember, no food or drink is allowed in the laboratory. For the purpose of this experiment, we will be treating the soft drinks as if they were chemicals. We will be testing water, Sprite and diet Sprite. The sodas have been de-gassed (we removed the carbon dioxide).

For the first portion of this session, you and your research group will be attempting to answer the following question:

Your group will be given three types of apparatus that can measure liquid volumes (in milliliters):

With the help of the aides in the room use each apparatus, along with the analytical balances to separately determine the density of your liquid. The three data points from your measurements should be entered in the table provided on the next page. Once each group has finished section A, you should put your group’s data on the overhead. There will be a short class discussion on the data before beginning section B.

1. How do the ranges of data compare for the different devices used to measure volume? Which device gives the narrowest range? Which device gave the broadest range?

Fat, sugar, and salt are three food components that most Americans consume in excess. Almost all soft drinks that are not milk-based (Coke, Pepsi, Sprite, Kool-aid, Gatorade, etc) are essentially sugar solutions with small amounts of additives for flavoring and color. Fruit juices are also mostly sugar solutions.

Read the labels of the soft drinks and the fruit juices at your lab station. Note the lists of ingredients.

In this part of the experiment you will determine the sugar content of Sprite, diet Sprite, Gatorade, and apple juice by measuring the density of each beverage using a simple hydrometer. A hydrometer is a device designed to quickly measure the density of a liquid. It is based on the fact that floating objects displace their weight in liquid. A hydrometer is simply a floating object with a scale to measure how high it floats in various liquids.

1. Build your hydrometer according to the picture noted below. Then fill the pipet approximately half-full of water. Now place the pipet, bulb end down, into a 50 mL graduate cylinder nearly filled to the top with water. You may need to adjust the amount of water in the pipet so that it floats with the bulb near the bottom (but not touching the bottom) and with only a short length of the stem sticking out of the water. See the hydrometer assembly picture.

2. In order to estimate actual amount of sugar in a soft drink, the hydrometer must be calibrated. You must collect data of some known sugar solutions and plot the data on a graph. We can change the density of water by adding sugar to it. There is a set of graduated cylinders filled with water and reference sugar solutions available to you in the lab. You need to make measurements with your hydrometer in each solution and record the data. To avoid contaminating the solutions, you should always rinse your hydrometer with pure water and blot it gently before inserting in a new solution. Record your data in the chart labeled “Hydrometer Calibration” and then graph the results on the graph provided.

3. Now test the beverages - Sprite, diet Sprite, Gatorade, and apple juice. Record the data in the chart labeled “Beverages”. Use the graph to determine the density in each of the beverages.

4. Once each group has finished section B, you should put your group’s data on the blackboard.

Section A – There will be four aides in the room and we will divide the EYH participants into four groups to do section A. They will work as a group with the aide helping direct this part. Each group will need a graduated cylinder, a burets, and a pipets. Each group will need to rinse the their containers after section A in preparation for the next group.

After they complete calculations on the density of water. Have them report group averages and ranges. Then have them look at the class averages and ranges. What’s the best method for measuring volume?

Then give each group 60 mL of Sprite and Diet sprite. They will use their buret and graduated cylinder to make one measurement. Then collect all data on the board and calculate averages/ranges.

Section B –Divide each of the four groups into 2 so we will have a total of 8 groups – each group has 2-3 EYH participants in it. Make sure each group of 2-3 students has a hydrometer. We have set up four stations in the lab of 9 graduated cylinders (water, 4% sugar, 8% sugar, 12% sugar, 16% sugar, sprite, diet sprite, Gatorade, and apple juice.) NO ONE NEEDS TO POUR!!!!!!

Requires very, very little prelab lecture. Define density and have them give examples of dense substances and less dense substances. Section A data collection will take about 15-20 minutes. Putting data on the board and collecting the pipet data and discussion will take another 10 minutes.

Section B data collection should take about 15 minutes. Graphing will take 3-4 minutes. Discussion of data will take another 10 minutes.