SPECIFIC GRAVITY & SOFT DRINKS

1. Prepare a hydrometer using a large Beral pipette.
2. Obtain four known sugar solutions samples.
3. Calibrate your hydrometer.
4. Use your data to prepare a standard curve of hydrometer depth versus sugar concentration.
5. Perform a linear regression analysis and determine a line of best fit.
6. Obtain several soft and juice drink samples.

CONSTRUCTING & CALIBRATING A HYDROMETER Fill a thin stem plastic pipet to about 1/3 with Zn dust. Squeeze and pull in the dust the same as you would water. Put about 25 mL of water in a 25 mL graduated cylinder. Float the pipet (bulb-end down) in the cylinder. The pipet may stick to the sides. Tap the bulb a bit to even the Zn dust, and straighten the tip if necessary. Float the pipet again to test it. The pipet should float with 5-8 cm of stem extended above the water. It it floats too high, add a bit more Zn and try again. If it floats too low, squeeze out some Zn. When it does float within the desired range, then remove and hot glue the stem closed. Calibrate the sealed pipet by marking the level with a solution of known density. Use permanent markers. With the pipet floating freely, mark the outside of the cylinder at the water level. Grasp the pipet, aligning the level of your finger with the top of the cylinder. Remove the pipet from the water, and hold it next to your mark, aligning the level of your finger with the top of the cylinder again. Dry the pipet tip with your other hand. Mark the plastic pipet to align with the mark on the cylinder.

Testing Soft Drinks

There are two precautions:

• The hydrometer must be free floating
• Carbonated drinks must first be de carbonated.

1. Follow steps 1-5 of calibrating the hydrometer and measure the exact height of the protruding stem of your hydrometer in several soft drinks. To avoid contaminating the test solution with the previous solution, rinse the graduated cylinder with a few milliliters of each drink you are going to use before testing.
2. Record your data in a data table.
3. Construct a graph of your data for the standard % sugar concentration and hydrometer height. From this graph determine the % sugar concentration for the soft drinks you tested.

Questions:

1. Calculate the percentage of sugar in the soft drinks you tested.
2. Suppose you wish to find the percent alcohol of and alcoholic beverage. Describe how you would use a hydrometer to accomplish the task. Alcohol has a density of .79g/mL. What modification might you have to make in your hydrometer?
3. Suggest several reasons why the assumption that "the density of the sugar in a soft drink is proportional to the % sugar" might not be correct. How might you test the validity of this assumption.
4. How could you modify your hydrometer to increase its accuracy?
5. Drinks such as Pepsi and Coke have a very high sugar content. After reading ingredient labels on these drinks, suggest a possible reason for this high sugar content.
6. Take your hydrometer with you (being careful not to squeeze out any of the water). Use it to test any other drinks you have about the school or at home. Write a brief report of your results.
7. How does density change with increasing concentration of sugar or salt?
8. Radiator fluid in automobiles is checked with a slightly different device for measuring the density of the solution. Why would the density of this solution be measured?
9. Two solutions are prepared:
   • 5 g of NaCl dissolved in 20 mL of water;
   • 5 g of sugar in 20 mL of water.
10. Are the densities of these solutions necessarily the same? Explain.