CUSTOMIZE CONTENT: !!!!!!!!! In order to complete this lab, you’ll need to download a spreadsheet.!!!!!!!
In this experiment you will determine the sugar content of commercially sold soft drinks using a home-built hydrometer.
Instructions for making a hydrometer:
Take a plastic drinking straw (narrower is better than wider) and plug the bottom end with mounting putty or plasticine or hot glue (you can try silly putty or clay if you like). Put a couple of small nails in the straw. The idea is to get the hydrometer to float upright in the various liquids (not tilting over and touching the side of the glass). In order to accomplish this, I needed to add even more weight to the bottom of my hydrometer (depending on the actual materials you use, you may or may not need to do this also). The weight needs to be added below the center of buoyancy, so just adding more small nails didn’t work – they ended up too high to help. I cut 3 or 4 short lengths of straw, put a nail or two in each, and attached them around the bottom of the central straw with mounting putty. You’ll have to try different things to see what works for you. The hydrometer will float higher in the more sugary liquids (which will tend to unbalance it), so be sure to test your hydrometer in the solution with the highest sugar concentration before you start. If you make any changes to your hydrometer midway through your experiment, you’ll have to go back and repeat the steps with the new hydrometer arrangement. The other big thing to watch is that there are no bubbles hiding on your hydrometer; they will throw your measurements off in a way to make your results invalid.
There are a couple of ways to measure the distance from the surface of the liquid to the top of the hydrometer: You’ll need to be able to measure to 1 millimeter accuracy. One possibility is to just use a tape measure or ruler. The other is to mark millimeters on your straw and record the number at the liquid’s surface.
One thing I’d like to bring your attention is the need to read the concentrations of your unknowns off the calibration curve rather than from the data points directly. The calibration curve is the way we average in this lab, so it will give better results.
Materials: hydrometer from above, 4%,8%,12%, 16% known sugar solutions, 50-ml or so glass/cup, ruler (mm), various soft drinks (try fruit juices and diet drinks as well as normal soft drinks!)
A hydrometer is a flotation device used to measure the density of a liquid. The greater the density of the liquid, the higher the hydrometer floats. In this exploration, how high the hydrometer floats in 4 standard sugar solutions will be measured. The greater the sugar content of the solution, the greater its density, hence, the higher the hydrometer floats. A calibration curve will be graphed showing the height of the hydrometer on the y-axis and the concentration of sugar on the x-axis. How high the hydrometer floats in various drinks, which are essentially sugar solutions with small amounts of other materials, will then be measured and compared to this curve to determine the estimated sugar contents.
How high the hydrometer floats out of the fluid is the distance between its tip and the liquid surface (use units of millimeters). Make sure that the hydrometer is not held to the sides of the container – it should float as vertically as possible. The hydrometer must be sensed and dried before each testing. Also, carbonated beverages must be “decarbonated” because bubbles will collect on the hydrometer affecting its buoyancy. To decarbonate them, leave them out over night or boil them and allow to cool before testing.
Calibrating your Hydrometer:
Test your hydrometer you made above by placing it , sealed side first, in your container using only water (50mL). You want it to float with about 2.5cm of the top floating out of the water. If it sticks out more or less, that add/remove weight (see above) as necessary.
Step 2: When you have adjusted the amount of weight so that it is 2.5cm out of the water, measure the height of the stem above the surface of the water. Measure to the nearest millimeter and record this height in Table 1 of your spreadsheet.
Step 3: Remove the hydrometer from the container. Being careful not to alter any of the weight, rinse the outside surface of the hydrometer and dry completely. If you are using the same container, empty and dry the container as well.
Step 4: Place 50mL of the 4% sugar solution in your container, place the hydrometer in the solution, and measure and record the height of the stem above the surface of the solution.
Step 5: Repeat steps 3 and 4 for the 8%,12%,16% solutions and enter all data into your spreadsheet.
Step 6: A calibration curve will auto display for the points you entered. If not, please make sure you only input numbers in the cells, units only go in row and column titles, not in with the numbers. Use this curve for the rest of the lab, not the data points.
Determination of sugar content in Beverages
Step 1: Following the procedure above, measure the stem height for each of your beverages you selected and record the names and heights in Table 2.
Step 2: Using the calibration curve, find the stem height for each beverage and follow it across to the calibration line. Where it hits the calibration line, follow it down to the sugar concentration. Record the approximate sugar concentration for each drink in Table 2.
Step 3: Copy your tables and graph into the appropriate part your lab report and label appropriately.
Make sure you include your prelab info and work. Make any corrections to your work.
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