Beverage Density-1(ready4excel

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Lone Star College System, Woodlands *

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1402

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Chemistry

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Jan 9, 2024

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pdf

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“ How Sweet It Is ” A Beverage Density Experiment Introduction: It is known that popular beverages often contain large amounts of sugar. Nutritionists have raised concern in recent years as to the high levels of sugar in these drinks and it’s detrimental effects such as tooth decay, hyperactivity and obesity. Do you know how much sugar is in your favorite beverage? In this lab we will determine the amounts of sugar in various soda, juice, and sports drink. Background: The density of a pure substance is a characteristic physical property that can be used to identify the substance. Density is defined as the ratio of mass per unit volume. It is an “intensive” property, that is, it does not depend on the amount of the substance. The density of any material is determined by measuring its mass and volume and then dividing the mass by the volume. The mass of a substance can be measured directly by using a balance. The volume of a liquid can also be measured directly using special laboratory glassware, such as a graduated cylinder, a buret, or a pipet. In this experiment, liquid volumes will be measured using a pipet. A pipet is designed to deliver an accurate and precise volume of liquid to another container. The density of a solution depends on its concentration, that is, how much solute (solid) is dissolved in the solvent (liquid). The higher the concentration of solute, the greater the density of the solution. A convenient way to express concentration is in units of weight percent, which corresponds to the number of grams of solute that are present in 100g of solution. A 20% salt solution is prepared by dissolving 20g of sodium chloride in 80g of water. (Notice that the final mass of the solution is 100g). If the density of a solution is plotted on a graph against the concentration of solute, a regular pattern is evident. Density is directly proportional to concentration. A 20% salt solution, for example, has a greater density than a 10% salt solution. If the densities of several solutions of known concentration are determined experimentally, a calibration curve (graph) can be constructed that shows a straight line relationship between the density of a solution and the concentration of solute. The calibration curve can then be used to find the concentration of solute in an unknown solution. Experiment Overview: The purpose of this experiment is to determine the percent sugar content in beverages. The density of five sugar “reference” solutions will be measured in Part A. The reference solutions contain known amounts of sugar (0-20%) and have been dyed with food coloring to make it easier to tell them apart. Their densities will be plotted on a graph to obtain a calibration curve of density versus percent sugar concentration. In Part B, the densities of two beverages will also be determined and the calibration curve used to find how much sugar they contain. The results will be compared against the information provided on the nutrition labels for these beverages. Materials: distilled water various beverages* 0%, 5%, 10%, 15%, and 20%, 25% sugar solutions Balance 100mL beaker 125mL E. flask 10mL volumetric pipet pipet bulb *Any carbonated beverages must be “flattened.”

Procedure: Part A: Density of Reference Solutions 1. Place an empty 100-mL beaker on the balance a nd hit the “tare” or “rezero” button. The scale should read 0.00g. 2. Draw up 10.00 mL of 0% sugar into a pipet and transfer the liquid to the beaker. 3. Record the mass of the solution in Data Table A. 4. Rezero the balance using the tare button. 5. Blot the tip of the pipet gently with a paper towel to clean out any residual solution. 6. Repeat steps 2-5 for the other four sugar reference solutions, proceeding in order from the least concentrated to the most concentrated. • Rinse the pipet once with each new solution before using the pipet to transfer the new solution to the beaker. • Drain the rinse solutions into an Erlenmeyer flask for later disposal. • Don’t forget to rezero the balance prior to each new mass measurement. 7. Calculate the density of each solution and record the value in Data Table 1. HINT: Since the volume is always 10.00mL, the calculation should be easy-- you don’t even need a calculator! Part B: Beverage Densities 8. Use the procedure in Part A to determine the density of three beverages of your choice. Use clean glassware and record all mass and volume data in Data Table B. Repeat each measurement 2 or 3 times and take an average to use for your calculations; this will reduce the error in your final answer. Rinse the pipet with the next beverage between successive beverage measurements.

Data Table A. Density of Reference Solutions Solution Mass, g Sample Volume, mL Density, g/mL 0% Sugar 10.00 5% Sugar 10.00 10% Sugar 10.00 15% Sugar 10.00 20% Sugar 10.00 25% Sugar 10.00 Data Table B. Beverage Densities Beverage Mass, g Sample Volume, mL Density, g/mL 10.00 10.00 10.00 Average Beverage Mass, g Sample Volume, mL Density, g/mL 10.00 10.00 10.00 Average

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Lab Questions: (be sure you understand these before working on lab calculations) 1. If the following mass and volume data are used to calculate the density of solution, how many significant figures are allowed in the calculated density? Mass of solution = 12.53g; volume of solution = 8.27 mL. 2. Calculate the density of the solution described in Question #1. 3. According to its nutrition label, orange soda contains 49g of sugar per 355 mL serving. If the density of the beverage is 1.043 g/mL, what is the percent sugar concentration in orange soda? HINT: This is a two-step problem. First, use the density to convert the 355 mL serving size to grams. Then calculate percent sugar in the beverage. Calculations and Analysis: 1. Plot density versus concentration for the six reference solutions on a graph using excel. The concentration is the independent variable (x-axis) and the density is the dependent variable (y-axis). Add the “best - fit” straight line through the data points. 2. Use the graph to estimate the unknown sugar concentration in the first beverage. To do this, locate the point on the y-axis that corresponds to the density value of the beverage. Follow that point on the y- axis horizontally to where it meets the “best - fit” straight line through the data. Now read down vertically from this po int on the “best - fit” line to the x - axis. The point where this vertical “line” meets the x-axis equals the percent concentration of sugar in the beverage solution. Construct a Results Table and record the density of the beverage and the estimated percent sugar concentration. 3. Repeat step 2 to determine the percent sugar concentration of the second beverage. Record all information in your Results Table. 4. Calculate the actual or accepted value of the sugar concentration in weight percent for each beverage, using the nutrition label information and the measured density value. HINT: Record both the nutrition label information and the actual percent sugar concentration in your Results Table. 5. Use the following equation to calculate the percent error in your experimental determination of the sugar content in each beverage. Enter the percent error in your Results Table . Percent error = l measured value - accepted value l x 100% accepted value 6. What was your measured density for pure water (0% sugar solution)? The density of water is usually quoted as 1.00 g/mL, but this precise value is for 4 o C. Comment on why your measured density might be higher or lower than 1.00 g/mL.

7. This lab looks at the relationship between the density of a beverage and its sugar content. What assumption is made concerning the other ingredients in the beverage and their effect on the density of the solution? Do you think this is a valid assumption? Explain. 8. When plotting data such as that obtained in this experi ment, why is it not appropriate to “connect the dots?” If you were to repeat the lab, do you think you would get exactly the same results? Comment on three potential sources of error in this experiment and their likely effect on the results.