Experiment 2 Is volume conserved “The sneaky ethanol molecules” PDF

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Chemistry 10600 Experiment 2: Is volume conserved? “The sneaky ethanol molecules” Introduction: In this experiment, the main question we are attempting to answer is if volume is conserved in a chemical reaction. Unlike matter, which is always conserved in a chemical reaction, the amount of volume can increase, decrease, or remain constant during a given reaction. In this lab, we are mixing water and ethanol together in graduated cylinders. We record data, such as the density and volume of the solution, in a chart for five experiments. By mixing five different ratios of ethanol and water, we are able to observe how volume is not always conserved in a chemical reaction. Materials: -

Goggles

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10 mL graduated cylinder

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25 mL graduated cylinder

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Ethanol

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Distilled Water

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1 mL acetone

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Pasteur Pipet

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Digital scale

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Beaker(s)

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Calculator

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Google sheets or Microsoft Excel

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Lab Manual

Observations and Experimental: Part 1 Calculations: ● Empty cylinder mass: 25.34 g ● Volume of graduated cylinder: V=10 mL ● Mass of cylinder with water: 35.03 g ● Mass of water: 35.03 g - 25.34 g = 9.69 g of water ● d=m/V ● Density of water = 9.69 g / 10 mL = 0.969 g/mL of water

● Mass of cylinder with ethanol: 32.95 g ● Mass of ethanol: 32.95 - 25.34 g = 7.61 g of ethanol ● Density of ethanol = 7.61 g / 10 mL = 0.761 g/mL

Part 3 Calculations: Experiment 4: Sample calculations for trial 1 ● V= 19.3 mL ● Mass of Empty 25 mL graduated cylinder: m = 44.19 g ● Mass of cylinder with solution: m = 61.65 g ● Mass of solution: 61.65 g - 44.19 g = 17.46 g ● Experimental density of solution: 17.46 g / 19.3 mL = 0.905 g/ mL

● Trial 2 (done using the same method as shown above) yielded an experimental density of 0.9 g/mL. ● Average density = (Trial 1 + Trial 2) / 2 = (0.905 g/mL + 0.9 g/mL)/2 = 0.9025 g/mL Table showing results of two trial experiments:

Experiment 1 (sample calculations for volume %) ● Formula: Volume % = V ethanol / (V solution x 100%) ● Volume % ethanol = 4 mL / ((19.7mL+19.6mL+19.8mL+19.4mL+19.1mL+19.1mL)/6) x 100%= 20.566 % ● Volume % of water = 16 mL / ((19.7mL+19.6mL+19.4mL+19.1mL+19.1mL)/6) x 100% = 82.262 %

Experiment 1 (sample calculations for expected density) ● Formula: Expected Density = ( ( V water x d water ) + (V ethanol d ethanol) )/ expected total volume ● Expected density: (16 mL) (0.969 g/mL) + (4 mL) (0.762 g/mL) = 0.9274 g/mL

Table showing the results for volume % ethanol, volume % water, experimental density, and expected density calculations: Volume % Ethanol

Volume % Water

Experimental density

Expected Density,

g/mL

g/mL

0

100

0.969

0.969

20.566

82.262

0.955

0.9274

40.764

61.146

0.889

0.886

51.151

51.151

0.91

0.865

62.581

41.721

0.904

0.844

82.848

20.712

0.84

0.803

100

0

0.761

0.761

Graph of results:

Discussion and Conclusion: According to the graph, there is an inverse relationship between density and volume % of ethanol, meaning that as volume % of ethanol increases, the density of the solution decreases. The decrease in density of the solution is a result of ethanol being less dense than water. As you increase the amount of ethanol in the solution and decrease the amount of water, you are decreasing the density of the solution. Water is more dense than ethanol because of its tight arrangement of molecules. The molecules in water are tightly packed which allows there to be more room for more molecules in a given volume. If you have two graduated cylinders of equal volumes, one filled with water and another filled with ethanol, the graduated cylinder with water would be heavier and more dense because there are more molecules in that cylinder of water than there are in the cylinder of ethanol. The calculations done in part 1 of the experiment prove that water is more dense. We calculated

water as 0.969 g/mL and ethanol as 0.761 g/mL. Although they both had the same volume of 10 mL, their densities are different. When analyzing the table that shows the results for volume % ethanol, volume % water, experimental density, and expected density calculations, we observed that the expected densities are lower than the experimental density. The experimental density is greater than the expected density. The equation d=m/V shows the relationship between density, mass, and volume. According to this equation, as volume decreases, density increases. Because mass always remains the same, we know that volume is the value that changed in these reactions. The greater experimental density than expected density indicates a decrease in volume during the reaction. After conducting this experiment, it is clear that the volume of ethanol is not conserved.

Focus Questions: Question: When you mix alcohol and water is the volume conserved? Why or why not? Explain using your data and think about molecular packing mentioned in the introduction above. No, volume is not conserved when you mix alcohol and water. The volume is not conserved because the ethanol molecules disrupt water’s hydrogen bonds and cause there to be less open spaces in water. Water and ethanol will pack closer together when they are mixed in a solution, causing the volume to reduce. Additionally, the discrepancy between the expected density and experimental density data indicate a change in volume. For example, for experiment 4 (where volume of water is 12 mL and volume of ethanol is 8 mL) the experimental density is

0.906 g/mL, while the experimental density is 0.844 mL. The actual result of the experiment is more dense and therefore has less volume.

References ● Carolina,https://www.carolina.com/teacher-resources/Interactive/chemistry-lost-volumedemonstration/tr10785.tr, “The Lost Volume Demonstration” ● Smeureanu, Gabriela, and Stephanie Geggier. General Chemistry Laboratory . LAD Custom Publishing, Inc., 2018. Post Lab Questions 1. Based on what you did and learned in today’s lab what can you predict if ethyl alcohol is mixed with distilled water? Are the mass and volume conserved? If ethyl alcohol is mixed with distilled water, the mass is conserved, however, volume is not. The volume will decrease in this reaction as a result of ethyl alcohol disrupting the water molecule’s structures and also because of the tighter packing of molecules in the new mixture. 2. When you mix two gases what can you predict about the conservation of volume in this gas? When you mix two gases, the volume of the gas will not be conserved. Gases do not have definite volumes and instead they take on the volume of whatever container they are in. Additionally, gases are more spread out, making it more difficult to keep it from escaping. 3. Hydrogen gas burns in the presence of oxygen gas to form liquid water. What can you say about the volume and mass conservation in this chemical reaction?

In this reaction, the mass is conserved, but there will not be any volume conservation. The volume of liquid water would be a much smaller amount than the volume the oxygen and hydrogen reactants. 4. Based on your graph from part 3, predict the density of a 38% solution of ethanol in water. According to my trendline equation, a 38% solution of ethanol would have a density of 0.987 g/mL. First I found the trendline equation y= -0.0019x+0.9876. Next, I plugged 0.38 in for x and got y= -0.019(0.38)+0.9876=0.987. 5. Using the data you collected and the graphs you constructed compare the experimental density of the water/alcohol mixtures with the expected densities. Explain your results from a molecular perspective. The experimental density values of my data are greater than the expected values. The expected density values do not take into consideration the molecules being more tightly packed together in the water and ethanol solution, which causes a decrease in their volume....