CHEM 105 Sink or Swim lab PDF

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Virtual Sink or Swim Name

McKenzie Hutchins

INTRODUCTION: You may remember being fooled as a child by the riddle, “which weighs more, a pound of feathers, or a pound of bricks?” Hopefully, you know by now that the answer lies in examining the differences in mass/volume ratios, or density. This lab is designed to provide other situations where the results may be unexpected. The density of a material depends partly on how closely the molecules of that material are packed. As molecules are more tightly arranged, a material becomes more dense. For objects within a fluid, substances that are more dense will sink to the bottom, while things that are less dense float to the top. For example, a rock sinks in water, but a piece of wood will float. Density is equal to mass/volume. PROCEDURE: PART A: Open the Virtual Physics Lab and select the Density module. Use the table below to calculate the density of the three given solids. You can calculate mass by taring the scale, and then dragging a mass down to rest on the scale. To calculate volume, toggle the arrows on the liquid dispenser until it reads “water”. Then fill a cylinder with water. Place the solid at the top of the cylinder. Click on the cylinder to zoom in and write down the original volume of liquid. Be careful, because the marks on the cylinders go up by twos, not ones. Drop the solid into the liquid and record the new volume. The difference between these two values is the volume of the solid. Solid

Mass

Chocolate Granite Sulfur

25.254 g 38.854 g 35.228 g

Volume of Water Without Solid 112 mL 112 mL 111 mL

Volume of Water with Solid 131 mL 133 mL 131 mL

Volume of Solid 19 21 20

Density 1.3 g/mL 1.9 g/mL 1.8 g/mL

PART B: Calculate the density of the three given liquids. You can calculate volume by looking at the volume markings on the filled graduated cylinder. To calculate mass, place the beaker on the scale. Tare the scale. Then, pour the cylinder into the beaker. Note that the cylinder needs to be in a specific place in order to pour. The easiest way to find this place is to hold the cylinder and hover around the beaker until the cylinder snaps into place. Then let go of the mouse and the cylinder will pour into the beaker. Liquid Jet Fuel Corn Syrup Mercury

Mass 93.024 g 155.642 g 1540.251 g

Volume 112 mL 110 mL 111 mL

Density 0.83 g/mL 1.41 g/ mL 13.9 g/mL

PART C: Using the densities that you found, complete the following chart, predicting whether each solid will sink or float in each liquid. (If you’re not sure of your guess you can check it in the Virtual Physics Lab.)

Jet Fuel Corn Syrup Mercury Bromine (D=3.1 g/mL) Grape Soda (D=1.045 g/mL)

Chocolate

Granite

Sulfur Sink Sink Float Float

Tungsten (D=19.3 g/mL) Sink Sink Sink Sink

Red Oak (D=0.74 g/mL) Float Float Float Float

Sink Float Float Float

Sink Sink Float Float

Float

Sink

Sink

Sink

Float

PART D: Fill one cylinder with alcohol and one with water. Drop a piece of ice into each one. Rank the three substances (alcohol, water, and ice) from most dense to least dense. Water, ice, alcohol PART E: Fill two cylinders with water. Place a cesium solid and a sodium solid over the cylinders, and then drop the solids. What happened? Both of the cylinders blew up

QUESTIONS: 1. Imagine you were to mix all three solids (chocolate, granite, and sulfur) with all three liquids (jet fuel, corn syrup, and mercury) in a large cylinder. Describe what you would see from the top of the cylinder to the bottom of the cylinder either in words or as a labeled diagram.

Because they are all different densities they will separate and wont mix. From the top you would see jet fuel first, then the chocolate (would be at the bottom of the jet fuel and would float over next liquid), corn syrup, sulfur, granite, then mercury would be at the very bottom

2. To determine density you need to know both the volume and mass of a substance. How is it possible to determine the volume of solids such as sodium or cesium if you cannot use water? Imagine that you do not know the density, cannot look it up, and cannot use geometry formulas such as those for the volume of a sphere. Because cesium is reactive you can’t measure mass using water which means you would need to find the molecular mass. You would determine the molecular formula of the molecule and then go to the periodic table and use the atomic mass of each element in the molecule. Multiply each element's atomic mass by the number of atoms of that element in the molecule. Add these values together for each

different atom in the molecule. Use mass spectrometers to measure mass of all elements. Masses of the elements is an average of weights of the isotopes. Optional Exploration Activity (Not required): Try experimenting with some different solids and liquids that interest you. What are the three most dense solids? You can also try ranking the four virtual fluids or the four virtual solids by density....