Lab work with given data

Chemistry 201 Laboratory – Harold Washington College

Density

Full Name: ________________________ ID #: __________

Date: __________

Introduction

In this experiment you will measure the densities of a solid metal cylinder, pure water and two salt solutions. You will then determine the concentration of an unknown salt solution by measuring its density and comparing its density with your known solutions.

Density is one of the fundamental properties of matter. It is defined as mass per unit volume:

ρ = m/V (ρ = density, m = mass, V = volume)

The density of a pure substance can be used to aid in its identification. Densities of solutions may be used to determine their concentration.

Materials and equipment

· Solid Sample · 5g of sodium chloride (NaCl) · 100mL of deionized water in a beaker · 25 mL graduated cylinder · 10.00mL volumetric pipet and pipet pump · 50 and 100mL beakers · electronic balance

Procedures:

Density of Solid Cylinder: (displacement method)

1. Select a solid cylinder and record its color.

2. Determine the mass of the cylinder to the precision available on the balance.

3. Place a known volume of water in the 25 mL graduated cylinder. Measure this volume to 0.5 mL.

4. Carefully slide the solid sample into the water.

5. Record the total volume in the cylinder.

6. Determine the density of the cylinder.

Density of Water

1. Weigh a clean, dry 100mL beaker and record the mass to the nearest 0.01 g.

2. Obtain some deionized water in another clean beaker or flask. Using a volumetric pipet, transfer 10.00mL of water to the weighed beaker.

3. Weigh the beaker with the 10.00mL of water to the nearest 0.01 g.

4. Calculate the mass of the water.

5. Calculate the density of the water. Measure the temperature of the water. Refer to the table that provides values of the density of pure water as a function of temperature. Repeat this experiment until you perform two consecutive trials with results within 0.3% of this value.

6. Show your results to your instructor.

Density of NaCl Solutions

You will now prepare two sodium chloride solutions of known concentration and measure their densities. Then you will measure the density of a sodium chloride solution of unknown concentration to determine its concentration.

Preparations and Measurements of 5.0% NaCl Solution

1. Use weighing paper to help you weigh out 1.58 g NaCl.

2. Transfer the NaCl to a dry 100 mL beaker.

3. Using a volumetric pipet, add 30.0 mL deionized water to the beaker.

4. Carefully swirl the beaker or stir the solution with a stirring rod until the salt dissolves. Do not stir with the volumetric pipet. Do not spill any of the solution. You now have a 5.0% by mass NaCl solution.

5. Rinse the volumetric pipet with the 5.0% NaCl solution. Obtain the data needed to calculate the density of the 5.0% NaCl solution. You will be following the procedure you used to find the density of pure water.

Preparations and Measurements of 10.0% NaCl Solution

1. Weigh out 3.33 g of salt and transfer it into a 100mL beaker.

2. Add 30.0mL deionized water to the beaker with the volumetric pipet and carefully stir the solution. You now have a 10.0% NaCl solution.

3. Rinse the volumetric pipet with the 10.0% salt solution. Obtain the data needed to calculate the density of the 10.0% salt solution. You will be following the procedure you used to find the density of pure water.

Density of an Unknown NaCl Solution

1. Obtain approximately 15 mL of unknown salt solution from the laboratory instructor. Use a clean, dry beaker or flask to obtain your sample.

2. Rinse the volumetric pipet with the unknown NaCl solution. Obtain the data needed to measure the density of the unknown NaCl solution. You will be following the procedure you used to find the density of pure water.

Data, Calculations and Questions Name

Density of Solid Cylinder

Color of sample Gray

Mass of sample 18.22 g

Initial volume of water in graduated cylinder 15.0 mL

Total volume of water and solid cylinder 21.5 mL

Volume of solid cylinder

Density of unknown solid cylinder

CALCULATIONS: Show all your work and use correct number of significant figures.

Density of Water Temperature of Water 25 ⁰C

Density of water (from table in laboratory materials) 0.9970 g/mL

	TRIAL 1	TRIAL 2	TRIAL 3
Mass of empty beaker (measured)	52.81 g	52.81 g	52.81 g
Mass of beaker and water (measured)	62.79 g	62.81 g	62.78 g
Mass of water (measured)
Volume of water (measured)	10.00 mL	10.00 mL	10.00 mL
Density of water (calculated)

CALCULATIONS: Show all your work and use correct number of significant figures.

Data for 5.0% NaCl Solution

Mass of 50mL beaker 28.93 g____

Mass of beaker + 10.00mL of 5.0% NaCl solution 39.28 g

Density of 5.0% NaCl solution

CALCULATIONS: Show all your work and use correct number of significant figures.

Data for 10.0% NaCl Solution

Mass of 50mL beaker 28.93 g

Mass of beaker + 10.00mL of 10.0% NaCl solution 39.65 g

Density of 10.0% NaCl solution

CALCULATIONS: Show all your work and use correct number of significant figures.

Data for Unknown NaCl Solution Unknown Number 6

Mass of 50 mL beaker 28.94 g

Mass of beaker + 10.00mL of unknown NaCl solution 39.16 g

Density of unknown NaCl solution

CALCULATIONS: Show all your work and use correct number of significant figures

Summary of Density Calculations

	Concentration of NaCl (%)	Density
pure water
First NaCl solution
Second NaCl solution

Plot the above "Density versus Concentration" on the graph below. Remember to clearly label your axes and the units on each axis. Draw a single, straight line of "best fit" that correlates the data. This is a linear x-y plot. Use this line to determine the concentration of the unknown salt solution from its density.

Concentration of unknown solution

(from graph above)

1. The solid cylinder you used was one of the following substances whose densities are given below.

Aluminum: 2.70 g/mL Copper 8.92 g/mL

Brass 8.42 g/mL Iron 7.86 g/mL

Identify your cylinder:

2. Discuss some of the possible errors in finding the density of the solid cylinder using the techniques in this experiment.

3. Clearly explain how you could use the displacement method to determine the density of an irregular solid which floats in water.

4. Discuss some of the possible errors in finding the density of a liquid using the techniques in this experiment.

5. Think about a person floating in a body of water. What would you expect to be the difference between floating in Lake Michigan (fresh water) and in the Atlantic Ocean (3.5% salt solution)? Explain your answer.

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