CHEM 1411 Lab Manual-14th Edition PDF

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Table of Contents

Graphical Analysis

2

The Chemical Contents of Commercial Sodas

7

Avogadro Goes to Court

19

Determination of an Empirical Formula

22

A Copper-Iron Replacement Reaction

27

Determination of the Concentration of Ba2+

33

Determination of the Heat of Formation of MgO from Hess’ Law

39

Atomic Spectra

45

Atomic Orbitals

52

Determination of Solution Concentration Using Beer’s Law

60

Atomic Orbitals and Hybridization

66

Structures of Molecules

71

Evaluation of the Gas Law Constant

75

Gas Chromatography

79

1

Graphical Analysis By Michael Sundermann, Ph. D. Introduction: A graph is a diagram that allows data to be visualized more easily than by using a table. Although there are many types of graphs, including bar graphs and circle graphs, the type most commonly used by scientists is the XY graph, sometimes called the line graph . The horizontal axis is called the x-axis, and the vertical axis is called the y-axis. In most experiments, one variable is changed in a controlled manner. This is called the independent variable and is generally plotted on the x-axis. As the independent variable changes, it effects the second variable, called the dependent variable. The dependent variable is plotted on the y-axis. For instance, the graph below shows the temperature of a liquid sample as it cools and freezes into a solid. Notice how much easier it is to see patterns in the graph than the table. time (s) temp (oC) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

94 86 81 76 72 69 66 67 67 66 67 67 66 64 62 61 60 58 57 56 55

95 90 85 80 temp (oC) 75 70 65 60 55 0

10

20

30

40

50 60 time (s)

70

80

90 100

The graph shown above is clearly not linear. As the liquid freezes, the temperature stops decreasing. The temperature starts to decline again only when the frozen solid begins to cool. However, in many cases, plotting one variable versus another will give a straight line. When the relationship is linear, a best-fit line can be drawn. The graph on the next page shows the sales of a lemonade stand versus the number of signs advertising the stand.

2

4.50 4.00 3.50 3.00 sales ($) 2.50 2.00 1.50 1.00 0

1

2

3

4 5 6 number of signs

slope = 0.287

7

8

9

10

y intercept = 1.11

In this case, the increase in sales is linear, and a best-fit line can be calculated. The y-intercept of the line indicates the value of y (the dependent variable) when the value of x (the independent variable) is zero. The slope of the line indicates how much the value of y changes for a given change in x. A large slope means that the value of y will change a lot for a given change in x. A small slope indicates that the value of y will change only a little for a given change in x. Any straight-line graph can be described by the equation y = mx + b where m is the slope and b is the y-intercept. In the graph above, m = 0.287 and b = 1.11. It is possible to interpolate a graph to determine where a data point would be. By choosing a value of x in between the highest and lowest data point, you can calculate the value of y by either finding the desired point on the line, or plugging the values of x, m, and b into the above equation. For instance, you can say with some confidence that with 7 signs, sales would have been approximately 0.287 x 7 + 1.11 = 3.12 dollars. It is sometimes possible to extrapolate a graph by extending the line outside the graph, but this can sometimes lead to problems. Some phenomena might be linear over a certain range, but nonlinear beyond it. There will be certain point at which more signs will not increase sales. In some linear graphs, if the value of x doubles, than the value of y doubles. When this relationship holds, the variables x and y are directly proportional. Note that when this happens, the y-intercept will be zero. The values for sales versus number of signs on the previous graph are not directly proportional. On some graphs, when x doubles, y will be cut in half. When this relationship holds, the variables are inversely proportional. A graph of inversely proportional variables will not be linear.

3

Name________________________ Assignment: Note: If the data for any plot is not linear leave the spaces for the slope and yintercept blank and do not include a trend line on the corresponding plot. 1. Make a graph of the following data points. Is the relationship linear? If so, find the slope and y-intercept. Are the variables directly proportional?

mL base added 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

pH 2.82 3.97 4.34 4.60 4.82 5.04 5.30 5.67 8.94 12.15 12.44 12.60 12.71 12.80 12.87

Linear?_______________ Slope_________________ Y-Intercept____________ Directly proportional?____

2. Make a graph of the following data points. Is the relationship linear? If so, find the slope and y-intercept. Are the variables directly proportional?

voltage (V)

current (A)

1.0 1.5 2.0 2.5 3.0 3.5 4.0

3.45 x 10-3 5.02 x 10-3 6.88 x 10-3 8.60 x 10-3 1.01 x 10-2 1.22 x 10-2 1.36 x 10-2

Linear?_______________ Slope_________________ Y-Intercept____________ Directly proportional?____ 4

Name________________________ 3. In some cases, the relationship between two variables is not linear, but the data can be manipulated to make a linear relationship. Using the data below, make a graph of the volume vs. pressure of a container, with volume being the independent variable. Is the relationship linear? If it is not, make a graph of volume versus 1/pressure. What would the pressure of the container be if the volume were 2.4 L? Show your calculation.

volume (L) 0.86 1.94 2.96 4.03 5.02 5.59

pressure (atm) 22.9 10.3 6.7 5.0 3.9 3.5

Is V vs. P linear?______________ P at 2.4L_______________

5

Name________________________ Indicate which graph would best match the situations given below. 4. A roller coaster goes up the large hill at a steady pace and then starts down the hill. (a)

(b)

(c)

speed

speed

speed

time elapsed

time elapsed

(d) speed

time elapsed

time elapsed

5. A company’s sales experience rapid growth followed by slow growth. (a)

(b)

sales

(c)

sales

time

(d)

sales

time

sales

time

time

6. A woman takes a ride on a ferris wheel. (a) distance from ground

(b)

(c)

distance from ground

distance from ground

time

time

(d) distance from ground time

time

7. A boy grows very quickly when young, and then the rate of growth slows, and then has a burst of growth at puberty. (a)

(b)

(c)

height

height

height

age

age

(d) height

age

age

6

The Chemical Contents of Commercial Sodas by Janice Chadwick, Ph.D. You probably recognize two important physical properties when you pick up an apple in the kitchen: The apple has a weight associated with it and the apple occupies a certain amount of space in your hand. In scientific terms, the apple has a mass associated with it and a volume. The ratio of the mass to the volume is known as density and has units of either g/cm3 or g/mL. The measurement of density is necessary for a variety of important chemical procedures such as measuring Avogadro’s number, 6.022 x 1023 per mole, the concentration of a pure liquid such as water, or the molar mass of a gas. An understanding of density is useful in the everyday world as well. In winemaking, the grape juice density is measured to determine whether enough sugar is present to begin the fermentation process. The simple measurement of density in the case of regular cola or diet cola illustrates the importance of recognizing both the difference of the contents in a can of soda and the role of measuring devices in both the laboratory and the kitchen. Experiment Objective Today you will study the densities of regular and diet cola for the following reasons: 1. To quantitatively determine the density of regular and diet cola. 2. Discover the difference in measuring liquids with a graduated cylinder, pipet, and buret.

Introduction It may surprise you to know that the amount of sugar and calories in soft drinks is about the same as many fruit juices. An 8-ounce (240 mL) serving of Seven-Up®, for example, contains no more sugar and calories than 8 ounces (240 mL) of orange juice, and less sugar and fewer calories than 8 ounces (240 mL) of apple juice or grape juice.

Sugar and Caloric Content of Selected Foods 8 oz. (240 mL) Seven-Up® orange juice apple juice grape juice

Sugar (grams) 27 27 28 32

Calories 97 112 111 128

Source: Food Values of Portions Commonly Used, 15th ed, Pennington. The body can't tell the difference between the sugar you get from fruit juice and that added to soft drinks. The sugar in sodas and fruit juices is sucrose, which is formed from glucose and fructose.

7

HO H

HO

HO HO

H OH

H

H OH

O

H

glucose

CH 2OH O H HO

HOH 2C H

sucrose fructose

However, a diet soda such as Diet Seven-Up®, does not contain any sugar in the form of sucrose, but contains aspartame. Aspartame is known by its trade name Equal®. The chemical formula of aspartame is shown on the left. Aspartame is metabolized in the body to its components: aspartic acid, phenylalanine, and methanol. Like other amino acids, it provides 4 calories per gram. Since it is about 180 times as sweet as sugar, the amount of aspartame needed to achieve a given level of sweetness is less than 1% of the amount of sugar required. Thus 99.4% of the calories can be replaced. H H H H

O

H

NH 2

C

C C

C

O

H

O

N O

H H C C H

C C

C C

C H

C C

H

H

H

O C

H

H

Aspartame

8

Pre-Lab Questions Name____________________________ Which weighs more, a pound of bricks or a pound of feathers? Why?

Pre-Lab Concept of density: List in the two columns three pairs of items that are of similar size, but have different densities.

High Density

Low Density

1. ________________

________________

2. ________________

________________

3. ________________

________________

Certain types of bowling balls when placed in water float. Explain how this is possible.

9

Experimental Procedure (Work in Pairs) Note: Soda samples were stirred for 24 hours to remove CO 2 from the solution. Section I Using a clean, dry 50-mL beaker, tare it on the analytical balance. Obtain a 200-mL sample of regular or diet cola in a 400-mL beaker. Follow the instructions below and enter the data in the table Section I Data Sheet, Parts A through C. Calculate the density of the soda and record this density in the Data Table. Instructions on how to average and graph this data will be provided by your instructor. 1. Weigh a clean, dry 50-mL beaker and record the mass of the 50-mL beaker in Table A. 2. Measure 25 mL of soda with a 50-mL graduated cylinder. 3. Pour it into the 50-mL beaker, and reweigh the beaker. 4. Record the mass of the 50-mL beaker containing the soda sample in Table A. 5. Dispose of the soda down the drain. Clean and dry the beaker. 6. Re-tare and weigh the clean, dry beaker again. Record the mass of the 50-mL beaker in Table B. 7. Using a 25-mL volumetric pipet, measure 25 mL and pour it into the 50-mL beaker. 8. Record the mass of the 50-mL beaker containing the soda sample in Table B. 9. Dispose of the soda down the drain and clean and dry the beaker. 10. Re-tare and weigh the beaker again. Record the mass of the 50-mL beaker in Table C. 11. Repeat the procedure with a 50-mL buret. Drain the sample into a waste beaker and stop at 10 mL. Use the 10 mL mark as the initial measurement. Drain the soda into the 50-mL beaker until the final measurement is near 35 mL. (You just delivered 25 mL of soda from the buret into the beaker. 12. Record the mass of the 50-mL beaker containing the soda sample in Table C. 13. Repeat Steps 1-12, except use diet cola this time. Important Note: Make sure you have cleaned the graduated cylinder, pipet, and buret with soapy water, rinsed well with tap water, and then rinse well with distilled water. Condition the graduated cylinder, pipet, and buret with diet cola before repeating steps.

Section II Each student will be assigned three different volumes between 1 and 30 mL by the instructor. Enter the three volumes in Section II Data Sheet as Volume 1, Volume 2, and Volume 3. You will measure the mass associated with each of the assigned volumes for both regular and diet cola using only the buret. This means you will conduct three mass determinations for each soda: a total of six determinations. Enter the data in Section II Tables A through C for both regular and diet cola. Procedure for Part II 1. Weigh a clean, dry 50-mL beaker and record the mass of the 50-mL beaker in Table A.

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2. Using the 50-mL buret, drain the sample into a waste beaker and stop at 10 mL. Use the 10 mL mark as the initial measurement. Drain the soda into the 50-mL beaker until you have delivered the amount of soda assigned to you for volume 1. 3. Record the mass of the beaker and the soda sample on the Section II Data Sheet. 4. Dispose of the soda down the drain, clean, dry, and re-tare the beaker. 5. Using the buret, repeat steps 1-4 for each of the other three volumes assigned using regular cola. 6. Repeat Steps 1-4, except use diet cola this time. Important Note: Make sure you have cleaned the graduated cylinder, pipet, and buret with soapy water, rinsed well with tap water, and then rinse well with distilled water. Condition the graduated cylinder, pipet, and buret with diet cola before repeating steps. When you are finished with the three determinations in Part II, make sure you have thoroughly cleaned all of your glassware with soapy water and rinsed with tap, then distilled water at least three times. The solutions can ruin the glassware (very sticky stuff!) so please make sure everything is clean. Do not wait until the end of the lab period to do this, do it now. After you have calculated your densities, record the mass for each volume measured and the density on the blackboard. This will be your contribution to the class data.

Section III The mass density data for all of the glassware of each soda will be pooled together. Enter the density weighed for the 25-mL samples of regular and diet cola you measured in the graduated cylinder, pipet, and buret from Section I on the board. Record all of the class data in Section III, Table D. Based on the class data, calculate the average density for each soda measured in graduated cylinder, pipet, and buret reported on the board below Table D.

Section IV

This class data will be recorded on the blackboard and analyzed using graphs later. You will contribute to the class data by reporting your results on the blackboard along with the rest of the class. To do this, record the mass measurements for each volume you were assigned on the blackboard. When the experiment is completed by all of your classmates, record all of the data on the blackboard. Instructions on how to average and graph this data will be provided by your instructor.

11

Section I Data Sheet

Name_________________________

Partner/Group Members_________________________ Table A Graduated Cylinder Enter mass in grams and calculate density

Regular Cola

Diet Cola

Mass of 50-mL beaker grams

grams

grams

grams

grams

grams

Mass of 50-mL beaker + soda Mass of soda Volume of soda 25.0 mL Density

25.0 mL

grams mL

grams mL

Table B Pipet Enter mass in grams and calculate density

Regular Cola

Diet Cola

Mass of 50-mL beaker grams

grams

grams

grams

grams

grams

Mass of 50-mL beaker + soda Mass of soda Volume of soda 25.00 mL Density

25.00 mL

grams mL

grams mL

Table C Buret Enter mass in grams and calculate density

Regular Cola

Diet Cola

Mass of 50-mL beaker grams

grams

grams

grams

grams

grams

Mass of 50-mL beaker + soda Mass of soda Volume of soda 25.00 mL Density

25.00 mL

grams mL

grams mL 12

Section II Data Sheet

Name_________________________

Write Down the Volumes You Were Assigned Here: Volume 1 _________

Volume 2 _________

Volume 3 _________

Table A Buret Measurement for Volume 1 Enter mass in grams and calculate density

Regular Cola

Diet Cola

Mass of 50-mL beaker grams

grams

grams

grams

grams

grams

Mass of 50-mL beaker + soda Mass of soda Volume of soda Density

________ mL grams mL

________ mL grams mL

Regular Cola

Diet Cola

Table B Buret Measurement for Volume 2 Enter mass in grams and calculate density

Mass of 50-mL beaker grams

grams

grams

grams

grams

grams

________ mL grams mL

________ mL grams mL

Regular Cola

Diet Cola

Mass of 50-mL beaker + soda Mass of soda Volume of soda Density

Table C Buret Measurement for Volume 3 Enter mass in grams and calculate density

Mass of 50-mL beaker grams

grams

grams

grams

grams

grams

________ mL grams mL

________ mL grams mL

Mass of 50-mL beaker + soda Mass of soda Volume of soda Density

13

Class Data Sheet

Name_________________

Section III. Class Data. Enter the density weighed for the 25-mL samples of regular and diet cola you measured in the graduated cylinder, pipet, and buret from, Section I on the board. Then record your data in the first line below. Record all of the class density data on the board below your data in Table D. Table D Graduated Cylinder Regular cola g/mL Diet cola g/mL

Pipet Regular cola g/mL Diet cola g/mL

14

Name____________________ Buret Regular cola g/mL Diet cola g/...