Laboratory Guide Packet

Gt Chemistry

Name: ______MOD: ______

Unit: Kinetic & Equilibrium

This packet includes all of the labs for this unit. Once a lab has been completed you will turn in the whole lab packet to be graded and returned. This does not take the place of your laboratory notebook. All worksheets are only to be used to turn in work all calculations should be done in your lab notebook. (Please note the only time this lab packet will not be turned in is when there are lab assignments given back to back).

Table of Contents

Title Pages

The Iodine Clock …………………………………………………………………………………………………….. 3-7

EquilibriuM&M ……………………………………………………………………………………………………….. 7-12

LeChatelier’s Principle ……………………………………………………………………………………………… 12-16

THE IODINE CLOCK REACTION

Suppose you work in a chemical plant that produces a valuable compound. The compound is produced at specific conditions, but now your company has asked you to increase the speed of the reaction. Can you change the conditions to make the reaction faster? In order to speed up the reaction, you must know something about the factors that influence the reaction rates. To test the influence of these factors on the rate of your reaction, you must be able to find out how long it takes to produce a certain amount of product or how long it takes to use up a certain amount of one of the reactants.

The time it takes for a reaction to go to completion is easy to measure if a color change signals when one of the reactants is used up. This kind of reaction is called a clock reaction. To tell how long a clock reaction takes, all you need to do is time the reaction from the moment the reactants are mixed to the moment that the color appears.

In this experiment, you will conduct a quantitative study of the effect of concentration on the rate of a clock reaction.

OBJECTIVES

When you have completed this activity, you should be able to:

Collect experimental data in order to calculate the rates of several iodine clock reactions.

MATERIALS

Goggles, Lab Aprons, Thermometer, 2 25-mL graduated cylinders, 1 100-mL beaker,1 stirring rod,1 plastic wash bottle, Solution A: KIO3 in distilled water, Solution B: Na2S2O5 + H2SO4 + soluble starch in water

PROCEDURE

Label two clean, dry graduated cylinders with the letters “A” and “B”. Measure the amounts of each solution according to the volumes listed in Data Table 1. Begin by measuring volumes for “Mixture 1”. Pour the solutions given for mixture 1 into these cylinders. Try to measure as accurately as possible. Make sure you do not “cross-contaminate” the cylinders.

Data Table 1: Proportions for Mixtures
Mixture / Solution A (KIO3) / Solution B (NaS2O5 + H2SO4 + starch)
1 / 25.0 mL / 25.0 mL
2 / 20.0 mL + 5.0 mL water / 25.0 mL
3 / 15.0 mL + 10.0 mL water / 25.0 mL
4 / 10.0 mL + 15.0 mL water / 25.0 mL
5 / 5.0 mL + 20.0 mL water / 25.0 mL
6 / 25.0 mL / 20.0 mL + 5.0 mL water
7 / 25.0 mL / 15.0 mL + 10 mL water
8 / 25.0 mL / 10.0 mL + 15.0 mL water

Pour the 25 mL of SOLUTION A into a clean 100-mL beaker. One person should be ready to signal the other person when to pour SOLUTION B into the beaker. At the signal, the other person should pour the second solution into the beaker and stir the mixture occasionally until a bluish-purple color appears. Note the time that the solutions were poured together as “zero” and the exact time the blue color appears. Record the temperature of the solution and the time required, in seconds, for the bluish-purple color to appear in Data Table 2.
Discard the solutions in the waste beaker. Wash the beaker and rinse it well with distilled water. Dry the beaker and repeat the reaction with mixture 1 until you can obtain two approximately equal reaction times.
Repeat the experiment using the other mixtures. Try to predict the outcome of each trial before you do it.
Put your data in the teacher excel sheet using the teacher’s computer.

DATA TABLE 2: Reaction Times
Mixture / Temperature (°C) / Time for color to Appear (s)
Trial 1 Trial 2 / Average Time of Reaction (s)
1
2
3
4
5
6
7
8

ANALYSIS AND CONCLUSIONS

The mechanism of the reaction is unknown; however, the first step in all the proposed mechanisms is the following reaction:

H2O + S2O52-  2 HSO3-

Calculate the concentration of HSO3- in stock solution B : ______

Calculate the initial concentration of KIO3 and HSO3- for each reaction. Report the values in data table 3.
Assume that the rate of the reaction is determined by the change in concentration of HSO3- over the change in time: Report these rate values in Table 3

DATA TABLE 3: Rate Determination for Each Mixture
Mixture / [KIO3] (M) / [HSO3-] (M) / Average Time of Reaction (s) / Rate (M/s)
1
2
3
4
5
6
7
8

Describe how the concentrations of each reactant affect the rate of the iodine clock reaction. Be sure to reference data from Table 3 in your statement.

How do you think the rate of reaction would change if you performed each reaction at 60 C? Explain your prediction using kinetic molecular theory.

EquilibriuM&M

Chemical reactions are represented as proceeding in one direction: from the reaction, to the products. This is depicted using a single headed arrow pointing toward the product side. Another type of reaction is represented as proceeding in both directions simultaneously. This type is called equilibrium, and it is defined as when both forward and reverse reactions occur at the same rate. These reactions are depicted as having a double headed arrow between the reactants (R) and the products (P), as shown in Figure 1.

R P

Figure 1

This activity will model the equilibrium process. M & M candies will be used to represent both the reactants and products for this equilibrium simulation.

OBJECTIVES

When you have completed this activity, you should be able to:

1. Collect data in order to describe the process of equilibrium.

MATERIALS

1 blank sheet of paper, 40 M&M candies

PROCEDURE

SET-UP

Have students pair up and obtain a clean sheet of paper and 40 M&M candies from the instructor.
Arrange the paper in landscape orientation. Draw a line down the middle of the sheet of paper. Label the left side of the paper “R” for reactants and the right side “P” for products, as shown in Figure 2.

R / P

Figure 2

PART 1

Place 40 M&M’s on the reactant side of the paper.
Begin Trial 1 by having one partner move half of the M&M’s on the reactant side to the product side. Then have the other partner move one-fourth of the M&M’s from the product side to the reactant side. If the number of candies moved should be a decimal, round up to the nearest whole number.
End this trial by counting the number of M&M’s on the R side and P side of the paper. Report these values in Data Table 1.
Repeat steps 2 and 3 until ten trials total have been completed.
At the end of ten trials, calculate the ratio of products to reactants for each trial. Use the following equation.

Ratio = P / R

Report these ratios in Data Table 1.

DATA TABLE 1
Trial / R / P / Ratio
1
2
3
4
5
6
7
8
9
10

PART 2

Repeat the steps in PART 1 except change the starting amounts of R and P. Count out a portion of M&M’s that is less than 40 and put those on the “R” side of the paper. Put the remainder of the M&M’s on the “P” side.
Repeat steps 2 through 5 listed in PART 1; however, record all data in DATA TABLE 2.

DATA TABLE 2
Trial / R / P / Ratio
1
2
3
4
5
6
7
8
9
10

PART 3

Combine each pair of students with another pair to make a group of four.
Count out 40 M&M’s and put them on the “R” side of the paper.
Repeat steps 2 and 3 from PART 1. This time, stop after five trials. Record all data in DATA TABLE 3.
After the fifth trial is completed add 40 M&M’s from another pair to the “R” side of the paper. Complete an additional 10 trials by repeating steps 2 and 3 from PART 1 with these new amounts. Record all data in DATA TABLE 3.
At the end of the 15 trials, calculate the ratio of Products to Reactants as described in the previous parts.

DATA TABLE 3
Trial / R / P / Ratio
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

ANALYSIS AND CONCLUSIONS

When did you reach equilibrium in PART 1? Explain in terms of amounts of candies and ratio of candies.

Why do you think this phenomenon is often described as “dynamic” equilibrium?

Compare the calculated ratios at the end of each part of the experiment. What do the ratio values tell you about equilibrium and the amounts of reactants and products?

Do you think that temperature would affect these systems in any way? Explain your choice

LeChâtelier’s Principle

As you have seen in class, many chemical reactions do not completely react. In these reactions, there will always be measurable quantities of all reactants and products in equilibrium. Once the equilibrium is reached, the forward and reverse reactions proceed at the same rate, so the concentrations of all reactants and products no longer change.

The equilibrium can be disturbed, however, by acting on it in some way. According to LeChâtelier’s Principle, applying some stress to the equilibrium will cause the equilibrium to shift until the stress has been alleviated.

In this experiment, you will study how different changes to a chemical equilibrium will respond to different stressors.

OBJECTIVE

Students will be able to apply LeChâtelier’s principle to experimental observations in order to predict changes to a chemical equilibrium.

MATERIALS

Gt Chemistry

Goggles, Petri dish,White sheet of paper, Stirring rod, Pipets or dropper bottles, Two 250 mL beakers, 10 mL graduated cylinder, Four test tubes, Test tube rack, Distilled water, Ice cubes or crushed ice,0.2 M Fe(NO3)3, 0.2 M KSCN,Aqueous, saturated KNO3, 0.1 M CuCl2, 0.1 M NaOH, 6 M NH4OH, 0.1 M HCl, Solid KNO3 crystals

Gt chemistry

PROCEDURE

Part 1

Put 20 mL of distilled water into the Petri dish and place it on the white sheet of paper. Add five drops of the Fe(NO3)3 solution, five drops of the KSCN solution, and stir the mixture with the stirring rod to ensure that the solutions are evenly mixed. Record your observations about the resulting solution.

To one side of the Petri dish, add three drops of the KSCN solution. Record your observations about what happens on that side of the Petri dish.

To the other side of the Petri dish, add three drops of the Fe(NO3)3 solution. Record your observations about what happens on that side of the Petri dish.

To the side that you added the Fe(NO3)3 solution, add three drops of the KSCN solution. Record your observations about what happens.

Data Table 1: Concentration Effects on Equilibrium
Fe3+(aq) + SCN-(aq) [FeSCN]2+(aq)
Step / Observations
Fe(NO3)3 and KSCN solutions are mixed
KSCN solution is added to one side
Fe(NO3)3 solution is added to one side
KSCN solution is added to the just-added Fe(NO3)3

Part 2

In a test tube, place 5 mL of saturated KNO3 solution.
Add a solid KNO3 crystal. If the solution is saturated, the crystal will not dissolve.
Fill a 250 mL beaker with ice and then fill the beaker with water to create an ice bath.
Place the test tube with saturated KNO3 solution into the ice bath. Leave it there for five to ten minutes.
Remove the test tube from the ice bath. Record your observations about what has happened in the test tube.
Allow the test tube to return to room temperature. Record your observations about what has happened in the test tube.

Data Table 2: Temperature Effects on Equilibrium
KNO3(s) K+(aq) + NO3-(aq)
Step / Observations
Saturated KNO3 solution after ice bath
Saturated KNO3 solution after returning to room temperature

Part 3

In each of three test tubes, place 5 mL of CuCl2 solution.
To each test tube, add 0.1 M NaOH solution dropwise until the Cu(OH)2 precipitate forms.
In the first test tube, add 0.1 M NaOH solution dropwise until you notice a change in the amount of Cu(OH)2 precipitate in the solution. Record your observations about what the solution in the test tube looks like before and after the reaction.
In the second test tube, add 6 M NH4OH solution dropwise until you notice a change in the amount of Cu(OH)2 precipitate in the solution. Record your observations about what the solution in the test tube looks like before and after the reaction.
In the third test tube, add 0.1 M HCl solution dropwise until you notice a change in the amount of Cu(OH)2 precipitate in the solution. Record your observations about what the solution in the test tube looks like before and after the reaction.

Data Table 3: Common Ion Effects on Equilibrium
Cu(OH)2(s) Cu2+(aq) + 2OH-(aq)
Test Tube / Observations Before Additional Reagent / Observations After Additional Reagent
1
2
3

ANALYSIS AND CONCLUSIONS

1. What colors are each of the following ions in aqueous solution?

Fe3+ / SCN- / [FeSCN]2+

2. When more of one reactant is added to the [FeSCN]2+ equilibrium, what happens in the reaction?

3. When both reactants are added to the [FeSCN]2+ equilibrium, what is actually being added? What effect does this have on the reaction?

4. Is the dissociation of KNO3 (separating KNO3 into K+ ions and NO3- ions) exothermic or endothermic? How do you know?

5. What do you think would happen if the test tube with saturated KNO3 solution was heated? Why?

Consider the last equilibrium experiment. The equation for the equilibrium is:

Cu(OH)2(s) Cu2+(aq) + 2OH-(aq)

For the reactions with Cu(OH)2, complete the following chart:

Test Tube / Affected Species in the Equilibrium Equation / Added or Removed? / Direction Equilibrium Shifts
1
2
3