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Lab: Catalysts
Objectives
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Evaluate different catalysts to determine which is the best
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Illustrate the difference between using a heterogeneous and homogeneous catalyst
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Demonstrate how varying the quantities of a catalyst can affect the reaction
Introduction
If you’ve ever used hydrogen peroxide (H2O2) on a wound, you’ve most likely noticed the immediate reaction that causes bubbles to form. This reaction is accelerated by what is known as a catalyst – in this case an enzyme in blood that accelerates the decomposition of the hydrogen peroxide into oxygen (O2) gas and water (H2O). Scientists use many different types of catalysts to control the speed of a reaction.
In addition to speeding up a chemical reaction, another beneficial feature of a catalyst is that it is not consumed during the reaction – in other words it does not form or change the products of the reaction. Enzymes are biological catalysts and are necessary for many of the reactions that take place in your body.
Chemical reactions require a small amount of energy, known as activation energy, to begin the reaction. If a chemist cannot change the other conditions of the reaction (temperature, concentration, etc.) to increase the reaction rate, then the chemist may select a catalyst that will lower the activation energy and speed up the reaction. There are many different types of catalysts and frequently there are several catalysts that will work for a given reaction. Selecting the correct
Figure 1: One day soon, homeowners everywhere may be protected from deadly carbon monoxide fumes, thanks to a device, invented at NASA Langley Research Center, which converts deadly carbon monoxide to carbon dioxide. The chemical catalysts - tin oxide and platinum - are applied to a surface. Air passing over the surface reacts with the catalysts, transforming carbon monoxide into carbon dioxide. The device requires no energy for operation, doesn't need to be plugged in, has no moving parts, and lasts a long time.
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catalyst is important. Catalysts only react with the other chemicals in a reaction to a limit; at some point adding more of the catalyst will have no effect on the reaction rate.
Chemists choose catalysts based upon such factors as cost, toxicity, improved reaction speed, life of the catalyst, and the phase of the catalyst. There are two categories of catalysts: homogeneous catalysts are in the same phase as that of the reaction materials, while heterogeneous catalysts are in a phase that is different from the reaction materials. Homogenous catalysts tend to react faster than heterogeneous catalysts; however, heterogeneous catalysts are easier to remove from the final products.
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Pre-lab Questions
1.
What is a catalyst?
2.
Will adding more of a catalyst to a reaction always cause the speed of the reaction to increase? Why or why not?
3.
Write a balanced chemical equation that expresses the reaction that will occur during this experiment and that will convert hydrogen peroxide (H2O2) to oxygen (O2) gas and liquid water (H2O).
4.
Is the solid catalyst in the carbon monoxide filter from Figure 1 an example of a homogeneous or heterogeneous catalyst?
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Experiment: Reactions with Catalysts
In this experiment, you will be working with a variety of substances that will act as catalysts to decompose hydrogen peroxide into oxygen and water.
Materials
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Safety glasses or goggles
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Clear plastic cups (10)
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Hydrogen peroxide (H2O2)
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Baker’s yeast
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Straw or dropper
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Permanent marker
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Chopstick or stir rod
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Clear glass jar
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Distilled water (warm, 45°C)
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Piece of carrot
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Piece of tomato
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Soil
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Measuring cups
Procedure
Part 1: Comparison of Different Catalysts
1.
Use the permanent marker to label four of the clear plastic cups, C, T, D, and Y, symbolizing carrot, tomato, soil, and yeast.
2.
Mix 118 milliliters (1/2 cup) warm water (45 degrees Celsius) with one packet of yeast in a clear glass jar. Stir with the chopstick until dissolved.
3.
Use a straw or dropper to add 3 milliliters (60 drops or 1/5 teaspoon) of hydrogen peroxide to EACH of the four labeled plastic cups.
4.
Carefully add a small piece (approximately 1 centimeter squared (cm2)) of carrot to the plastic cup labeled C, and a small piece of tomato to the plastic cup labeled T. Add a similar small amount of soil to the plastic cup labeled D.
5.
Slowly add 3 milliliters (1/5 of a teaspoon) of yeast solution to the plastic cup labeled Y. Swirl until all bubbling and foaming stops. This will indicate the completion of the reaction.
6.
Record observations for each of the reactions in the Initial Observations column in Table 1 in the Data section. Let the reactions continue until the end of the next part of the procedure.
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Part 2: Catalyst Quantity Comparison
7.
Use a permanent marker to label the six remaining plastic cups, 1, 5, 10, 1A, 5A, and 10A.
8.
Fill plastic cup 1A, 5A, and 10A with 1, 5, and 10 milliliters of yeast solution, respectively.
9.
Use a 10-milliliter graduated cylinder and dropper to add 1 milliliter of hydrogen peroxide to the plastic cups labeled 1, 5, and 10.
10.
Simultaneously (or as close to the same time as possible), pour the yeast solution from plastic cups 1A, 5A, and 10A into the corresponding plastic cups 1, 5, and 10 containing the hydrogen peroxide.
11.
Record your observations of the three reactions in Table 2 of the Data section. HINT: Be sure to note observations both of similarities and differences in the bubbling and foaming among the reactions.
12.
Return to the plastic cups in Part 1 and make final observations. Record your observations in the Final Observations Column in Table 1 of the Data section.
13.
To clean-up, decant the liquid from the heterogeneous catalysts and wash all solutions down the sink with plenty of water. Dispose of the carrot, tomato, and soil in the trash.
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Data and Observations
Table 1: Catalyst Comparison
Type of Catalyst
Initial Observations
Final Observations
Carrot
Tomato
Soil
Yeast
Table 2: Catalyst Quantity Comparison
Amount of Yeast
Observations
1 mL
5 mL
10 mL
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Post-lab Questions
1.
Classify each catalyst that was used in the experiment as either homogeneous or heterogeneous.
Homogeneous catalysts:
Heterogeneous catalysts:
2.
Which catalyst sped up the reaction the most?
3.
Which catalyst would be the easiest to separate from the water product?
4.
Which yeast solution produced the greatest effect? Why?