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6.05 Rate & Collision Theory

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Ashleigh Mangum

on 4 August 2014

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Transcript of 6.05 Rate & Collision Theory

6.05 Rate & Collision Theory
The reaction you will be investigating is the reaction that occurs when an Alka-Seltzer tablet is placed into a given amount of water. Alka-Seltzer is an over-the-counter antacid and pain relief medication that is dissolved in water before it is ingested. Each tablet contains aspirin (acetylsalicylic acid), citric acid, and sodium bicarbonate. As the tablet dissolves in water, the bicarbonate ions in the tablet react with the hydrogen ions from the acids that are also contained in the tablet. The carbon dioxide gas produced by the reaction is what causes the bubbling that can be observed.

HCO3- (aq) + H+ (aq) → H2O (l) + CO2 (g)

In this investigation, you will design two experiments which will compare two different factors that may affect the rate of the Alka-Seltzer reaction. Possible factors to be investigated include temperature, surface area, agitation, and amount of reactants. Remember to make sure there is only one independent variable in your experimental design for each experiment. You can only test one factor at a time.

- 3 cups
- 3 balloons
- Water
- Timer
- Alka-Seltzer tablets
Experiment 1
Step 1: Fill one of the cups with water.
Step 2: Get your timer ready and then place an alka-seltzer tablet into the water.
Step 3: Quickly place the balloon over the top of the cup to collect the carbon dioxide produced and start your timer.
Step 4: Note any observations and record the time it took for the balloon to inflate.
Experiment 2
Step 1: Fill a cup with water.
Step 2: Crush an alka-seltzer tablet, get a timer ready, and add the broken tablet to the water.
Step 3: Quickly place a balloon over the cup and start the timer.
Step 4: Note any observations made and record the time it took for the balloon to inflate.
1. What two factors did you investigate in your procedure, and why did you choose to compare these two factors?
Experiment 3
Step 1: Fill a cup with warm water at almost
boiling point.
Step 2: Get a timer ready and drop an
alka-seltzer tablet into the water.
Step 3: Quickly place the balloon over the cup and begin timing.
Step 4: Note any observations and be sure to record the time it took for the balloon to inflate.
I chose to investigate the effects of heat and surface area on the dissolving of alka-seltzer tablets. I chose these two factors because I wanted to know which would cause the tablet to produce more CO2 and dissolve quicker.
2. What other factors did you need to control during your investigation? Explain how you controlled each one in your procedure.
The amount of air allowed into the experiment was controlled by placing the balloon over the cup and containing the reaction. Also, the amount of water used in the cups were all the same as was the type of cup used and the type of balloon used to trap the CO2.
3. What was your prediction about the results of each factor tested in your two lab procedures? Explain your prediction based on your knowledge of the dissolving process, collision theory, and reaction rates.
I predicted that heat would have sped up the reaction because heat gets the particles moving faster which increases the rate of reaction. I also predicted that spreading out the surface area would speed up the reaction because when surface area increases so does the rate of reaction due to there being more contact between the particles.
4. In your own words, describe the collision theory and what is necessary for a collision to be successful.
The collision theory states that gas-phase reactions occur when particles collide with each other. In order for a successful collision to occur, there has to be enough activation energy in the reaction.
5. A specific catalyst was not provided for this reaction, but catalysts are useful for increasing the rate of many slow reactions. In your own words, give a detailed explanation of how catalysts can increase the rate of a reaction or process.
Catalysts lower the activation energy needed to start a reaction by creating a different way for energy to flow. If a reaction is happening slowly, it's probably due to there being little activation energy. So by adding a catalyst the reaction is being forced to speed up.
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