Alka Seltzer Lab: Reaction rate - Factors that affect the rate of chemical reactions Materials Lead Scribe Reporter/Questioner Clean-up WRITE ALL NOTES / DATA / OBSERVATIONS ON YOUR DATA SHEET The rate of a chemical reaction is affected by the physical size of the reactants. Decreasing the size of the particles which make up a given weight will increase the number of particles represented by the same weight. Smaller particle size results in an increase in the rate of reaction because the surface area of the reactant has been increased. Changing the temperature of a reaction can also increase or decrease the rate of reaction. If the reactants temperature is increased, the rate of the chemical reaction can also be increased. Because by adding heat energy, we are driving the particles apart, but also increasing the chances that particles will come into contact with one another. Changing the pressure in the system where a reaction is taking place can also have an effect on the reaction. Increasing the pressure will decrease the rate of reaction. Part 1: Surface Area - 3 clear glasses - 3 antacid tablets - Mortar and pestle - Stopwatch - Graduated cylinder Procedure: A. Whole tablet 1. Fill a clear glass with 250 ml of room temperature or lukewarm water 2. Drop 1 whole tablet into the water. Measure and record the time to dissolve B. Tablet broken into ~8 pieces 1. Place 1 tablet onto a sheet of paper and break into approximately 8 pieces of about equal size 2. Fill a clear glass with exactly 250 ml of room temperature or lukewarm water 3. Slide broken tablet into the water from the sheet. Measure and record the time to dissolve. C. Powdered tablet 1. Place 1 tablet into mortar and grind to a fine powder 2. Transfer powder into a clear cup. (Note: it s important to have the powder in the cup before adding water.) 3. Add 250 ml of room temperature or lukewarm water to the glass. Measure and record the time to dissolve. Observations: Particle size Time for reaction to be completed Whole tablet seconds 8 Pieces seconds Powder seconds Summary Questions: 1. As particle size decreases, the rate of reaction. 2. The rate of reaction for the powder was times faster than for the whole tablet. 3. As particle size decreases, the total surface area of a reactant. As a result, the probability of interactions between atoms/ions, and the rate of reaction.
4. Particle size appears to have less / more (choose one) of an effect on the rate of reaction than Part 2: Temperature - 3 clear cups - Thermometer - 3 tablets - Stopwatch - Mortar and pestle - Ice cubes - Hot water - Graph paper Procedure: A. Hot water 1. Run water from the hot tap until it is as hot as possible. Fill a clear glass with exactly 250 ml of hot water. 2. Use the thermometer to take the temperature and record it on your data sheet. 3. Remove 1 tablet from its package. Drop it into water. Measure the time required for tablet to fully dissolve. Be prepared to start and stop on time. The reaction will take less than 15 seconds. B. Room temperature water 1. Fill a clear glass with exactly 250 ml of room temperature or lukewarm water. 2. Use the thermometer to take the temperature and record it on your data sheet. 3. Drop 1 tablet into the water. Measure the time required for the reaction to be completed. C. Cold water 1. Fill a clear glass with 125 ml of water and add enough ice to adjust the level to 250 ml. Stir the ice water for about 15 seconds so the temperature will come to equilibrium. 2. Use the thermometer to take the temperature and record it on your data sheet. (Then remove ice cubes.) 3. Drop 1 tablet into the water. Measure the time required for the reaction to be completed. Hot water o C seconds Room temperature water o C seconds Ice water o C seconds Graph your data points (water temperature vs. time to fully dissolve) to show the effect of temperature on rate of reaction. Summary questions 1. As the temperature increases, the rate of reaction. 2. At a temperature of 10 0 C, it would take seconds for 1 tablet to react with 250 ml of water. 3. If the temperature is doubled from 20 o C to 40 o C, the time for the rate of reaction by approximately. 4. Using the hot water, the rate was times faster than at 0 o C. Part 3: Pressure - Safety goggles - Test tube 16 x 150mm - 2 tablet - Water
Procedure: A. Rate of reaction at normal pressure 1. Fill a 16 x 150mm test tube ½ full of water. The water should be at about room 2. Break a tablet in half and drop the pieces into the test tube. 3. Measure the time required for the reaction between the tablet and water to be completed. B. Rate of reaction under increased pressure 1. Fill the 16 x 150 mm test tube ½ full of water. The water should be about room 2. Break a tablet in half. Drop the pieces into the test tube. 3. Immediately put your palm over the top of the test tube to seal it. This will slow down the escape of carbon dioxide gas. The pressure being exerted upon the reactants inside the test tube is equal to the pressure you feel being exerted against your hand. Release your hand and note what changes you observe. DO NOT KEEP IT SEALED FOR LONG. 4. When gas bubbles are no longer visible in the liquid contained in the test tube, consider the reaction to be over. Observe and record the time of the reaction. 5. Release the pressure on your hand. Note that the reaction starts again. Increase pressure with your palm and the reaction stops. Note that there is still a small amount of tablet left in the bottom of the test tube. You have now reached the point when you are able to exert enough pressure to be equal to the pressure exerted by the gas inside the test tube. As a result, the reaction stops. When you release your pressure, the reaction is able to start again. 6. Remove your hand. Observe and record what happens to the remaining tablet.
Data Sheet Alka Seltzer Rates of Reaction Lab Name: Date: Period: Partners: Part 1: Surface Area Observations: Particle size Time for reaction to be completed Whole tablet seconds 8 Pieces seconds Powder seconds What did you see: A. B. C. Summary Questions: 5. As particle size decreases, the rate of reaction. 6. The rate of reaction for the powder was times faster than for the whole tablet. 7. As particle size decreases, the total surface area of a reactant. As a result, the probability of interactions between atoms/ions, and the rate of reaction. 8. Particle size appears to have less / more (choose one) of an effect on the rate of reaction than Part 2: Temperature Hot water o C seconds Room temperature water o C seconds Ice water o C seconds
Graph your data points (water temperature vs. time to fully dissolve) to show the effect of temperature on rate of reaction. Summary questions 5. As the temperature increases, the rate of reaction. 6. At a temperature of 10 0 C, it would take seconds for 1 tablet to react with 250 ml of water. 7. If the temperature is doubled from 20 o C to 40 o C, the time for the rate of reaction by approximately. 8. Using the hot water, the rate was times faster than at 0 o C. Part 3: Pressure Test tube o C seconds High pressure o C seconds What did you see?