Lab Activity 3: Factors Affecting Reaction Rate

Transcription

1 Chemistry 3202 Lab #3 factors affecting Reaction Rate Page 1 of 5 Lab Activity 3: Factors Affecting Reaction Rate Introduction Several factors influence how fast a reaction proceeds. In this activity, you will conduct experiments to determine the effect of changes in temperature, molar concentration, surface of a solid, and nature of reactants on reaction rate. Safety Before you start this lab activity be sure to: 1. Contact your supervising teacher to ask permission to access the lab/science room at your school. 2. Read all the safety data and safety instructions for the materials and apparatus to be used. 3. Read the purpose of the activity. 4. Read the procedure section of the lab activity carefully so you are thoroughly familiar with the steps to be carried out. 5. Prepare or copy any data tables you will need to record observations in the lab. 6. HCl is corrosive. Wear safety glasses, a lab coat, and close-toed shoes at all times during the activity. Purpose To determine the effect of changes in temperature, molar concentration, surface area of a solid and nature of reactants on the rates of chemical reactions. Pre-Lab Exercises (included these in your write up) 1. Write a balanced chemical equation for: i. sodium hydrogen carbonate (baking soda) reacting with hydrochloric acid.(hint: we did this reaction in the last lab!) ii. calcium carbonate (limestone) reacting with hydrochloric acid. 2. Make a quantitative prediction (faster/slower) about the effect of decreasing the molar concentration of HCl from 1.0 M to 0.75 M. 3. Make a quantitative prediction (faster/slower) about the effect of a 10 C temperature increase on the reaction rate. 4. Make a qualitative prediction about the effect of increasing the surface area of a solid reactant on the rate of reaction. 5. Which substance, sodium hydrogen carbonate or calcium carbonate should react faster with hydrochloric acid? (Be prepared to justify your answer. Hint: consider their relative solubility's in water.)

2 Chemistry 3202 Lab #3 factors affecting Reaction Rate Page 2 of 5 Materials All amounts of materials are based on groups of two students. See text p 464 for set-up. 1 centrigram or electronic balance that reads mass to two decimal places 1 pneumatic trough or a large plastic dish pan stopwatch ml Erlenmeyer flask 1 one-hole rubber stopper to fit flask 1 short piece of glass tubing to fit stopper 1 length (approx cm) plastic tubing to fit glass tubing 1 25 ml graduated cyclinder (or larger size up to 100 ml) 1 large test tube or a large ( ml graduated cylinder) 100 ml 1.0 mol/l HCl at room temperature (per group of two students) o 10 g baking soda (sodium hydrogen carbonate) 2 g powdered calcium carbonate 2 g marble chips - solid lumps of calcium carbonate 2 scoopulas 1 thermometer filter paper folded in half (or a clean square 10 cm x 10 cm of white paper) distilled water (at room temperature) hot water bath (e.g. a large beaker of warm water) cold water bath (e.g. a large beaker containing ice cubes) paper towels Procedure Part A: Effects of concentration Assemble the reaction vessel and gas collection apparatus. (see text p 464) The flask will contain the reaction. The tubing will transport the carbon dioxide gas produced to the inverted test tube that is full of water. You will measure the time it takes for the gas to displace the water in the tube in each trial. Measure and record the volume of the tube by filling it with water and transferring the water to a larger graduated cylinder. You will need a partner to carry out the following procedures. 1. Using a clean dry graduated cylinder, measure 20.0 ml of 1.0 M HCl. The temperature of the HCl solution should be 20 C. Pour it carefully into the Erlenmeyer flask. 2. Using a piece of folded filter paper, a clean scoopula, and a centigram balance, obtain 1.00 g of baking soda (NaHCO3).

3 Chemistry 3202 Lab #3 factors affecting Reaction Rate Page 3 of 5 3. If you have a pneumatic trough, place a test tube or graduated cylinder full of water over the tubing. If you are using a large pan of water, have your partner hold the tube or cylinder in place over the tubing. Make sure the tubing remains under water at all times. 4. Remove the stopper from the Erlenmeyer flask and add the baking soda to the HCl. 5. Quickly replace the stopper and start the stopwatch. 6. Stop the stopwatch when all the water has been displaced from the inverted tube. 7. Record the elapsed time in your data table. 8. Dispose the contents of the flask in the sink and flush with plenty of water. Rinse the flask and reassemble the gas collection apparatus. 9. Using a clean graduated cylinder, measure 5.0 ml of water and add it to the Erlenmeyer flask. Measure out and add 15.0 ml of 1.0 M HCl to the flask. 10. Repeat Steps 2-7. Do two more trials, 1. one using 10 ml or water and 10 ml of HCl 2. and the other using 15 ml of water and 5 ml of HCl. Part B: The Effect of Changes in Temperature 1. Reassemble the gas collection apparatus, but leave the flask disconnected. 2. Measure 10 ml of water and 10 ml of 1.0 M HCl into the clean flask. 3. Place the flask in an ice bath so that the temperature of the solution drops to 10 C. 4. Obtain 1.0 g of baking soda. 5. Carefully but quickly add the baking soda to the HCl solution in the flask and reattach the stopper. Record the time it takes to displace all the water in the tube. 6. Rinse the contents of the flask into the sink, flush with water thoroughly. 7. Repeat steps 1-6, this time use a hot bath to raise the temperature of the water/hcl to 30 C. Part C: Effect of Nature of Reactants and the Effect of Surface Area 1. Reassemble the gas collection apparatus, but leave the flask disconnected. 2. Measure 10 ml of water and 10 ml of 1.0 M HCl into the clean flask. The temperature of the mixture should be 20 C. 3. Obtain 1.0 g of powdered calcium carbonate. 4. Carefully but quickly add the powdered calcium carbonate to the HCl solution in the flask and reattach the stopper. Record the time it takes to displace all the water in the tube. 5. Rinse the contents of the flask into the sink, flush with water thoroughly. 6. Repeat steps 1-5, this time use 1.0 g of marble chips (a lump of CaCO3).

4 Chemistry 3202 Lab #3 factors affecting Reaction Rate Page 4 of 5 Name(s): School: page: of Results: Table 3.1. Reaction rates data Part A: Effects of concentration Volume of Tube (use same tube for all trials): ml Trial Mass of NaHCO3 Volume of HCl (ml) Volume of H2O (ml) g 20.0 ml 0.0 ml g 15.0 ml 5.0 ml g 10.0 ml 10.0 ml g 5.0 ml 15.0 ml Time to Fill Tube (s) Average Reaction rate (ml/s) Part B: The Effect of Changes in Temperature 10 C trial 1.00 g 10.0 ml 10.0 ml 30 C trial 1.00 g 10.0 ml 10.0 ml Part C: Effect of Nature of Reactants and the Effect of Surface Area Mass of CaCO3 powder 1.00 g 10.0 ml 10.0 ml lumps 1.00 g 10.0 ml 10.0 ml

5 Chemistry 3202 Lab #3 factors affecting Reaction Rate Page 5 of 5 Analysis Part A: Effects of concentration. 1. Calculate the average reaction rate by dividing the volume of the tube by the time for each trial. Show all workings. 2. Calculate the molar concentration of the hydrochloric acid solution in trials 2, 3, and 4 of Part 1. Using the dilution formula, Show all workings. Rewrite and place all data in a data as below. Sample table Trial Average rate (ml/s) (from part A above) Concentration (mol/l) 3. Identify the independent (manipulated) and dependent (responding) variables in Part 1 of the procedure. 4. List three controlled variable in Part 1 of the procedure. 5. Draw a properly labelled and scaled graph of molar concentration of HCl (x-axis) versus average reaction rate (y-axis). Be sure to title your graph. 6. With reference to the graph, state the relationship between the molar concentration of HCl and the average reaction rate. Discuss the relationship in terms of the collision theory. Analysis Part B: The Effect of Changes in Temperature 1. Compare the average rate of reaction of HCl and NaHCO3 at 10 C, 20 C, and 30 C. What effect does doubling the temperature of the reactants have on the average rate of reaction? Discuss the relationship in terms of the collision theory. Analysis Part C: Effect of Nature of Reactants and the Effect of Surface Area 1. In terms of nature of reactants, specifically bonding and solubility, compare the rates of reaction of CaCO3 and NaHCO3 with HCl. Discuss the relationship in terms of the collision theory. 2. In terms of surface area of reactants, compare the rates of powdered CaCO3 and lumps of CaCO3. Discuss the relationship in terms of the collision theory. Conclusion Compare the results obtain in this activity with the predictions you made in the pre-lab exercise. State whether your predictions were supported or not supported by the results. Account for any differences (sources of error) between your results and your predictions.