SNC 2D Factors Affecting Rates of Reaction
Concentration
Background: Concentration of a reactant how much chemical (such as an acid) there is in a certain amount of water; sometimes measured as a percentage.
Objective: Determine the effect of increasing concentration on the rate of reaction.
Materials:
\snc2D\chem\rates concent.doc
2 – graduated cylinders
5 – medium sized beakers
4 – small sized beakers
1 – large beaker
mossy zinc
electronic balance
stop watch
HCl (hydrochloric acid) supply
\snc2D\chem\rates concent.doc
Procedure: Complete the table below.
Solution # / Volume of HCl (mL) / Volume of Water (mL) / Total Volume of mixture (mL) / Concentration of Acid (by volume)1 / 50 / 0 / 50 / 100%
2 / 40 / 50 / 80%
3 / 25 / 50%
4 / 50 / 40%
1. Obtain about 150 mL of HCl from the supply in the large beaker.
2. Use the graduated cylinders to prepare the four (4) solutions in separate clean beakers. The volumes of each chemical from the table above should be used.
3. Place 1 g of mossy zinc in each of the empty small beakers. Label them ‘A’ – ‘D’.
4. Pour solution #4 into beaker ‘A’ with the zinc and start the stopwatch. Do the same for the other 3 labeled beakers.
5. Observe the reactions. Stop timing when there are no more visible bubbles being produced.
6. Convert all times from minutes : seconds to total seconds. (ex. 2 min : 32 sec is equal to 152 s)
7. Complete the observation table on the reverse.
8. Answer the Discussion questions.
Observations:
Solution # / Concentration (%) / Time to React (s) / Rate (1/time)1
2
3
4
Discussion:
1. Use Excel to produce an XY-scatter graph (with data connected by a smoothed line) with
a) concentration on the x-axis and time on the y-axis
b) concentration on the x-axis and rate (x 1000) on the y-axis
· make the graph location “as new sheet” to have a full page graph
· title the graphs “Effect of Concentration on the Rate of Reaction”
2. Print the second graph (#1 b). Based on your graph, what would the rate of reaction be for 60% concentration of HCl?
3. What did you observe as the reaction was going that indicated a faster rate of reaction was happening?
4. How does increasing the concentration of one of the reactants affect the rate of reaction? Use the collision theory to explain your answer in #4.
5. Why was it useful to start with solution #4 first?
6. In the experiment, why was it important to use the same volume of acid and the same mass of zinc in each test? What if they weren’t the same?
7. Why do you think the volume of the acid and the mass of the zinc are sometimes referred to as “controlled variables”?
8. Instead of letting the reaction go to completion, describe how else you could test the effect of the concentration on the rate of reaction.
9. Print the answers to the above questions and attach them to the graph produced in #1b.
\snc2D\chem\rates concent.doc