Investigating Factors Influencing Rates of Chemical Reactions
In this investigation, students will observe the rate at which aluminum replaces hydrogen in a hydrochloric acid solution. Based on what they have learned about rates of reaction, they will then form a hypothesis about what factors in this experiment could influence the rate of reaction. They will then write a modified procedure to test their hypothesis. Data will be collected and compared to draw a conclusion.
2. The student will develop a procedure to test his/her hypothesis about the factors influencing the rate of this reaction.
3. The student will work cooperatively with a partner to complete the activity.
4. The student will present data in an understandable format.
5. The student will draw a conclusion based on his/her data.
Vocabulary: rate of reaction, concentration, temperature, reactants, products
Key concepts: 1) The rate of reaction depends on the frequency of collisions between particles (atoms or ions) of the reactants. 2) When temperature increases, particles (atoms or ions) move more rapidly and frequency of collisions increases. (ie. temperature ↑, rate ↑) 3) Concentration is directly proportional to the rate of reaction. (ie. concentration ↑, rate ↑)
Context for Use
Resource Type: Activities:Lab Activity
Grade Level: High School (9-12)
Description and Teaching Materials
My changes include a few minor material changes and some additional questions. I have submitted these as a separate file attachment.
In short, the student does the activity basically as outlined in the Alka Seltzer activity. As I ask more questions of them, they will realize that they don't have enough data to actually draw a conclusion about what is affecting the rate at which hydrogen gas is being generated in this reaction system. They will then modify the procedure to test another factor that could be affecting the rate of their reaction (temperature or concentration of acid) and run the activity again. They will compare their two sets of data and draw a conclusion. Rate of Reaction Lab (Microsoft Word 27kB Aug1 09)
Teaching Notes and Tips
I have not yet had opportunity to use this activity in my classroom but a few possible issues or concerns that come to mind are –
- Will the amount of either reactant affect the rate at which the gas is produced? i.e. if we don't measure out exactly the amount of aluminum and the amount of HCl each time can the results really be compared? I have addressed the acid, but not the metal.
- Will not having a heat source slow the rate so much that the reaction won't be measurable?
- I can think of two ways to modify the procedure – 1) take away the heat OR 2) lower the concentration of HCl. Are there other ways to modify it that I haven't thought of yet?