AP Chemistry Lab 06
Investigation 10How Long Will That Marble Statue Last?
Note From Clinch: This is a full-on inquiry lab. Each group is expected to investigate a different variable with different procedures, and different results. Decide what variables you want to manipulate, how you will test them, how you will time or measure them, and what constitutes “completion” of a reaction. Consistency in procedure is something that is lacking in most of your lab techniques. This means you may have to do this lab SEVERAL times to get consistent data. If you do “throw out” data you must report it and explain why it was discarded and what made it unreliable (aka sources of error).
You all did the “alka-seltzer” lab last year in Regents Lab. You should have enough knowledge of reaction rates to know what to expect with your different variables, you will need to collect data that support that previous knowledge.
Central Challenge
To investigate how the speed of the chemical reaction between solid calcium carbonate and a solution of hydrochloric acid is affected by changing variables relating to the two reactants, by first constructing, and then testing, a hypothesis.
Context for This Investigation
Many historic buildings and monuments are made from limestone or marble. Limestone and marble are minerals that contain large amounts of calcium carbonate, CaCO3. Since the industrial revolution, air pollutants (chiefly in the form of oxides of sulfur and nitrogen) have been absorbed into the atmosphere, leading to the production of rainwater that has become significantly more acidic. This acidrain will react with the limestone buildings, eroding the stone and causing much disfigurement and damage.
Learning Objective
4.1: The student is able to design and/or interpret the results of an experiment regarding the factors (i.e., temperature, concentration, surface area) that may influence the rate of a reaction. [See SP 4.2, 5.1]
4.2: The student is able to analyze concentration vs. time data to determine the rate law for a zeroth-, first-, or second-order reaction. [See SP 5.1, 6.4, connects to 4.A.3]
Associated Science Practice:SP 3.1, SP 3.2, SP 4.1, SP 4.2, SP 4.3, SP 5.1, SP 5.2, SP 5.3, SP 6.1, SP 6.2, SP 6.4, SP 7.1, SP 7.2
Materials
Marble or limestone (limestone/calcium carbonate,CaCO3), (medium, small chips, powder)= 1.20–1.40 g / Distilled Water / timers6.0 Mhydrochloric acid (HCl) to dilute to varying concentration, (e.g., 6.0M, 5.0 M, 4.0 M, 3.0 M) / Stoppers / rubber tubing
125 mL Erlenmeyer flasks / Digital balance / Syringes
Hot plate/magnetic stirrer / Stir bar
Safety and Disposal
Safety: 6.0 M hydrochloric is hazardous and needs to be handled with care. Goggles are required. Students should not generate gases in closed containers since there is a risk of explosion as pressure builds. When diluting acids, acid should be added to water, not water to acid.
Disposal: Any excess solid calcium carbonate should be removed from the solution and disposed of in the trash. All solutions can be diluted and washed down the sink with plenty of water.
Part I: Pre-lab Questions(required in the write-up, not a prerequisite to do the lab work)
1. List the factors that you think may affect the speed at which calcium carbonate will react with acid. (The hydrochloric acid will be available to you to dilute to varying concentrations, and the calcium carbonate will be available in “chunks” of varying size. You will have access to a heat source.)
2. If a chemical reaction produces a gas, suggest a way of monitoring the production of that gas as the reaction proceeds.
3. Discuss how increasing the surface area of a solid might influence the rate of a chemical reaction.
Explanation to Strengthen Student Understanding
The rate of a chemical reaction is explained by collision theory. Collision theory can be condensed into three large ideas that apply to the rate of all chemical reactions where two or more molecules, atoms, or ions come together.
1. When substances are brought together in chemical reactions, the particles that make up those substances collide with one another. The collisions that occur between the particles are the first criteria for a reaction to take place. In potential reactions where two or more molecules, atoms, or ions come together without those collisions, no actual reaction is possible.
2. The collisions that take place have to occur with a certain minimum energy. That minimum energy is called the activation energy. If the particles collide with insufficient energy, i.e., with an energy less than the activation energy, no reaction occurs and the particles simply bounce off one another without producing any products. Collisions that do not result in a reaction are called “unsuccessful.”
3. The collisions must occur with the correct orientation, i.e., the particles must come together in a certain specific, physical way in which the atoms “line up” with one another, allowing a reaction to occur.
For a collision to be “successful”, i.e., for a collision to result in a chemical reaction where reactants turn into products, the particles of the reactants must fulfill each of the three conditions of collision theory.
Investigation - 2HCl(aq) + CaCO3(s) → CaCl2(aq) + CO2(g) + H2O(l)
To write a testable research question to address how certain conditions affect the rate of reaction between hydrochloric acid and calcium carbonate. Use the format below:
To what extent does A affect B? (where A is the independent variable and B is the dependent variable)
Additionally, answer the following questions:
1. Which variable will you measure throughout the experiment (the dependent or independent)?
2. Why are you measuring what you are measuring?
3. What factors of the experimental setup are you going to hold constant?
4. What is the ultimate goal of the data collection?
Procedure - design an experiment for to collect data that will allow them to draw conclusions about the effect of those variables on the rate of this reaction.
1. You will need to monitor some aspect of the reactions in order to find a rate of reaction.
2. In each experimental design, you should consider the potential role of factors that might affect the rate of the reaction. You should formulate a hypothesis for the factors that have identified and design an experiment that helps you collect data to support or refute your hypotheses. Accordingly, you must consider the general principles behind experimental design, such as what constitutes a “fair test,” which variables can be manipulated and changed, and practical considerations including time constraints.
3. You will need to show your proposed procedure to the teacher before attempting your experiments. Once your initial experimental designs have been carried out and data collected, students you consider improvements to their procedures and perform the investigations once more; they must show the teacher your procedures with changes before trying them. Identify a pattern in your data.
Data Collection and Computation
1. List the measurements that you took during the experiments.
2. Consider how the data or measurements should be recorded and presented to illustrate your findingsfor the purpose of engaging in whole-group discussion about the variables that affect the rate of reaction between hydrochloric acid and calcium carbonate.
Argumentation and Documentation
1. Using your data the comment on whether or not their data supported or refuted their hypotheses.
2. What changes did you make to your labs to ensure consistency in the data collection?
3. Why did you choose a particular treatment of the data to illustrate their findings to the class?
4. Much of the acid rain produced is from the presence of sulfuric acid in rainwater. Countries with coal-burning power plants release sulfur dioxide as a byproduct of burning the coal. Such sulfur dioxide gas combines with water and oxygen in the atmosphere to produce sulfuric acid.
2SO2 (g) + O2 (g) →2SO3 (g)
SO3 (g) + H2O (l) →H2SO4 (aq)
If this acid rain pours down on marble or limestone statues, such a reaction is represented below:
H2SO4 + CaCO3→CaSO4 + CO2 + H2O
From your findings of your experiment, how long it would take marble statues to disintegrate under these specific conditions.
Post-lab Assessment
1. An experiment was carried out in order to investigate the rate of reaction between magnesium and dilute hydrochloric acid. 0.07 g of magnesium ribbon was reacted with excess dilute acid. The volume of gas produced every 5.00 seconds was recorded. Plot a graph of these results
Seconds / Volume of Gas Collected (mL)0 / 0
5 / 18
10 / 34
15 / 47
20 / 57
25 / 63
30 / 67
35 / 69
40 / 70
45 / 70
b. When is the reaction fastest? How can you use the graph to determine when the reaction is the fastest?
c. How long does it take for the 0.07g of magnesium to react completely with the dilute hydrochloric acid?
d. Sketch another curve onto your graph that might have been obtained if 0.07g of magnesium powder had been used instead of magnesium ribbon.
e. Suggest two other factors that would alter the rate of this reaction.
f. Write a chemical reaction for this process.