Name ________________________________ Chem 178L Sp 01 Experiment #2 Section __________
The pH of acid and bases computer simulation to accompany this tutorial is located at the following URL:http://www.chem.iastate.edu/ChemEdGroup/GREENBOWE/sections/projectfolder/flashfiles/acidbasepH/ph_meter.html We are using Macromedia's Flash/Shockwave plug-in.
The computer simulation will allow you to test the pH of different concentrations and volumes of acid and base solutions. Before doing anything with the simulation, please answer the following questions. Work in groups of three. When you have completed a problem or activity, explain your answers to your TA. Your TA will listen and offer advice, but he or she will not tell you if you are right or wrong. Please turn in this tutorial to your TA when you have complete all of the problems and activities on both sides of the paper. Thank you.
1. Identify the following solutions using one of these terms: strong acid, weak acid, strong base, weak base, acidic salt, basic salt, or neutral solution. Write an equation that supports your answer showing how H+, OH- or neither is generated
a. HNO3 (aq)
b. HNO2 (aq)
c. HONH2 (aq)
d. NaOH (aq)
2. If we change the pH of a HCl solution from pH = 6.00 to pH = 3.00. By what factor does this change the concentration of [H3O+] in the solution?
3. Which solution has the highest pH (largest number)? Which has the lowest pH?
a. 50.0 mL 0.0500 M nitric acid, HNO3 (aq)
b. 50.0 mL 0.0500 M nitrous acid, HNO2 (aq)
c. 50.0 mL 0.0500 M sodium hydroxide, NaOH (aq)
d. 50.0 mL 0.0500 M calcium hydroxide, Ca(OH)2 (aq)
Measuring the pH of Acid Solutions Using the pH Simulation. Work in groups of three.
Activity 1. This activity will help you get use to using the computer simulation. This computer simulation is in a draft stage. We are still working on it. If you think you already know how to use it, you can skip Activity 1. Use a web browser on your computer to access the URL for the computer simulation. At the bottom right-hand corner of the page select acid solutions. Select HCl. Use the slider bar or type in a number to select a concentration, in units of molarity. Note that if you type in 50.00 you can select "X 10-3" or "X 10-2". 50.00 X 10-2 is 0.500 M. Use the slider bar or type in a volume. Click-on the pink "insert probes" button on the pH meter. The pH meter will read the pH and temperature of the solution. You will need to record the pH, concentration and volume of the solution. Click-on the blue "remove probes" button on the pH meter to remove the probes. Select a new concentration and volume to test the same solution, or click-on another solution. You can see that if the probes are in the solution and you change the concentration of the solution, it will not change the pH reading. This is a limitation of the computer program. In order to make a pH measurement of a new concentration you have to remove the probe (just as you would in lab).
Activity 2. Compare the pH of 100.0 ml of 0.500 M HCl pH = _____________ to the pH of 100.0 ml of 0.0500 M pH = ________________. Does this seem right to you?
Activity 3. Compare the pH of 50.0 mL 0.500 M nitric acid, HNO3 (aq) pH = ______________ to the pH of 50.0 mL 0.0500 M nitrous acid, HNO2 (aq) pH = _____________________.
Does this seem right to you?
Activity 4. Use the computer simulation to design a series of experiments that will allow you to compare the pH of a weak acid to a strong acid using concentration of the acid as written on the label of the bottle (the initial concentration) as a variable. You will need to choose at least 5 different initial concentrations of [H3O+]. Plot a graph to show a relationship between initial concentration of [H3O+] (M) and pH. Before you do your experiment on the computer simulation explain your experimental design to your TA.
Write a statement that tells the relationship between pH and the initial concentration of an acid solution.
What is the difference between the pH of strong acid and the pH of a weak acid at the same concentration. Explain why this is so.