Procedure:
Go to the pH simulation at the University of Colorado’s PhET project
Procedure:
Click on H3O+/OH– ratio box to view the hydronium and hydroxide molecules as model dots in solution.
Lab 2 picture
Spend a few minutes becoming familiar with the simulation and its controls. Observe the pH of some common liquids.
Look for this in the interactive:
Lab 3 picture
Part I: Changes in Hydronium H3O+ and Hydroxide OH– Concentrations
Click on My Solution.
Lab 4 picture
Make sure you are viewing concentrations in mol/L.
Move the pH slider to create custom liquids with varying pH.
Lab 5 picture
Observe how increasing the pH on the slider affects the pH and concentrations of hydronium [H3O+] and hydroxide [OH–].
Part I Analysis
Click the word Answer to check your response.
As pH increases, the concentration of hydronium [H3O+] ________.
decreases
As pH increases, the concentration of hydroxide [OH–] ____.
increases
For any substance, when I multiply [H3O+] by [OH–] I always get ______.
1.0 x 10-14
How does adding more or less of a liquid change the [H3O+]?
Adding more water makes the hydronium concentration go down. Temoving liquid has no effect on the hydronium concentration.
Part II: pH – [H3O+] Calculations
- Go back to the “Micro” option. Choose several of the sample liquids and observe their H3O+ concentrations.
- Find the “pH” of a few sample liquids by taking the negative logarithm of the liquids H3O+ concentration.
- Complete the table below.
Sample Liquid Used | [H3O+] Concentration (M) | pH (-log [H3O+]) |
---|---|---|
Part II Analysis
How do your calculations for pH match the pH identified in the simulation?
They should be equal
How does the pH change as [H3O+] increases?
As the hydronium concentration increases, the pH decreases.
Part III: Volume and Molarity
- On the “My Solution” section, use the slider bar on each nozzle, and increase or decrease the volume of your liquids.
- You can toggle between concentration and number of moles with the selection buttons.
- Observe the effect of changing volumes on the number of moles of H3O+ and OH–.
- Choose several of the sample liquids and observe their H3O+ concentrations
- Find the number of moles of a few sample liquids by multiplying [H3O+] by volume.
- Complete the table below. Do the calculation for moles and check your work in the simulation by selecting “Number of moles (mol)”
Sample Liquid Used | [H3O+] Concentration (M) | Volume Used (L) | Number of Moles (mol) |
---|---|---|---|
Part III Analysis
The unit that is the product of concentration (mol/L) and volume (L) is _______.
mol
How do your calculations for moles match the moles in the simulation?
Answer
They shouldn’t be equal.