Acid and Base Lab

Procedure:

Go to the   pH simulation at the University of Colorado’s PhET project

Procedure:

Lab 1 picture

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+] ________

Answer

decreases

 
As pH increases, the concentration of hydroxide [OH] ____. 

Answer

increases

 

For any substance, when I multiply [H3O+] by [OH] I always get ______.

Answer

1.0 x 10-14

 
How does adding more or less of a liquid change the [H3O+]?

Answer

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?

Answer

They should be equal

 

How does the pH change as [H3O+] increases?  

Answer

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 _______.

Answer

mol

 

How do your calculations for moles match the moles in the simulation?

Answer

They shouldn’t be equal.

 

 

 

source