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.

 

 

 

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