15 May 2016

Introduction to Equilibrium and Aqueous Acids

In-Class Activity

Submitted by Adam R. Johnson, Harvey Mudd College
Course Level: 
Topics Covered: 

Equilibrium reactions are those that are dynamic: the reaction can shift to form more reactants or more products depending on the physical or chemical conditions present. They were discovered and described empirically, but have a thermodynamic basis in the Gibbs Energy of the reaction. A reaction at equilibrium has both reactants and products present, and the rate of formation of products is equal to the rate of formation of reactants. A common application of equilibrium is the chemistry of aqueous acids. Acid strength is measured by the pH scale.

This unit could be a stand-alone unit, but I used it as the first day of a three-day series of in-class exercises designed to get students thinking about a real problem on the international space station that could be solved using equilibrium calculations.

Learning Goals: 

1.    Write the equilibrium constant expression from the law of mass action
2.    Predict the response of a reaction at equilibrium to an external “stress”
3.    Determine whether a given species is an acid or base
4.    Calculate the pH of a solution of a weak acid in water
5.    Write the chemical equation for the autoprotolyis of water
6.    Calculate the solubility of a sparingly soluble salt

Equipment needs: 


Implementation Notes: 

This was the first day of a 3-day equilibrium activity. The 2nd two days are presented in the linked activity entitled "Water reclamation on the ISS: "Houston, we have a problem."

Students worked problems in class or as homework. For our class, the problems were submitted electronically on Sakai.

Time Required: 
1 50 minute class period
Evaluation Methods: 

the problems were evaluated electronically as a Sakai "quiz." Each question was graded right or wrong and added to the semester long homework score.

Creative Commons License: 
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