Ch.15 - Acid and Base EquilibriumWorksheetSee all chapters
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Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
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Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
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Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Solution: Lactic acid (CH3 CH(OH)COOH) has one acidic hydrogen. A 0.10 M solution of lactic acid has a pH of 2.44.Calculate Ka.

Solution: Lactic acid (CH3 CH(OH)COOH) has one acidic hydrogen. A 0.10 M solution of lactic acid has a pH of 2.44.Calculate Ka.

Problem

Lactic acid (CH3 CH(OH)COOH) has one acidic hydrogen. A 0.10 M solution of lactic acid has a pH of 2.44.

Calculate Ka.

Solution

We’re being asked to calculate the Ka of Lactic acid (CH3CH(OH)COOH) (The pH of 0.10 M lactic acid is 2.44) 


Lactic acid (CH3CH(OH)COOH) is a weak acid. Remember that weak acids partially dissociate in water and that acids donate H+ to the base (water in this case). The dissociation of Lactic Acid is as follows:


CH3CH(OH)COOH (aq) + H2O(l) CH3CH(OH)COOH(aq) + H3O+(aq)


From this, we can construct an ICE table. Remember that liquids are ignored in the ICE table.


The Ka expression for CH3CH(OH)COOH  is:


Ka = productsreactants= [CH3CH(OH)COO-][H3O+][CH3CH(OH)COOH]Liquids are ignored in the Ka expression.


Note that each concentration is raised by the stoichiometric coefficient: [CH3CH(OH)COOH], [H3O+] and [CH3CH(OH)COO-] are raised to 1.


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