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.

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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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Problem Details

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.

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Weak Acids concept. If you need more Weak Acids practice, you can also practice Weak Acids practice problems.

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