Monday
December 22, 2014

Homework Help: chemistry

Posted by Sarah on Sunday, April 6, 2008 at 10:42pm.

Lactic acid, HC3H5O3(aq) is a weak acid that gives yougurt its sour taste(Yeeeeecccckkk). Calculate the pH of a 0.0010 mol/L solution of Lactic acid. The Ka for lactic acid is 1.4 x 10^-4


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chemistry - DrBob222, Saturday, April 5, 2008 at 7:39pm
Let's call Lactic acid HL.
HL ==> H^+ + L^-

Ka = (H^+)(L^-)/(HL) = 1.4 x 10^-4

initially before ionization:
(HL) = 0.001 M
(H^+) = 0
(L^-) = 0

change:
(H^+) = +x
)L^-) = +x
(HL) = 0.001 - x

equilibrium:
(H^+) = +x
(L^-) = +x
(HL) = 0.001 - x

Substitute the equilibrium values shown into the Ka expression and solve for x.
Then convert (H^+) to pH by pH = -log(H^+)


Here is my work
Ka = H^+)(L^-)/(HL) = 1.4 x 10^-4
=(+x)(+x)/(0.001 - x ) = 1.4 x 10^-4
= (x^2) / (0.001 - x) = 1.4 x 10^-4

What is my next step sorry:)

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