October 28, 2016

Homework Help: chemistry

Posted by Sarah on Sunday, April 6, 2008 at 10:47pm.

Methanoic acid HCO2H(aq) also known as formic acid, is partly responsible for the characterisitic itchy rash produced by the leaves of the stinging nettle plant. Calculate the pH of 0.150 mol/L methanoic acid. The Ka for methanoic acid is 1.8 x 10^-4.

My Work:
Lets call Methanoic acid HL

HL--> H^+ plus L^-

Ka = (H+)(L-)/(HL) = 1.8 x 10^-4

HL --> H+ plus L-
I 0.150 0 0
C -x +x +x
E 0.150-x +x +x

Ka = (+x)(+x)/(0.150-x) = 1.8 x 10^-4
= (x^2) / (0.150-x) = 1.8 x 10^-4

Im having problems with the next step

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