Question

What am i doing wrong?

150 mL 0.1 M NaOH was mixed with 200mL 0.1 M Formic acid, diluted to a total V of 1 L. Ka=1.78*10^-4

moles of NaOH = 0.15 L *0.1 M = 0.015
moles of formic acid= 0.1M*0.2 L= 0.02

moles of formic acid after neutralization= 0.005

Molarity of formic acid = 0.005 moles/1L = 0.005 M

\(Ka=\dfrac{[H^+]*[A^-]}{[HA]}=\dfrac{x^2}{0.005}\)

x=[H+]=(0.005*1.78*10^-4)^(1/2)=9.43*10^-4

pH=-log(9.43*10^-4)=3.02

the book says pH=4.23

did the book make an error, or did i?