29.3k views
5 votes
Acetic acid (HC2H3O2, Ka=1.8x10^-5) is a weak acid. Calculate the pH of an aqueous solution of .25M acetic acid.

User Saro
by
4.8k points

1 Answer

4 votes

Answer: The pH of an aqueous solution of .25M acetic acid is 2.7

Step-by-step explanation:


HC_2H_3O_2\rightarrow H^+C_2H_3O_2^-

cM 0 0


c-c\alpha
c\alpha
c\alpha

So dissociation constant will be:


K_a=((c\alpha)^(2))/(c-c\alpha)

Give c= 0.25 M and
\alpha = ?


K_a=1.8* 10^(-5)

Putting in the values we get:


1.8* 10^(-5)=((0.25* \alpha)^2)/((0.25-0.25* \alpha))


(\alpha)=0.0084


[H^+]=c* \alpha


[H^+]=0.25* 0.0084=0.0021

Also
pH=-log[H^+]


pH=-log[0.0021]=2.7

Thus pH is 2.7

User Martinfleis
by
5.2k points