Question

In: Chemistry

Calculate [H3O + ] for a 2.5 x 10-4 M solution of weak acid (Ka =...

Calculate [H3O + ] for a 2.5 x 10-4 M solution of weak acid (Ka = 5.3 x 10-4 )

A.
1.4 x 10^-4 M
B.
2.1 x 10^-4 M
C.
6.2 x 10^-4 M
D.
7.3 x 10^-4 M
E.
1.9 x 10^-4 M

Solutions

Expert Solution

Let us represent weak acid as HA. Its dissociation is as shown below:

The equilibrium constant

The initial concentration of HA is .
Let x M be the change in the concentration of HA to reach equilibrium.
Prepare an ICE table.


Initial concentration (M)	0	0
Change in concentration (M)
Equilibrium concentration (M)

Substitute values in the equilibrium constant expression

This is quadratic equation with solution

The negative value is discarded as concentration cannot be negative.

Hence,

Hence, option E is the correct answer.

Note: One can also calculate the pH as shown below:

queen_honey_blossom answered 8 months ago

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