# Finding pH given molarity and volume problem

pmart491

## Homework Statement

If you mix 200mL of a 1.8M HCl solution with 300mL of a 1.16M NaOH solution, what will be the pH of the solution?

## The Attempt at a Solution

Well I am really lost with this problem. I am pretty sure you need to convert each to moles.

.2L HCl x 1.8moles HCl
------------------
1L HCl

.3L NaOH x 1.16 moles NaOH
---------------------------
1L NaOH

HCl=.36moles

NaOH=.348moles

HCl + NaOH -> NaCl + H2O

not too sure where u go from there

Homework Helper
Gold Member
The acid and the base react 1:1, so which is in excess, and by how much?

pmart491
is it .36-.348=.012 moles of HCl which = number of H+ ions?

pH=-log(.012) = 1.92?

pmart491
or do u have to change moles of HCl back to molarity?

.012moles HCl
-------------
.5L total

=.024

pH=-log(.024)=1.62

Homework Helper
Gold Member
HCl in aqueous solution is strongly ionized, or completely ionized for most practical purposes. For pH, you want the hydrogen ion CONCENTRATION AS MOLARITY...., and then find the negative logarithm.

Last edited:
pmart491
yea so itd be 1.62 right?

Mentor
Yep, 1.62 it is.

Homework Helper
Gold Member
Welcome back, Borek! You were missed.

Mentor
Welcome back, Borek! You were missed.

I am planning to spend some time here now ;)