# Finding pH given molarity and volume

1. Apr 27, 2008

### pmart491

1. The problem statement, all variables and given/known data
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?

3. The attempt at a solution
Well im really lost with this problem. Im 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

2. Apr 27, 2008

### symbolipoint

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

3. Apr 27, 2008

### pmart491

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

pH=-log(.012) = 1.92?

4. Apr 27, 2008

### pmart491

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

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

=.024

pH=-log(.024)=1.62

5. Apr 27, 2008

### symbolipoint

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: Apr 27, 2008
6. Apr 27, 2008

### pmart491

yea so itd be 1.62 right?

7. Apr 28, 2008

### Staff: Mentor

Yep, 1.62 it is.

8. Apr 28, 2008

### chemisttree

Welcome back, Borek! You were missed.

9. Apr 28, 2008

### Staff: Mentor

I am planning to spend some time here now ;)

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