Question

Consider the titration of a 23.2 −mL sample of 0.115 M RbOH with 0.110 M HCl. Determine each of the following. 1)the initial pH. 2) the volume of added acid required to reach the equivalence point. 3)the pH at 5.9 mL of added acid. 4)the pH at the equivalence point. 5) the pH after adding 4.9 mL of acid beyond the equivalence point. Thank you in advance.

Answer 1

Notice that the calculations are done with L instead o mL since the concentration is in M (moles/L)

1) initial pH

you have a concentration of 0.115M RbOH <----strong base

2) to reach the equivalent point you need to add the same moles of as the moles of base you have.

moles of base---->

you nedd 2.668x10-3 moles of acid with a concentration 0.110 M

<--------Volume of acid

3) at 5.9 mL of acid you have added <---this is the base neutralized

the base remaining is:

The concentration of the base is calculated using the moles remaing and the volume (initial volume plus volume added)

4) you are titrating a strong base with a strong acid the pH at the equivalence point is 7.

5) at the equivalence pointo you have the same moles of acid and base, so the pH is given by the excess of acid,

calculate the excess moles of acid added:

and the new concentration of acid using the volume (initial volume+volume to reach the equivalent point+volume of excess)

0.0232L+0.02425+.0049=0.05235L

<----since this is acid, this is the concentration of H⁺