00:01
First we will write the balanced chemical reaction.
00:03
We have one mole of perchloric acid, hclo4, reacting with one mole of sodium hydroxide to produce one mole of sodium perchlorate and one mole of water.
00:20
So to determine the milliliters of sodium hydroxide needed to reach the equivalence point, we start with the hundred milliliters of perchloric acid and we convert that into liters by dividing by a thousand.
00:37
Then we convert the liters into moles using molarity.
00:41
One liter is 0 .0160 moles perchloric acid and from the stoichiometry one mole hclo4 requires one mole sodium hydroxide.
00:59
Then knowing the mole sodium hydroxide we can determine the liters of the sodium hydroxide solution using its molarity.
01:06
One liter sodium hydroxide contains 0 .04 moles and then last of all we'll convert the liters to milliliters and we will need 40 milliliters of sodium hydroxide.
01:31
Because this is a strong acid, strong base titration, then all we have is a neutral salt and water at the equivalence point and the ph at the equivalence point is neutral at 7.
01:50
There's no calculating required.
01:54
To determine the ph after 10 milliliters have been added, we recognize that this is pre -equivalence so we still have extra or excess perchloric acid.
02:07
So ph can be calculated by determining the excess perchloric acid concentration.
02:13
We'll start with the moles of perchloric acid we we initially had.
02:19
That's 100 milliliters or 0 .100 liters at a concentration of 0 .0160 moles per liter.
02:28
That's what we started with but every mole of sodium hydroxide we add consumes a mole of perchloric acid.
02:36
So we subtract off the 10 milliliters of sodium hydroxide added which is 0 .010 liters at the concentration of sodium hydroxide 0 .040 moles per liter.
02:51
This then gives us the moles of perchloric acid still left in solution and we divide that by the new volume...