This video introduces buffers and what they are for, and what's needed to prepare them.

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0:00you'll find out what buffer solutions are and how they are prepared the buffer
0:10solution can be defined as a solution that minimizes changes in pH when small
0:15amounts of acid or base are added to it or it can also be defined as a solution
0:21that maintains a relatively constant ph1 small amounts of acid or base are added
0:26to it to get an idea of what a buffer solution does we'll start with one liter
0:32of pure water water is unbuffered and it has an initial ph of seven now will add
0:39. one mole of strong acid HCl to the water watch the ph meter will note here
0:51that the final ph is one the ph went from seven all the way down to one so we
0:58can see that it has decreased by six whole units
1:02now we'll go back again and start with one liter of pure water again it's
1:07neutral pH is seven and remember water is unbuffered
1:11this time we'll add . one mole of the strong base anyway watch the ph meter
1:23we'll make a note here that the
1:25ages 13
1:27dh1 from seven all the way up to 13 so that's an increase of six whole units
1:34what we'll do now is replace the water with the buffer solution this particular
1:38solution contains one molar acetic acid and one molar sodium acetate
1:44we see that the initial ph is 4.74
1:48now we'll add . one mole of the strong acid HCl to this buffer solution and see
1:53what happens
2:02we see that the ph is gone down
2:04down but only down two 4.66
2:08in going from 4.74 down to 4.66 the ph is dropped only by . 08 this is a very
2:16small change in pH
2:19comparatives with the very large drop of 68 units when . one mole of HCL was
2:25added to unbuffered pure water
2:27now we'll go back and start again with our buffer solution that has an initial
2:32ph of 4.7 for this time we'll add . one mole of the strong base anyway h21
2:39leader of this buffer solution and see what happens
2:42make a prediction
2:50as a result of adding the base to ph rose slightly to a final value of 4.83
2:58the ph started at 4.74 and rolls to 4.83 so that is an increase of only . 09
3:06which is a very small increase
3:09compare this with an increase of six whole ph units when any wages added to
3:14peer unbuffered water
3:16will summarize our results when a small amount of acid is added to peer
3:20unbuffered water the pH drops dramatically
3:24and when a small amount of base is that it appear unbuffered water the ph Rises
3:29dramatically
3:31but when a small amount of acid is added to a buffer solution the pH drops very
3:36slightly
3:37and when a small amount of base is added to about four solution to ph rises very
3:42slightly
3:43so now we know what a buffer solution does it minimizes changes in pH when a
3:48small amount of acid or base is added to it
3:52so now what we'll do is take a look at how buffer solutions are prepared
3:57to be able to minimize changes in pH buffer solution must be able to
4:02partially neutralized both acids and bases that are added to it
4:09in order to do this it must contain relatively high amounts of both the base
4:13and acid
4:16this can only occur if the base and acid are both week
4:22a buffer solution consists of a weak conjugate acidbase pair in which both
4:27the acid in the base have relatively high concentrations
4:32an example is a solution that contains one molar ethanoic or acetic acid which
4:38is a weak acid and one molar evaluate our acetate ion which is a weak base
4:44we use the more familiar names acetic acid and a sedate I in here in this
4:49solution and equilibrium is established in which the concentration of acetic
4:53acid and the acetate ion are both 1 molar
4:57and the hydronium ion concentration is quite low
5:01the one molar acetic acid is available to neutralize small amounts of strong
5:05base that might be added to this solution