EXPERIMENT 3: Suppose you had a buffer containing 0.5 moles...

Name: EXPERIMENT 3: Suppose you had a buffer containing 0.5 moles of sodium dihydrogen phosphate and 0.5 moles of sodium hydrogen phosphate. How many moles of hydrochloric acid would this phosphate buffer be able to accept before the pH of the solution began to change drastically?
Uploaded: 2022-07-10T18:55:43-08:00
Duration: 5 min 29 s
Channel: Luke Monroe
Description: EXPERIMENT 3: Suppose you had a buffer containing 0.5 moles of sodium dihydrogen phosphate and 0.5 moles of sodium hydrogen phosphate. How many moles of hydrochloric acid would this phosphate buffer be able to accept before the pH of the solution began to change drastically?

EXPERIMENT 3: Suppose you had a buffer containing 0.5 moles of sodium dihydrogen phosphate and 0.5 moles of sodium hydrogen phosphate. How many moles of hydrochloric acid would this phosphate buffer be able to accept before the pH of the solution began to change drastically?

Transcript

00:01 Okay, we're told we have a buffer that contains 0 .5 moles of sodium -dihigrogen phosphate and 0 .5 moles of sodium hydrogen phosphate.

00:09 How many moles of hydrochloric acid before the h -t -l, or before the ph, changes a lot? and so let's look at the, break these chemicals down into their molecular formula, and it might be a little clearer what this question is asking.

00:24 So our buffer contains h2 -p -o -4 minus, so the sodium is a counter -ion to this minus.

00:31 Sign so that was a plus when you put in solution we lose the sodium because it's a spectator ion so this is the actual um relevant molecule we have here we also have sodium and hydrogen phosphate so we went from die hydrogen to single hydrogen you could you'd be technically be correct in saying this is mono hydrogen but mono's often left out when naming things and so you can see we lost another hydrogen here and then hydrochloric gas it is just hcl.

01:06 So, chemically, what's going on here when we put hcl in solution? it's going to react with one of these before it starts to react with the other.

01:16 And it's going to react with the more basic one.

01:19 The more basic one is going to be the one with fewer hydrogens.

01:23 So hcl will react with our sodium hydrogen phosphate long before it reacts with our sodium -dhyrogen phosphate.

01:33 So the actual chemical reaction, reaction is hcl plus h .p .o .4.

01:39 2 -minus makes h2p .o4 minus.

01:45 So this is the reaction we care about.

01:49 And you might be thinking, while there's a negative here, couldn't we also continue to react to make phosphoric acid, which is h3p -o -4? and we could.

01:59 The problem is this happens after, steep ph change.

02:14 So if we're looking at a buffer, your buffer is valid at its ph range, as long as these two are in semi -equal quantities.

02:22 When you get to 100 % is this, and you start adding h -dl, your ph will start changing wildly.

02:28 And it's asking, and we're trying to avoid that, right? it wants to know at what point do we start changing wildly.

02:32 Well, it's going to be when this reaches 100 % of our species.

02:36 And so we could neutralize more h -cl by making a lot of all the way to phosphoric acid, but that goes beyond this range we care about.

02:44 So we only care about this reaction right here...

Question

EXPERIMENT 3: Suppose you had a buffer containing 0.5 moles of sodium dihydrogen phosphate and 0.5 moles of sodium hydrogen phosphate. How many moles of hydrochloric acid would this phosphate buffer be able to accept before the pH of the solution began to change drastically?

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