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4.06 Part 1 Aqueous Equilibria Worked Example

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4.06 Part 1 Aqueous Equilibria Worked Example

This unit continues and expands on the theme of equlibria. You will examine buffers, acid/base titrations and the equilibria of insoluble salts.

A chemistry course to cover selected topics covered in advanced high school chemistry courses, correlating to the standard topics as established by the American Chemical Society. Prerequisites: Students should have a background in basic chemistry including nomenclature, reactions, stoichiometry, molarity and thermochemistry.

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教学方

Dr. Allison Soult
Lecturer
Dr. Kim Woodrum
Sr. Lecturer

脚本

going to be doing several calculations for this learning objective.

Lot of practice or calculating the pH.

Along a titration curve when you have, in this case,

a weak acid and then a strong base.

The process is very similar if it was a strong acid and a weak base but

we're going to see it here at various points.

The purpose of this video is to give you an overview of all the different processes

and to think about how the calculations are different at each point along the way.

Let's kind of get a vision in our mind of what's going on.

We've got a flask and in this flask is our butanoic acid which is a weak acid.

And we are going to be titrating it with sodium hydroxide.

So we have got a burette with a little stopcock here, and

in this burette is sodium hydroxide.

And we're going to be adding that sodium hydroxide drip by drip into this, and

seeing how the pH changes along the way.

Now at the very beginning, at point (a),

we only have the weak acid, all right?

So we only have the weak acid present in solution at point (a).

So we would work the problem very similar

to how you saw problems worked in the previous unit on acid base equilibrium.

At point (b) we're at 10 mL, so that's here.

At point (c) we're at 15 mL, so right here.

So here's (b) and here's (c).

And at those points we are in buffer range.

And we can work the problem as a buffer solution.

At point (d) and (e), we're fast approaching the equivalence point, so

we're at 19 mL and 20 mL, we're really close, (d) and

(e) to the equivalence point, but we haven't reached it yet.

We are not going to do the calculation for (d) and (e).

Because there's some complications that we would have to consider

that I do not want to get into in our units here.

At point (f), we have added exactly the right amount sort of concentrations

of butanoic gas, we see right up here, and the sodium hydroxide as the same.

Then we're at the same volume of base that we had of s,

it will be at the equivalence point.

So part (f) is at the equivalence point.

(g), we've just barely gone beyond the equivalence point.

And at point (h) we're up here at 25 mL, so here's point (h).

At point (h) we have excess, Sodium hydroxide,

we have gone beyond the equivalence point.

We've converted all of the weak acid to the conjugate base, and

we also have some extra base left over.

We'll get to base the problem strictly upon the amount

of hydroxide due to the strong base at this point.

So we've got several different types of problems will have to work,

at the beginning it's just weak acid.

Here is this zone we have a buffer and we'll work a buffer.

A point f we're at the equivalent point and we have converted all the weak acid to

it's conjugate base, which is weak, and we will be doing it at weak base problem.

And then we will be beyond the equivalent point and have extra strong base.

So as you work through that, be thinking about how each part along the titration

curve is a different type of reaction.

And that's what's really challenging for students often is to see the different

ways you work the problem depending upon where you are in the titration curve.

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