Thursday, 16 October 2014


If we think of buffers as solutions made up of weak acids and their respective conjugate bases, these are not much harder than working with weak acids. The only real difference is that we know the (desired) pH, so know the H3O+ ion concentration. Also, [H3O+] is not equal to [conjugate base] in the Ka expression.

Tuesday, 14 October 2014

Equivalence Point

This is a very tough concept to get started on, but not too tough once you work out the concentration of the salt made at the equivalence point.

This video is very long, so it may be worth having a past exam question handy and regularly using the pause button:

Friday, 19 September 2014

Sketching Titration Curves

These look daunting, but it isn't actually very hard to get the general shape correct. We used a weak acid vs. strong base example:

Thursday, 18 September 2014

Titration Curves - Introduction

This was a whirlwind introduction to Titration Curves. Tomorrow, we will look at the calculations to determine the initial and final pH. Next term, we will look at how to calculate equivalence point volume and pH, and in the buffer region.

Tuesday, 16 September 2014

pH of Weak Acids

This is a very difficult concept. Every student should be able to write a hydrolysis equation, base dissociation expression (KB), and calculate KB from pKA or KA (provided in the question). Beyond that, it will take a lot of practice:

Thursday, 11 September 2014

Weak Acids

It is a bit trickier to calculate the pH of a weak acid. This is because they only partially dissociate. However, this means that these acids have an equilibrium constant (called the acid dissociation constant), which can be used to calculate the hydronium ion concentration:

The process for doing this is:
  1. Write the balanced equation for the dissociation with water.
  2. Write the acid dissociation expression.
  3. Substitute and solve
    • [hydronium] = [conjugate base] = x
    • [acid] = original concentration stated in the question (only partially dissociated)
  4. Calculate pH

Wednesday, 10 September 2014

Acids and Bases

This was a recap of last year. The videos are from the topic being taught to a Level 2 class.