Buffers

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.

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:

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:

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.

pH of Weak Acids

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

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

Acids and Bases

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

Solubility Overview

Solubility and Solubility Product

The dissolving of a sparingly soluble solute can be represented by an equilibrium equation:

As this is an equilibrium, we can write an equilibrium expression, called the Solubility Product:

The smaller the Solubility Product, the less soluble a solute is.

Solubility is usually expressed in one of two units: grams per litre (g L^-1); or moles per litre (mol L^-1).

We can use the solubility of a solute to calculate the Solubility Product, and use the the Solubility Product to calculate the solubility of a solute. Once we master these two skills, we have a good understanding of solubility.

Ionic Product and The Common Ion Effect

Ionic Product is the same as Solubility Product, but when two solutions (of known concentration) are combined and the ions may form a precipitate. If Ionic Product is larger than Solubility Product, a precipitate does form. If they are equal, it is a saturated solution. If Solubility Product is larger, no precipitate will form.

Aqueous Solutions Introduction - Species in Solution

This entire unit is about things dissolved in water - aqueous solutions. If they are not dissolved in water, we do not have to consider them (too much).

 The examples we need to work through by tomorrow are:

We also did a brief experiment to show why some salts are alkaliine or acidic:

Organic Chemistry Revision

We made hexagons to represent every functional group we studied in Organic Chemistry earlier in the year:

We are putting brief study notes on the back of these, and playing a few revision games with them:

Practical Electrochemistry

Today, we made some half-cells and combined them with a salt-bridge and a voltmeter. Then, we were asked to make sense of our observations.

Standard Electrode Potentials and EMF

This is a big idea and we will spend the rest of the week exploring it:

1. What are standard electrode potentials?
2. How are they used to find the EMF of a cell?
3. What happens if a cell has a negative EMF?
4. How can EMF be used to predict what would be observed in a redox reaction?
5. How can standard electrode potentials be used to rank oxidant- and reductant-strength?

Electrochemical Cells - Introduction

We started the lesson by making an electrochemical cell using zinc chloride, a zinc electrode, copper (II) sulfate, a copper electrode. We found that this generated about 1.4V

Electrolysis

Electricity can be used to split compounds up into their elements. This is an example of oxidation-reduction.

Redox Half Equations

Balancing Redox Half Equations

Another recap of Level 2 work...

Thanks to Sam for finding these FLASH CARDS

Logan found these FLASH CARDS which are also excellent.

Oxidation Numbers

This is just a recap of last year's work. We discussed the allocation of oxidation numbers:

Chemical Minds

Check out this wikispace, set up by Michele McMahon from St Cuthbert's College.