Conjugate acid base pairs

Some things to remember:

Conjugate acid base pairs differ by H⁺. When an acid donates a proton it becomes its conjugate base. When a base accepts a proton it becomes it conjugate acid.  Some Substances can behave as an acid or base and they are called are amphoteric. Even an acid can be made to behave as a base if it is put with a stronger acid.

Complex ions

From our discussions today we could see the link between the Lewis theory on acids and bases and how it could be used to classify a complex formation as acid base. You can see the importance of definitions and the need for clarification in terms of which definition you are using. The following is a good link to complex ions and is a useful recap on this topic.

Complex ions

Strong and Weak Acids

Remember strong acids and Bases completely ionise and therefore the concentration of H⁺ or OH^- ions respectively can be easily seen and the pH calculated. PH = log 1/[H⁺] and

 Kw = [H⁺] [OH^-] = 1.0 x 10^-14 at 25⁰C (Note this increases at higher temperatures and decreases at lower temperatures). You should be able to explain why. This does not mean that hot water is acidic!! It’s neutral as [H⁺] = [OH^-], but the pH will be less than 7. PH 7 only means neutral at 25⁰C

Weak acids and Bases only partially ionise and therefore, you cannot use the initial concentration alone in order to determine the concentration of H⁺ or OH^- ions, you need to have the Ka or Kb values.

Weak/Strong Acids and Bases

The Ionic Product of Water

Acid Base Definitions

Acid Base Theories

Quadratic Equation

Having said that IB questions on equilibria don't usually involve the quadratic equation, I managed to include one on your test! Surprisingly it was only worth 2 marks. here's a link to help remind you about the quadratic equation.

The quadratic equation

Vapour Pressure and homework

Remember your homework is to finish the next sheet of equilibrium questions and to make some notes on liquid vapour equilibria. You should read through the whole chapter in your text book.

The following site on vapour pressure is worth looking at:

Vapour Pressure

Equilibia

Some useful sites:

Equilibria Introduction

La Chatalier's principle

Kc Equilibrium constants

The effect of changing conditions