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

Equilibium

CHEMICAL EQUILIBRIUM

Many reactions are not reversible and just occur in one direction. For example it would be rather difficult to get the combustion of petrol to go in the opposite direction! However, some reactions and physical processes are reversible i.e. can occur in the forward or reverse direction. When the products are never fully formed and the reactants never used up a state of equilibrium is reached. At this point the rate of the forward and back reactions is the same. For example if bromine is put in a gas jar, initially the liquid evaporates at a faster rate than the gas condenses and the gas gets observably thicker. However after a while the gas density and volume of liquid remain constant. This does not mean that nothing is happening but there is no observable change as the system has reached equilibrium. This means that the forward and back directions are occurring at the same rate. The system is said to be in a state of dynamic equilibrium and for this to occur there must be:

1. A closed system

2 .No observable change

3. Both directions occurring at an equal rate

4. The equilibrium can be achieved starting from either direction

This is rather like walking up the escalators at the same rate as they are travelling down, you are both moving but you remain in the same position. Of course this can occur at different points on the escalators, the same is true in chemistry i.e. you can have different positions of equilibrium. For example if some bromine is removed from a gas jar by connecting another vessel,  then the bromine will evaporate at a faster rate and a new position of equilibrium will be established. Every equilibrium system has an equilibrium constant Kc which is simply the concentration of the products divided by the concentration of the reactants raised to the power of their stoichiometric coefficients. Kc has the advantage over the position of equilibrium as it is only affected by temperature i.e. nothing else will affect the value of Kc.  If more of one of the reactants is added then the position of equilibrium will move towards the right i.e. the products and equilibrium will again be established. When the new concentrations of reactants and products are fed into the  equilibrium constant expression the value of Kc will be the same. If more product is added then the position of equilibrium will move to the left and equilibrium will again be established with the Kc value remaining constant. Only temperature affects Kc values and so they are useful to compare equilibrium systems. A large Kc value means that that the equilibrium is towards the products and a small one indicates that the equilibrium is towards the reactants.

Useful Chemistry site

You don't need to know all the salt chemistry but this site has some useful information:

General chemistry information site

Link to IB1 Blog

IB1 Blog

IB1 blog

Periodic Table

Link to periodic table

periodic table