Further Chemistry

Just some revision notes for anyone studying GCSE Chemistry. Most of this stuff, if not all are about Further Chemistry so C7 notes basically. 

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Strong Acids and Weak Acids

Dynamic Equilibrium is sometimes used to explain the difference between a strong acid and a weak acid. Examples of these strong acids include; hydrochloric acid, nitric acid and sulfuric acid. 

Strong acids ionise completely in water meaning that all of the acid molecules ionise so there's no equilibrium reaction. An example of this is when hydrogen chloride gas dissolves in water. All of the molecules ionise to give hydrogen ions and chloride ions. 

Carboxylic acids are an example of weak acids. Weak acids only partially ionise (roughly about 1%) in water so dynamic equilibrium is formed. Weak acid particles are constantly being ionised at the same exact time as their ions are reforming the weak acid molecules. So, going with the idea of dynamic equilibrium: the forward reaction is happening at the same rate as the backward reaction

The formula for the ionisation of a weak acid is as follows (when writing the equation, write all numbers and "+" or "-" symbols in the equation in subscript):

  • CH3COOH(aq) + H20(l) <---> CH3COO-(aq) + H+(aq)

Before you tackle that equation, let's get some things cleared up. Remember that in a dynamic equilibrium, the equation is always already balanced. So no need to try and balance that bad boy. Next, the double-edged arrow sign obviously means reversible otherwise it wouldn't be dynamic equilibrium. Finally the states, aq is aqueous which means a watery substance and l which means liquid. 

Now, weak acids have a higher pH than strong acids because the concentration of positive H ions in the solution is much lower. 

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