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This is one of the tougher topics in year 13 chemistry. In this post David deals with calculating the pH of strong acids and introduces some neat simulations.
This topic is mostly about equilibria so it is important to understand that concept first. Before tackling this topic make sure you :
Use this animation to remind yourself of the difference between strong and weak acids
When an acid molecule ionises completely when in solution in water, it is regarded as a strong acid. It is said to dissociate completely.
If we consider this ionisation to be an equilibrium - it would lie completely to the right.
At A level you might say that the equilibrium constant (Kc) would be a very large value and not really useful.
When calculating pH values for strong acids we assume that the concentration of H+(aq) ions is equal to to the concentration of the acid.
NOTE: The aqueous form of H+ is often represented as H3O+
There are three modes in this animation (below) by PHET
: 1. Macro, 2. Micro, 3. My Solution. Have a go with each in turn...
This is useful to simulate the measurement of pH values. You drag the green pH probe into the solution to measure the pH. Try adding battery acid and measure the pH.
Work out how much you need to dilute the battery acid to increase its pH by one unit...
This mode gives you the ability to "see" the particles involved in acid/alkali reaction. The H3O+ ion is usually abbreviated as H+(aq) . Use the animation to measure the pH value of the everyday substances. Use the switch below the scale on the left to select logarithmic or linear . Why do you think we use a logarithmic change for pH ?
In this simulation you can use the sliders on the logarithmic scale to change [H3O+] or [OH-]
Use the sliders to adjust one or other concentration to give five different pH values between 0 and 14. Make a note of each concentration for each pH value in a table.
The common (base 10) logarithm of x is the power to which the number 10 must be raised to obtain the value x. For example, the common logarithm of 10 is 1, the common logarithm of 100 is 2 and the common logarithm of 1000 is 3
