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This will probably be the first type of titration you meet. An acid is neutralized by an alkali or the other way around. An acid-base indicator will be needed so that we can see when the reaction is complete. The colour change at the end-point will depend on the indicator that you are using and on whether it is the acid or the alkali being added. Students often remember the colour changes for well-known indicators, but can get the colour change backwards. If we are adding acid, the final solution will have excess acid and so the indicator will show the acid colour at the end. A corresponding situation will occur if alkali is being added. Make sure that you know which solution you are starting with and which solution is being added from the burette. Usually, the acid goes in the burette. |
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A typical reaction would be that between hydrochloric acid and sodium hydroxide which react in a 1 to 1 ratio:
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HCl(aq) + NaOH(aq) ⇒ NaCl(aq) + H2O(l) |
This is often written in shorthand as HCl º NaOH. The º means "is equivalent to". In other words, for every one HCl there is one NaOH. The link between the number of moles of acid and alkali is very important for the titration calculation and can be found in the correctly balanced equation for the reaction. It is, therefore, important that you can write and balance neutralization equations.
The choice of indicator for an acid-alkali titration depends on the type of acid and alkali involved (weak or strong).
