Page 35 - Curriculum Visions Dynamic Book

This flask contains the alkali and
a chemical indicator, in this case methyl orange
This piece of glassware with a tap at the base is called a burette
ion: an atom, or group of atoms, that has gained or lost one or more electrons and so developed an electrical charge.
titration: a process of dripping one liquid into another
in order to find out the amount needed to cause a neutral solution. An indicator is used to signal change.
Neutralising
When an acid and an alkali react, the hydrogen ions of the acid react with the hydroxide ions
of the alkali to produce water. If there are appropriate amounts of acid and alkali to react, then the result will be a neutral substance (a salt) and water.
For example, when equal amounts of sodium hydroxide (NaOH) and hydrochloric acid (HCl) are mixed, the hydrogen ions and hydroxide ions react to form water, leaving only the sodium ions and chloride ions in solution. The result is a neutral salt solution (sodium chloride).
If the amount of acid exceeds the alkali then the reaction will still occur, but after all reacting has been completed, the result will still be an acidic solution. Similarly, if the amount of acid is less than the alkali, then the result will be an alkaline solution. When scientists want to find out how much of one chemical is needed to neutralise another, they use a method called titration, which is shown here.
Also...
How to find out the amount of acid needed to neutralise a base
During the process of adding acid to alkali (a process chemists call titration) an indicator is used to show when the acid introduced from a burette exactly neutralises the alkali in a flask. At this point the hydrogen ions from the acid in
the flask exactly match the number of hydroxide ions from the alkali and the liquid turns from yellow to pink.
In the example shown here the solution has not been shaken so that you can see both the pink and yellow colours of the indicator. It is, however, normal practice to shake the flask continually so that the indicator shows a change throughout the liquid.
EQUATION: Titration of hydrochloric acid and sodium hydroxide
Hydrochloric acid + sodium hydroxide ➪ sodium chloride + water HCl(aq) + NaOH(aq) ➪ NaCl(aq) + H2O(l)
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