Neutralisation reactions Acids and bases are opposite One makes pH lower and the other makes pH higher When acids and bases react they make pure water and a salt Because pure water is pH 7 neutral this reaction is called a neutralisation reaction ID: 336303
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Slide1
Neutralisation reactionsSlide2
Neutralisation reactions
Acids and bases
are opposite. One makes pH lower and the other makes pH higher. When acids and bases react they make pure water and a salt. Because pure water is pH 7 (neutral), this reaction is called a neutralisation reaction.
General word equation:
Acid + Base
Salt + Water
An example of an acid base reaction you have studied in class already is the reaction of sodium hydroxide and hydrochloric acid.
Word equation:
Hydrochloric acid + sodium hydroxide _______________+_______________ Slide3
Milk of Magnesia and Vinegar reaction
Milk of Magnesia is Magnesium hydroxide (Mg(OH)
2
) solution.
But the magnesium hydroxide does not dissolve very well.
Most of the magnesium hydroxide is solid particles floating in the solution. This is called a suspension.
Milk is an example of a suspension and that’s why this is called milk of magnesia.
This suspension gives the reaction is interesting properties.Slide4
Milk of Magnesia and Vinegar reaction
Milk of magnesia is basic as it contains hydroxide ions
Vinegar is a weak acid as it releases hydrogen ions.
When we add the vinegar to the milk of magnesia there is a neutralisation reaction with this equation.
Magnesium hydroxide + Ethanoic acid
Magnesium Ethanoate + Water
(excess)
There is not enough hydroxide ions dissolved in the milk of magnesia suspension to react with all the hydrogen ions from the vinegar and as a result the pH decreases.
But then….. Because all the magnesium hydroxide that was dissolved in the solution has reacted with the vinegar, some more of the suspension of magnesium hydroxide can then dissolve. This reacts with the remaining vinegar bringing the pH up again.
Magnesium
hydroxide + Ethanoic acid
Magnesium Ethanoate +
Water
(excess)