Preparation of Mineral Acids

 Today we would look at the preparation of acids. Remember I told you that most of the acids occur in nature and that they may also be prepared in the laboratory. In the first few lessons, we showed that the so called vital force theory that opined that organic compounds were synthesized as a result of some vital force in living things is a fallacy. Organic compounds just like any other compound can be synthesized in the laboratory.


However, our discussion here would be limited to the synthesis of mineral acids. You would recall that mineral acids are the acids that are prepared in the laboratory. As such, we are going to use the usual laboratory methods that we are conversant with to make up these acids.


Methods of preparing Mineral acids;

1) Dissolving acid anhydride in water: The term acid anhydride refers to a substance that is dissolved in water to give an acid. Many of oxides of non metals are acid anhydrides. Let us look at two examples;

i) CO2(g) + H2O(l) ---> H2CO3(aq)

ii) SO3 (g) + H2O(l) -->H2SO4(aq)

2) Combination of constituent elements: The halogen acids are often prepared by allowing hydrogen and the halogen gas to react over activated charcoal at a certain temperature or in the presence of a catalyst. E.g

H2(g) + Cl2 ------->2HCl(g) 

                    Charcoal

The HCl gas can now be dissolved in water to give the acid.

3) Displacement Reaction: When we talk about a displacement reaction in chemistry, we mean that one ion in a compound would replace another ion in another compound with which it reacts. Lets see an instance; AB + CD --> AD + BC. We call this particular instance a double replacement reaction since all the ions in the reactants (AB and CD) exchanged partners in the products formed. See if you can spot this from the reaction equation.


The kind of displacement reaction that we are talking about here occurs between a salt and an acid. Observe the reaction shown below;

2NaNO3(s) + H2SO4(aq) --> Na2SO4(aq) + 2HNO3(aq)

Now compare this reaction with the template of a double replacement reaction shown above. Any similarity?

4) Precipitation reaction: This is quite useful in the preparation of organic acids such as ethanoic acid(acetic acid). In this method, a solid separates out of the solution as a precipitate. Look at the example below;

(CH3COO)2Pb(aq) + H2S(aq) -> PbS(s) + 2CH3COOH(aq)


Hope today’s lesson is clear? Reach out to us if any confusion persists.


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