General properties and acidity

The polarity of the bonds encourages ionisation to give the carboxylate anion. An alkyl group such as the methyl group feeds electron density towards the COOH group this lessens the tendency to ionise, so ethanoic acid is weaker than methanoic acid. 

The OH group has acidic properties due to the H tending to ionise. This is because the O atom is more electronegative than the H, and draws the bonding electrons towards itself and away from the H. In the presence of water, some of the acid molecules lose protons to the water  

It is these hydrated protons which give acid solutions their acidic properties. Carboxylic acids are usually only slightly ionised in solution -they are weak acids. 

Carboxylic acids ionise when in water, some more easily than others, but all of those discussed above are weak acids. The equilibrium in the 

Methanoic and ethanoic acids show the typical properties of acids, and will react with magnesium metal to give off hydrogen gas and liberate carbon dioxide gas from carbonates and hydrogen carbonates  

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