Acids and Bases

bonkysleuth SG

Sulphuric acid is known to be a strong acid while lactic acid is a weak acid.

Describe, how you would carry out an experiment, using sodium carbonate, to determine the strength of these 2 acids. You are to state the necessary conditions required to carry out the experiment.

Is it simply Acid and carbonate reaction? Reaction with sulphuric acid would be faster than with lactic acid because the former ionises fully in water while the latter only partially. Amount of H+ ions in H2SO4 is thus higher.

Is there any other additional points which I need to add to secure marks for the explanation?

thanks man.

UltimaOnline SG

If equal molarity and volumes are used, then the total volume of CO2 gas from using sulfuric acid will be twice that of lactic acid, as the fomer is a diprotic acid, and the latter a monoprotic acid.

In terms of rate of reaction, indeed the complete dissociation of the 1st acidic proton of H2SO4 is complete (when dissolved in water), meaning it is a strong monoprotic acid, compared to lactic acid a weak monoprotic acid, hence molarity of protons higher will result in a faster rate of evolution of CO2 gas.

UltimaOnline SG

Make sure you use excess carbonate, so that the position of equilibrium will shift totally towards the RHS (where one of the products is a gas that leaves the reaction mixture). This will ensure that all of the protons from both acids will dissociate and react completely with the carbonate.