How to determine strong acids when reacting with magnesium?

[mbeaumont99]

Homework Statement

I have to design a lab which will determine nitric, hydrochloric and sulfuric acid from containers A, B and C - i.e. It is unknown which acid is held in which container. This has to be done by reacting the unknown acids with magnesium

Homework Equations

Mg + 2H(+) → Mg(2+) + H2

The Attempt at a Solution

So sulfuric acid is a diprotic acid and therefore once it has dissociated its first proton [becoming HSO4(-)] which we can assume happens at 100% effectiveness, the hydrogen sulfate will further dissociate into SO4(2-) but this is a weak acid and therefore only partially dissociates its H(+) ion. This means that my rate of hydrogen gas production will be higher than the other two strong acids (if only marginally) due to a higher concentration of H(+) ions. I assume that hydrogen gas production rate would be my source of determining the acid??

Then comes the problem: how would I be able to see a noticeable difference in nitric acid and hydrochloric acid hydrogen gas production rates? Both are strong, monoprotic acids and therefore we can assume 100% dissociation of their protons. Would we have to refer to acid dissociation constants and therefore be able to say 'x' had a faster rate of hydrogen gas production than 'y' and therefore this means that 'x' is HCl as this has a higher K(a) value and thus will have a greater concentration of H(+) ions at equilibrium than 'y' leading to a greater production of hydrogen gas according to the 'relevant formula'.

Would really appreciate any help that can be contributed. Oh, and I'm new here so please correct me on any little formalities that I should have done/abided to.

 

[Borek]

You have not stated if you are given concentrations of these acid. If not - you can't do much.

Nitric acid is relatively easily reduced by evolving hydrogen to ammonia.

 

[mbeaumont99]

Apologies Borek. I DID forget to mention that we know the concentration of all the acids are 1 molar solutions.

 

[Borek]

No problem.

If so, combine the information about amount of hydrogen produced and consumed in the reaction mixture. Ammonia dissolves in water pretty well. I guess that should be enough to determine which acid is which.

 

[DeeNos]

As a scientist, the best approach to determine the strong acids when reacting with magnesium would be to first measure the rate of hydrogen gas production during the reaction. This can be done by collecting the gas in a gas syringe and measuring the volume of gas produced over a certain period of time. The higher the rate of gas production, the stronger the acid.

However, as mentioned in the attempt at a solution, both nitric and hydrochloric acid are strong monoprotic acids and will have similar rates of hydrogen gas production. In this case, it would be necessary to refer to the acid dissociation constants (K(a)) of each acid. The higher the K(a) value, the stronger the acid. Therefore, the acid with the higher K(a) value will have a higher concentration of H(+) ions at equilibrium and will produce a higher rate of hydrogen gas.

In order to determine the acid in each container, you can compare the rate of hydrogen gas production and the K(a) values of each acid. The acid with the highest rate of gas production and the highest K(a) value is most likely sulfuric acid, as it is a diprotic acid and will have a higher concentration of H(+) ions. The remaining two acids can then be differentiated based on their K(a) values, with the acid with the higher K(a) value being hydrochloric acid and the acid with the lower K(a) value being nitric acid.

It is also important to note that other factors, such as temperature and concentration of the acids, can affect the rate of hydrogen gas production and should be controlled for in the experiment. Additionally, multiple trials should be conducted to ensure accuracy and reliability of the results. Overall, by measuring the rate of hydrogen gas production and considering the acid dissociation constants, it is possible to determine the strong acids when reacting with magnesium.