How to determine strong acids when reacting with magnesium?

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Discussion Overview

The discussion centers around designing a laboratory experiment to identify unknown strong acids (nitric, hydrochloric, and sulfuric) by observing their reactions with magnesium. The focus is on the production of hydrogen gas as a means of differentiation among the acids based on their dissociation properties.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant proposes that sulfuric acid's diprotic nature leads to a higher rate of hydrogen gas production compared to the monoprotic strong acids, suggesting this could be a distinguishing factor.
  • Another participant questions how to differentiate between nitric and hydrochloric acid, both of which are strong and monoprotic, and suggests considering acid dissociation constants to assess their rates of hydrogen gas production.
  • A later reply emphasizes the importance of knowing the concentrations of the acids, stating that without this information, the experiment's effectiveness is limited.
  • One participant mentions that ammonia can form from the reduction of nitric acid, which could be relevant in identifying it during the experiment.
  • Another participant confirms that the concentrations of the acids are known to be 1 molar, which may influence the experimental approach.
  • There is a suggestion to combine information about the amounts of hydrogen produced and consumed in the reaction mixture to aid in the identification of the acids.

Areas of Agreement / Disagreement

Participants express varying views on the best approach to differentiate between the acids, particularly between nitric and hydrochloric acid. There is no consensus on a definitive method for identification, and the discussion remains unresolved regarding the most effective experimental design.

Contextual Notes

Limitations include the dependence on the known concentrations of the acids and the potential influence of ammonia formation on the identification process. The discussion does not resolve the complexities involved in measuring and interpreting hydrogen gas production rates.

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

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