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Here's the original question , I was asked in an exam :

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Edit : the question in the picture is a single correct multiple choice question

I have concluded the the reaction of Barium chloride and Sodium sulphate will give BaSO4 as a white precipitate but I am having difficulty determining its solubility in HCl and HNO3

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    $\begingroup$ Have you tried searching with keywords baryum sulphate solubility dilute mineral acids ? $\endgroup$
    – Poutnik
    Oct 11 at 14:47
  • $\begingroup$ Yes I did see you answer to that question and your conclusion that " The BaSO4 solubility in concentrated HCl is limited, in diluted one is very low The solubility in concentrated sulphuric acid would be much higher " , but in this scenario with HNO3 and HCl in frame , what could be the best answer to the question ( in the picture ) $\endgroup$ Oct 11 at 15:08
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    $\begingroup$ My answers are not all available resources... :-) // The question is a wrong question, having 2 correct answers. $\endgroup$
    – Poutnik
    Oct 11 at 15:13
  • $\begingroup$ I did research a lot before asking this question here , tried to find YouTube videos of the reactions and articles but I was unable to find any such video on this reaction although there were some Quora threads which had contrasting answers $\endgroup$ Oct 11 at 15:17
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    $\begingroup$ Rather ask yourself, why should be $\ce{BaSO4}$ soluble in dilute acids, if it is insoluble in water ? ( Be aware of rather fuzzy definition of insoluble.) $\endgroup$
    – Poutnik
    Oct 11 at 15:19
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$\ce{BaSO4}$ is insoluble in dilute solutions of acids, because this dissolution would produce the following ions in solution : $\ce{Ba^{2+}, H^+}$ and $\ce{SO4^{2-}}$. And the preceding reaction has shown that $\ce{Ba^{2+}}$ and $\ce{SO4^{2-}}$ cannot exist simultaneously in solution : they must react to produce a precipitate of $\ce{BaSO4}$.

On the other hand, Baryum sulfate is known to be soluble in hot and concentrated sulfuric acid, because of the formation of $\ce{HSO4−}$ ions. But $\ce{BaSO4}$ is not even soluble in hot concentrated hydrochloric acid, according to F.-P. Treadwell, Analytical Chemistry, 1924.

As a consqquence, the answers $a)$ and $d)$ are to be chosen without any doubt.

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    $\begingroup$ Not quite. At pH<2 sulfate ion gets protonated. You need to develop a reaction equilibrium between solid BaSO4 and dissolved barium and sulfate ions using the Ksp of Barium sulfate and the Ka of bisulfate ion. $\endgroup$ Oct 11 at 14:58
  • $\begingroup$ @Oscar Lanzi. You are right. But the problem mentions "dilute solutions" . Baryum sulfate is known to be soluble in hot and concentrated sulfuric acid, because of the formation of $\ce{HSO4^-}$ ions. But $\ce{BaSO4}$ is not even soluble in hot concentrated hydrochloric acid, according to F.-P. Treadwell, Analytical Chemistry, 1924. $\endgroup$
    – Maurice
    Oct 11 at 15:35
  • $\begingroup$ Reference that in the answer. Thank you. $\endgroup$ Oct 11 at 17:00

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