An unknown white solid consists of two compounds, each containing a different cation. As suggested in the illustration, the unknown is partially soluble in water. The solution is treated with \(\mathrm{NaOH}(\mathrm{aq})\) and yields a white precipitate. The part of the original solid that is insoluble in water dissolves in \(\mathrm{HCl}(\mathrm{aq})\) with the evolution of a gas. The resulting solution is then treated with \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}(\mathrm{aq})\) and yields a white precipitate. (a) Is it possible that any of the cations \(M g^{2+}, C u^{2+}\) \(\mathrm{Ba}^{2+}, \mathrm{Na}^{+},\) or \(\mathrm{NH}_{4}^{+}\) were present in the original unknown? Explain your reasoning. (b) What compounds could be in the unknown mixture (that is, what anions might be present)?

Step by step solution

01

Evaluate possible cations

The problem describes that a part of the unknown solid mixture forms a white precipitate after adding \(\mathrm{NaOH}(\mathrm{aq})\). This suggests the presence of cations that could form a insoluble hydroxide when react with NaOH. This would rule out \(\mathrm{Na}^{+}\) and \(\mathrm{NH}_{4}^{+}\), since their hydroxides (\(\mathrm{NaOH}\) and \(\mathrm{NH}_4\mathrm{OH}\)) are soluble in water. The remaining cations to consider are \(M g^{2+}, C u^{2+}\), and \(\mathrm{Ba}^{2+}\)

02

Identify cations that react with \(\mathrm{HCl}(\mathrm{aq})\)

The problem also describes that the part of the original solid that is insoluble in water could dissolve in \(\mathrm{HCl}(\mathrm{aq})\) with the evolution of a gas. The only cation from those remaining that could undergo such reaction is \(\mathrm{Ba}^{2+}\), since \(\mathrm{BaCO}_3\) is insoluble in water, soluble in \(\mathrm{HCl}\), and produces \(\mathrm{CO}_2\) gas. Therefore, the original compound could contain \(\mathrm{Ba}^{2+}\) cation

03

Evaluate possible anions

The problem mentions that the solution obtained after treating with \(\mathrm{HCl}(\mathrm{aq})\) yields a white precipitate when treated with \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}(\mathrm{aq})\). This reaction indicates the presence of a cation that can form an insoluble sulphate. This again points toward \(\mathrm{Ba}^{2+}\) as \(\mathrm{BaSO}_4\) is insoluble. Therefore, one of the anions in the original compound could be \(\mathrm{SO}_4^{2-}\)

04

Identify the original unknown mixture

From steps 2 and 3, the unknown solid could possibly be a mixture of two compounds containing \(\mathrm{Ba}^{2+}\) cation and one of these compounds might contain \(\mathrm{SO}_4^{2-}\) anion. A possible compound consistent with the solubility properties could be \(\mathrm{BaCO}_3\), which dissolves in \(\mathrm{HCl}\) with the evolution of gas.

Unlock Step-by-Step Solutions & Ace Your Exams!

• Full Textbook Solutions

  Get detailed explanations and key concepts

• Unlimited Al creation

  Al flashcards, explanations, exams and more...

• Ads-free access

  To over 500 millions flashcards

• Money-back guarantee

  We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!