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Chapter 4: Problem 5

You are presented with a white solid and told that due to careless labeling it is not clear if the substance is barium chloride, lead chloride, or zinc chloride. When you transfer the solid to a beaker and add water, the solid dissolves to give a clear solution. Next a \(\mathrm{Na}_{2} \mathrm{SO}_{4}(a q)\) solution is added and a white precipitate forms. What is the identity of the unknown white solid? \([\) Section 4.2\(]\)

Short Answer

Expert verified
The unknown white solid can be identified as either barium chloride (BaCl₂) or lead chloride (PbCl₂). This is based on the fact that the addition of sodium sulfate (\(Na_2SO_4\)) to the clear solution formed a white precipitate, indicating the presence of an insoluble sulfate salt, which is consistent with either barium sulfate (BaSO₄) or lead sulfate (PbSO₄). Zinc chloride (ZnCl₂) can be ruled out as it would not form a precipitate with sodium sulfate because zinc sulfate (ZnSO₄) is soluble.

Step by step solution

01

Recall the solubility rules

Generally, salts containing Group 1 elements (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and ammonium (NH₄⁺) are soluble. Additionally, nitrates (NO₃⁻), acetates (CH₃COO⁻), and most perchlorates (ClO₄⁻) are soluble. Sulfates (SO₄²⁻) are usually soluble, with barium, strontium, and lead sulfates being exceptions. A common saying to remember this is "all sulfates are soluble, except those of barium, strontium, and lead".
02

Analyze the initial solubility observations

When the unknown white solid is transferred to a beaker and mixed with water, it dissolves to give a clear solution. This observation indicates that the solid is an ionic compound that dissociates in water, forming ions. All of the given chloride salts (barium chloride, lead chloride, and zinc chloride) are water-soluble, so this information does not help us distinguish the identity of the unknown solid.
03

Analyze the reaction with sodium sulfate

When a sodium sulfate (Na₂SO₄) solution is added to the clear solution obtained in Step 2, a white precipitate forms. This precipitate suggests that one of the cations in the unknown chloride salt forms an insoluble compound with the sulfate anion (SO₄²⁻).
04

Identify the insoluble sulfate salt

Based on the solubility rules mentioned in Step 1, we know that barium sulfate (BaSO₄) and lead sulfate (PbSO₄) are insoluble, while zinc sulfate (ZnSO₄) is soluble. Given that the addition of sodium sulfate led to the formation of a white precipitate, the unknown solid should be either barium chloride (BaCl₂) or lead chloride (PbCl₂). Zinc chloride (ZnCl₂) can be ruled out since it would not form a precipitate with sodium sulfate.
05

Conclusion

Based on the reactions observed with water and sodium sulfate, the unknown white solid is either barium chloride or lead chloride. The fact that a white precipitate formed after the addition of sodium sulfate indicates the presence of an insoluble sulfate salt, consistent with either barium sulfate or lead sulfate. Zinc chloride could be ruled out since its sulfate salt is soluble.

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Most popular questions from this chapter

Write balanced molecular and net ionic equations for the reactions of (a) manganese with dilute sulfuric acid, (b) chromium with hydrobromic acid, (c) tin with hydrochloric acid, (d) aluminum with formic acid, HCOOH.

Can oxidation occur without oxygen? Can oxidation occur without reduction?

Using the activity series (Table 4.5 ), write balanced chemical equations for the following reactions. If no reaction occurs, simply write NR. (a) Nickel metal is added to a solution of copper(II) nitrate; (b) a solution of zinc nitrate is added to a solution of magnesium sulfate; (c) hydrochloric acid is added to gold metal; (d) chromium metal is immersed in an aqueous solution of cobalt(II) chloride; (e) hydrogen gas is bubbled through a solution of silver nitrate.

Formic acid, \(\mathrm{HCOOH},\) is a weak electrolyte. What solute particles are present in an aqueous solution of this compound? Write the chemical equation for the ionization of \(\mathrm{HCOOH}\).

Explain the following observations: (a) \(\mathrm{NH}_{3}\) contains no \(\mathrm{OH}^{-}\) ions, and yet its aqueous solutions are basic; (b) HF is called a weak acid, and yet it is very reactive; (c) although sulfuric acid is a strong electrolyte, an aqueous solution of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) contains more \(\mathrm{HSO}_{4}^{-}\) ions than \(\mathrm{SO}_{4}^{2-}\) ions.
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