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Chapter 21: Problem 110

Unlabeled test tubes contain solid \(\mathrm{AlCl}_{3} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) in one, \(\mathrm{Ba}(\mathrm{OH})_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O}\) in another, and \(\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}\) in the other. How could you find out what is in each test tube, using chemical tests that involve only these compounds plus water?

Short Answer

Expert verified
Use NaOH to identify Al鲁鈦�, H鈧係O鈧� for Ba虏鈦�, and Na鈧侰O鈧� confirms Mg虏鈦�.

Step by step solution

01

Dissolve Each Compound

Start by dissolving a small amount of the solid from each test tube in water to make a solution. Test tubes containing hydrates like AlCl鈧兟�6H鈧侽, Ba(OH)鈧偮�8H鈧侽, and MgSO鈧劼�7H鈧侽 will all dissolve, but they will produce different ions in solution.
02

Identify the Aluminum Ions

To identify the test tube containing AlCl鈧兟�6H鈧侽, add a few drops of dilute NaOH solution to each prepared solution. The solution producing a white gelatinous precipitate identifies the presence of Al鲁鈦� ions, thus containing AlCl鈧兟�6H鈧侽.
03

Identify the Barium Ions

To identify the test tube containing Ba(OH)鈧偮�8H鈧侽, add a few drops of dilute H鈧係O鈧� to the remaining solutions. The solution that forms a white precipitate confirms the presence of Ba虏鈦� ions, indicating Ba(OH)鈧偮�8H鈧侽.
04

Confirm the Magnesium Ions

The last test tube that remains should contain MgSO鈧劼�7H鈧侽, as you've identified the other two compounds. To confirm, add a few drops of Na鈧侰O鈧� solution. A white precipitate indicating MgCO鈧� identifies the presence of Mg虏鈦� ions.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Chemical Tests
Chemical tests are essential techniques used in laboratories to help identify unknown substances. In this case, we're using chemical tests to identify specific ions present in hydrate compounds. The goal is not just to recognize the ions but also to differentiate between the given compounds, namely - 1. Aluminum Chloride Hexahydrate 2. Barium Hydroxide Octahydrate 3. Magnesium Sulfate Heptahydrate
These tests involve adding reagents that will react with one of the ions present in the compounds to form a precipitate. This visible change helps confirm which ions are present in your solutions.
Ion Identification
Ion identification is a critical part of analyzing chemical solutions. In this exercise, we are using different reagents to identify - Aluminum ions - Barium ions - Magnesium ions from their respective hydrated compounds once dissolved in water.
  • For Aluminum ions, a white gelatinous precipitate forms when sodium hydroxide ( NaOH ) is added to the solution containing Aluminum Chloride Hexahydrate ( AlCl鈧兟�6H鈧侽 ).
  • Barium ions produce a white precipitate when sulfuric acid ( H鈧係O鈧� ) is introduced to the solution of Barium Hydroxide Octahydrate ( Ba(OH)鈧偮�8H鈧侽 ).
  • Magnesium ions are confirmed by the formation of magnesium carbonate ( MgCO鈧� ) when sodium carbonate ( Na鈧侰O鈧� ) is added to the Magnesium Sulfate Heptahydrate ( MgSO鈧劼�7H鈧侽 ).
Each precipitate has specific characteristics that help confirm the ion's presence through visual inspection.
Hydrated Compounds
Hydrated compounds are substances that include water molecules within their crystal structure. For instance:
- Aluminum Chloride Hexahydrate ( AlCl鈧兟�6H鈧侽 ) contains six water molecules. - Barium Hydroxide Octahydrate ( Ba(OH)鈧偮�8H鈧侽 ) contains eight water molecules. - Magnesium Sulfate Heptahydrate ( MgSO鈧劼�7H鈧侽 ) includes seven water molecules.
These water molecules are integral to the structure of the hydrate and can affect the way the compound dissolves and reacts. The water molecules are often released when the compound dissolves in a solvent like water, breaking the ionic bonds and releasing the ions into the solution, which then participate in chemical tests.
Solution Preparation
Preparing the solution is the first important step in many chemical analyses. To begin with, you would dissolve each solid hydrate in water, which would separate them into their respective ions.
Steps include:
  • Measure and record a small amount of each solid substance from the test tubes.
  • Add distilled water to each into separate containers to fully dissolve the samples.
  • Stir appropriately to ensure complete dissolution.
By preparing a solution, you create an environment where ions are free to interact with added reagents. This is vital for conducting proper chemical tests and ensuring accurate results in identifying the compounds at hand.

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Most popular questions from this chapter

Sodium perchlorate, \(\mathrm{NaClO}_{4}\), is produced by electrolysis of sodium chlorate, \(\mathrm{NaClO}_{3}\). If a current of \(2.50 \times 10^{3}\) A passes through an electrolytic cell, how many kilograms of sodium perchlorate are produced per hour?

The main ingredient in many phosphate fertilizers is \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2} \cdot \mathrm{H}_{2} \mathrm{O} .\) If a fertilizer is \(17.1 \% \mathrm{P}\) (by mass), and all of this phosphorus is present as \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2} \cdot \mathrm{H}_{2} \mathrm{O},\) what is the mass percentage of this salt in the fertilizer?

Complete and balance the following equations. \(\mathrm{LiHCO}_{3}(s) \stackrel{\Delta}{\longrightarrow}\) \(\mathrm{Na}_{2} \mathrm{SO}_{4}(a q)+\mathrm{BaCl}_{2}(a q) \longrightarrow\) \(\mathrm{K}_{2} \mathrm{CO}_{3}(a q)+\mathrm{Ca}(\mathrm{OH})_{2}(a q) \longrightarrow\) \(\mathrm{Li}(s)+\mathrm{HCl}(a q) \longrightarrow\) e \(\mathrm{Na}(s)+\mathrm{ZrCl}_{4}(g) \longrightarrow\)

An antacid tablet consists of calcium carbonate with other ingredients. The calcium carbonate in a \(0.9863-\mathrm{g}\) sample of the antacid was dissolved in \(50.00 \mathrm{~mL}\) of 0.5068 \(M \mathrm{HCl}\), then titrated with \(41.23 \mathrm{~mL}\) of \(0.2590 \mathrm{M} \mathrm{NaOH}\). What was the mass percentage of \(\mathrm{CaCO}_{3}\) in the antacid?

\(\mathrm{NaClO}\) solution is made by electrolysis of \(\mathrm{NaCl}(a q)\) by allowing the products \(\mathrm{NaOH}\) and \(\mathrm{Cl}_{2}\) to mix. How long must a cell operate to produce \(1.00 \times 10^{3} \mathrm{~L}\) of \(5.25 \%\) NaClO solution (density \(=1.00 \mathrm{~g} / \mathrm{mL}\) ) if the cell current is \(3.00 \times 10^{3} \mathrm{~A} ?\)
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