Assume that you have three white solids: NaCl, KCl, and MgCl2. What tests could you do to tell which is which?

Verified step by step guidance

Dissolve a small amount of each solid in water to form three separate solutions. Observe the solubility and any immediate reactions in water.

Perform a flame test on each solution. Dip a clean wire loop into each solution and then place it in a flame. Observe the color of the flame: NaCl typically produces a yellow flame, KCl produces a lilac flame, and MgCl2 produces a bright white flame.

Add silver nitrate (AgNO3) solution to a small sample of each of the original solutions. Observe the precipitate formation. NaCl and KCl will form a white precipitate (AgCl), while MgCl2 will not form a precipitate.

To differentiate between NaCl and KCl, which both formed a white precipitate with AgNO3, use a conductivity test. Prepare a conductivity apparatus and test each solution. The solution with higher conductivity likely contains more ions, which could help indicate the presence of Na+ or K+.

As a confirmatory test, add sodium carbonate (Na2CO3) to the solutions. NaCl and KCl will not react significantly, but MgCl2 will form a white precipitate of magnesium carbonate (MgCO3).

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Solubility and Ionic Compounds

Ionic compounds like NaCl, KCl, and MgCl2 are generally soluble in water, but their solubility can vary. Understanding the solubility rules helps predict how these compounds will behave in solution. For instance, while NaCl and KCl are highly soluble, MgCl2 has a different solubility profile due to the presence of magnesium, which can affect the ionic interactions in water.

Conductivity of Solutions

When ionic compounds dissolve in water, they dissociate into their constituent ions, allowing the solution to conduct electricity. By measuring the conductivity of the solutions formed from each solid, one can differentiate between them. For example, MgCl2 produces more ions in solution compared to NaCl and KCl, leading to higher conductivity due to its dissociation into three ions (Mg²⁺ and 2 Cl⁻).

Flame Tests

Flame tests are a qualitative analysis technique used to identify the presence of certain metal ions based on the color they emit when heated in a flame. Sodium ions produce a bright yellow flame, potassium ions yield a lilac flame, and magnesium ions do not impart a significant color. Performing a flame test on the solids can help distinguish between NaCl, KCl, and MgCl2 based on the characteristic colors observed.

Recommended video:

Guided course

14:42

Test for Anions

Related Practice

Textbook Question

Using the qualitative analysis flowchart in Figure 17.18

, tell how you could separate the following pairs of ions. (a) Ag+ and Cu2+

Textbook Question

Give a method for seperating the following pairs of ions by the addition of no more than two substances. (a) Hg2+ and Co2+

Textbook Question

In quantitative analysis, Ag+, Hg2+, and Pb2+ are seperated from other cations by the addition of HCl. Calculate the concentration of Cl-ions required to just begin the precipitation of (a) AgCl, (b) Hg2Cl2, (c) PbCl2 in a solution hav-ing metal-ion concentrations of 0.030 M. What fraction of the Pb2+ remains in solution when the Ag+ just begins to precipitate?

Textbook Question

Write the expression for the solubility product constant of MgF2 (see Problem 4.139). If [Mg2+] = 2.6 * 10-4 mol/L in a solution, what is the value of Ksp?