Solubility Practice Test- Questions and Answers

Solubility Practice Test: Questions and Answers

You're here because you need to practice solubility problems. Not because your teacher assigned homework, but because you actually want to get these right on test day. Let's skip the warm-up and get straight to work.

What Is Solubility?

Solubility tells you how much of a substance dissolves in a solvent at a specific temperature. That's it. A substance that dissolves well has high solubility. One that barely dissolves has low solubility.

When a solution holds the maximum amount of solute at a given temperature, you have a saturated solution. Push past that point and the excess solute just sits at the bottom—undissolved.

Core Solubility Rules You Must Know

These rules are your foundation. Memorize them before attempting any practice questions.

• Nitrates (NO₃⁻) — always soluble
• Alkali metals (Li⁺, Na⁺, K⁺, etc.) — always soluble
• Ammonium (NH₄⁺) — always soluble
• Chlorides, bromides, iodides — soluble, except Ag⁺, Pb²⁺, Hg₂²⁺
• Sulfates (SO₄²⁻) — soluble, except Ba²⁺, Pb²⁺, Ca²⁺, Sr²⁺
• Carbonates (CO₃²⁻) — generally insoluble, except Group 1 and NH₄⁺
• Hydroxides (OH⁻) — generally insoluble, except Group 1, Ca²⁺, Ba²⁺, Sr²⁺
• Sulfides (S²⁻) — generally insoluble, except Group 1, 2, and NH₄⁺

Solubility Rules Quick Reference Table

Practice Questions and Answers

Question 1

Is PbCl₂ soluble or insoluble?

PbCl₂ is an exception to the chloride rule. Lead chloride is insoluble in cold water. It only dissolves when heated—that's why hot water can sometimes get it into solution.

Question 2

Predict whether Ag₂SO₄ is soluble.

Silver sulfate breaks the sulfate rule. It's slightly soluble, not completely insoluble like most silver salts, but it won't fully dissolve. You'll see some solid remaining in the beaker.

Question 3

What happens when you mix Na₂CO₃ with CaCl₂?

Double displacement occurs. The products are NaCl and CaCO₃. Using the rules:

• NaCl — soluble (Na⁺ is always soluble)
• CaCO₃ — insoluble (carbonates except Group 1 and NH₄⁺)

You'll get a precipitate of calcium carbonate forming.

Question 4

Is KOH soluble?

Yes. Potassium is an alkali metal. All compounds containing K⁺ are soluble. KOH dissolves completely in water.

Question 5

What is the precipitate when FeCl₃ reacts with NaOH?

Products: Fe(OH)₃ and NaCl. NaCl is soluble. Fe(OH)₃ is not—it's a hydroxide, and iron falls under the general exception list.

The precipitate is iron(III) hydroxide, which appears as a reddish-brown solid.

Question 6

Is Mg(OH)₂ soluble?

No. Magnesium hydroxide is insoluble. It's the active ingredient in milk of magnesia, but that doesn't mean it dissolves well—it forms a suspension, not a true solution.

Question 7

Predict the solubility of (NH₄)₂S.

Ammonium overrides almost everything. (NH₄)₂S is soluble. Any ammonium salt dissolves.

Question 8

What color precipitate does CuSO₄ form with NaOH?

Copper hydroxide, Cu(OH)₂, forms as a blue precipitate. This is a classic lab demonstration—the pale blue solid appearing immediately upon mixing.

How to Solve Solubility Problems

Follow this step-by-step process every time:

1. Identify the ions present in each compound
2. Apply the solubility rules to each ion pair
3. Check for exceptions—these trip up most students
4. Determine the products if a reaction occurs
5. Identify the precipitate if one forms

Example Walkthrough

Problem: Does AgNO₃ + KCl produce a precipitate?

Step 1: Ions are Ag⁺, NO₃⁻, K⁺, Cl⁻

Step 2: Products would be AgCl and KNO₃

Step 3: Check each product:

• KNO₃ — K⁺ (always soluble) + NO₃⁻ (always soluble) = soluble
• AgCl — Cl⁻ is usually soluble, but Ag⁺ is an exception = insoluble

Answer: Yes, AgCl precipitates out.

Common Mistakes to Avoid

• Forgetting exceptions — Ag⁺ and Pb²⁺ break almost every anion rule
• Confusing "slightly soluble" with "insoluble" — some compounds like Ag₂SO₄ fall in between
• Ignoring temperature — solubility increases with temperature for most solids
• Forcing a reaction — sometimes both products are soluble and nothing precipitates

Quick Practice Drill

Without looking at the rules, classify these compounds as soluble or insoluble:

1. BaSO₄
2. NH₄Cl
3. Pb(NO₃)₂
4. CaCO₃
5. MgS

Answers: BaSO₄ is insoluble, NH₄Cl is soluble, Pb(NO₃)₂ is soluble, CaCO₃ is insoluble, MgS is insoluble.

Got those right? You're ready for the real test. Missed any? Go back to the table and figure out which exception bit you.