Solubility Rules Practice Worksheet for chemistry students to test understanding of solubility rules and compound formation.

Let’s go step by step through each question on the worksheet. We’ll use basic solubility rules to figure out what dissolves in water and what doesn’t.

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Question 1: Classify each substance as soluble or insoluble in water.

We use these common solubility rules:
- Most nitrate (NO₃⁻), acetate (CH₃COO⁻), and alkali metal (Group 1) compounds are soluble.
- Most chlorides, bromides, iodides are soluble — except with Ag⁺, Pb²⁺, Hg₂²⁺.
- Sulfates are usually soluble — except with Ba²⁺, Sr²⁺, Pb²⁺, Ca²⁺ (sometimes).
- Hydroxides are mostly insoluble — except Group 1 and some Group 2 like Ca(OH)₂ (slightly).
- Carbonates, phosphates, sulfides are mostly insoluble — except with Group 1 or NH₄⁺.

Now let’s classify:

I. Mg(PO₄)₂ → Phosphates are generally insoluble → Insoluble

II. KOH → Potassium is Group 1 → All Group 1 hydroxides are soluble → Soluble

III. NiCl₂ → Chlorides are soluble unless with Ag⁺, Pb²⁺, Hg₂²⁺ → Nickel isn’t one of those → Soluble

IV. NH₄OH → Ammonium compounds are always soluble → Soluble

V. Hg₂SO₄ → Mercury(I) sulfate — sulfates are usually soluble, but Hg₂²⁺ is an exception → Insoluble

VI. KBr → Potassium bromide — Group 1 + halide → always soluble → Soluble

VII. Pb(CO₃) → Lead carbonate — carbonates are insoluble except with Group 1/NH₄⁺ → Insoluble

VIII. PbI₂ → Lead iodide — iodides are insoluble with Pb²⁺ → Insoluble

IX. BaSO₄ → Barium sulfate — classic insoluble sulfate → Insoluble

X. NiCl₂ → Same as III → Soluble

*(Note: X is same as III — probably a typo in worksheet, but we answer based on formula)*

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Question 2: Show the ions that formed the following compounds

Break down each compound into its positive and negative ions.

I. Zn₃(PO₄)₂
→ Zinc ion is Zn²⁺, phosphate is PO₄³⁻
→ So: Zn²⁺ and PO₄³⁻

II. Al₂S₃
→ Aluminum is Al³⁺, sulfur forms S²⁻
→ So: Al³⁺ and S²⁻

III. Iron (III) sulfide
→ Iron (III) = Fe³⁺, sulfide = S²⁻
→ Formula would be Fe₂S₃, so ions: Fe³⁺ and S²⁻

IV. Ammonium cyanide
→ Ammonium = NH₄⁺, cyanide = CN⁻
→ So: NH₄⁺ and CN⁻

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Question 3: Form 4 water-soluble compounds from given ions

Given ions: Cl⁻, CO²⁻, PO₄³⁻, Li⁺, Sr²⁺

Rules for solubility:
- All lithium (Li⁺) compounds are soluble (Group 1).
- Strontium (Sr²⁺) compounds: sulfates and carbonates are often insoluble, but chlorides are soluble.

So let’s pick combinations that are definitely soluble:

1. LiCl → Lithium chloride → soluble ✔
2. Li₂CO₃ → Lithium carbonate → soluble (Group 1) ✔
3. Li₃PO₄ → Lithium phosphate → soluble (Group 1) ✔
4. SrCl₂ → Strontium chloride → soluble (chlorides are soluble except with Ag/Pb/Hg) ✔

*(Note: SrCO₃ and Sr(PO₄)₂ are insoluble, so avoid those.)*

So four soluble compounds:
→ LiCl, Li₂CO₃, Li₃PO₄, SrCl₂

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Question 4: Identify the precipitate in the reaction

Precipitate = solid that forms when two solutions mix.

a. Li₂CO₃ + Co(CH₃COO)₂ → 2 LiCH₃COO + CoCO₃

Check products:
- LiCH₃COO → lithium acetate → soluble (Group 1)
- CoCO₃ → cobalt carbonate → carbonates are insoluble except Group 1/NH₄⁺ → CoCO₃ is precipitate

b. Pb(NO₃)₂ + Li₂SO₄ → PbSO₄ + 2 LiNO₃

Products:
- LiNO₃ → soluble (Group 1 + nitrate)
- PbSO₄ → lead sulfate → sulfates are insoluble with Pb²⁺ → PbSO₄ is precipitate

So circle:
a. CoCO₃
b. PbSO₄

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Question 5: Name or give chemical formula, and state solubility

Use naming rules and solubility rules.

Row 1: Chemical Formula = Zn₃(PO₄)₂
→ Name: Zinc phosphate
→ Solubility: Phosphates are insoluble except with Group 1/NH₄⁺ → Insoluble

Row 2: Name = Silver bromide
→ Formula: AgBr (silver is Ag⁺, bromide is Br⁻)
→ Solubility: Bromides are insoluble with Ag⁺ → Insoluble

Row 3: Formula = KNO₃
→ Name: Potassium nitrate
→ Solubility: All nitrates and Group 1 salts are soluble → Soluble

Row 4: Name = Aluminum sulfide
→ Formula: Al₂S₃ (Al³⁺ and S²⁻)
→ Solubility: Sulfides are insoluble except Group 1/2/NH₄⁺ → aluminum not included → Insoluble

Row 5: Name = Silver acetate
→ Formula: AgC₂H₃O₂ or AgCH₃COO
→ Solubility: Acetates are usually soluble, BUT silver acetate is slightly soluble — often considered “soluble” in intro chem, but technically low solubility. However, most worksheets treat it as Soluble because acetates are generally soluble. Let’s check standard rule: “All acetates are soluble” — yes, even silver acetate is listed as soluble in many tables. So → Soluble

*(Note: Some sources say silver acetate is sparingly soluble, but for high school level, it’s usually marked soluble.)*

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Final Answer:

Question 1:
I. Insoluble
II. Soluble
III. Soluble
IV. Soluble
V. Insoluble
VI. Soluble
VII. Insoluble
VIII. Insoluble
IX. Insoluble
X. Soluble

Question 2:
I. Zn²⁺ and PO₄³⁻
II. Al³⁺ and S²⁻
III. Fe³⁺ and S²⁻
IV. NH₄⁺ and CN

Question 3:
LiCl, Li₂CO₃, Li₃PO₄, SrCl₂

Question 4:
a. CoCO₃
b. PbSO₄

Question 5:
| Chemical Formula | Name | Solubility |
|------------------|------------------|----------|
| Zn₃(PO₄)₂ | Zinc phosphate | Insoluble |
| AgBr | Silver bromide | Insoluble |
| KNO₃ | Potassium nitrate| Soluble |
| Al₂S₃ | Aluminum sulfide | Insoluble |
| AgCH₃COO | Silver acetate | Soluble |