Rucete ✏ AP Chemistry In a Nutshell
3. Ionic Compounds, Formulas, and Reactions — Practice Questions
This chapter introduces ionic compounds, their formulas, naming conventions, solubility rules, and how to predict and balance chemical reactions.
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(Multiple Choice — Click to Reveal Answer)
1. What is the correct formula for aluminum sulfate?
(A) Al3(SO4)2
(B) AlSO4
(C) Al2(SO4)3
(D) Al2(SO3)3
Answer
(C) — Aluminum has a +3 charge and sulfate a –2 charge, thus Al2(SO4)3.
2. Which are spectator ions when K₂Cr₂O₇ reacts with Pb(NO₃)₂?
(A) Pb²⁺, K⁺
(B) Cr²⁺, NO₃⁻
(C) Cr²⁺, K⁺
(D) K⁺, NO₃⁻
Answer
(D) — K⁺ and NO₃⁻ ions remain unchanged.
3. Which is a driving force for chemical reactions?
(A) Gas formation
(B) Formation of weak electrolyte
(C) Formation of water
(D) All of these
Answer
(D) — All listed conditions are reaction drivers.
4. Which ionic compound pair has the strongest coulombic attraction and thus lowest solubility?
(A) Fe³⁺ and N³⁻
(B) Na⁺ and Br⁻
(C) Ca²⁺ and Br⁻
(D) Fe³⁺ and Br⁻
Answer
(A) — High charges result in stronger attraction and lower solubility.
5. Which ion is isoelectronic with neon?
(A) F⁻
(B) Ga³⁺
(C) P³⁻
(D) All are isoelectronic
Answer
(A) — F⁻ has the same electron configuration as neon.
6. Ionic compounds' formulas represent the:
(A) Actual number of atoms
(B) Simplest whole-number ratio
(C) Molecular structure
(D) Covalent bonding arrangement
Answer
(B) — Ionic compounds show simplest whole-number ratio.
7. What charge does the sulfate ion have?
(A) –1
(B) –2
(C) +1
(D) +2
Answer
(B) — Sulfate ion is SO₄²⁻.
8. Name the compound MgCl₂.
(A) Magnesium chlorite
(B) Magnesium chloride
(C) Magnesium dichloride
(D) Magnesium(I) chloride
Answer
(B) — MgCl₂ is magnesium chloride.
9. Identify a decomposition reaction.
(A) AB → A + B
(B) A + B → AB
(C) AB + CD → AD + CB
(D) A + BC → AC + B
Answer
(A) — Decomposition reactions break down compounds.
10. The iodate ion is represented by:
(A) IO⁻
(B) IO₂⁻
(C) IO₃⁻
(D) IO₄⁻
Answer
(C) — The iodate ion is IO₃⁻.
11. What type of reaction is KOH + HCl → KCl + H₂O?
(A) Combustion
(B) Neutralization
(C) Decomposition
(D) Synthesis
Answer
(B) — Reaction between acid and base is neutralization.
12. Which formula correctly represents barium nitrite?
(A) BaNO₃
(B) Ba(NO₂)₂
(C) Ba(NO₃)₂
(D) Ba₃N₂
Answer
(B) — Barium nitrite is Ba(NO₂)₂.
13. Name Na₂CrO₄ correctly.
(A) Sodium chromite
(B) Sodium dichromate
(C) Sodium chromate
(D) Disodium chromate
Answer
(C) — Na₂CrO₄ is sodium chromate.
14. Ionic compounds dissolve in water to form:
(A) Molecules
(B) Atoms
(C) Cations and anions
(D) Covalent bonds
Answer
(C) — Ionic compounds dissociate into ions.
15. Name Cr(NO₃)₃.
(A) Chromium nitrate
(B) Chromium(I) nitrate
(C) Chromium(III) nitrate
(D) Chromium trinitrate
Answer
(C) — Cr(NO₃)₃ is chromium(III) nitrate.
16. Which is the correct formula for tin(IV) chloride?
(A) SnCl₂
(B) SnCl₄
(C) Sn₂Cl₄
(D) Sn₄Cl
Answer
(B) — Tin(IV) indicates Sn⁴⁺, requiring four Cl⁻ ions to balance charge: SnCl₄.
17. What is the name of Fe₂O₃?
(A) Iron oxide
(B) Iron(II) oxide
(C) Iron(III) oxide
(D) Diiron trioxide
Answer
(C) — Fe₂O₃ contains Fe³⁺ ions, so it is iron(III) oxide.
18. Which of the following is an insoluble compound?
(A) NaCl
(B) PbCl₂
(C) KNO₃
(D) NH₄NO₃
Answer
(B) — Lead(II) chloride is only slightly soluble in cold water.
19. What type of compound is formed from a metal and a nonmetal?
(A) Molecular
(B) Ionic
(C) Covalent
(D) Metallic
Answer
(B) — Ionic compounds form from metals and nonmetals.
20. Which pair of ions would result in the least soluble compound?
(A) Na⁺ and NO₃⁻
(B) K⁺ and Cl⁻
(C) Ba²⁺ and SO₄²⁻
(D) NH₄⁺ and NO₃⁻
Answer
(C) — BaSO₄ is insoluble in water.
21. Which compound is named incorrectly?
(A) CaBr₂ — calcium bromide
(B) FeCl₂ — iron(II) chloride
(C) Na₂S — sodium sulfide
(D) CuO — copper(I) oxide
Answer
(D) — CuO contains Cu²⁺, so it is copper(II) oxide.
22. The formula of ammonium phosphate is:
(A) NH₄PO₄
(B) (NH₄)₃PO₄
(C) NH₄₃PO₄
(D) (NH₄)PO₄
Answer
(B) — Three NH₄⁺ ions are needed to balance one PO₄³⁻.
23. Which of the following compounds contains a transition metal?
(A) KCl
(B) Na₂O
(C) CuCl₂
(D) MgBr₂
Answer
(C) — Copper is a transition metal.
24. Which polyatomic ion is found in KNO₃?
(A) NO₂⁻
(B) NO₃⁻
(C) NH₄⁺
(D) OH⁻
Answer
(B) — Nitrate ion (NO₃⁻) is in KNO₃.
25. Which of the following represents a correct net ionic equation?
(A) Na⁺ + Cl⁻ → NaCl(s)
(B) Ag⁺ + Cl⁻ → AgCl(s)
(C) Pb²⁺ + NO₃⁻ → Pb(NO₃)₂(s)
(D) K⁺ + NO₃⁻ → KNO₃(s)
Answer
(B) — AgCl is an insoluble salt that forms a precipitate.
26. Which of the following correctly predicts the product and identifies the reaction type for: Ba(NO₃)₂ + Na₂SO₄ → ?
(A) NaNO₃; combination
(B) BaSO₄; double replacement
(C) BaSO₄; decomposition
(D) Ba(NO₃)₂; single replacement
Answer
(B) — BaSO₄ precipitates; this is a double replacement reaction.
27. Which compound is most likely to form a precipitate in aqueous solution?
(A) Na₂CO₃
(B) NH₄Cl
(C) AgBr
(D) KNO₃
Answer
(C) — Silver bromide is insoluble in water.
28. In a net ionic equation, what is removed?
(A) Water molecules
(B) Gases
(C) Spectator ions
(D) Strong electrolytes
Answer
(C) — Spectator ions do not participate in the chemical change.
29. Which species acts as a weak electrolyte in solution?
(A) H₂O
(B) HCl
(C) CH₃COOH
(D) NaCl
Answer
(C) — Acetic acid only partially ionizes in solution.
30. Which compound is not soluble in water at room temperature?
(A) NH₄NO₃
(B) BaSO₄
(C) NaCl
(D) LiBr
Answer
(B) — Barium sulfate is poorly soluble in water.
31. The correct formula for copper(I) phosphate is:
(A) Cu₃PO₄
(B) CuPO₄
(C) Cu₃(PO₄)₂
(D) Cu₂PO₄
Answer
(A) — Cu⁺ and PO₄³⁻ combine in a 3:1 ratio.
32. Which ion is formed by sulfur in ionic compounds?
(A) S⁺
(B) S²⁺
(C) S⁻
(D) S²⁻
Answer
(D) — Sulfur typically forms S²⁻ ions.
33. Which of the following has the highest lattice energy?
(A) NaCl
(B) CaO
(C) KBr
(D) MgF₂
Answer
(B) — CaO has highly charged small ions, increasing lattice energy.
34. Identify the correct name for SnS₂.
(A) Tin(I) sulfide
(B) Tin(II) sulfide
(C) Tin(IV) sulfide
(D) Tin(III) sulfide
Answer
(C) — Two S²⁻ requires Sn⁴⁺, so it is tin(IV) sulfide.
35. The formula of cobalt(III) nitrate is:
(A) CoNO₃
(B) Co(NO₃)₂
(C) Co(NO₃)₃
(D) Co₃(NO₃)₂
Answer
(C) — Cobalt(III) has a +3 charge; combine with 3 nitrate ions.
36. Write the chemical formula for calcium phosphate.
Answer
Ca₃(PO₄)₂ — Calcium is Ca²⁺, phosphate is PO₄³⁻, combine in a 3:2 ratio.
37. Provide the correct name for MnO₂.
Answer
Manganese(IV) oxide — Mn has a +4 oxidation state to balance O²⁻.
38. What is the formula for ammonium sulfate?
Answer
(NH₄)₂SO₄ — Two NH₄⁺ ions balance one SO₄²⁻ ion.
39. Write the net ionic equation for the reaction of AgNO₃ and NaCl.
Answer
Ag⁺(aq) + Cl⁻(aq) → AgCl(s) — Silver chloride precipitates out.
40. Name the compound Cu₃(PO₄)₂.
Answer
Copper(II) phosphate — Cu²⁺ with PO₄³⁻ in a 3:2 ratio.
41. Write the formula for iron(III) carbonate.
Answer
Fe₂(CO₃)₃ — Two Fe³⁺ ions and three CO₃²⁻ ions balance charges.
42. What is the oxidation number of chromium in Cr₂O₃?
Answer
+3 — Oxygen is –2, so Cr must be +3 to balance.
43. Name the compound with the formula Pb(NO₃)₂.
Answer
Lead(II) nitrate — Pb²⁺ combined with two nitrate ions.
44. Write the net ionic equation for BaCl₂(aq) + Na₂SO₄(aq).
Answer
Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s) — Barium sulfate precipitates.
45. What is the correct name of Sn₃(PO₄)₄?
Answer
Tin(IV) phosphate — Sn⁴⁺ ions balanced with PO₄³⁻.
46. Write the chemical formula for sodium dichromate.
Answer
Na₂Cr₂O₇ — Two Na⁺ ions with one dichromate ion Cr₂O₇²⁻.
47. Name the compound Hg₂Cl₂.
Answer
Mercury(I) chloride — Hg₂²⁺ is the mercury(I) ion.
48. What is the formula for potassium permanganate?
Answer
KMnO₄ — Potassium ion K⁺ and permanganate MnO₄⁻.
49. Name the compound (NH₄)₂CrO₄.
Answer
Ammonium chromate — Two ammonium ions balance one CrO₄²⁻.
50. What is the name of Ni(NO₃)₂?
Answer
Nickel(II) nitrate — Nickel ion is in the +2 oxidation state.