Rucete ✏ AP Chemistry In a Nutshell
3. Ionic Compounds, Formulas, and Reactions — Practice Questions 3
This chapter introduces ion prediction, naming rules, reaction driving forces, solubility trends, and writing molecular, ionic, and net ionic equations.
Need a quick review?
📘 Go to the Concept Summary
(Multiple Choice — Click to Reveal Answer)
1. Which of the following represents a binary ionic compound?
(A) NaCl
(B) H₂O
(C) NH₃
(D) C₂H₆
Answer
(A) — Binary ionic compounds contain a metal and nonmetal only; NaCl fits this definition.
2. Which of the following has the highest lattice energy?
(A) KBr
(B) MgO
(C) NaCl
(D) CaS
Answer
(B) — Mg²⁺ and O²⁻ have the highest product of charges and small radii, leading to high lattice energy.
3. Which pair of ions is isoelectronic?
(A) Na⁺ and Cl⁻
(B) O²⁻ and Mg²⁺
(C) F⁻ and Na⁺
(D) Cl⁻ and K⁺
Answer
(D) — Cl⁻ and K⁺ both have 18 electrons, matching argon's configuration.
4. What drives a double replacement reaction to proceed?
(A) Formation of a strong base
(B) Transfer of electrons
(C) Formation of a precipitate or gas
(D) Bond breaking
Answer
(C) — A driving force is typically a precipitate, gas, or weak electrolyte formation.
5. Which of the following ions has the largest radius?
(A) F⁻
(B) O²⁻
(C) Na⁺
(D) Mg²⁺
Answer
(B) — O²⁻ has the most electrons per proton, leading to the largest radius.
6. Which compound is most likely to dissolve completely in water?
(A) AgCl
(B) BaSO₄
(C) NaNO₃
(D) PbI₂
Answer
(C) — Na⁺ and NO₃⁻ form a salt that is always soluble in water.
7. Which ion has the electron configuration 1s² 2s² 2p⁶?
(A) O²⁻
(B) F
(C) Na⁺
(D) Cl⁻
Answer
(A) — O²⁻ gains 2 electrons, matching neon’s configuration.
8. What is the correct name for the compound Cu₂S?
(A) Copper(I) sulfide
(B) Copper(II) sulfide
(C) Dicopper monosulfide
(D) Copper sulfate
Answer
(A) — Each Cu has a +1 charge to balance S²⁻, so it's copper(I) sulfide.
9. What is the formula of a compound made of Ca²⁺ and PO₄³⁻?
(A) CaPO₄
(B) Ca₃(PO₄)₂
(C) Ca₂(PO₄)₃
(D) Ca(PO₄)₂
Answer
(B) — 3 Ca²⁺ (total +6) and 2 PO₄³⁻ (total –6) balance.
10. Which of the following is the correct dissociation for AlCl₃ in water?
(A) AlCl₃ → Al³⁺ + 3Cl⁻
(B) AlCl₃ → Al + Cl₂
(C) AlCl₃ → Al⁺ + Cl₂⁻
(D) AlCl₃ → Al²⁺ + Cl⁻
Answer
(A) — AlCl₃ dissociates into 1 Al³⁺ and 3 Cl⁻ ions.
11. What is the name of (NH₄)₂SO₄?
(A) Ammonium sulfate
(B) Ammonium sulfide
(C) Ammonium hydrogen sulfate
(D) Diammonium sulfate
Answer
(A) — Two NH₄⁺ ions balance one SO₄²⁻ ion.
12. Which of the following correctly shows a synthesis reaction?
(A) 2H₂ + O₂ → 2H₂O
(B) NaCl → Na + Cl₂
(C) AgNO₃ + NaCl → AgCl + NaNO₃
(D) Zn + CuSO₄ → Cu + ZnSO₄
Answer
(A) — Synthesis involves combining elements to make a compound.
13. Which of the following is a spectator ion in the reaction between HCl and NaOH?
(A) H⁺
(B) OH⁻
(C) Cl⁻
(D) H₂O
Answer
(C) — Cl⁻ is unchanged on both sides of the full ionic equation.
14. What is the oxidation state of Fe in Fe₂O₃?
(A) +2
(B) +3
(C) –2
(D) –3
Answer
(B) — Oxygen is –2, and there are three of them (–6). Each Fe must be +3 to total +6.
15. Which of the following shows the correct balanced formula for barium hydroxide?
(A) BaOH
(B) Ba(OH)₂
(C) Ba₂OH
(D) BaOH₂
Answer
(B) — Ba²⁺ requires two OH⁻ to balance charge.
16. Which of the following is most likely to form a colored compound?
(A) NaCl
(B) MgO
(C) FeCl₃
(D) LiBr
Answer
(C) — Transition metals like Fe³⁺ often form colored ionic compounds.
17. Which of the following correctly lists all strong electrolytes?
(A) NaCl, HCl, CH₃COOH
(B) KNO₃, Ba(OH)₂, NH₃
(C) H₂SO₄, KBr, NaOH
(D) HF, HNO₃, CaCl₂
Answer
(C) — These all dissociate completely in solution.
18. What is the name of PbO₂?
(A) Lead(I) oxide
(B) Lead(II) oxide
(C) Lead(IV) oxide
(D) Lead peroxide
Answer
(C) — Oxygen is –2, so Pb must be +4; the name is lead(IV) oxide.
19. Which compound will not dissociate in water?
(A) NaCl
(B) CH₄
(C) HNO₃
(D) KOH
Answer
(B) — CH₄ is a covalent molecule and does not dissociate into ions.
20. Which one is the correct net ionic equation for the reaction of HNO₃ and KOH?
(A) HNO₃ + KOH → KNO₃ + H₂O
(B) H⁺ + OH⁻ → H₂O
(C) H⁺ + K⁺ + OH⁻ → K⁺ + H₂O
(D) K⁺ + NO₃⁻ → KNO₃
Answer
(B) — The actual reaction is between H⁺ and OH⁻ forming water.
21. Which compound contains a transition metal?
(A) MgCl₂
(B) Fe₂O₃
(C) CaO
(D) NaNO₃
Answer
(B) — Iron (Fe) is a transition metal.
22. Which of the following represents the formation of a gas in a double displacement reaction?
(A) BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl
(B) HCl + NaHCO₃ → CO₂ + H₂O + NaCl
(C) NaCl + AgNO₃ → AgCl + NaNO₃
(D) Zn + CuSO₄ → Cu + ZnSO₄
Answer
(B) — Acid + bicarbonate → carbon dioxide (gas), water, and salt.
23. What is the formula of an ionic compound made of Li⁺ and Br⁻?
(A) Li₂Br
(B) LiBr₂
(C) LiBr
(D) Li₂Br₂
Answer
(C) — Li⁺ and Br⁻ combine in a 1:1 ratio.
24. Which polyatomic ion has a –1 charge?
(A) SO₄
(B) PO₄
(C) NO₃
(D) CO₃
Answer
(C) — Nitrate (NO₃⁻) has a –1 charge.
25. Which of the following is a redox reaction?
(A) NaOH + HCl → NaCl + H₂O
(B) BaCl₂ + Na₂SO₄ → BaSO₄ + NaCl
(C) Zn + CuSO₄ → ZnSO₄ + Cu
(D) AgNO₃ + NaCl → AgCl + NaNO₃
Answer
(C) — Zn is oxidized and Cu²⁺ is reduced — a redox reaction.
26. Which of the following correctly represents the formation of an insoluble compound in aqueous solution?
(A) NaCl + AgNO₃ → AgCl(s) + NaNO₃
(B) KNO₃ + NaCl → no reaction
(C) HCl + NaOH → NaCl + H₂O
(D) NH₄NO₃ + BaCl₂ → Ba(NO₃)₂ + NH₄Cl
Answer
(A) — AgCl is insoluble and precipitates out of solution.
27. Which of the following compounds is most likely to conduct electricity in aqueous solution?
(A) CH₃OH
(B) Na₂SO₄
(C) C₆H₁₂O₆
(D) CO₂
Answer
(B) — Na₂SO₄ dissociates into ions and is a strong electrolyte.
28. A 1:2 ionic compound is formed between a metal M and a polyatomic ion. Which of the following formulas is most likely?
(A) M₂(NO₃)₃
(B) M(NO₃)₂
(C) M₃(PO₄)₂
(D) M₂SO₄
Answer
(B) — A 1:2 compound suggests M²⁺ and two NO₃⁻ ions.
29. Which of the following pairs of reactants will form a gas during a chemical reaction?
(A) Na₂SO₄ + BaCl₂
(B) Na₂CO₃ + HCl
(C) NaOH + HNO₃
(D) KNO₃ + AgCl
Answer
(B) — Acid + carbonate forms CO₂ gas, water, and salt.
30. A precipitate forms when aqueous solutions of calcium nitrate and sodium phosphate are mixed. What is the formula of the precipitate?
(A) Ca₃(PO₄)₂
(B) Ca(NO₃)₂
(C) Na₃PO₄
(D) NaNO₃
Answer
(A) — Calcium phosphate is insoluble and precipitates out.
31. Which combination will result in no reaction in aqueous solution?
(A) H₂SO₄ + NaOH
(B) AgNO₃ + NaCl
(C) Na₂CO₃ + HCl
(D) NaNO₃ + KCl
Answer
(D) — All products are soluble spectator ions → no net change.
32. What is the oxidation state of Mn in KMnO₄?
(A) +2
(B) +4
(C) +6
(D) +7
Answer
(D) — O is –2, total –8; K is +1, so Mn must be +7 to balance.
33. Which compound would most likely form a basic solution in water?
(A) NaCl
(B) NH₄NO₃
(C) Na₂CO₃
(D) KBr
Answer
(C) — Carbonate ions hydrolyze to form OH⁻, making solution basic.
34. What is the net ionic equation for: Ca(OH)₂ + HCl → CaCl₂ + H₂O?
(A) Ca²⁺ + 2OH⁻ + 2H⁺ + 2Cl⁻ → Ca²⁺ + 2Cl⁻ + 2H₂O
(B) OH⁻ + H⁺ → H₂O
(C) Ca²⁺ + 2OH⁻ + 2H⁺ → Ca²⁺ + 2H₂O
(D) 2OH⁻ + 2H⁺ → 2H₂O
Answer
(D) — Net ionic focuses on the acid–base neutralization only.
35. Which ionic compound is least soluble in water at room temperature?
(A) KNO₃
(B) NaCl
(C) PbI₂
(D) NH₄Br
Answer
(C) — Lead iodide is only slightly soluble in water.
36. Write the complete ionic equation for the reaction between sodium carbonate and hydrochloric acid.
Answer
2Na⁺ + CO₃²⁻ + 2H⁺ → H₂O + CO₂ + 2Na⁺ — Carbonate reacts with acid to form water and carbon dioxide gas.
37. Predict the products when zinc reacts with hydrochloric acid.
Answer
ZnCl₂ and H₂ — Single displacement reaction: Zn + 2HCl → ZnCl₂ + H₂
38. What is the name of the compound Fe(NO₂)₂?
Answer
Iron(II) nitrite — Fe²⁺ paired with two nitrite ions (NO₂⁻).
39. Write the net ionic equation for the formation of barium sulfate precipitate.
Answer
Ba²⁺ + SO₄²⁻ → BaSO₄(s) — Barium sulfate is insoluble and precipitates.
40. What is the charge on the phosphate ion?
Answer
–3 — The formula PO₄³⁻ indicates a –3 charge.
41. Write the formula for calcium hypochlorite.
Answer
Ca(ClO)₂ — Ca²⁺ and ClO⁻ combine in a 1:2 ratio.
42. Identify the spectator ions in the reaction: AgNO₃ + NaCl → AgCl + NaNO₃
Answer
Na⁺ and NO₃⁻ — They remain unchanged on both sides.
43. What is the oxidation number of chromium in Cr₂O₇²⁻?
Answer
+6 — Oxygen is –2 × 7 = –14; total charge is –2 → Cr must total +12 → each Cr = +6.
44. Name the compound with the formula Hg₂Cl₂.
Answer
Mercury(I) chloride — Hg₂²⁺ indicates mercury(I).
45. Write the chemical formula of strontium acetate.
Answer
Sr(C₂H₃O₂)₂ — Sr²⁺ needs two acetate ions to balance.
46. Give the formula of the ionic compound formed between potassium and nitrate.
Answer
KNO₃ — K⁺ and NO₃⁻ form a 1:1 neutral ionic compound.
47. What is the correct name for MnO₂?
Answer
Manganese(IV) oxide — O is –2 × 2 = –4 → Mn = +4.
48. Write the formula for iron(III) carbonate.
Answer
Fe₂(CO₃)₃ — 2 Fe³⁺ balance 3 CO₃²⁻ for neutrality.
49. Predict the color of the precipitate formed when Cu²⁺ reacts with OH⁻.
Answer
Blue — Cu(OH)₂ forms a pale blue precipitate.
50. Write the chemical formula for aluminum dichromate.
Answer
Al₂(Cr₂O₇)₃ — 2 Al³⁺ balance 3 Cr₂O₇²⁻ ions.