The questions are on the net ionic equation test. Take it under real conditions before reading the mark scheme.
Quick answer: A net ionic equation shows only the species that change, leaving out spectator ions. This mark scheme gives the model answers and the marks for the 8 questions of the AP Chemistry test on net ionic equation, from oxidation numbers to spectator ions, with the equivalent answers to accept.
This is the net ionic equation test answers for AP Chemistry, with the marks for each answer. First sit the test without notes, then mark it here and revise with the lesson.
Marking points follow each answer. Give method marks for correct working even if the final value has a rounding slip, and accept equivalent wording in explanations. Equations need correct species, states and balance to earn full marks.
Level: AP Chemistry · Curriculum: AP Chem Unit 4
Net ionic equation test answers: answers and marks
Question 1 Oxidation numbers (2 marks)
K is +1 and O is −2: Mn = +7. H is +1 and O is −2: 2(+1) + x + 3(−2) = 0, so S = +4. Answers: +7 and +4.
Marking: 1 each.
Question 2 Net ionic equation (3 marks)
2Ag⁺(aq) + CO₃²⁻(aq) → Ag₂CO₃(s)
Marking: 1 species, 1 states, 1 balanced atoms and charge.
Question 3 Predict precipitates (2 marks)
(a) Yes, PbCl₂. (b) No: all combinations are soluble.
Marking: 1 each.
Question 4 Titration calculation (3 marks)
n(HCl) = 0.01560 × 0.1200 = 1.872 × 10⁻³ mol = n(KOH); c = 1.872 × 10⁻³ / 0.02000 = 0.0936 mol/L.
Marking: 1 moles, 1 ratio, 1 answer.
Question 5 Limiting reagent (3 marks)
n(Ba²⁺) = 5.00 × 10⁻³ mol; n(SO₄²⁻) = 3.00 × 10⁻³ mol. Na₂SO₄ is limiting.
m = 3.00 × 10⁻³ × 233.39 = 0.700 g.
Marking: 1 amounts, 1 limiting reagent, 1 mass.
Question 6 Redox agents (2 marks)
Cu²⁺ is the oxidising agent (reduced); Al is the reducing agent (oxidised).
Marking: 1 each.
Question 7 Titration curve (3 marks)
a. About 25 mL and pH 7.
b. n(NaOH) = 0.0250 × 0.100 = 2.50 × 10⁻³ mol = n(HCl); c = 2.50 × 10⁻³ / 0.0250 = 0.100 mol/L.
Marking: 1 + 2.
Question 8 Spectator ions (2 marks)
A spectator ion is present on both sides of the equation and takes no part in the reaction. Here Na⁺ and Cl⁻ are spectators; the net change is H⁺ + OH⁻ → H₂O.
Marking: 1 definition, 1 ions.
