What scoring guidelines are
After each exam, College Board posts the scoring guidelines评分标准 for every FRQ on AP Central. They go part by part, listing the points: each point is worth 1, states exactly what earns it, and often comes with a sample answer and an accepted range of values. Readers award points strictly by these conditions, not by an overall impression.
So understanding scoring guidelines means understanding what the reader is looking for.
Common kinds of points
- Calculation points: “correct setup and answer.” The reader needs to see how you got the result; a bare number may not earn the point.
- Explanation points: “the explanation refers to …” The answer has to contain the key idea (such as “hydrogen bonding,” “effective nuclear charge” or “Q < K”) and connect it to the conclusion. A conclusion alone earns nothing.
- Consistency: “consistent with the answer to (b).” If an earlier part is wrong but a later part uses that wrong result correctly, the later part can usually still earn its point; the same mistake isn’t penalized twice.
- Claim with justification: “correct claim with a valid justification.” A right claim with no reason, or with a wrong reason, usually doesn’t earn the point.
- Drawing points: the drawing must show each listed feature, such as “the pH at equivalence is above 7” (4.3.4).
Two general reminders:
- Don’t write contradictory statements. If one part contains both a right and a wrong statement, the reader won’t pick the right one for you, and the point is usually lost.
- Write each answer under its own part, labeled (a), (b), and so on. Readers look for answers part by part.
Scoring your own answers
- After working a released FRQ, go through the points one by one, asking only whether you met the stated condition, not whether you were “basically right.”
- For each lost point, write down why: missing content, an arithmetic slip, no work shown, an incomplete reason, or wrong units or sign.
- Tally the reasons and practice the most common one.
Be the reader: read the student’s answer, tick the points you think it earns, then check:
Question: 5.00 g of NH₄Cl (M = 53.49 g/mol) dissolves in 100.0 g of water, and the temperature falls from 22.0 °C to 18.6 °C. Take the specific heat of the solution as 4.18 J/(g·°C). Calculate ΔH of solution for NH₄Cl in kJ/mol.
n = 5.00 g ÷ 53.49 g/mol = 0.0935 mol
ΔH = 1.49 kJ ÷ 0.0935 mol = −15.9 kJ/mol
Question: Methanol, CH₃OH, boils at 65 °C, much higher than methanethiol, CH₃SH, at 6 °C. Explain this in terms of intermolecular forces.
Question: In part (b), a student found 0.0300 mol of H₂ (the correct answer is 0.0150 mol). Part (c): find the volume of this H₂ at 25 °C and 1.00 atm.
Example 1: one point, three answers
The scoring guidelines say: “1 point: explains that Mg has a higher first ionization energy than Na, citing Mg’s greater nuclear charge with valence electrons in the same shell.” Which of these answers earn the point?
- (a) “Mg has the higher ionization energy because it’s farther to the right in the periodic table.”
- (b) “Mg’s nucleus has one more proton, and both atoms’ valence electrons are in the n = 3 shell, so Mg’s valence electrons are attracted more strongly and are harder to remove.”
- (c) “Mg has the higher ionization energy because its atomic radius is larger than Na’s and its full 3s orbital is more stable.”
- Break the condition into parts. The point needs two things: ① greater nuclear charge (or effective nuclear charge); ② valence electrons in the same shell (similar distance). Only an answer with both, leading to “stronger attraction,” is complete.
- (a) earns nothing. “Farther right” is a location, not a reason; it mentions neither nuclear charge nor shells.
- (b) earns the point. One more proton means greater nuclear charge; both in n = 3 means similar distance; and it concludes stronger attraction, harder to remove. Both conditions are met.
- (c) earns nothing. “Mg’s atomic radius is larger than Na’s” is false (Mg is smaller). With a wrong statement in the answer, the point is lost even though the rest mentions stability, and “a full orbital is more stable” isn’t the reason the guidelines ask for anyway.
Example 2: credit for consistency
A question asks: (a) a titration uses 22.50 mL of 0.100 M NaOH; find the moles of NaOH. (b) The monoprotic acid titrated had a mass of 0.180 g; find its molar mass. A student writes:
- (a) n = 22.50 × 0.100 = 2.25 mol
- (b) M = 0.180 g ÷ 2.25 mol = 0.0800 g/mol
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The correct answer to (a). The volume must be in liters:
The student didn’t convert mL to L, so (a) earns nothing.
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Judge (b) by its method. The student used M = m/n with their own answer from (a), and the arithmetic is right:
When the guidelines say “consistent with (a),” part (b) usually earns its point.
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The correct (b).
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The lesson. Consistency saved only the point for (b). A molar mass of 0.0800 g/mol is obviously unreasonable and should have sent the student back to check the units in (a), which would have earned both points.
- Requirement: calculate the pH, with correct setup and answer. Answer: just “pH = 2.87.”
With no work shown, the calculation point may be lost.
- Requirement: compare Q with K and predict the direction. Answer: “Q = 0.25 < K = 1.6, so the reaction proceeds forward.”
It compares and predicts.
- Requirement: explain a boiling point using intermolecular forces. Answer: “HF has a high boiling point because the H–F bond is strong.”
That’s a chemical bond, not an intermolecular force (hydrogen bonding).
- Requirement: consistent with the answer to (a). Part (a) is wrong; (b) uses that result with the right method and arithmetic.
Consistency credit: the same mistake isn’t penalized twice.
- Requirement: identify the direction of electron flow in the wire, with a reason. Answer: “Electrons flow from Zn to Cu.”
A claim with no reason (such as Zn being oxidized at the anode).
- Requirement: write the net ionic equation. Answer: “Ag⁺(aq) + Cl⁻(aq) → AgCl(s)”
Spectator ions left out, states correct.
- Requirement: identify the limiting reactant. Answer: “The limiting reactant is O₂ … or it could be H₂.”
Two contradictory answers; the reader won’t choose for you.
- Requirement: calculate ΔH with correct sign and units. Answer: “ΔH = −57 kJ/mol” (correct value)
Value, sign and units all correct.
Common mistakes
Mistake 1: “The more I write, the more likely something earns credit.” Extra writing adds no points, and if it contradicts the right answer, the point is lost. Write what the condition asks for.
Mistake 2: “If an early part is wrong, everything after it is wrong too.” Guidelines often award points “consistent with” an earlier part: if a later part uses your earlier result with the right method, it usually still earns credit. So keep going even when you’re unsure of an earlier part.
Mistake 3: “A right answer is enough; work is optional.” Calculation points are for “setup and answer.” A bare number gives the reader no way to see where it came from, while written work can earn partial credit even if the final arithmetic slips.
Quick check
How much is one point in a scoring guideline usually worth?
Each point is worth 1 and is tied to one specific requirement.
Which answer is most likely to earn the point for “explain why H₂O boils at a higher temperature than H₂S”?
It covers both substances and links the forces to energy.
Part (a) is wrong, and part (b) uses that result with the right method. How is (b) usually scored?
Guidelines often say “consistent with (a),” so the same mistake isn’t penalized twice.
A student writes, “This reaction is endothermic … actually it’s exothermic.” How is that point usually handled?
When an answer contains contradictory statements, the reader won’t choose for you.
Where can you find scoring guidelines for past AP Chemistry FRQs?
College Board posts each year’s FRQs, scoring guidelines and sample-response commentary.
A calculation point requires “correct setup and answer,” and a response gives only the correct final number. What can happen?
The reader needs to see how the calculation was done.
AP-style practice
Here is a short question, its scoring points and a student’s answer.
Question: (a) Calculate the pH of 0.10 M CH₃COOH (Ka = 1.8 × 10⁻⁵). (b) Is 0.10 M CH₃COONa acidic, neutral or basic? Justify your answer.
Scoring: (a) 1 point for correct setup and pH; (b) 1 point for “basic” with a justification that CH₃COO⁻ reacts with water to produce OH⁻ (or that CH₃COO⁻ is the conjugate base of a weak acid).
Student answer: (a) “pH = 2.87”; (b) “Basic, because CH₃COO⁻ + H₂O ⇌ CH₃COOH + OH⁻ produces OH⁻.”
(a) Score this answer using the scoring points, and explain.
(b) Rewrite the student’s (a) so that it earns the point.
(c) Would (b) earn the point if it said only “basic”? Why or why not?
(d) Would (b) earn the point if it said “basic, because CH₃COONa releases OH⁻ in water”? Why or why not?
(e) State two answering habits this question teaches.
Model answer and scoring
(a) 1 point in total. Part (a) earns nothing: only the answer is given, with no work. Part (b) earns its point: the claim is right and the reason shows CH₃COO⁻ reacting with water to produce OH⁻.
(b) HA ⇌ H⁺ + A⁻; let x ionize: Ka = x² ÷ (0.10 − x) ≈ x² ÷ 0.10 = 1.8 × 10⁻⁵, so x = √(1.8 × 10⁻⁶) = 1.3 × 10⁻³ M; check 1.3 × 10⁻³ ÷ 0.10 ≈ 1.3% < 5%; pH = −log(1.3 × 10⁻³) = 2.87.
(c) No. The point requires a claim with a justification, and there’s only the claim.
(d) No. The reason is wrong: CH₃COONa releases Na⁺ and CH₃COO⁻, not OH⁻ directly; the OH⁻ comes from CH₃COO⁻ reacting with water.
(e) For example: on calculations, write the equation, the substitution and the result; on claims, always give a reason that is correct and supports the claim; never write contradictory statements. (Any two sensible habits.)
Scoring: (a) 1 point, with what happened in each part; (b) a pH calculation with work; (c) the missing reason; (d) the wrong reason; (e) two sensible habits.
Summary
- One point, one requirement: calculation points need setup and answer, explanation points need the key idea and its link to the conclusion, claims need reasons, drawings need the listed features.
- Consistency credit: a later part with the right method can still earn credit after an earlier mistake, so attempt every part.
- Don’t write contradictory statements; write each answer under its labeled part.
AP tip: Before the exam, work at least two or three released FRQs in full, score them point by point with the official guidelines, and keep a list of why you lost each point. Most lost points turn out to come from the same few habits.
Sources: the structure of scoring guidelines follows the AP Chemistry scoring guidelines College Board posts on AP Central; the questions and student answers in this lesson were written by this site.