FRQs 4-6 – Short Answer Questions

Overview

• This guide covers the 4 short free-response questions on the AP Chemistry exam
• Each short FRQ is worth 4 points (16 points total out of 50 FRQ points)
• Budget about 7-9 minutes per question (35 minutes total out of 105 minutes)
• These questions make up 16% of your total exam score
• Same calculator, formula sheet, and periodic table available as other sections

Short FRQs are focused and direct - typically 3-4 parts that test one specific topic area deeply rather than integrating multiple concepts. Unlike long FRQs, each short question stands alone. You might see topics like photoelectron spectroscopy, molecular structure, laboratory calculations, or focused equilibrium problems. Think of these as sprints rather than marathons - get in, show specific knowledge, and move on.

Short FRQs are predictable. Once you recognize the question type, you know exactly what's coming. A photoelectron spectroscopy question will ask you to identify an element, explain peak positions, and predict spectra for related elements. A molecular structure question will have you draw Lewis structures, predict geometry, and explain properties. This predictability is your advantage.

Strategy Deep Dive

Short FRQs differ fundamentally from long ones. They're laser-focused on one topic - testing specific knowledge rather than integration. This focused nature becomes an advantage when you recognize the patterns.

Pattern Recognition is Everything

Pattern recognition is crucial. Within 30 seconds, identify the question type: "molecular geometry" or "PES question." Each type follows predictable patterns. Photoelectron spectroscopy questions analyze spectra, explain peak positions using Coulomb's law, then predict changes. Molecular structure questions require Lewis structures, geometry determination, then property explanations. Laboratory scenarios involve data processing, calculations, then error analysis.

This recognition transforms anxiety into confidence, directly improving performance.

Precision Over Elaboration

Short FRQs have less room for error - with only 4 points available, each part typically earns just 1 point. This means your answers must be precise and complete but not verbose. Where a long FRQ might ask you to "explain" with multiple points available for thorough reasoning, a short FRQ wants the key idea stated clearly and correctly.

The difference in practice: Long FRQs expect extended explanations about HF vs HCl boiling points. Short FRQs need concise answers: "HF has hydrogen bonding (F is small and highly electronegative), HCl has only dipole-dipole. H-bonding > dipole-dipole, so HF has higher BP." Direct, complete, efficient.

The Power of Systematic Approaches

Each question type has an optimal approach that works every time:

For photoelectron spectroscopy:

1. Count peaks to determine total electrons
2. Use peak positions to identify shells (1s, 2s, 2p, etc.)
3. Use relative heights for electron count in each subshell
4. Match to element on periodic table

For molecular structure:

1. Count valence electrons
2. Draw Lewis structure
3. Count electron domains around central atom
4. Determine geometry from VSEPR
5. Assess polarity from geometry and bond polarities

For laboratory calculations:

1. Identify what you're solving for
2. List given information with units
3. Select appropriate formula
4. Calculate with attention to significant figures
5. Check answer for reasonableness

Following these systematic approaches consistently improves scores from partial to full credit. Success comes from methodical execution, not just understanding.

Rubric Breakdown

Short FRQ rubrics are binary - no partial credit within parts. Each response either earns the point or doesn't. This strict scoring actually simplifies the approach: focus on being precisely correct.

Drawing/Representation Points (1 point per structure)

Whether it's Lewis structures, orbital diagrams, or particle representations, accuracy is everything:

• Correct number of valence electrons (even one extra or missing electron costs the point)
• Proper placement of atoms and bonds
• Accurate representation of lone pairs
• For resonance structures, all valid structures must be shown

Common error: Drawing NH₃ with 4 bonds on nitrogen for symmetry. Correct structure requires 3 bonds + 1 lone pair. Any deviation costs the entire point.

Calculation Points (1 point per calculation)

These require both correct method AND correct execution:

• Right formula selection
• Proper substitution of values
• Correct arithmetic
• Appropriate significant figures and units

Important distinction: calculation errors lose the entire point. Unlike long FRQs, there are no "method points." Double-checking calculations takes 30 seconds but preserves the point.

Explanation Points (1 point per explanation)

These demand precision in language and concept:

• Must address the specific question asked
• Must use correct scientific terminology
• Must make the logical connection explicit

Example of insufficient explanation: "Why does ice float?" Answer: "It's less dense." Points earned: 0. Required answer: "Ice's hydrogen bonds form an open hexagonal structure with more space between molecules than liquid water." Graders need the chemical explanation, not just the observation.

Comparison Points (1 point per comparison)

When asked to compare, you must address both things being compared:

• State the property for both substances/scenarios
• Identify which is greater/smaller/different
• Provide the chemical reasoning

Key for comparison questions: ALWAYS discuss both substances. "NaCl has ionic bonding" = incomplete = 0 points. "NaCl has ionic bonding (strong) while CH₄ has only London forces (weak), so NaCl has much higher melting point" = complete = 1 point.

Common Short FRQ Types

Understanding the standard question types lets you prepare targeted strategies for each.

Photoelectron Spectroscopy (PES)

These follow a predictable pattern:

• Part (a): Identify element from spectrum (match peaks to electron configuration)
• Part (b): Explain relative binding energies (use Coulomb's law and shielding)
• Part (c): Predict spectrum change for different element (add/remove peaks)
• Part (d): Sometimes asks about peak heights (related to number of electrons)

PES fundamentals: Electrons closer to nucleus have higher binding energy (harder to remove). More protons create stronger attraction and higher binding energy. Peak height indicates number of electrons in that energy level.

Molecular Structure and Properties

Standard progression:

• Part (a): Draw Lewis structure for given molecule
• Part (b): Identify molecular geometry and bond angles
• Part (c): Determine polarity or compare properties
• Part (d): Explain property differences using structure

Critical VSEPR distinction: molecular geometry ≠ electron geometry. NH₃ has 4 electron domains (tetrahedral electron geometry) but only 3 bonds (trigonal pyramidal molecular geometry). Confusing these costs the point.

Laboratory Data Analysis

Common scenarios:

• Determining concentration from absorbance data
• Calculating percent composition from mass data
• Finding rate constants from kinetics data
• Determining equilibrium constants from concentration data

Lab calculations require extreme precision. Using the wrong data row, forgetting unit conversions (mL to L), or using incorrect values (H₂O as 16 g/mol instead of 18) all result in zero points. Triple-check all values and conversions.

Focused Equilibrium Problems

Unlike the comprehensive equilibrium questions in long FRQs, these target specific aspects:

• Calculate K from concentrations
• Determine Q and predict shift direction
• Find one concentration given K and others
• Explain Le Chatelier shifts for specific stresses

Most common equilibrium error: including solids/liquids in K expressions. For CaCO₃(s) ⇌ CaO(s) + CO₂(g), K = [CO₂] only. Solids and pure liquids never appear in equilibrium expressions.

Time Management Reality

Seven minutes passes quickly during focused work. Maintain steady progress without perfectionism or second-guessing.

Spend the first minute reading all parts. Part (c) often contains hints about expected answers in part (a). If part (c) says "Using your answer from part (b)," those parts are linked and must be completed sequentially.

Allocate time proportionally. If the question has four parts worth 1 point each, spend roughly 2 minutes per part. Don't perfectionist your way through part (a) for 4 minutes, leaving only 3 minutes for the remaining parts. Equal points deserve equal time.

If you're stuck on a calculation, make a reasonable estimate and move on. Writing "approximately 0.50 M" with some work shown is better than leaving it blank while you struggle with arithmetic. You might get lucky with a generous grader, but more importantly, you preserve time for parts you can definitely complete.

Specific Tips by Question Type

PES Questions

PES binding energy ranges: 1s peaks appear around thousands of eV (far left), 2s around hundreds, 2p from tens to hundreds, 3s around tens. Within any shell, s electrons have higher binding energy than p electrons, so s peaks appear left of p peaks.

Lewis Structure Questions

Essential molecular geometry angles: Linear 180°, trigonal planar 120°, tetrahedral 109.5°, trigonal bipyramidal 90°/120°, octahedral 90°. Lone pairs compress bond angles slightly below these ideal values.

Laboratory Calculation Questions

Units serve as an error detection system. Include units with every number throughout calculations. If calculating molarity and units don't simplify to mol/L, an error exists. Circle final answers with proper significant figures for clear identification.

Buffer Questions

Buffer questions use Henderson-Hasselbalch equation: pH = pKa + log([A⁻]/[HA]). When concentrations are equal, pH = pKa. Adding strong acid converts A⁻ to HA; adding strong base converts HA to A⁻. These relationships determine buffer behavior.

Final Thoughts

Short FRQs reward focused practice. Unlike integrated long questions, these test pure execution of specific skills.

Short FRQs follow predictable patterns. PES spectrum appears → apply PES protocol. Lewis structure requested → follow Lewis protocol. The challenge lies in maintaining precision under time pressure.

Practice until responses become automatic. When a PES spectrum appears, immediately count peaks. For Lewis structures, automatically count valence electrons. This automaticity frees mental energy for the analytical components of questions.

With these insights, you're ready to tackle short FRQs strategically. Each pattern you've mastered, each protocol you've internalized, transforms potential stress into confident execution. Walk into that exam knowing these questions aren't obstacles—they're opportunities to show the precise chemical thinking you've developed. Trust the patterns, execute with precision, and watch those points accumulate.