Physical Science: Chemistry — Sample exam worked answers

A rehearsal paper with separate worked solutions; use it before the final.

24 questions · 48 points · suggested 90 minutes

Student instructions

Suggested time: 90 minutes; allow breaks or accommodations and record them.
Work independently with a calculator, blank paper and the reference relationships printed in this paper. Grades 9, 11 and 12 may also use the course-linked NYSED reference tables. Use no lesson notes or answer key during an assessed attempt.
Show reasoning and units for written tasks. All supplied datasets are illustrative; do not present them as measurements you collected.
Objective items: 1 point each. Written items: 3 points each, one per criterion. A parent or teacher marks the written work; the app never grades an explanation automatically.
Sample exam: try the whole paper before opening the worked key, then revisit the linked chapters. The sample and final are different papers; this is a course assessment, not an official Regents examination.

Reference relationships

Relationship, constant or reference	Use / conditions
Density	ρ=m/V; Mass and volume in consistent units
Amount	n=m/Mm; N=nNA; Mm is molar mass, not molarity
Concentration	M=n/V; M₁V₁=M₂V₂; Solution liters; dilution without reaction or loss
Ideal gas	PV=nRT; Kelvin and absolute pressure; R matched to units
Heating	q=mcΔT; qphase=mL; One phase versus phase change
Reaction heat	qreaction≈−qsurroundings; Include apparatus/loss terms when needed
Free energy	ΔG=ΔH−TΔS; Kelvin and matching energy units; not reaction rate
Equilibrium	Q, K=products/reactants with powers; Omit pure phases in the school approximation
Acidity	pH≈−log[H₃O⁺]; Concentration approximation; neutral near 7 at 25°C
Buffer	pH≈pKa+log([A⁻]/[HA]); Both conjugate species appreciable
Cell potential	E°cell=E°cathode−E°anode; Both table values are reduction potentials
Radioactive parent	N=N₀(½)^(t/thalf); Closed parent accounting; statistical model
NA=6.022×10²³ mol⁻¹	Avogadro constant, rounded for school calculations
h=6.626×10⁻³⁴ J·s	Planck constant, rounded
c=3.00×10⁸ m/s	Vacuum light speed, rounded
e=1.602×10⁻¹⁹ C	Elementary charge magnitude; 1 eV=1.602×10⁻¹⁹ J
g=9.8 m/s²	Typical near-surface Earth approximation; use a supplied local value if given
R=8.314 J/(mol·K)	Use SI pressure Pa and volume m³
R=0.0821 L·atm/(mol·K)	Use atmosphere pressure and liter volume
F≈96485 C/mol electrons	Faraday constant
1 u·c²≈931.5 MeV	Mass-energy conversion for consistent nuclear mass accounting
T(K)=T(°C)+273.15	Use 273 only when a question specifies that rounded convention
1 L=1000 mL; 1 mL=1 cm³	Volume conversions
1 kWh=3.60×10⁶ J	Energy conversion
cwater≈4.18 J/(g·°C)	Approximate liquid-water specific heat in ordinary conditions
Lf,water≈334 J/g; Lv,water≈2260 J/g	Water fusion and vaporization near ordinary-pressure transition conditions
H	1.008 g/mol
C	12.01 g/mol
N	14.01 g/mol
O	16.00 g/mol
Na	22.99 g/mol
Mg	24.31 g/mol
Al	26.98 g/mol
P	30.97 g/mol
S	32.06 g/mol
Cl	35.45 g/mol
K	39.10 g/mol
Ca	40.08 g/mol
Fe	55.85 g/mol
Cu	63.55 g/mol
Zn	65.38 g/mol
Ag	107.87 g/mol
NH₄⁺ / OH⁻ / NO₃⁻	Ammonium +1; hydroxide −1; nitrate −1
CO₃²⁻ / SO₄²⁻ / PO₄³⁻	Carbonate −2; sulfate −2; phosphate −3

Coverage and marks

Chapter	Questions	Points
Investigating Matter	1, 2	4
Atoms, Electrons & Periodicity	3, 4	4
Bonding, Formulas & Molecular Structure	5, 6	4
Reactions, Moles & Composition	7, 8	4
Stoichiometry & Yield	9, 10	4
States of Matter & Gases	11, 12	4
Solutions & Dissolved Particles	13, 14	4
Acids, Bases & Titration	15, 16	4
Chemical Energy & Thermodynamics	17, 18	4
Rates & Equilibrium	19, 20	4
Redox, Cells & Nuclear Chemistry	21, 22	4
Organic Chemistry & Material Design	23, 24	4

Parent / teacher marking guide

Mark objective answers after submission. Written marks remain pending until a parent or teacher applies the three-point criteria.
Accept scientifically equivalent wording and valid alternative methods. Award stated method credit for a correct model or substitution even if later arithmetic fails.
A raw percentage describes this paper only; it is not a validated course grade or a certification. Review chapter-level evidence and the learner’s independent explanations.
Record support and accommodations, save corrections and reassess with different tasks. Do not count copied solutions as independent mastery.

Question 1 · 1 point

A 18.0 g sample occupies 6.00 mL. Find density.

Worked answer

3 g/mL

18.0/6.00=3.00.

1 point for the correct objective answer; no written-method marks for this item.

Question 2 · 3 points

Recover dry sand and salt from their mixture.

Worked answer

Separate by solubility, filtration, and evaporation.

Add water to dissolve salt.

Filter and dry sand.

Allow the filtrate to evaporate safely in a shallow dish.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: Add water to dissolve salt.
1 point: reach a scientifically supported conclusion: Separate by solubility, filtration, and evaporation.

Question 3 · 1 point

Which particle has a mass roughly 1/1836 that of a proton?

nucleus
alpha particle
neutron
electron

Worked answer

electron

Electrons are almost weightless compared with protons and neutrons, so they contribute almost nothing to atomic mass.

1 point for the correct objective answer; no written-method marks for this item.

Question 4 · 3 points

A supplied level diagram has states at 0, 2, and 5 energy units. List downward differences.

Worked answer

Possible differences: 2, 3, and 5 units.

5→2 releases 3 units.

5→0 releases 5; 2→0 releases 2.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: 5→2 releases 3 units.
1 point: reach a scientifically supported conclusion: Possible differences: 2, 3, and 5 units.

Question 5 · 1 point

When a chlorine atom gains one electron, the ion it forms is called…

a molecule
a cation
an anion
a proton

Worked answer

an anion

Gaining an electron gives the atom a negative charge, making it an anion (Cl⁻).

1 point for the correct objective answer; no written-method marks for this item.

Question 6 · 3 points

Count valence electrons in CO₃²⁻.

Worked answer

24 valence electrons.

C contributes 4 and three O contribute 18.

Add 2 for the negative charge.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: C contributes 4 and three O contribute 18.
1 point: reach a scientifically supported conclusion: 24 valence electrons.

Question 7 · 1 point

Which equation represents a combustion reaction?

CaCO₃ → CaO + CO₂
CH₄ + 2O₂ → CO₂ + 2H₂O
AgNO₃ + NaCl → AgCl + NaNO₃
2Na + Cl₂ → 2NaCl

Worked answer

CH₄ + 2O₂ → CO₂ + 2H₂O

A fuel (methane) reacting with oxygen to give carbon dioxide and water is complete combustion.

1 point for the correct objective answer; no written-method marks for this item.

Question 8 · 3 points

Would mixing aqueous NaNO₃ and KCl create a precipitate in the usual dilute model?

Worked answer

No net precipitation reaction.

Both possible products KNO₃ and NaCl are soluble.

All ions remain dissolved.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: Both possible products KNO₃ and NaCl are soluble.
1 point: reach a scientifically supported conclusion: No net precipitation reaction.

Question 9 · 1 point

For 2H₂ + O₂ → 2H₂O, how many moles of water form from 4.0 mol of hydrogen reacting with excess oxygen?

Worked answer

4 mol

The mole ratio of H₂O to H₂ is 2 : 2 = 1 : 1, so 4.0 mol H₂ → 4.0 mol H₂O.

1 point for the correct objective answer; no written-method marks for this item.

Question 10 · 3 points

Mix .010 mol HCl and .006 mol NaOH. Find acid excess.

Worked answer

0.004 mol HCl equivalent remains.

Ratio is 1:1.

NaOH limits and consumes .006 mol acid.

Subtract .010−.006.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: Ratio is 1:1.
1 point: reach a scientifically supported conclusion: 0.004 mol HCl equivalent remains.

Question 11 · 1 point

In the ideal-gas particle model, which state has particles far apart with intermolecular forces treated as negligible?

solid
liquid
gas
they are identical in all states

Worked answer

gas

In a gas, kinetic energy dominates: particles spread far apart and move quickly with almost no attraction between them.

1 point for the correct objective answer; no written-method marks for this item.

Question 12 · 3 points

Why does boiling water not keep warming under fixed pressure?

Worked answer

Phase-change energy increases internal energy without a comparable temperature rise.

Energy is still being transferred.

It largely separates molecules into gas during phase coexistence.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: Energy is still being transferred.
1 point: reach a scientifically supported conclusion: Phase-change energy increases internal energy without a comparable temperature rise.

Question 13 · 1 point

A solution that contains the maximum amount of dissolved solute at a given temperature is described as…

nonpolar
unsaturated
saturated
dilute

Worked answer

saturated

A saturated solution holds all the solute it can at that temperature.

1 point for the correct objective answer; no written-method marks for this item.

Question 14 · 3 points

Compare equal molality NaCl and sugar ideally.

Worked answer

NaCl gives roughly twice the depression in the ideal dilute model.

Sugar gives one particle per molecule.

NaCl gives about two ions per formula unit.

Use ΔTf proportional to i.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: Sugar gives one particle per molecule.
1 point: reach a scientifically supported conclusion: NaCl gives roughly twice the depression in the ideal dilute model.

Question 15 · 1 point

In the Brønsted-Lowry model, a base is defined as a…

proton donor
proton acceptor
electron donor
hydroxide crystal

Worked answer

proton acceptor

A Brønsted-Lowry base accepts a proton (H⁺).

1 point for the correct objective answer; no written-method marks for this item.

Question 16 · 3 points

Buffer pKa=4.76 and [A⁻]/[HA]=10. Estimate pH.

Worked answer

5.76

Use pH=pKa+log ratio.

log 10(10)=1.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: Use pH=pKa+log ratio.
1 point: reach a scientifically supported conclusion: 5.76

Question 17 · 1 point

How much heat (in J) is absorbed when 50.0 g of water is warmed from 15.0°C to 35.0°C? (c = 4.18 J/g°C)

Worked answer

4180 J

ΔT = 35.0 − 15.0 = 20.0°C, so q = mcΔT = 50 × 4.18 × 20 = 4180 J.

1 point for the correct objective answer; no written-method marks for this item.

Question 18 · 3 points

ΔH=40kJ/mol and ΔS=.080kJ/mol·K. Find crossover.

Worked answer

500 K, with the constant-value assumption.

At ΔG=0, T=ΔH/ΔS.

40/.080.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: At ΔG=0, T=ΔH/ΔS.
1 point: reach a scientifically supported conclusion: 500 K, with the constant-value assumption.

Question 19 · 1 point

According to collision theory, an effective collision requires…

enough energy and the correct orientation
that a catalyst be present
that the reaction be exothermic
only that the particles touch

Worked answer

enough energy and the correct orientation

A collision only produces a reaction if the particles collide with at least the activation energy and are properly oriented.

1 point for the correct objective answer; no written-method marks for this item.

Question 20 · 3 points

For K=4, current Q=.5, predict direction.

Worked answer

Net forward adjustment.

Compare .5 with 4.

Products are low relative to equilibrium ratio.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: Compare .5 with 4.
1 point: reach a scientifically supported conclusion: Net forward adjustment.

Question 21 · 1 point

Find carbon oxidation number in CO₂ using O=−2.

Worked answer

x−4=0, x=+4.

1 point for the correct objective answer; no written-method marks for this item.

Question 22 · 3 points

Write the daughter counts for alpha decay of 238U with Z=92.

Worked answer

234Th plus an alpha particle.

Mass number 238−4=234.

Atomic number 92−2=90.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: Mass number 238−4=234.
1 point: reach a scientifically supported conclusion: 234Th plus an alpha particle.

Question 23 · 1 point

Find hydrogen count for a simple acyclic alkane with seven carbon atoms.

Worked answer

16 H atoms

2×7+2=16.

1 point for the correct objective answer; no written-method marks for this item.

Question 24 · 3 points

Reusable cup production impact is 500 units; disposable impact 10/use, reusable washing 2/use. Find break-even.

Worked answer

At 63 uses the modeled reusable impact is lower.

500+2n=10n.

500=8n; n=62.5.

Use whole completed uses.

Marking criteria

1 point: identify the appropriate model or mechanism for this task.
1 point: show the calculation or evidence in the worked steps: 500+2n=10n.
1 point: reach a scientifically supported conclusion: At 63 uses the modeled reusable impact is lower.

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