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Chemistry Quiz

14 Questions 9 min
This general chemistry quiz checks equation balancing, stoichiometry, and quantitative reasoning with moles, molarity, gas laws, and pH. Expect unit conversions, significant figures, and periodic trends like a lab report or Gen Chem exam. It suits chemistry students, lab technicians, and pre-health or engineering learners who rely on accurate calculations.
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1In the formula Ca3(PO4)2, how many oxygen atoms are in one formula unit?
2You stir table sugar into water until it “disappears.” Which best describes what happened?
3Balancing a chemical equation is done by changing coefficients only, not by changing subscripts in formulas.

True / False

4A beaker label says 250 mL. What is this volume in liters?
5What is the molar mass of CO2 (to two decimal places)?
6The atomic number of an element equals the number of protons in its nucleus.

True / False

7How many moles of H2O are in 18.0 g of water?
8Chlorine-35 has an atomic number of 17. How many neutrons does one atom of chlorine-35 have?
9You record a mass and a volume and multiply: 2.50 × 3.1 = 7.75. With correct significant figures, what should you report?
10You dissolve 5.00 g of NaCl (58.44 g/mol) and dilute to a final volume of 250.0 mL. What is the molarity?
11For propane combustion, C3H8 + O2 → CO2 + H2O. What coefficient is needed in front of O2 to balance the equation?
12The average atomic mass listed on the periodic table is usually exactly equal to the mass number of the most abundant isotope.

True / False

13For N2 + 3 H2 → 2 NH3, you have 1.00 mol N2 and 2.00 mol H2. Which reactant limits the amount of NH3 you can make?
14A sample has a mass of 13.50 g and displaces 10.0 mL of liquid. What is its density?
15How many mL of 6.00 M HCl are needed to prepare 250.0 mL of 1.50 M HCl?
16At 25 °C, pH + pOH = 14.00 for aqueous solutions.

True / False

17Which element has the higher first ionization energy? (This one surprises many people.)
18A solution has [H+] = 3.2 × 10^-5 M. What is the pH (to two decimal places)?
19Sodium reacts with chlorine gas: 2 Na + Cl2 → 2 NaCl. If you start with 10.0 g Na and 10.0 g Cl2, what mass of NaCl can form? (Na = 22.99 g/mol, Cl2 = 70.90 g/mol, NaCl = 58.44 g/mol)
20You mix 50.0 mL of 0.200 M AgNO3 with 25.0 mL of 0.300 M NaCl to precipitate AgCl: Ag+ + Cl- → AgCl(s). What mass of AgCl forms? (M(AgCl) = 143.32 g/mol)
21Baking soda decomposes when heated: 2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g). If 5.00 g of NaHCO3 decomposes completely, what volume of CO2 is produced at 1.00 atm and 298 K? (M(NaHCO3) = 84.01 g/mol, R = 0.08206 L·atm·mol⁻¹·K⁻¹)

General Chemistry Quiz Pitfalls: Units, Coefficients, and Log Scales

Most missed chemistry questions are not “concept gaps.” They are setup errors that snowball into the wrong choice.

1) Treating units as labels instead of algebra

Molarity uses liters, density might use g/mL, and gas laws require Kelvin. Convert first, then calculate. Keep units on every line and cancel them to catch mistakes early.

2) Balancing equations by changing subscripts

Changing a subscript changes the compound. Balance with coefficients only. After balancing, recount each element and check charge if you wrote a net ionic equation.

3) Skipping the mole ratio step in stoichiometry

A common trap is grams → moles → grams without using the balanced equation. Always include the coefficient ratio step (for example, mol CO2 per mol C3H8).

4) Forgetting the limiting reactant check

If two reactants are given, compute “possible moles of product” from each reactant. The smaller product amount identifies the limiter and drives theoretical yield.

5) Using the wrong molar mass or ignoring polyatomic grouping

Recalculate molar mass carefully, especially with parentheses (Ca(OH)2, (NH4)2SO4). One missing factor of 2 changes everything downstream.

6) Treating pH as linear

pH is logarithmic. A 1.00 unit drop in pH means a 10× increase in [H+]. Work from pH = −log[H+] and keep powers of ten explicit.

7) Rounding mid-problem

Early rounding can flip answer choices. Carry guard digits through intermediate steps, then round once at the end using significant figures from the given data.

Printable General Chemistry Quick Sheet: Formulas, Units, and Decision Steps

Tip: Print or save as PDF and keep it next to your scratch work for multi-step calculations.

Core constants and conversions

  • Avogadro’s number: 6.022 × 1023 particles/mol
  • Kelvin: T(K) = T(°C) + 273.15
  • Volume: 1.00 L = 1000 mL
  • Pressure (common): 1 atm = 760 mmHg = 101.325 kPa

Moles and mass

  • Moles from mass: n = m / M (g ÷ g/mol)
  • Molecules or atoms: particles = n × NA
  • Mass percent: % by mass = (mass part ÷ mass whole) × 100

Stoichiometry workflow (use this order)

  1. Write correct formulas for reactants and products.
  2. Balance with coefficients only.
  3. Convert all givens to moles.
  4. Use coefficient ratios to reach moles of the target.
  5. Convert to the requested units (g, L, particles, M).
  6. If multiple reactants are given, identify the limiting reactant before reporting yield.

Solutions and dilution

  • Molarity: M = n / V, with V in liters
  • Moles from molarity: n = M × V
  • Dilution (same solute moles): M1V1 = M2V2

Gas-law essentials

  • Ideal gas law: PV = nRT
  • R: 0.08206 L·atm·mol−1·K−1 (use units consistent with P and V)
  • Common error check: if T is in °C, the volume will come out wrong.

Acids, bases, and pH

  • pH: pH = −log[H+]
  • From pH to concentration: [H+] = 10−pH
  • A 2.00 pH-unit change equals a 100× change in [H+].

Significant figures checkpoint

  • Keep extra digits in intermediate steps, round once at the end.
  • Addition and subtraction use decimal place rules. Multiplication and division use sig-fig count rules.

Worked General Chemistry Example: Stoichiometry to Gas Volume With Correct Units

Problem: Calcium carbonate decomposes on heating: CaCO3(s) → CaO(s) + CO2(g). If 5.00 g of CaCO3 decomposes completely, what volume of CO2 is produced at 1.00 atm and 25.0°C?

Step 1: Confirm the balanced equation

The equation is already balanced: 1 mol CaCO3 produces 1 mol CO2.

Step 2: Convert grams CaCO3 to moles CaCO3

Molar mass CaCO3 = 40.08 + 12.01 + 3(16.00) = 100.09 g/mol.

n(CaCO3) = 5.00 g ÷ 100.09 g/mol = 0.04995 mol.

Step 3: Use the mole ratio to get moles CO2

From coefficients, 1 mol CaCO3 : 1 mol CO2, so n(CO2) = 0.04995 mol.

Step 4: Apply the ideal gas law with consistent units

Convert temperature: T = 25.0 + 273.15 = 298.15 K.

Use R = 0.08206 L·atm·mol−1·K−1.

V = nRT/P = (0.04995 mol)(0.08206 L·atm·mol−1·K−1)(298.15 K) ÷ (1.00 atm)

V = 1.22 L CO2 (3 significant figures).

Quick self-checks

  • If you forgot Kelvin, you would get a noticeably smaller volume.
  • Units cancel to liters because atm and mol and K cancel against R.
  • The 1:1 stoichiometry means moles CO2 must equal moles CaCO3 consumed.

Chemistry Quiz FAQ: Stoichiometry Choices, Unit Traps, and Concept Checks

How can I tell if an equation is balanced correctly?

Count atoms of each element on both sides using the coefficients. Do not “count subscripts” as adjustable values. After balancing, verify that every element has the same atom count on reactant and product sides, and check that you did not change any chemical formulas.

Which gas constant R should I use in PV = nRT?

Pick R to match your pressure and volume units. If P is in atm and V is in liters, use 0.08206 L·atm·mol−1·K−1. If your problem gives kPa, either convert kPa to atm or use an R value written with kPa. Always convert temperature to Kelvin.

What is the fastest way to identify the limiting reactant?

Convert each reactant to moles. Then compute the moles of the same product that each reactant could form using the balanced-equation mole ratio. The reactant that produces the smaller amount of product is limiting. Only after that step should you calculate theoretical yield or leftover excess reactant.

How do I avoid mistakes in molarity and dilution problems?

Write M = n/V and underline that V must be in liters. For dilution, use M1V1 = M2V2 and keep volumes in the same units on both sides. A common check is to confirm that dilution lowers concentration and increases volume.

What does a 1-unit change in pH actually mean?

It means a 10× change in hydrogen ion concentration. For example, pH 3 has [H+] = 10−3 M, while pH 5 has [H+] = 10−5 M. The pH 3 solution is 100× more acidic by [H+] than pH 5.

I keep losing points on unit conversions. What should I practice?

Practice writing conversion factors as fractions that equal 1, then cancel units line by line (mL with mL, kPa with kPa). This is the same habit used in environmental concentration and flow problems, so the Environmental Science Knowledge Practice Quiz can be a useful parallel drill for unit discipline.

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