Stoichiometry Quiz
Questions: 16 · 10 minutes
1. In the balanced equation 2CO + O₂ → 2CO₂, what does the coefficient 2 before CO represent?
The molar mass of CO must be multiplied by two before any calculation.
Two grams of CO react for every one gram of O₂.
Each CO molecule contains two carbon atoms.
Two moles of CO react for every one mole of O₂.
2. Which set of coefficients correctly balances C₃H₈ + O₂ → CO₂ + H₂O?
1, 4, 3, 4
1, 5, 3, 4
2, 5, 6, 4
1, 3, 3, 2
3. Using 2H₂ + O₂ → 2H₂O, a student claims that 2 g of H₂ must produce 2 g of H₂O because both coefficients are 2. What is the main error?
The student forgot that water is liquid under many laboratory conditions.
The student should use atomic oxygen rather than O₂ in the equation.
The student treated equation coefficients as gram ratios rather than mole ratios.
The student should compare gas volumes instead of masses in every reaction.
4. A compound is 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. Which empirical formula fits these data? Use C = 12, H = 1, and O = 16.
C₂H₂O₂, representing a 2:2:2 atom ratio
CH₂O, representing a 1:2:1 atom ratio
CHO₂, representing a 1:1:2 atom ratio
C₂H₄O, representing a 2:4:1 atom ratio
5. Hydrogen burns according to 2H₂ + O₂ → 2H₂O. Approximately what mass of water forms from 4.0 g of H₂ with excess O₂? Use H₂ = 2.0 g/mol and H₂O = 18.0 g/mol.
36.0 g
9.0 g
18.0 g
4.0 g
6. A 10.0 g limestone sample is 80% CaCO₃ by mass. How much CaCO₃ does it contain?
2.0 g
8.0 g
10.0 g
12.5 g
7. For N₂ + 3H₂ → 2NH₃, how many moles of NH₃ can form from 6.0 moles of H₂ when N₂ is in excess?
2.0 mol
3.0 mol
12.0 mol
4.0 mol
8. At the same temperature and pressure, N₂ + 3H₂ → 2NH₃. If 9.0 L of H₂ reacts completely with excess N₂, what volume of NH₃ forms?
3.0 L
4.5 L
9.0 L
6.0 L
9. A reaction has a theoretical yield of 10.0 g and an actual yield of 8.0 g. What is the percent yield?
20%
80%
125%
18%
10. A compound has the empirical formula CH₂O, with an empirical-formula mass of 30 g/mol. If its molar mass is 180 g/mol, what is its molecular formula?
CH₂O, containing one empirical-formula unit
C₃H₆O₃, containing three empirical-formula units
C₆H₁₂O₆, containing six empirical-formula units
C₁₂H₂₄O₁₂, containing twelve empirical-formula units
11. For 2H₂ + O₂ → 2H₂O, a container starts with 3.0 mol H₂ and 2.0 mol O₂. Which reactant is limiting?
H₂
O₂
H₂O
Neither reactant; both are consumed completely
12. Calcium carbonate decomposes according to CaCO₃ → CaO + CO₂. Approximately how much CO₂ forms from 25 g CaCO₃? Use CaCO₃ = 100 g/mol and CO₂ = 44 g/mol.
5.5 g
25 g
11 g
44 g
13. Approximately how many CO₂ molecules are present in 0.50 mol CO₂? Use Avogadro’s constant as 6.02 × 10²³ mol⁻¹.
8.30 × 10⁻²⁵ molecules
6.02 × 10²³ molecules
3.01 × 10²³ molecules
1.20 × 10²⁴ molecules
14. Carbon reacts completely with oxygen according to C + O₂ → CO₂. If 12 g C combines with 32 g O₂, what mass of CO₂ forms?
20 g
384 g
32 g
44 g
15. For 2H₂ + O₂ → 2H₂O, 5.0 mol H₂ reacts with 2.0 mol O₂. How much H₂ remains after the reaction is complete?
1.0 mol
0 mol
2.0 mol
3.0 mol
16. A solution contains 0.75 mol NaCl in a total volume of 1.50 L. What is its molarity?
0.50 M
0.75 M
1.13 M
0.25 M