Mole & Equation Quick Quiz

Chemistry Area 3 SHOULD DO 3 • rapid-fire review

Constants: Avogadro’s number = 6.022 x 10^23 | C = 12.01 g/mol | O = 16.00 g/mol | H = 1.008 g/mol | 1 mol gas = 22.7 L at STP
Type your answer (calculator allowed), then press Check. Use scientific notation like 1.20e24 for 1.20 x 1024. The worked solution appears only if you are wrong.
Quick quiz — solve, type, check
Q1
How many atoms are in 2.00 mol of carbon?
2.00 mol × 6.022 × 1023 atoms/mol = 1.20 × 1024 atoms.
Q2
What is the mass of 0.100 mol of water (H2O)? Give your answer in grams.
Molar mass H2O = 2(1.008) + 16.00 = 18.02 g/mol
0.100 mol × 18.02 g/mol = 1.80 g.
Q3
In 2H2 + O2 → 2H2O, how many moles of O2 react with 6.00 mol of H2?
6.00 mol H2 × (1 mol O2 ⁄ 2 mol H2) = 3.00 mol O2.
Q4
How many molecules are in 10.0 g of water?
10.0 g ⁄ 18.02 g/mol = 0.555 mol
0.555 mol × 6.022 × 1023 = 3.34 × 1023 molecules.
Q5
Count atoms on both sides to verify 2H2 + O2 → 2H2O conserves mass.
Left: 2H2 = 4 H, O2 = 2 O  |  Right: 2H2O = 4 H + 2 O
4 H = 4 H and 2 O = 2 O — mass is conserved.
Q6
What does the coefficient 3 in 3Na tell you? What does the subscript 2 in H2 tell you?
3 in 3Na = three Na atoms (or moles) participate in the reaction.
2 in H2 = each H2 molecule contains two H atoms (subscript counts atoms per molecule).
Q7
How many moles of helium occupy 45.4 L at STP?
45.4 L × (1 mol ⁄ 22.7 L) = 2.00 mol He.
Numbers with units are fine (e.g. 1.80 g) — the checker reads the number.