How much gas will you get? — questions

1. state

Supplement. What volume does one mole of any gas take up at room temperature and pressure (r.t.p.)?

Circle one answer.

• 24 cm³
• 24 dm³
• 1 dm³
• 2 dm³ for hydrogen and 44 dm³ for carbon dioxide

Nudge (only if you are stuck): It is the same for every gas. Which unit?

2. calculate

Supplement. (a) What is the volume of 0.250 mol of oxygen at r.t.p., in dm³? (b) How many moles of hydrogen are in 120 cm³ of the gas at r.t.p.? Give your answers to 3 significant figures.

(a) Volume of oxygen: ______________ unit ________

(b) Amount of hydrogen: ______________ unit ________

Nudge (only if you are stuck): volume in dm³ = moles × 24. For a volume in cm³, use 24 000.

3. deduce

Supplement. Hydrogen burns: 2H₂ + O₂ → 2H₂O. 0.400 mol of hydrogen burns completely. (a) How many moles of oxygen does it need? (b) How many moles of water form? Give your answers to 3 significant figures.

(a) Oxygen needed: ______________ unit ________

(b) Water formed: ______________ unit ________

Nudge (only if you are stuck): Read the numbers in front of the formulae: H₂ : O₂ : H₂O = 2 : 1 : 2.

4. calculate

Supplement. 8.00 g of copper(II) oxide is reduced by hydrogen: CuO + H₂ → Cu + H₂O. What mass of copper forms? (Ar: O 16, Cu 64.) Give your answer to 3 significant figures.

Mass of copper: ______________ unit ________

Nudge (only if you are stuck): Three steps: moles of CuO, the ratio, then the mass of Cu.

5. calculate

Supplement. 2.00 g of calcium burns in oxygen: 2Ca + O₂ → 2CaO. What mass of calcium oxide forms? (Ar: O 16, Ca 40.) Give your answer to 3 significant figures.

Mass of calcium oxide: ______________ unit ________

Nudge (only if you are stuck): Ca : CaO is 2 : 2. What does that do to the moles?

6. calculate

Supplement. 0.325 g of zinc reacts with excess hydrochloric acid: Zn + 2HCl → ZnCl₂ + H₂. What volume of hydrogen forms, in cm³ at r.t.p.? (Ar: Zn 65.) Give your answer to 3 significant figures.

Volume of hydrogen: ______________ unit ________

Nudge (only if you are stuck): Moles of zinc, the ratio Zn : H₂, then × 24 000 for cm³.

7. calculate

Supplement. What mass of calcium carbonate must react with excess acid to give 1.20 dm³ of carbon dioxide at r.t.p.? CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. (Ar: C 12, O 16, Ca 40.) Give your answer to 3 significant figures.

Mass of calcium carbonate: ______________ unit ________

Nudge (only if you are stuck): Work backwards: start from the gas.

8. calculate

Supplement. What volume of 0.200 mol/dm³ hydrochloric acid reacts exactly with 0.500 g of calcium carbonate? CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Give your answer in cm³. (Ar: C 12, O 16, Ca 40.) Give your answer to 3 significant figures.

Volume of acid: ______________ unit ________

Nudge (only if you are stuck): Moles of CaCO₃, × 2 for HCl, then V = n ÷ c.

9. deduce

Supplement. Propane burns: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. 20 cm³ of propane burns completely. All volumes are measured at r.t.p. (a) What volume of oxygen does it need? (b) What volume of carbon dioxide forms?

(a) Volume of oxygen: ______________ unit ________

(b) Volume of carbon dioxide: ______________ unit ________

Nudge (only if you are stuck): Every substance you compare here is a gas, so the volumes come in the mole ratio.

10. calculate

Supplement. A car airbag fills with nitrogen in a fraction of a second. The gas comes from sodium azide: 2NaN₃ → 2Na + 3N₂. The bag needs 72.0 dm³ of nitrogen at r.t.p. What mass of sodium azide is needed? (Ar: N 14, Na 23.) Give your answer to 3 significant figures.

Mass of sodium azide: ______________ unit ________

Nudge (only if you are stuck): Start from the gas. The ratio NaN₃ : N₂ is 2 : 3.