EXAM STYLE QUESTIONS – GAS CALCULATIONS

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1. 10 cm³ of nitrogen reacted with 20 cm³ hydrogen to form ammonia. Calculate the total volume of gases at the end of the reaction.

N_2(g)  +  3H_2(g)  ⇾   2NH_3(g)

2. Calculate the volume of gases produced (at room temperature and pressure) when 0.0050 mol of calcium nitrate decomposes.

Ca(NO₃)_2(s)  ⇾  CaO_(s)  +  2NO_2(g)  +  ½O_2(g)

3. Three alkanes were combusted in excess oxygen at constant pressure. Which produced the largest volume of carbon dioxide?

A.  0.4 mol of ethane B.  0.3 mol of propane C.  0.1 mol of pentane

4. Calculate the mass of sodium that reacts with water to produce 960 cm³ hydrogen gas at RTP.

2Na_(s) + 2H₂O_(l) ⇾ 2NaOH_(aq) + H_2(g)

5. How many oxygen atoms are there in 44.0g of carbon dioxide?

6. (a)  Calculate the minimum volume of oxygen needed (in cm³ at RTP) needed to completely combust 0.55g of ethanal.

CH₃CHO_(l)  +  2½O_2(g)   ⇾   2CO_2(g)   +  2H₂O_(g)

      (b)   What percentage of the products (by mass) remain gases once they have been             cooled to room temperature?

7. Calculate the volume of carbon dioxide produced (at RTP) when 0.618g of copper carbonate decomposes.

CuCO_3(s)   ⇾   CuO_(s)   +   CO_2(g)

8. What is the effect on volume when the pressure of an ideal gas is doubled at the same time as its temperature in Kelvin in doubled?

9. What is the new volume of a gas (original volume = V) whose temperature is raised from 0°C to 20°C whilst the pressure remains constant?

A.  0.005V B.  0.93V C.  1.07V D.  20V

10. What volume of gas is produced (at RTP) when 1.00g of solid carbon dioxide is vaporised?

11.   A sample of  gas has a mass of x g occupies a volume of V m3 at a pressure of p Pa and a temperature of T K.  Which expression is correct for the M_r of the gas?

A.  xRT / pV B.  pV / xRT C.  xRT / npV

12. A gas syringe contains 2.0 kg of ethane. How many ethane molecules are there in the syringe?

13. A steel cylinder contains 187g of the gas dinitrogen oxide, N₂O. Given that the cylinder has a volume of 2.32 dm³ and is stored at 20°C, calculate the pressure in the cylinder. 

14. Determine the molar mass and molecular formula of an alkene, given that 0.1881g occupies a volume of 82.5 cm³ at 101 kPa and 373K.

15. Phosphoric acid decomposes on heating to produce the gas phosphine in a 4:1 molar ratio. Calculate the volume of phosphine formed (in cm³) from the decomposition of 0.032 mol of phosphoric acid at 101 kPa and 200°C.

16. A student injected a sample of a volatile liquid into a gas syringe. The gas syringe was placed in an oven and the volatile liquid vaporised. 

(a). Use the results of the experiment given below to find the relative molecular mass of the volatile liquid.

Initial mass of syringe and liquid /g	10.91
Mass of syringe and liquid after injection / g	10.70
Oven temperature / °C	98.1
Pressure / kPa	102
Increase in gas syringe volume after injection / cm3	85.0

(b). Afterwards, the student realised that some of the volatile liquid had remained in the nozzle of the gas syringe and had not evaporated. How would this effect the value of the relative molecular mass determined in part (a)? 

17. 194 mg of a volatile hydrocarbon was vaporised at a temperature of 100°C in a gas syringe. The pressure remained constant at 101 kPa and the volume of was recorded as being 72 cm³.  Determine the relative molecular mass of the hydrocarbon. 

18.   Two glass flasks are connected by a tap.

(a) Calculate the mass of ammonia in the larger flask.

(b) When the tap is opened ammonia diffuses into the smaller flask. The temperature falls by 5°C and the final pressure in both flasks equalises at 75.0 kPa. Calculate the volume of the smaller flask in cm³. 

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Answers