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We are going to determine the molar volume of hydrogen gas by letting known amount of magnesium react with dilute hydrochloric acid and carefully collecting the gas formed.
Hydrochloric acid, 2-molar
8 cm of magnesium ribbon
For details see instruction form
We connect the equipment according to the diagram and make sure we follow the instructions carefully, and then we weigh the 8 cm of magnesium ribbon and pour the HCl into the test tube. As we are ready to start the experiment we fold the mg ribbon on the hook and put the stopper into the test tube so that when we tilt the test tube the mg ribbon can easily fall into the acid. It is important to wait for the reaction to finish completely so that the equipment returns back to room temperature. For details see instruction form.
Measured weigh of 8 cm mg ribbon: 0.068 g (uncertainty is ï¿½ 0.0001)
Room temperature: 21.9 ï¿½C (uncertainty is ï¿½ 0.1)
Room pressure: 742.5 mmHg
Vapour pressure of water: 19.587 and 19.827
Vapour pressure: 19.587 + 19.827 / 2 = 19.707
1.333 x 102 x (mmHg) = Pa
Convert the room pressure in mmHg into Pa:
742.5 x 1.333 x 102 = 98975.25 Pa
Convert the vapour pressure of water into Pa:
19707 x 1.333 x 102 = 2626.9431
p(H2O) = 2626.9431 Pa
Room pressure (Pa) – Vapour pressure of water (Pa)
98975.25 Pa – 2626.9431 Pa = 96348.3069 Pa
p(H2) = 96348.3069 Pa
p(H2) + p(H2O) = p(room)
2626.9431 + 96348.3069 = 98975.25 p(room)
Calculation of molar volume for hydrogen gas at 0 C and 1 atmosphere
P1 x V1 / T1 = P2 + V2 / T2
1 atm = 1.013 x 105
P1 = 96348.3069 P2 = 1 atm = 101300
V1 = 70 cm3 (uncertainty is ï¿½1) V2 = 59cm3 (uncertainty is ï¿½0.5)
T1 = 21.9 ï¿½C = 294.9 K (uncertainty is ï¿½1.3466 ) T2 = 0 ï¿½C = 273 K
96348.3069 x 70 x 1 / 294.9 = 101300 x 59 x 0.5 / 273
Conclusion & Evaluation:
Our conclusion is that the molar volume of hydrogen gas at 0 ï¿½C and 1 atmosphere is -.
We reached the conclusion by first checking the room temperature and barometer pressure. Then we looked up the values for vapour pressure of water at the actual temperature from the Hand book of Chemistry and Physics. The full reference is: Chemistry for the IB diploloma G. Neuss. Oxford UP, 2001 p.28.