DA Determination Mass of Mg. Moles of Mg Moles of H2 Initial syringe reading, ml
ID: 1085522 • Letter: D
Question
DA Determination Mass of Mg. Moles of Mg Moles of H2 Initial syringe reading, mlL Final syringe reading, ml Volume H2 collected, ml 0.03 0016 0.0008000066A 0.000 0.000 66 A 0.00078n o6 O.000 620.000 66n 0m! 0.ooU 3.0C 296 k (Final reading-initial reading) 6.0m Volume H2 collected, L Temperature, oC Temperature, K Barometric pressure, mmHg Vapor pressure of H20, mmHg Corrected pressure, mmHg Corrected pressure, atm Calculated R value, L-atm/mol-K Average R value, L-atm/mol-K True value of R, L-atm/mol-K % error of average R 25. o'C 230' 3.0*e 29u k 030 ml 21 0821.03 21.030 67 63 87Explanation / Answer
Determination of R value
1. Balanced reaction,
Mg(s) + 2HCl(aq) --> MgCl2(aq) + H2(g)
For sample 1,
2. mass of Mg = 0.019 g
moles Mg = 0.019 g/24.305 g/mol = 0.00078 moles
moles H2 (n) = moles Mg = 0.00078 moles
3. Volume of H2(g) collected (V) = 8 ml/1000 = 0.008 L
4. Corrected pressure of H2(g) = (784 - 21.08) mmHg = 763 mmHg
in atm = 763/760 (P) = 1.004 atm
5. Temperature = 23 oC + 273 (T) = 296 K
6. calculated R values = PV/nT
= 1.004 x 0.008/0.00078 x 296
= 0.0348 L.atm/K-mol
Similarly values from other reading are calculated
From 2, calculated R values = PV/nT
= 1.004 x 0.006/0.00066 x 296
= 0.031 L.atm/K-mol
From 3, calculated R values = PV/nT
= 1.004 x 0.0085/0.00062 x 296
= 0.0465 L.atm/K-mol
From 4, calculated R values = PV/nT
= 1.004 x 0.0155/0.00066 x 296
= 0.08 L.atm/K-mol
From all,
average R value = 0.0481 L.atm/K-mol
7. % error R value = [(0.08206 - 0.0481)/0.08206] x 100 = 41.4%
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Lab discussion
Ideal gas equation, PV = nRT
Ideal gas are gases which have minimal volume in space and do not interact with any gases.
We did calculate value of R with 41.4% error. So the value is far off from the true value of R. Calculated value is thus not accurate.
If the Mg was put before sealing of the reaction, reaction would begin at that point and loss of H2 gas would occur. This would thus give lower volume of H2 gas formed and thus lower value of R calculated. It is also important to remove the oxide layer from Mg surface which would inhibit reaction of Mg with HCl in the system. Thereby lower moles of Mg and H2 would be produced. The R value will be much higher.
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