Consider the data recorded during and after the reaction in the flask took place
ID: 488911 • Letter: C
Question
Consider the data recorded during and after the reaction in the flask took place, but before attaching the gas syringe. Use your Lab Notes to fill out the following table. P_max and T_max are the maximum pressure and temperature achieved during the reaction, respectively. P_min and T_min are the minimum pressure and temperature achieved after the reaction was complete, respectively. And V_gas is the volume of the gas in the flask after the reaction. Refer to either the maximum or minimum data sets recorded in the table above. Using either of these data sets in the ideal gas equation, find the total number of moles of gas (air and hydrogen) in the flask. The gas constant has a value of 0.08206 L atm K^-1 mot^-1. 83.391 How many molecules of H_2 were produced in the reaction? Calculate the molar mass of magnesium. Magnesium reacts with hydrochloric acid according to the balanced chemical equation below. Mg(s) + 2HCl (aq) rightarrow MgCl(aq) + H_2(g) Suppose the sample of magnesium used this lab was contaminated with another metal that does not react with hydrochloric acid. How would they have changed your results?Explanation / Answer
Ans. 2. Ideal gas equation: PV = nRT - equation 1
Where, P = pressure in atm
V = volume in L
n = number of moles
R = universal gas constant= 0.08206 atm L mol-1K-1
T = absolute temperature (in K)
For maximum P and T: Putting the values in equation 1
1.83 atm x 0.1301 L = n x (0.08206 atm L mol-1K-1) x 307.95 K
Or, n = (1.83 atm x 0.1301 L) / [(0.08206 atm L mol-1K-1) x 307.95 K]
Hence, n = 0.009421 mol
For minimum P and T: Putting the values in equation 1
1.76 atm x 0.1301 L = n x (0.08206 atm L mol-1K-1) x 295.65 K
Or, n = (1.76 atm x 0.1301 L) / [(0.08206 atm L mol-1K-1) x 295.65 K]
Hence, n = 0.009438 mol
# Note: We will proceed with n = 0.009438 mol
Ans. 3. It’s assumed the total pressure in the vessel is solely due to H2 gas.
No. of H2 molecules = Moles of H2 produced x Avogadro number
= 0.009438 mol x (6.022 x 1023 molecules/ mol)
= 5.68x 1021 molecules
Ans. 4. Note that, in the stoichiometry of balanced reaction-
1 mol H2 gas is produced by 1 mol Mg metal.
So, mole of Mg = moles of H2 produced
Hence, moles of Mg = 0.009438 mol
Mass of Mg = Moles of Mg x Atomic mass
= 0.009438 mol x (24.305 g/mol)
= 0.23 g
Ans. 4. Note that the number of moles of H2 produced is eqal to the number of moles of Mg taken in the reaction.
In case the Mg metal sample is contaminated with some other non-reactive substance, the number of moles of Mg will reduce in the given mass. So, less number of moles of Mg produces lesser amount of H2.
Moreover, production of less H2 gas lead to lower pressure.