A sample of hydrogen gas is generated from a closed container (100mL) by reactin
ID: 814909 • Letter: A
Question
A sample of hydrogen gas is generated from a closed container (100mL) by reacting 3.500g of lithium metal 15.0 mL of 1.00 M nitric acid. A) write a balanced equation including all phases for this reaction and calculate the number of moles of hydrogen formed. B) Calculate the partial pressure at 20 degrees Celsius ignoring any solubility of the gas in the solution. C) the Henry's Law Constant for hydrogen gas in water at 20 degrees Celsius is 3.7 x 10^-4 mol/L x atm. Estimate the number of moles of hydrogen gas that remain dissolved in the solution. What fraction of the gas molecules in the system is dissolved in the solution? Was it reasonable to ignore any dissolved hydrogen in part b?
Explanation / Answer
a) 2Li (s) + 2HNO3 (Aq) ----------> 2LiNO3 (aq) + H2 (g)
b) From the above reaction -
The number of mosl of H2 (g) can be evolved from 3.5 g of Li(if its a limiting)
= (3.5 g/6.9 g/mol) (1 mol H2 / 2 mol Li)
= 0.253 mol
The number of mols of H2 (g) can be evolved from (0.015 L)(1 mol/L) = 0.015 mols of HNO3
= (0.015 mol HNO3)(1 mol H2 / 2mol HNO3) = 0.0075 mol HNO3
From the above calculations, we conclude that HNO3 is limiting as it is producing less mols of H2 gas
Since - P = nRT/ V = (0.0075 mol)(0.0821 L.atm/mol.K)(293 K) / (0.1L) = 1.80 atm
c) Since - solubility, s = (KH )(P)
= (3.7*10-4 mol/L / atm)(1.80 atm) = 6.67*10-4 mol
Therefore, number of mols of H2 gas remain dissolved in the reaction = (0.0075 mol - 6.67*10-4 mol)
= 6.832*10-3 mol
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