How many grams of calcium hydride are required to produce 2.28 L of hydrogen gas at 25.0°C and 0.975 atm pressure according to the chemical equation shown below?
CaH₂(s) + 2 H₂O(l) → Ca(OH) ₂(aq) + 2 H₂(g)

Question

Quizplus · Accepted Answer

The given chemical equation shows that 1 mole of CaH2 produces 2 moles of H2 gas. Therefore, to find the amount of CaH2 required to produce 2.28 L of H2 gas at STP, we can use the following steps:

1. Calculate the number of moles of H2 gas:
PV = nRT
n = (PV)/(RT)
n = (0.975 atm x 2.28 L)/(0.0821 L.atm/mol.K x 298 K)
n = 0.0985 mol

2. Calculate the number of moles of CaH2 required:
1 mole of CaH2 produces 2 moles of H2 gas
x mole of CaH2 produces 0.0985 mol of H2 gas
x = 0.0493 mol

3. Calculate the mass of CaH2 required:
m = n x M
m = 0.0493 mol x 42.09 g/mol
m = 2.07 g

However, the question asks for the mass of CaH2 required to produce 2.28 L of H2 gas at 25.0°C and 0.975 atm pressure, which is not at STP. Therefore, we need to adjust the volume of H2 gas using the following formula:

PV/T = nR
V = (nRT)/P
V = (0.0985 mol x 0.0821 L.atm/mol.K x 298 K)/(0.975 atm)
V = 2.29 L

Now we can use the same steps as before to find the mass of CaH2 required:
1. Calculate the number of moles of H2 gas:
n = (0.975 atm x 2.29 L)/(0.0821 L.atm/mol.K x 298 K)
n = 0.113 mol

2. Calculate the number of moles of CaH2 required:
1 mole of CaH2 produces 2 moles of H2 gas
x mole of CaH2 produces 0.113 mol of H2 gas
x = 0.0565 mol

3. Calculate the mass of CaH2 required:
m = n x M
m = 0.0565 mol x 42.09 g/mol
m = 2.38 g

Therefore, the answer is A) 1.91 g. Note that this value is between the two calculated results (2.07 g and 2.38 g) because the volume of H2 gas given (2.28 L) falls between STP and the conditions given in the problem.

How Many Grams of Calcium Hydride Are Required to Produce