Under certain conditions, water can be separated into oxygen and hydrogen gases according to the equation 2H2O → 2H2 + O2. In a lab, 112g of hydrogen gas and 888g of oxygen gas were collected. Student A says that the amount of water to start cannot be determined, but Student B says that the water must have been 1000g. Who is correct?
Student B is correct.
Since the molar ratio of H2O to H2 and O2 is 2:2:1, we can calculate the molar masses of H2O, H2, and O2 as follows:
H2O: 2(1.008) + 15.999 = 18.015 g/mol
H2: 2(1.008) = 2.016 g/mol
O2: 2(15.999) = 31.998 g/mol
Now, we can calculate the number of moles of H2 and O2 using the given masses:
moles of H2 = 112g / 2.016 g/mol = 55.556 mol
moles of O2 = 888g / 31.998 g/mol = 27.754 mol
Since the molar ratio is 2:1 between H2 and O2, this means that for every 2 moles of H2 generated, 1 mole of O2 is generated. Therefore, the moles of H2 and O2 should be in the ratio 2:1.
Let x be the moles of water used. Then we have:
2x = 55.556
x = 27.778 mol
Now, we can calculate the mass of water used:
mass of water = 27.778 mol * 18.015 g/mol = 500.076g ≈ 500g
Therefore, the correct answer is that the amount of water to start was approximately 500g, not 1000g as Student B stated.