an oxide of arsenic = 0.927g
76% arsenic and 24% oxygen
calculate the mass of oxygen that combines with one mole of arsenic atoms to form the oxide of arsenic.
How many moles of oxygen atoms does this mass represent?
Posted by Kirsty on Tuesday, February 6, 2007 at 3:50pm.
an oxide of arsenic = 0.927g
76% arsenic and 24% oxygen
calculate the mass of oxygen that combines with one mole of arsenic atoms to form the oxide of arsenic.
How many moles of oxygen atoms does this mass represent?
Take a 100 g sample.
You will have 76% As.
You will have 24% O.
mols As = 76/74.9 =??
mols O = 24/16=??
Now divide both numbers by the smaller of the two numbers (this forces the smaller number to be 1.00) and this should provide the small whole numbers for the subscripts. If the ratios are small whole numbers, then multiply them to make small whole numbers; i.e., if the ratio is 1.01 to 2.02 we would use 1 to 2. If the ratio is 1.01 to 1.5, then the ratio is 2 to 3.
To calculate the mass of oxygen that combines with one mole of arsenic atoms to form the oxide of arsenic, you need to first determine the molar ratios of arsenic and oxygen in the oxide.
First, assume you have a 100 g sample of the oxide. Since the proportion of arsenic in the oxide is 76%, the amount of arsenic in the sample is (76/100) * 100 g = 76 g.
Similarly, the proportion of oxygen in the oxide is 24%. So the amount of oxygen in the sample is (24/100) * 100 g = 24 g.
Next, you need to convert the masses of arsenic and oxygen to moles. Divide the mass of arsenic by its molar mass (74.9 g/mol) and divide the mass of oxygen by its molar mass (16 g/mol) to calculate the moles of each element.
moles of As = 76 g / 74.9 g/mol = 1.015 mol
moles of O = 24 g / 16 g/mol = 1.5 mol
Now, divide both numbers by the smaller of the two numbers (1.015) to get the small whole-number ratio of moles. In this case, you would divide both numbers by 1.015:
moles of As / 1.015 = 1.015 mol / 1.015 = 1 mol
moles of O / 1.015 = 1.5 mol / 1.015 = 1.48 mol
Now you have the mole ratio of arsenic to oxygen in the oxide as 1:1.48. However, we need to express the ratio in whole numbers, so multiply both numbers by 2 to get the simplified ratio:
moles of As = 1 mol
moles of O = 2.96 mol
Therefore, in one mole of arsenic atoms, 2.96 moles of oxygen atoms combine to form the oxide of arsenic.