A sample of black mineral hematite, an oxide of iron found in many iron ores, contains 34.97 g of iron and 15.03 g oxygen. What is the empirical formula for hematite?
To find the empirical formula, we need to determine the moles of each element in the sample.
The molar mass of iron (Fe) is 55.85 g/mol, and the molar mass of oxygen (O) is 16 g/mol.
First, let's find the moles of iron (Fe):
moles of Fe = mass of Fe / molar mass of Fe
moles of Fe = 34.97 g / 55.85 g/mol
moles of Fe = 0.626 mol
Next, let's find the moles of oxygen (O):
moles of O = mass of O / molar mass of O
moles of O = 15.03 g / 16 g/mol
moles of O = 0.939 mol
Now, let's find the mole ratio of Fe to O:
Fe:O = 0.626 mol Fe / 0.939 mol O
Fe:O ≈ 1:1
Therefore, the empirical formula for hematite is FeO.
To determine the empirical formula for hematite, we need to find the ratio of elements present in the compound.
Step 1: Convert the mass of iron (Fe) and oxygen (O) into moles.
Molar mass of iron (Fe) = 55.845 g/mol
Molar mass of oxygen (O) = 15.9994 g/mol
Number of moles of iron (Fe) = mass / molar mass = 34.97 g / 55.845 g/mol = 0.626 mol
Number of moles of oxygen (O) = mass / molar mass = 15.03 g / 15.9994 g/mol = 0.939 mol
Step 2: Divide the moles of each element by the smallest number of moles.
Dividing by 0.626 (the smallest number of moles), we get:
Fe: 0.626 mol / 0.626 mol = 1 mole
O: 0.939 mol / 0.626 mol = 1.5 moles
Step 3: If needed, multiply the resulting ratios by small whole numbers to obtain whole numbers for the empirical formula.
Since both numbers are already close to whole numbers, there is no need for further multiplication.
Therefore, the empirical formula for hematite is Fe2O3.
To determine the empirical formula of hematite, we will use the given mass of iron and oxygen.
Step 1: Find the molar mass of iron (Fe) and oxygen (O)
The molar mass of iron (Fe) is 55.845 g/mol.
The molar mass of oxygen (O) is 15.999 g/mol.
Step 2: Calculate the number of moles for each element
To do this, divide the mass of each element by its molar mass.
Number of moles of iron (Fe) = Mass of iron (Fe) / Molar mass of iron (Fe)
Number of moles of iron (Fe) = 34.97 g / 55.845 g/mol
Number of moles of iron (Fe) ≈ 0.626 mol
Number of moles of oxygen (O) = Mass of oxygen (O) / Molar mass of oxygen (O)
Number of moles of oxygen (O) = 15.03 g / 15.999 g/mol
Number of moles of oxygen (O) ≈ 0.940 mol
Step 3: Determine the mole ratio
Divide the number of moles of each element by the smallest number of moles for any element.
Mole ratio (Fe:O) ≈ 0.626 mol / 0.626 mol : 0.940 mol / 0.626 mol
Mole ratio (Fe:O) ≈ 1 : 1.5
The empirical formula is obtained by rounding the mole ratio to the nearest whole number:
Empirical formula: Fe2O3
Therefore, the empirical formula for hematite is Fe2O3.