This problem involves a molecular compound so both empirical and molecular formulas are required. A compound composed of Carbon, Hydrogen, and Bromine is analyzed. It is found to contain 0.3194 g of C, 0.05361 g of H and 2.125 g Br. What is the empirical formula of the compound? If the compound is known to have 12 H atoms in it, what is the molecular formula of the compound?
0.3194 g of C, 0.05361 g of H and 2.125 g Br
Convert grams to mols.
mols C = 0.3194/12.01 = approx 0.0265
mols H = 0.05361/1.008 = about 0.0536
mols Br = 2.125/79.9 = about 0.0265
Now you want to find the ratio of each element to the others with the smallest number being 1 and all small whole numbers. The easy way to do that is to divide the smallest number by itself, then divide the others number by the same small number.
C = 0.0265/0.0265 = 1.00
H = 0.05361/0.0265 = 2.02
Br = 0.0265/0.0265 = 1.00
Rounding the 2.02 to 2.00 the empirical formula is C1H2O1 or CH2O.
If the molecular compound is known to contain 12 H atoms, just multiply everything by 6 to get C6H12O6 for the molecular formula.
To determine the empirical formula of the compound, you need to find the simplest whole-number ratio of the elements present. Here's how you can calculate it:
Step 1: Determine the number of moles for each element.
To find the number of moles, divide the mass of each element by its molar mass. The molar mass of carbon (C) is 12.01 g/mol, hydrogen (H) is 1.008 g/mol, and bromine (Br) is 79.90 g/mol.
Moles of C = 0.3194 g / 12.01 g/mol
Moles of H = 0.05361 g / 1.008 g/mol
Moles of Br = 2.125 g / 79.90 g/mol
Step 2: Find the smallest mole value.
Compare the mole values obtained in step 1 and determine the smallest mole value. It represents the element with the fewest atoms in the compound, so it will be the reference point for the ratio.
In this case, the smallest mole value is for hydrogen (H).
Step 3: Calculate the ratio.
Divide the moles of each element by the smallest mole value (in this case, H) rounded to the nearest whole number. This will give you the subscripts for each element in the empirical formula.
The ratio for carbon (C) = moles of C / moles of H ≈ 0.3194 / 0.05361 ≈ 5.95 ≈ 6
The ratio for bromine (Br) = moles of Br / moles of H ≈ 2.125 / 0.05361 ≈ 39.64 ≈ 40
Therefore, the empirical formula of the compound is C6H1Br40. However, to simplify it further, you need to divide the subscripts by the greatest common divisor (GCD), which in this case is 1.
The simplified empirical formula is C6H1Br40.
Now, to determine the molecular formula of the compound when it is known to contain 12 H atoms, you can calculate the molecular mass of the empirical formula and compare it to the known molecular mass.
Step 4: Calculate the molecular mass of the empirical formula.
To calculate the molecular mass, multiply the atomic mass of each element by its subscript in the empirical formula and sum them all up.
Molecular mass = (C x 6) + (H x 1) + (Br x 40)
Molecular mass = (12.01 x 6) + (1.008 x 1) + (79.90 x 40)
Step 5: Compare the molecular mass with the known molecular mass.
If the calculated molecular mass is the same as the known molecular mass, then the empirical formula is also the molecular formula. Otherwise, you need to find the empirical formula mass and divide the known molecular mass by the empirical formula mass to determine the number of empirical formula units present in the molecule.
Let's say the known molecular mass is M.
Empirical formula mass = (C x 12.01) + (H x 1) + (Br x 79.90)
If Molecular mass (M) / Empirical formula mass = N (whole number), then the molecular formula is (empirical formula)N.