A compound with an empirical formula of C 2H 4Br has a molar mass of 215.90 g/mol. What is the molecular formula?
C2 H4 Br ?
C = 12 grams / mol
H = 1 gram / mol
Br = 80 grams / mol
x * (24 + 4 + 80) = 216
x * 108 = 216
x= 2
so
C4 H8 Br2
Well, let's do a little chemical math, shall we? The empirical formula tells us the simplest ratio of atoms in a compound. In this case, we have 2 carbon atoms, 4 hydrogen atoms, and 1 bromine atom in the empirical formula C2H4Br.
To find the molecular formula, we need to know the molar mass of the compound. The molar mass of the empirical formula C2H4Br is:
(2 * molar mass of C) + (4 * molar mass of H) + (1 * molar mass of Br)
Now, let's do a bit of trickery and use a periodic table to look up the molar masses of each element. The molar mass of carbon (C) is approximately 12 g/mol, the molar mass of hydrogen (H) is roughly 1 g/mol, and the molar mass of bromine (Br) is approximately 80 g/mol.
So, plugging in the values, we get:
(2 * 12 g/mol) + (4 * 1 g/mol) + (1 * 80 g/mol)
Calculating that, we find the molar mass of the empirical formula C2H4Br to be 108 g/mol.
However, you mentioned that the molar mass of the compound is 215.90 g/mol. This means that the molecular formula is 2 times bigger than the empirical formula. So, the molecular formula would be:
(2 * C2) + (2 * H4) + (2 * Br)
Which simplifies to C4H8Br2.
So, the molecular formula of the compound is C4H8Br2. But hey, don't worry, I'm sure you won't be in double trouble with that knowledge! *wink*
To determine the molecular formula, we need to find the molecular mass of the compound.
1. Calculate the empirical formula mass:
- Empirical formula: C2H4Br
- Empirical formula mass = (2 × atomic mass of C) + (4 × atomic mass of H) + (atomic mass of Br)
= (2 × 12.01 g/mol) + (4 × 1.01 g/mol) + 79.90 g/mol
= 24.02 g/mol + 4.04 g/mol + 79.90 g/mol
= 108.96 g/mol
2. Calculate the ratio of the molecular mass to the empirical formula mass:
- Molecular mass / Empirical formula mass = 215.90 g/mol / 108.96 g/mol
= 1.981
3. Find the whole number ratio by rounding the ratio to the nearest whole number:
- Rounded ratio ≈ 2
4. Multiply the subscripts of the empirical formula by the rounded ratio to get the molecular formula:
- Molecular formula = (C2H4Br)2
= C4H8Br2
Therefore, the molecular formula of the compound is C4H8Br2.
To determine the molecular formula, you need to follow these steps:
1. Find the empirical formula mass: Calculate the sum of the atomic masses of the empirical formula.
- C: Atomic mass of carbon = 12.01 g/mol
- H: Atomic mass of hydrogen = 1.01 g/mol
- Br: Atomic mass of bromine = 79.90 g/mol
Empirical Formula Mass = (2 × C) + (4 × H) + (1 × Br)
= (2 × 12.01 g/mol) + (4 × 1.01 g/mol) + (1 × 79.90 g/mol)
= 24.02 g/mol + 4.04 g/mol + 79.90 g/mol
= 108.96 g/mol
2. Calculate the ratio of the molecular formula mass to the empirical formula mass:
- Molar mass of the compound = 215.90 g/mol
- Ratio = Molar mass of the compound / Empirical Formula Mass
= 215.90 g/mol / 108.96 g/mol
= 1.981
3. Multiply the subscripts in the empirical formula by the ratio calculated in the previous step to get the molecular formula:
- C2H4Br × 1.981 = C3.962H7.924Br
Since we can't have fractional subscripts in a molecular formula, we round C3.962 to C4 and H7.924 to H8. Therefore, the molecular formula is C4H8Br.