A carbohydrate P contains 40% carbon,6.67% hydrogen.If P has a relative molecular mass of 60.Determine it; 1)Empirical formula 2)molecular formula [H=1,C=12,O=16]
Take a 100 g sample which gives you
50 g C
6.67 g H
100-6.67-40 = 53.33 g O
mols C = 40/12 = 3.33
mols H = 6.67/1 = 6.67
mols O = 53.33/16 = 3.33
Find the ratio to each other with the smallest being no less than 1.00. The easy way to do that is to divide all of the numbers by the smallest.
3.33/3.33 = 1 = C
6.67/3.33 = 2 = H
3.33/3.33 = 1 = O
Empirical formula = CH2O
Empirical mass = 12 + 2 + 16 = 30
So molecular formula must be 60/30 = 2 or (CH2O)2 = C2H4O2
To determine the empirical formula of the carbohydrate P, we need to determine the ratio of atoms present in the compound. We are given the percentages of carbon (40%) and hydrogen (6.67%).
1) Empirical formula:
Step 1: Assume that we have 100 grams of the compound P. This assumption simplifies the calculations, as percentages can be directly converted to grams.
- Carbon (C) = 40% of 100g = 40g
- Hydrogen (H) = 6.67% of 100g = 6.67g
Step 2: Convert the grams of each element to moles. To do this, divide the grams of each element by its molar mass.
- Moles of carbon = 40g / 12 g/mol = 3.33 mol
- Moles of hydrogen = 6.67g / 1 g/mol = 6.67 mol
Step 3: Find the mole ratio between carbon and hydrogen. Divide the number of moles of each element by the smallest number of moles obtained.
- Carbon ratio = 3.33 mol / 3.33 mol = 1
- Hydrogen ratio = 6.67 mol / 3.33 mol = 2
Step 4: Apply the mole ratios to obtain the empirical formula.
The empirical formula is C1H2.
2) Molecular formula:
To determine the molecular formula, we also need the relative molecular mass of the compound, which is given as 60.
Step 1: Calculate the empirical formula mass.
- Empirical formula mass = 1*(12 g/mol) + 2*(1 g/mol) = 14 g/mol
Step 2: Divide the given relative molecular mass by the empirical formula mass to determine the multiple.
- Multiple = Relative molecular mass / Empirical formula mass
- Multiple = 60 / 14 ≈ 4.29
Step 3: Multiply the subscripts of the empirical formula by the multiple obtained in Step 2 to determine the molecular formula.
- Molecular formula = C1H2 * 4 ≈ C4H8
Therefore, the empirical formula of the carbohydrate P is C1H2, and its molecular formula is approximately C4H8.