Answer:
Molecular formula naphthalene → C₁₀H₈
Empirical formula naphthalene → C₅H₄
Explanation:
Centesimal composition means that in 100 g of compound we have x g of the element. Therefore in 100 g of naphthalene we have:
93.7 g of C
6.3 g of H
Let's make a rule of three:
In 100 g of naphthalene we have 93.7 g of C and 6.3 g of H
In 128 g of naphthalene we would have:
128 . 93.7 / 100 = 120 g of C
128. 6.3 / 100 = 8 g of H
We convert the mass to moles, by molar mass:
120 g . 1mol / 12 g = 10 moles C
8 g . 1mol/ 1g = 8 moles H
Molecular formula naphthalene → C₁₀H₈
Empirical formula naphthalene → C₅H₄
(The sub-index of each element is divided by the largest possible number)
Answer:
The empirical formula is C5H4
The molecular formula is C10H8
Explanation:
Step 1: Data given
Suppose the mass = 100 grams
Naphthalene contains:
93.7 % C = 93.7 grams
6.3 % H = 6.3 grams
atomic mass of C = 12.01 g/mol
atomic mass of H = 1.01 g/mol
Molar mass of naphthalene = 128 g/mol
Step 2: Calculate moles
Moles = mass / molar mass
Moles C = 93.7 grams / 12.01 g/mol
Moles C = 7.80 moles
Moles H = 6.3 grams / 1.01 g/mol
Moles H = 6.24 moles
Step 3: Calculate mol ratio
We divide by the smallest amount of moles
Moles C: 7.80 moles / 6.24 moles
Moles C: 1.25
Moles H: 6.24 moles / 6.24 moles
Moles H: 1
The empirical formula is C5H4
The molecular weight is 64.09 g/mol
128 g/mol / 64.09 g/mol = 2
We have to multiply the empirical formula by 2
2*(C5H4) = C10H8
The molecular formula is C10H8
