if 0.78g of X was found to contain 0.72g of carbon
i) determine the percentage composition of X
ii)determine the empirical formula of X
iii)determine the molecular formula of X given that the vapour density of X is 39
To determine the percentage composition of X, we need to find the percentage of carbon in X.
The percentage composition of carbon in X is calculated as follows:
Percentage composition of carbon = (mass of carbon / mass of X) * 100
Given that 0.78g of X contains 0.72g of carbon, the percentage composition of carbon in X is:
Percentage composition of carbon = (0.72g / 0.78g) * 100 = 92.31%
Therefore, the percentage composition of X is: Carbon - 92.31% and other elements (assumed to be hydrogen, oxygen, etc.) - 7.69%.
To determine the empirical formula of X, we need to find the simplest ratio of the elements in X.
Since the percentage composition of X indicates that carbon is the major component, we assume that X is composed mainly of carbon.
To find the empirical formula, we assume that X contains 100g of mass for ease of calculation.
Given that X contains 92.31g of carbon, the empirical formula of X is:
C92.31 = C3H0.81 (approximately)
Since we cannot have a fractional subscript in a empirical formula, we multiply all the subscripts by 4, which gives us:
C12H3 (empirical formula of X)
To determine the molecular formula of X, we need the vapour density of X.
Vapour density is calculated as follows:
Vapour density = (molecular weight of X) / 2
Given that the vapour density of X is 39, we can calculate the molecular weight of X as follows:
Molecular weight of X = 39 * 2 = 78
The empirical formula of X has a molecular weight of 12 + 3(1) = 15.
To find the molecular formula, we divide the molecular weight of X (78) by the empirical formula weight (15), which gives us:
78 / 15 = 5.2 (approximately)
Therefore, the molecular formula of X is:
(C12H3)n, where n ≈ 5