Question

Массовая доля углеводорода в алкане равна 83.72%. Определить молекулярную формулу этого вещества. (Напишите полное решение)

Answer 1

CnH2n+2
m(C) = 12*n
m(CnH2n+2) = (12*n + 2*n + 2) = (14*n + 2)
ω(C) = 100*12*n/(14*n + 2)
100*12*n/(14*n + 2) = 83,72
Далее решаем и получаем:
n = 6, тогда молекулярная формула этого алкана C6H14

Answer 2

Calculation of Molecular Formula

To determine the molecular formula of a substance, we need to know the mass percentage of each element present in the compound. In this case, we are given that the mass percentage of carbon (C) in the alkane is 83.72%.

Let's assume that we have 100 grams of the alkane. This means that 83.72 grams of the alkane is composed of carbon.

Using the molar mass of carbon (12.01 g/mol), we can calculate the number of moles of carbon in the alkane:

Number of moles of carbon = mass of carbon / molar mass of carbon

Number of moles of carbon = 83.72 g / 12.01 g/mol

Number of moles of carbon ≈ 6.97 mol

Since the alkane is composed solely of carbon and hydrogen, the remaining mass (100 g - 83.72 g = 16.28 g) must be due to hydrogen.

Using the molar mass of hydrogen (1.008 g/mol), we can calculate the number of moles of hydrogen in the alkane:

Number of moles of hydrogen = mass of hydrogen / molar mass of hydrogen

Number of moles of hydrogen = 16.28 g / 1.008 g/mol

Number of moles of hydrogen ≈ 16.14 mol

Now, we need to find the simplest whole number ratio between the number of moles of carbon and hydrogen. Dividing both values by the smaller value (6.97 mol), we get:

Number of moles of carbon ≈ 6.97 mol / 6.97 mol ≈ 1 mol Number of moles of hydrogen ≈ 16.14 mol / 6.97 mol ≈ 2.32 mol

Rounding the number of moles of hydrogen to the nearest whole number, we have:

Number of moles of hydrogen ≈ 2 mol

Therefore, the empirical formula of the alkane is CH₂.

To determine the molecular formula, we need to know the molar mass of the alkane. Unfortunately, the molar mass is not provided in the given information. Without the molar mass, we cannot determine the molecular formula of the alkane.

Please provide the molar mass of the alkane or any additional information to proceed further with the calculation.