Find the formula of a substance with a density of 1.97 g / l, when 3.5 g is burned in oxygen, 10.5 g of carbon

| November 19, 2020 | education

Find the formula of a substance with a density of 1.97 g / l, when 3.5 g is burned in oxygen, 10.5 g of carbon dioxide and 5.76 g of water are formed.

We represent the formula of an unknown compound in the form of CxHy, then the reaction of its combustion will be:
CxHy + O2 = xCO2 + y / 2H2O.
The coefficients are expressed in terms of x and y.
Let’s calculate the molar mass of the substance:
M (CxHy) = Vm ρ = 22.4 l / mol 1.97 g / l = 44 g / mol.
We make up the proportions:
From 3.5 g of CxHy, 10.5 g of CO2 is formed, and from 44 g of CxHy – x • 44 g of CO2.
x = 44 * 10.2 / 44 * 3.5 = 3.
From 3.5 g of CxHy, 5.76 g of H2O are formed, and from 44 g of CxHy, 9 • y g of H2O.
y = 44 * 5.76 / 3.5 * 9 = 8.
CxNy = 3: 8.
The formula of this substance C3H8 is propane.



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