Question

При спалюванні вуглеводню масою 4.2 г утворилось 13.2 г карбон (IV) оксиду і 5.4 г води. Відносна густина парів вуглеводню за воднем - 42. Знайдіть молекулярну формулу вуглеводню.

Answer 1

Дано
m(CxHy)=4.2 g
m(CO2)=13.2g
m(H2O)=5.4g
D(H2)=42
----------------
CxHy-?
0.05              0.3      0.3
CxHy+O2-->CO2+H2O
1 mol            x mol 0.5y
Mr(CxHy)=42*2=84 
n(CxHy)=4.2/84=0.05 mol
n(CO2)=13.2/44=0.3 mol
x=0.3*1/0.05=6  - (C)
m(C)=0.3*12=3.6 g
m(H)=4.2-3.6=0.6 g
n(H)=0.6/1=0.6 mol
n(H2O)=0.6*0.5=0.3 mol
0.3*0.5=0.15
y=6*0.3/0.15=12 - (H)
CxHy=6:12
C6H12
ответ гексен

Answer 2

Finding the Molecular Formula of the Hydrocarbon

To find the molecular formula of the hydrocarbon, we can start by analyzing the given information.

Given: - Mass of hydrocarbon = 4.2 g - Mass of carbon (IV) oxide formed = 13.2 g - Mass of water formed = 5.4 g - Relative density of hydrocarbon to water = 42

Calculating the Molecular Formula

First, let's calculate the moles of carbon and hydrogen in the hydrocarbon using the given masses of carbon (IV) oxide and water formed.

The molar mass of carbon (IV) oxide (CO2) is 44 g/mol, and the molar mass of water (H2O) is 18 g/mol.

The moles of carbon in the carbon (IV) oxide can be calculated as: Moles of carbon = Mass of carbon (IV) oxide / Molar mass of carbon (IV) oxide Moles of carbon = 13.2 g / 44 g/mol Moles of carbon = 0.3 mol

The moles of hydrogen in the water can be calculated as: Moles of hydrogen = Mass of water / Molar mass of water Moles of hydrogen = 5.4 g / 18 g/mol Moles of hydrogen = 0.3 mol

This means that the moles of carbon and hydrogen in the hydrocarbon are in a 1:1 ratio.

Next, we can calculate the molar mass of the hydrocarbon using the given mass and relative density.

The relative density of hydrocarbon to water is 42, which means the mass of 1 cm^3 of the hydrocarbon is 42 times the mass of 1 cm^3 of water.

Using the molar volume of gases at standard temperature and pressure (STP), which is 22.4 L/mol, we can calculate the molar mass of the hydrocarbon.

Molar mass of hydrocarbon = Relative density * Molar mass of water Molar mass of hydrocarbon = 42 * 18 g/mol Molar mass of hydrocarbon = 756 g/mol

Now, we can calculate the number of moles of the hydrocarbon using its mass.

Moles of hydrocarbon = Mass of hydrocarbon / Molar mass of hydrocarbon Moles of hydrocarbon = 4.2 g / 756 g/mol Moles of hydrocarbon ≈ 0.0056 mol

Determining the Molecular Formula

With the moles of carbon and hydrogen in the hydrocarbon in a 1:1 ratio, and the number of moles of the hydrocarbon calculated, we can determine its molecular formula.

The molecular formula of the hydrocarbon is C1H1, which simplifies to CH.

Therefore, the molecular formula of the hydrocarbon is CH.