10. ALTERNATIVE B
The elementary analysis of 22 g hydrocarbon sample results in 18 g C and 4 g H.
a) Choose the correct chemical formula of the hydrocarbon:
i) CH4
ii) C2H4
iii) C3H8
b) What is the amount of CO2 in grams formed by the total combustion of hydrocarbon? Assume complete
combustion, meaning that only CO2 and H2O is formed.
To determine the correct chemical formula of the hydrocarbon, we need to compare the amount of carbon and hydrogen in the sample. From the given data, we have 18 g of carbon and 4 g of hydrogen.
a) Let's calculate the ratio of carbon to hydrogen in the sample:
- Number of moles of carbon = mass of carbon / molar mass of carbon
= 18 g / 12 g/mol (molar mass of carbon)
= 1.5 moles
- Number of moles of hydrogen = mass of hydrogen / molar mass of hydrogen
= 4 g / 1 g/mol (molar mass of hydrogen)
= 4 moles
Now, let's simplify the ratio by dividing both moles by the smallest value:
- Simplified ratio = 1.5 moles of carbon / 1.5 moles of hydrogen
= 1 mole of carbon / 1 mole of hydrogen
From the simplified ratio, we can conclude that the ratio of carbon to hydrogen in the hydrocarbon is 1:1. Therefore, the correct chemical formula of the hydrocarbon is CH4 (Option i).
b) To find the amount of CO2 formed by the total combustion of the hydrocarbon, we need to consider the balanced chemical equation for complete combustion of hydrocarbons. In this case, the hydrocarbon is CH4.
The balanced chemical equation for complete combustion of CH4 is:
CH4 + 2O2 -> CO2 + 2H2O
From the equation, we can see that 1 mole of CH4 reacts to produce 1 mole of CO2. The molar mass of CO2 is 44 g/mol.
To find the amount of CO2 formed, we need to calculate the number of moles of CH4 in the hydrocarbon and convert it to grams:
- Number of moles of CH4 = mass of CH4 / molar mass of CH4
= 22 g / (12 g/mol + 4 g/mol) (molar mass of CH4)
= 22 g / 16 g/mol
= 1.375 moles
Since 1 mole of CH4 produces 1 mole of CO2, the number of moles of CO2 formed is also 1.375 moles.
Finally, we can calculate the amount of CO2 in grams using the molar mass:
- Amount of CO2 = moles of CO2 * molar mass of CO2
= 1.375 moles * 44 g/mol (molar mass of CO2)
= 60.5 g
Therefore, the amount of CO2 formed by the total combustion of the hydrocarbon is 60.5 grams.