Ethanol has a molecular formula C2H5OH. A sample of ethanol has a mass of 2.3 grams. The sample was completely burnt in oxygen. i. How many molecules are present in the sample of ethanol? il. How many hydrogen atoms are present in the sample of ethanol? ill. Write down a balanced chemical equation for the combustion of ethanol in oxygen. iv. Calculate how many moles of water molecules were produced in the combustion of ethanol in oxygen. V. Calculate mass of carbon dioxide was produced in the combustion of ethanol in oxygen. Vi. Calculate how many oxygen molecules were used up in the combustion of ethanol in oxygen.
The Correct Answer and Explanation is :
To analyze the combustion of ethanol (C(_2)H(_5)OH) with a mass of 2.3 grams, we can go through the required calculations step by step:
i. How many molecules are present in the sample of ethanol?
- Calculate moles of ethanol:
The molar mass of ethanol (C(_2)H(_5)OH) = 2(12.01) + 6(1.008) + 16.00 = 46.08 g/mol.
[
\text{Moles of ethanol} = \frac{\text{mass}}{\text{molar mass}} = \frac{2.3 \, \text{g}}{46.08 \, \text{g/mol}} \approx 0.04985 \, \text{mol}
] - Calculate number of molecules:
Using Avogadro’s number (6.022 × 10²³ molecules/mol):
[
\text{Molecules of ethanol} = 0.04985 \, \text{mol} \times 6.022 \times 10^{23} \approx 3.00 \times 10^{22} \, \text{molecules}
]
ii. How many hydrogen atoms are present in the sample of ethanol?
Ethanol has 6 hydrogen atoms (C(_2)H(_5)OH).
[
\text{Total hydrogen atoms} = 3.00 \times 10^{22} \, \text{molecules} \times 6 = 1.80 \times 10^{23} \, \text{H atoms}
]
iii. Write down a balanced chemical equation for the combustion of ethanol in oxygen.
The balanced equation for the combustion of ethanol is:
[
\text{C}_2\text{H}_5\text{OH} + 3 \text{O}_2 \rightarrow 2 \text{CO}_2 + 3 \text{H}_2\text{O}
]
iv. Calculate how many moles of water molecules were produced in the combustion of ethanol in oxygen.
From the balanced equation, 1 mole of ethanol produces 3 moles of water.
[
\text{Moles of water} = 0.04985 \, \text{mol ethanol} \times 3 \approx 0.14955 \, \text{mol water}
]
v. Calculate the mass of carbon dioxide produced in the combustion of ethanol in oxygen.
From the balanced equation, 1 mole of ethanol produces 2 moles of carbon dioxide.
[
\text{Moles of CO}_2 = 0.04985 \, \text{mol ethanol} \times 2 \approx 0.09970 \, \text{mol CO}_2
]
The molar mass of CO(_2) = 12.01 + 2(16.00) = 44.01 g/mol.
[
\text{Mass of CO}_2 = 0.09970 \, \text{mol} \times 44.01 \, \text{g/mol} \approx 4.39 \, \text{g}
]
vi. Calculate how many oxygen molecules were used up in the combustion of ethanol in oxygen.
From the balanced equation, 1 mole of ethanol requires 3 moles of O(_2).
[
\text{Moles of O}_2 = 0.04985 \, \text{mol ethanol} \times 3 \approx 0.14955 \, \text{mol O}_2
]
Using Avogadro’s number:
[
\text{Molecules of O}_2 = 0.14955 \, \text{mol} \times 6.022 \times 10^{23} \approx 8.99 \times 10^{22} \, \text{molecules}
]
Summary of Results:
- Molecules of ethanol: (3.00 \times 10^{22})
- Hydrogen atoms: (1.80 \times 10^{23})
- Moles of water: (0.14955)
- Mass of carbon dioxide: (4.39 \, \text{g})
- Molecules of oxygen used: (8.99 \times 10^{22})
In conclusion, this combustion process illustrates the conversion of ethanol into carbon dioxide and water while providing a clear understanding of stoichiometry and molecular relationships during combustion reactions.