Q. Molar mass \( \mathrm{C_2H_5OH} \).

Q: What is the molar mass of ethanol, \mathrm{C_2H_5OH} ?

\mathrm{C_2H_5OH} = \mathrm{C_2H_6O} . Molar mass =2(12.01)+6(1.008)+16.00 \approx 46.07\,\mathrm{g/mol}.

Q: What is the molar mass of \mathrm{C_2H_6O} using standard atomic masses?

Using \mathrm{C}=12.01, \mathrm{H}=1.008, \mathrm{O}=16.00: 2(12.01)+6(1.008)+16.00=46.068\,\mathrm{g/mol}\approx 46.07\,\mathrm{g/mol}.

Q: Should \mathrm{C_2H_5OH} be counted as \mathrm{C_2H_6O} ?

Yes. The \mathrm{OH} group contributes \mathrm{O_1H_1} . So \mathrm{C_2H_5OH} becomes \mathrm{C_2H_6O} .

Q: What common mistake occurs when converting \mathrm{C_2H_5OH} to atomic counts?

Forgetting the extra H from \mathrm{OH} . If you incorrectly use \mathrm{C_2H_5O} , you’ll miss one hydrogen and get too low a molar mass.

Q: What is ethanol’s molar mass to two decimal places?

46.07\,\mathrm{g/mol}. (From 2(12.01)+6(1.008)+16.00.)

Answer

To find the molar mass of ethanol \( \text{C}_2\text{H}_5\text{OH} \), note the formula is \( \text{C}_2\text{H}_6\text{O} \).

Using atomic masses \( \text{C} = 12.01 \), \( \text{H} = 1.008 \), \( \text{O} = 16.00 \) g/mol:

\[
\text{Molar mass} = 2(12.01) + 6(1.008) + 16.00
\]
\[
= 24.02 + 6.048 + 16.00 = 46.068 \approx 46.07 \text{ g/mol}
\]

Final result: \( \boxed{46.07 \text{ g/mol}} \)

Detailed Explanation

We want the molar mass of ethanol, whose chemical formula is \( \mathrm{C_2H_5OH} \).

Step 1: Rewrite the formula in standard element counts.

\( \mathrm{C_2H_5OH} \) contains:

\(2\) carbon atoms (\(\mathrm{C}\))
\(6\) hydrogens total (\(\mathrm{H_5}\) plus the \(\mathrm{H}\) in \(\mathrm{OH}\))
\(1\) oxygen atom (\(\mathrm{O}\))

So the formula is equivalently \( \mathrm{C_2H_6O} \).

Step 2: Use atomic masses.

Use typical periodic table atomic masses:

\( \mathrm{C}: 12.01\ \mathrm{g/mol} \)
\( \mathrm{H}: 1.008\ \mathrm{g/mol} \)
\( \mathrm{O}: 16.00\ \mathrm{g/mol} \)

Step 3: Compute molar mass by multiplying and adding.

The molar mass is:

\[
\text{Molar mass} = 2(12.01) + 6(1.008) + 1(16.00)
\]

Step 4: Calculate each contribution.

\(2(12.01) = 24.02\ \mathrm{g/mol}\)
\(6(1.008) = 6.048\ \mathrm{g/mol}\)
\(1(16.00) = 16.00\ \mathrm{g/mol}\)

Step 5: Add them up.

\[
\text{Molar mass} = 24.02 + 6.048 + 16.00 = 46.068\ \mathrm{g/mol}
\]

Final Answer:

The molar mass of \( \mathrm{C_2H_5OH} \) (ethanol) is \( \boxed{46.07\ \mathrm{g/mol}} \) (rounded to 2 decimal places).

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General Chemistry FAQs

What is the molar mass of ethanol, \( \mathrm{C_2H_5OH} \)?

\( \mathrm{C_2H_5OH} = \mathrm{C_2H_6O} \). Molar mass \(=2(12.01)+6(1.008)+16.00 \approx 46.07\,\mathrm{g/mol}\).

What is the molar mass of \( \mathrm{C_2H_6O} \) using standard atomic masses?

Using \( \mathrm{C}=12.01\), \( \mathrm{H}=1.008\), \( \mathrm{O}=16.00\): \(2(12.01)+6(1.008)+16.00=46.068\,\mathrm{g/mol}\approx 46.07\,\mathrm{g/mol}\).

Should \( \mathrm{C_2H_5OH} \) be counted as \( \mathrm{C_2H_6O} \)?

Yes. The \( \mathrm{OH} \) group contributes \( \mathrm{O_1H_1} \). So \( \mathrm{C_2H_5OH} \) becomes \( \mathrm{C_2H_6O} \).

Why does the molar mass calculation use \(2\) for carbon, \(6\) for hydrogen, and \(1\) for oxygen?

Molar mass sums atomic masses multiplied by their subscripts in \( \mathrm{C_2H_6O} \): \(2\) carbons, \(6\) hydrogens, \(1\) oxygen.

What common mistake occurs when converting \( \mathrm{C_2H_5OH} \) to atomic counts?

Forgetting the extra H from \( \mathrm{OH} \). If you incorrectly use \( \mathrm{C_2H_5O} \), you’ll miss one hydrogen and get too low a molar mass.

What is ethanol’s molar mass to two decimal places?

\(46.07\,\mathrm{g/mol}\). (From \(2(12.01)+6(1.008)+16.00\).)

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