Question

Find the % of composition of carbon in methane:

• A. 25%
• B. 75%
• C. 20%
• D. 80%
• E. 90%

Hint:

To check your work, calculate the percentage of all elements. They must add up to 100%. Here, Hydrogen is \((4/16) \times 100 = 25%\). And \(75% + 25% = 100%\).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Percentage composition defines the mass percentage of each element present in a compound. It represents what portion of the total mass of the compound is contributed by a specific element.
Step 2: Key Formula or Approach:
The formula to calculate the mass percentage of an element is:
\[ \text{Mass % of an element} = \left( \frac{\text{Mass of that element in 1 mole of compound}}{\text{Molar mass of the compound}} \right) \times 100 \]
Step 3: Detailed Explanation:
The chemical formula for methane is \(\text{CH}_4\).
First, we need the standard atomic masses of the constituent elements:
- Atomic mass of Carbon (\(\text{C}\)) \(\approx 12 \text{ g/mol}\)
- Atomic mass of Hydrogen (\(\text{H}\)) \(\approx 1 \text{ g/mol}\)
Next, calculate the total molar mass of methane (\(\text{CH}_4\)):
\[ \text{Molar mass} = (1 \times \text{Mass of C}) + (4 \times \text{Mass of H}) \]
\[ \text{Molar mass} = (1 \times 12) + (4 \times 1) \]
\[ \text{Molar mass} = 12 + 4 = 16 \text{ g/mol} \]
Now, calculate the mass percentage of Carbon:
\[ % \text{ Carbon} = \left( \frac{\text{Mass of C in compound}}{\text{Total Molar mass}} \right) \times 100 \]
\[ % \text{ Carbon} = \left( \frac{12}{16} \right) \times 100 \]
Simplify the fraction: \(\frac{12}{16} = \frac{3}{4} = 0.75\)
\[ % \text{ Carbon} = 0.75 \times 100 = 75% \]
Step 4: Final Answer:
The percentage composition of carbon in methane is 75%.