Understanding the Percentage of Carbon in CO₂

The question asks for the percentage of carbon present in the carbon dioxide (CO₂) molecule. To find this, we need to know the molecular mass of CO₂ and the atomic mass of carbon.

Atomic Masses of Elements in CO₂

First, let's look up the atomic masses of the elements involved:

• Atomic mass of Carbon (C) is approximately 12.01 u (or g/mol). For simple calculations like this, we often use the rounded value of 12.
• Atomic mass of Oxygen (O) is approximately 16.00 u (or g/mol).

A molecule of CO₂ contains one carbon atom and two oxygen atoms.

Calculating the Molecular Mass of CO₂

The molecular mass of CO₂ is the sum of the atomic masses of the atoms in the molecule:

Molecular mass of CO₂ = (Atomic mass of C) + 2 × (Atomic mass of O)

Using the rounded atomic masses:

Molecular mass of CO₂ = \(12 + 2 \times 16\)

Molecular mass of CO₂ = \(12 + 32\)

Molecular mass of CO₂ = \(44\) u (or g/mol)

Calculating the Percentage of Carbon in CO₂

To find the percentage of a specific element in a compound, we use the following formula:

Percentage of element = \(\frac{\text{Total mass of the element in the compound}}{\text{Molecular mass of the compound}} \times 100\%\)

In CO₂, the total mass of carbon is simply the mass of one carbon atom, which is 12.

So, the percentage of carbon in CO₂ is:

Percentage of Carbon = \(\frac{\text{Mass of Carbon}}{\text{Molecular mass of CO}_2} \times 100\%\)

Percentage of Carbon = \(\frac{12}{44} \times 100\%\)

Performing the Calculation

Let's perform the division and multiplication:

\(\frac{12}{44} \approx 0.272727...\)

Percentage of Carbon \(\approx 0.272727... \times 100\%\)

Percentage of Carbon \(\approx 27.27\%\)

Rounding this to one decimal place, we get 27.3%.

Therefore, the percentage of carbon in CO₂ is approximately 27.3%.

Comparing with Options

Let's look at the given options:

1. 44
2. 27.3
3. 14
4. 12

Our calculated value of approximately 27.3% matches option 2.

Revision Table: Key Calculations for CO₂ Composition

Percentage of Carbon = \(\frac{12}{44} \times 100\% \approx 27.3\%\)

Additional Information: Understanding Molecular Composition

Understanding how to calculate the percentage composition of a compound is fundamental in chemistry. Here are a few related concepts:

• Molecular Formula: Represents the actual number of atoms of each element in a molecule (e.g., CO₂).
• Empirical Formula: Represents the simplest whole-number ratio of atoms in a compound (e.g., for glucose C₆H₁₂O₆, the empirical formula is CH₂O).
• Molar Mass: The mass of one mole of a substance (equivalent to molecular mass in grams per mole). Used for calculations involving larger quantities.
• Law of Constant Proportions: States that a chemical compound always contains the same proportion of elements by mass, regardless of the source of the compound. Our calculation of percentage composition is based on this law.

Calculating percentage composition is useful for determining the purity of a sample, finding the empirical formula of a compound, and stoichiometric calculations in chemical reactions.