Calculate the percentage by mass of the indicated element in the following compounds: a. carbon in acetylene, C2H2, a gas used in welding

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Determine the molar mass of acetylene (C2H2). This involves adding the atomic masses of all the atoms in the molecule. Carbon has an atomic mass of approximately 12.01 g/mol and hydrogen has an atomic mass of approximately 1.008 g/mol. The formula for acetylene is C2H2, so the molar mass is calculated as follows: (2 \times 12.01 \text{ g/mol}) + (2 \times 1.008 \text{ g/mol}).

Calculate the total mass of carbon in one mole of acetylene. Since there are two carbon atoms in acetylene, multiply the atomic mass of carbon by 2.

To find the percentage by mass of carbon in acetylene, use the formula: \(\text{Percentage by mass} = \left(\frac{\text{mass of carbon in the compound}}{\text{molar mass of the compound}}\right) \times 100\%\).

Substitute the values obtained in the previous steps into the formula to calculate the percentage by mass of carbon.

Interpret the result to understand the contribution of carbon to the overall mass of acetylene and how it relates to the compound's chemical properties.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all the atoms in a molecule. For acetylene (C2H2), the molar mass is determined by adding the molar masses of two carbon atoms and two hydrogen atoms, which is essential for calculating the percentage by mass of carbon in the compound.

Percentage by Mass

Percentage by mass is a way to express the concentration of an element in a compound, calculated by dividing the mass of the element by the total mass of the compound and multiplying by 100. This concept is crucial for understanding how much of a compound's mass is contributed by a specific element, such as carbon in acetylene, allowing for comparisons between different compounds.

Empirical Formula

The empirical formula represents the simplest whole-number ratio of the elements in a compound. In the case of acetylene (C2H2), the empirical formula indicates that for every two carbon atoms, there are two hydrogen atoms. Understanding the empirical formula is important for determining the composition of a compound and calculating the mass percentages of its constituent elements.

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