Which formula is used to calculate the percent by mass of an element in a compound?

• A. percent by mass = (mass of element in 1 mole of compound / molar mass of compound) × 100%
• B. percent by mass = (mass of element in sample / total volume of sample) × 100%
• C. percent by mass = (molar mass of compound / mass of element in 1 mole of compound) × 100%
• D. percent by mass = (number of atoms of element / total number of atoms in compound) × 100%

Answer: (A)

Verified step by step guidance

1. Understand that percent by mass of an element in a compound represents the fraction of the compound's total mass that comes from that element, expressed as a percentage.
2. Identify the mass of the element in one mole of the compound. This is done by multiplying the number of atoms of the element in the compound by the atomic mass of that element.
3. Determine the molar mass of the entire compound by summing the atomic masses of all atoms present in one mole of the compound.
4. Use the formula for percent by mass: \(\text{percent by mass} = \left( \frac{\text{mass of element in 1 mole of compound}}{\text{molar mass of compound}} \right) \times 100\%\) to calculate the percentage.
5. Avoid incorrect formulas that involve volume, ratios of atoms without mass consideration, or inverted ratios, as these do not correctly represent percent by mass.