Which of the following sets of information is required to calculate the mass percent (percent composition) of an element in a compound?

• A. The empirical formula of the compound and its melting point
• B. The molar mass of the compound and the mass of the element in one mole of the compound
• C. The number of atoms of each element in the compound and the compound's density
• D. The boiling point of the compound and the atomic number of the element

Answer: (B)

Verified step by step guidance

1. Understand that mass percent (percent composition) of an element in a compound is calculated by the formula: \(\text{Mass percent} = \left( \frac{\text{mass of element in 1 mole of compound}}{\text{molar mass of compound}} \right) \times 100\%\).
2. Recognize that to use this formula, you need two key pieces of information: the mass of the element present in one mole of the compound and the molar mass of the entire compound.
3. Note that the empirical formula alone does not provide the molar mass unless the molecular formula is known, and melting or boiling points do not relate directly to mass percent calculations.
4. Understand that the number of atoms of each element can help find the mass of the element in the compound if atomic masses are known, but density is unrelated to mass percent calculation.
5. Conclude that the correct set of information required is the molar mass of the compound and the mass of the element in one mole of the compound, as these allow direct calculation of the mass percent.