For which compound does 0.256 mol have a mass of 12.8 g? (Assume the compound is pure.)

• A. $C_2{H}_6$
• B. $C_2{H}_4$
• C. $C_3{H}_8$
• D. $C_2{H}_2$

Answer: (B)

Verified step by step guidance

1. Identify the molar mass of the compound by using the relationship between moles, mass, and molar mass: \(\text{molar mass} = \frac{\text{mass}}{\text{moles}}\).
2. Calculate the molar mass using the given values: mass = 12.8 g and moles = 0.256 mol, so \(M = \frac{12.8\ \text{g}}{0.256\ \text{mol}}\).
3. Determine the molar mass of each given compound by summing the atomic masses of carbon (C) and hydrogen (H) atoms in their molecular formulas. Use atomic masses approximately 12.0 g/mol for C and 1.0 g/mol for H.
4. Compare the calculated molar mass from step 2 with the molar masses of the given compounds to find which one matches the calculated value.
5. Select the compound whose molar mass matches the calculated molar mass, confirming that 0.256 mol of this compound has a mass of 12.8 g.