Final answer:
The mole fraction of heptane in a solution made by mixing 31 g of heptane and 141 g of benzene is 0.146, when calculated to three significant digits.
Step-by-step explanation:
To calculate the mole fraction of heptane in the solution, we first need to find the number of moles of each component. The molar mass of heptane (C7H16) is approximately 100.21 g/mol, and the molar mass of benzene (C6H6) is about 78.11 g/mol. The number of moles of heptane is 31 g / 100.21 g/mol ≈ 0.309 moles, and the number of moles of benzene is 141 g / 78.11 g/mol ≈ 1.805 moles. Therefore, the total moles in the solution is 0.309 moles + 1.805 moles = 2.114 moles.
The mole fraction of heptane is calculated by dividing the number of moles of heptane by the total number of moles in the solution. So, the mole fraction of heptane is χHeptane = 0.309 moles / 2.114 moles ≈ 0.146. Since the question asks for the correct number of significant digits, we use three significant digits, resulting in a final answer of 0.146 for the mole fraction of heptane.