A sample of an unknown substance weighs 50.0 g and contains 0.625 moles. What is the molar mass of the substance? A. \( 40.0 \mathrm{~g} / \mathrm{mol} \) B. \( 80.0 \mathrm{~g} / \mathrm{mol} \) C. \( 100.0 \mathrm{~g} / \mathrm{mol} \) D. \( 120.0 \mathrm{~g} / \mathrm{mol} \)

To find the molar mass of the substance, you can use the formula: \[ \text{Molar Mass} = \frac{\text{mass}}{\text{moles}} \] In this case, you have a mass of 50.0 g and 0.625 moles. Plugging in the values gives: \[ \text{Molar Mass} = \frac{50.0 \text{ g}}{0.625 \text{ moles}} = 80.0 \text{ g/mol} \] Thus, the correct answer is B. \( 80.0 \mathrm{~g} / \mathrm{mol} \). Understanding molar mass can be fun because it helps us connect tiny atoms with the materials we encounter every day! For example, did you know that water (H₂O) has a molar mass of about 18.0 g/mol, which is crucial in everything from cooking to chemistry experiments? If you're ever in doubt about calculating molar mass, a common mistake is forgetting to convert grams to moles before using them in calculations. Always double-check that you have the correct number of moles and that you're dividing by the correct quantities. Happy calculations!