2.64 grams of an unknown compound was dissolved in water to yield 150 mL of solution. The concentration of the solution was 0.075 M. What was the molecular weight of the substance?

• A. 190 g/mol
• B. 30 g/mol
• C. 90 g/mol
• D. 230 g/mol
• E. 320 g/mol

Answer: (D)

Verified step by step guidance

1. Start by understanding the relationship between molarity, moles, and volume. Molarity (M) is defined as the number of moles of solute per liter of solution. Use the formula: \( M = \frac{n}{V} \), where \( n \) is the number of moles and \( V \) is the volume in liters.
2. Convert the volume of the solution from milliliters to liters. Since 1 liter = 1000 milliliters, divide 150 mL by 1000 to get the volume in liters.
3. Use the molarity formula to find the number of moles of the unknown compound. Rearrange the formula to solve for \( n \): \( n = M \times V \). Substitute the values for molarity and volume into the equation.
4. Once you have the number of moles, use the formula for molecular weight: \( ext{Molecular Weight} = \frac{ ext{mass of the compound}}{ ext{number of moles}} \). Substitute the mass of the compound (2.64 grams) and the number of moles calculated in the previous step.
5. Calculate the molecular weight using the values obtained. This will give you the molecular weight of the unknown compound, which you can compare to the options provided to identify the correct answer.