Question

Calculate the molarity of 21.3 g of MgS in 765 mL of solution. Molarity:

a. 0.02 M
b. 0.1 M
c. 0.5 M
d. 2 M

Answer 1

To find the molarity of 21.3 g of MgS in 765 mL of solution, we calculate the moles of MgS and divide by the volume in liters. The molarity is approximately 0.494 M which, when rounded to one significant figure, matches answer choice (c) 0.5 M.

Step-by-step explanation:

To calculate the molarity of 21.3 g of MgS in 765 mL of solution, we first need to determine the molar mass of MgS. The molar mass of magnesium (Mg) is approximately 24.305 g/mol, and the molar mass of sulfur (S) is approximately 32.065 g/mol. Therefore, the molar mass of MgS is 24.305 g/mol + 32.065 g/mol = 56.370 g/mol.

Next, we calculate the number of moles of MgS as follows:

Moles of MgS = mass (g) / molar mass (g/mol)

Moles of MgS = 21.3 g / 56.370 g/mol ≈ 0.378 moles

To find the molarity, we need to convert the volume of the solution from milliliters to liters:

Volume in liters = 765 mL * (1 L/1000 mL) = 0.765 L

Molarity (M) = moles of solute / liters of solution

Molarity = 0.378 moles / 0.765 L ≈ 0.494 M

When rounding to one significant figure, the closest answer is (c) 0.5 M.