Question

A student dissolves of styrene in of a solvent with a density of . The student notices that the volume of the solvent does not change when the styrene dissolves in it. Calculate the molarity and molality of the student's solution. Be sure each of your answer entries has the correct number of significant digits.

Answer 1

Answer:

0.576M and 0.655m

Explanation:

...Dissolves 15.0g of styrene (C₈H₈) in 250.mL of a solvent with a density of 0.88g/mL...

Molarity is defined as moles of solute (Styrene in this case) per liter of solution whereas molality is the moles of solute per kg of solvent. Thus, we need to find the moles of styrene, the volume in liters of the solution and the mass in kg of the solvent as follows:

Moles styrene:

Molar mass C₈H₈:

8C = 12.01g/mol*8 = 96.08g/mol

8H = 1.005g/mol* 8 = 8.04g/mol

96.08g/mol + 8.04g/mol = 104.12g/mol

Moles of 15.0g of styrene are:

15.0g * (1mol / 104.12g) = 0.144 moles of styrene

Liters solution:

250mL * (1L / 1000mL) = 0.250L

kg solvent:

250mL * (0.88g/mL) * (1kg / 1000g) = 0.220kg

Molarity is:

0.144 moles / 0.250L =

0.576M

Molality is:

0.144 moles / 0.220kg =

0.655m