Concentration Problems

Question

A 250 mL glass of orange juice contains

30.0 mg of riboflavin, C17H20N4O6.

What is the molarity of the riboflavin in this glass?

Answer 1

Molarity (M) = moles of solute per liter of solution.

You have 250 mls of solution which is = 0.250 L of solution

You have 30.0 mg of riboflavin = 0.0300 g riboflavin

molar mass riboflavin (C₁₇H₂₀N₄O₆) = 376 g/mol

The moles of riboflavin = 0.0300 g x 1 mol / 376 g = 7.98x10^-5 mols

Molarity = 7.98x10^-5 mols / 0.250 L = 3.19x10^-4 M