Question

Pepsi brand soft drinks contain 38 mg of caffeine (molar mass = 194.19 g/mol) for every serving (355 mL of solution) What is the molarity of caffeine in this solution?

Answer 1

Answer:

Molarity is 5.51 *10^-5 mol/dm3

Explanation:

Molarity shows the number of solutes in moles per litre of solution.

step 1: Calculate the concentration in g/dm3

38 mg in 355 mL of solution

38/ 1000 g in 355/1000 L of solution

Concentration in g/dm3 = 0.0038 / 0.355

=  0.0107 g/dm3

step 2: Calculate the concentration in mol/dm3

Concentration in mol/dm3 = concentration in g/dm3 / RMM

RMM = 194.19 g/mol

Molarity = 0.0107 / 194.19

molarity = 5.51 * 10^-5 mol/dm3 of solution.