Calculate the concentration of the dye Blue #1 if 0.610 g are used to prepare 5.0 L of solution. The molar mass of Blue #1 is 792.86 g/mol.

Answer 1

They are asking for the concentration of blue dye #1, and presumably want that answer in molar (M). Of course, concentrations can be expressed any number of ways, such as grams/liter, grams/ml, moles/liter (M), moles/kg solvent (molal), etc. etc. The question is a little vague as it doesn't state the units requested, but the most common form would probably be molarity (M) which is moles of solute/liter of solution.

We know the liters of solution = 5.0 L. So, all we need to find are how many moles of solute (Blue dye) there are. This is easy to find from the mass (0.610 g) and the molar mass (792.86 g/mole). Using dimensional analysis, we have...

0.610 g x 1 mol/792.86 g = 0.0007694 moles (using scientific notation that is 7.694x10^-4 moles)

Since we want moles/L, we thus have 7.694x10^-4 moles/5.0 liters = 1.5388x10^-4 moles/liter

Correcting for significant figurers, the answer will be 1.5x10^-4 moles/liter = 1.5x10^-4 M

Answer 2

First you want to find the Moles by taking

Moles = Mass / Molar Mass

Moles = 0.610 g / 792.86 g/mol

Moles = 0.000769 mol

Then to find the concentration (Molarity) you want to divide by the total volume of the solution

Molarity(M) = Moles of solute / Volumes of solution (L)

Molarity = 0.000769 mol / 5.0 L

Molarity = 0.000154 M