Question

) how much of the primary standard benzoic acid (fm 122.12, density 1.27 g/ml) should you weigh out to obtain a 100.0 mm aqueous solution in a volume of 250 ml?

Answer 1

We must know that molarity is a unit for concentration and it is expressed as:

molarity = moles / liters

The molarity is 100 millimolar, or 0.1 molar. The volume is 250 ml, or 0.25 liters. Using the formula above, we find the moles of benzoic acid required.

moles = molarity * liters
moles = 0.1 * 0.25
moles = 0.025

Next, we know that the molar mass for benzoic acid is 122.12 g/mol and the moles of a substance are given by:
moles = mass / molar mass

mass = moles * molar mass
mass = 0.025 * 122.12
mass = 3.05 grams

You will need to weigh out 3.05 grams of benzoic acid