Question #7e44d

1 Answer
Jan 13, 2017

Just be sure to specify the units first!


Mixtures can be measured as weight percents (applicable to solids, liquids and gases), and volume percents (applicable to all phases, but all components must be in the same phase). In chemistry, molarity and molality are most often used because they include the relationship of the mass or volume to the moles of a substance.

A “20% NaOH solution” would normally be a weight ratio, because NaOH is a solid. In solution it may be calculated as either molar (Moles/L) or molal (grams/L water). With a given mass “20g” and a volume you can calculate either molarity or molality, or calculate the volume of solvent necessary to give you the desired molarity.

The designation “0.05M” already includes the definition of molar (M), so you can calculate how to prepare it, or how much NaOH is in a particular amount, volume or weight. You would NOT have a specification of “20g in 0.05M” unless it was an instruction to make an addition of mass to an existing solution.

Whenever you have a question about units or conversions, ASK for clarification before proceeding!! Too many accidents – many severe – have resulted from incorrect units being used in calculations.