Solutions

Molarity
Molality
% by mass
Mole fraction
Salinity

When will these people ever make up their minds????

Chemists, chemical engineers, food processors, and environmental scientists each use measurement systems which are different and convenient for themselves. So no-one can agree on what system of units should actually be used. Let’s make an analogy to building construction. Hardwood flooring is sold by the square foot, concrete is by the cubic “yard” and roofing is by the (10 foot by 10 foot) square. Another example of different units being used for convenience.

We’ll it’s no surprise Hank can enlighten us – here he’ll share with us his “Dirty Laundry”

Here are the formulas you need to know;

Molarity = (# moles solute) / (litres of solvent)

Molality = (# moles solute) / (kg of solvent)

Percent by mass = (mass of solute) / (mass of solution) x 100
note: solution is solvent + solute

Salinity = (kg salt) / (1,000 litres water)

You will find plenty of sample exercises in your reading package. You should do all the available problems before the quiz. You do not need to cover freezing point depression or boiling point elevation as we will cover these in the next lesson.

Here’s the least confusing webpage I can find on the definition of Salinity – this is from the National Snow and Ice Data Center (who would even imagine there was such a place).