Molarity

Chemistry: IB Diploma Higher Level, topic 1.9.1

Molar Calculations of Solutions

We can calculate the number of moles of a liquid or solution using the volume and concentration.

Solutions are sometimes known as homogenous mixtures and can be liquid, solid, or gas.
In solutions, the constituents have the same proportions throughout the sample, so the macroscopic properties of the solution are consistent throughout.
Heterogeneous mixtures have a non-uniform composition and the macroscopic properties vary depending on the constituents.
In heterogeneous mixtures, you can separate the individual components. An example would be a cup of water with gravel in.

Liquid solutions can be represented in a variety of ways. The most common way in a laboratory is "molarity".
It's much easier to look at a liquid and measure its volume than to evaporate any water and measure the mass of the remaining solid.
So we need a value that will let us know how much of a solid is dissolved in a solution simply from its volume.
If we know the concentration of a solution, we can calculate the number of moles in any sample volume of the solution.

Molarity is defined as moles per unit volume. The usual units of molarity are moles per liter (L).
So moles per liter is mol ÷ L.
This is often written as mol L ^-1 or just "M".
Molarity is sometimes written as moldm ^-3, where 1 L = 1 L. (Same thing, just different units!)