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Chemistry

Calculating Concentration

How can we Calculate Concentration?

This post will go through some formulae applied to find and manipulate concentrations for Prelim Chemistry.

Topic: Concentration and Molarity

  • Manipulate variables and solve problems to calculate concentration, mass or volume using:

    • C=n/V (molarity formula)
    • Dilutions (number of moles before dilution = number of moles of sample after dilution)

 

Introducing The Molarity Formula C = n/V

Last post we introduced concentration, this video will go in a little more depth and introduce the molarity formula C=n/V (concentration = (moles of solute) / (volume of solution)). (Note that this video spells litre like liter, don’t spell it like that.)

 

This next video goes through the molarity formula as well, have a look if you’re still confused or to see if you can understand it in a different context.

 

Dilution C1V1=C2V2

Recall the molarity formula, C=n/V, if we arrange this to make moles the subject: n = CV.

Now, let’s say an initial solution (1) has n1 moles (so n1 = C1V1), if the solution is diluted, which means more solvent is added, the same number of moles will be present in the final solution (2), which we can denote as n2 (so n2 = C2V2).

As the number of moles of the initial and final solution is the same, n1 = n2 and subsequently, C1V1 = C2V2, this is the dilution formula.

This video will take you through some dilution problems.

 

A form of dilution is serial dilution which is just many dilutions in a row, so a dilution on top of another dilution on top of another dilution. This video will explain a little more about serial dilution.