Today the 40% back to school sale of chemCal finished and the price was put back up to $4.99 USD.

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Continuing the series of posts on chemistry, which are connected to the release of the iPhone/iPod Touch chemistry calculator, chemCal, it is now time to look at dilutions, why we need them, and how to work them out.

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Units can be tricky. It is difficult to remember if 10^-6 is micro (µM) or milli-molar (mM). How do I convert between µM and mM? What is a nano-mole? And how many femto-moles are there in a pico-mole? These things can be tricky. chemCal, a basic chemistry calculator for the iPhone and iPod Touch, can help. But you still need an understanding….

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In two previous posts (Chemistry: Calculating Molarity I and Chemistry: Calculating Molarity II) I looked at calculating concentrations in the terms of Molarity (molar), however, scientists also use a slightly different way of expressing concentrations – the percentage concentration.

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In an earlier post I talked about what a mole is in chemistry. You need to understand what a mole of substance is before you can understand concentrations and how to make up a molar solution.

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So, how do you calculate the molarity of a solution? What is molarity? Come to that, what is a mole? (And I don’t mean the small furry kind that leaves hills in the middle of your lawn…)

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