Unit Conversions

Key Questions

  • To begin unit conversions you want to write down all the given information you have in the problem including what the question is asking for.

    Example: How many moles of sodium are there in a 0.59 gram sample of sodium metal.

    1. Given info: 0.59 grams Na
      moles Na=?
      In this simple example we see that the question is asking for the moles of sodium, so when we know that when we convert we should be left with moles as our only unit .
    2. Now that you know what units you need to end up with, we need to find something that relates our given units ( grams ) to our desired unit ( moles .)

    A simple connection for grams#->#moles is given by the molar mass !
    1 mol Na=23 grams Na

    Now , Set up your problem:

    0.59 grams Na #* (1 mol Na)/(23 grams Na)=0.026 mol Na#

    Since we cancelled our units properlly (#grams*(mol)/(grams)=mol#) we know that our solution must be correct!

  • I recommend that my students use a technique called dimensional analysis which is basically like multiplying fractions.

    To use this you need to identify conversion factors. Some examples of conversion factors are:
    1 hour = 60 min
    1m = 100cm
    1km = 1000m

    Here is a video of some easy conversion problems using these conversion factors solved using dimensional analysis:
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    Here is a video with some more challenging examples:

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    Hope this helps!