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The following units are common in chemistry problems.
|Density:||g/mL or g/cm3||--|
The following prefixes are useful abbreviations when working with very small or very large numbers. You might find it useful to memorize the most common prefixes: M, k, m, and µ.
Examples: One nm (nanometer) is 10-9 m (that's small), and 2 kg is 2000 g (that's about a six-pack of your favorite soda).
The "mole" is a fixed number of something. That number is 6.022142x1023. This number is called the Avogadro constant or Avogadro's number.
If you have one mole of fish, you have 6.022x1023 fish (that's a lot of fish). The mole is not the most useful unit for describing the number of fish in a supermarket.
So why do we work in units of moles? Because atoms and molecules are very small with very small masses. You would not notice if you had 1 or 10 or 100 gold atoms in your hand. You would notice, and you might be very happy, if you had one mole of gold atoms in your hand. Look at a periodic table and decide just how many grams of gold you would have?
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