The Mole Can You Dig It

In chemistry, you count very large numbers of particles, such as atoms and molecules. To count them efficiently and quickly, you need to use the count-byweighing method, which means you need to know how much individual atoms and molecules weigh. You can get the weights of the individual atoms on the 

Now try a little harder one. Calculate the formula weight of aluminum sulfate, Al2(SO03- In this salt, you have 2 aluminum atoms, 3 sulfur atoms, and 12 oxygen atoms. After you find the individual weights of the atoms on the periodic table, you can calculate the formula weight like this  

When we humans deal with objects, we often think in terms of a convenient amount. For example, when a woman buys earrings, she normally buys a pair of them. When a man goes to the grocery store, he buys eggs by the dozen. And when 1 go to the office supply store, 1 buy copy paper by the ream. 

We use words to represent numbers all the time — a pair is 2, a dozen is 12, and a ream is 500. All these words are units of measure, and they re convenient for the objects they re used to measure. Rarely would you want to buy a ream of earrings or a pair of paper. 

Likewise, when chemists deal with atoms and molecules, they need a convenient unit that takes into consideration the very small size of atoms and molecules. There is such a unit. It s called a mole. 

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