Chemistry 101 or How to understand chemistry. Part I

My grandma used to bake cakes.

To bake a cake for five people you have to mix:
1 cup of flour
3 eggs
1/2 cup of sugar
100 gram of butter

There was no such thing as fat free cakes at that time. That is why they tasted so good.:)

What if you need to bake a cake for 20 people? She did not know chemistry, but she had common sense to calculate proportions.

20 is 4 times greater than 5. So, you have to take 4 times greater number of cups of flour, 4 times greater number of eggs and so on. As a result, you will get a new recipe.

1 * 4=4 cups of flour
3 * 4=12 eggs
1/2 * 4 = 2 cups of sugar
100 * 4 = 400 grams of butter.

In the same way you can solve a problem with chemical reaction.

All chemical reactions occur in equivalent proportions.

If 10 grams of Na2CO3 react with CaCL2 how many grams of CaCO3 is produced?

     10g                                ? g
1. Na2CO3  +  CaCL2  =  CaCO3   + 2NaCL

All compounds react with each other in certain proportions In given reaction one mole of Na2CO3 produces one mole of CaCO3.

Mole is Molecular mass (MW) in grams.

Atomic mass of Na = 23
Atomic mass of C = 12
Atomic mass of O = 16

For Na2CO3 MW is 23 *2 + 12 + 16*3 = 106 g.    - 1 mole

For CaCO3 MW is 40 + 12 + 48 = 100g.   1 Mole.

106 g Na2CO3   produces   100g CaCO3

10 g Na2CO3   produces   X g CaCO3  

To calculate X multiply matched up values on the opposite ends of diagonal and divide the product by unmatched value as shows on the figure below.

106g 100 g
 Proportion 
10g X g

  X=10 * 100 / 106 = 9.4 g of CaCO3

Now you not only solved the chemical equation problem, but also prove to yourself that you can understand chemistry.

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Continue: Part II

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