Chemistry 101 or How to understand chemistry. Part I
Sign in for Chemistry Exercise with explanation and answers
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 | |
 | ||
| 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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