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 Na_{2}CO_{3} react with CaCL_{2} how many grams of CaCO_{3} is produced?

10g ? g

1. Na_{2}CO_{3} + CaCL_{2} = CaCO_{3} + 2NaCL

All compounds react with each other in certain proportions
In given reaction one mole of Na_{2}CO_{3} produces one mole of CaCO_{3}.

Mole is Molecular mass (MW) in grams.

Atomic mass of Na = 23

Atomic mass of C = 12

Atomic mass of O = 16

For Na_{2}CO_{3} MW is 23 *2 + 12 + 16*3 = 106 g. - 1 mole

For CaCO_{3} MW is 40 + 12 + 48 = 100g. 1 Mole.

106 g Na_{2}CO_{3} produces 100g CaCO_{3}

10 g Na_{2}CO_{3} produces X g CaCO_{3}

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 CaCO_{3}

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

The first link is for a eBook, the second link is for a paperback.

Chemistry for students and parents: Key Chemistry Concepts, Problems and Solutions

Chemistry for Students and Parents: Key chemistry concepts, problems and solutions

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