Chemistry Mysteries: Stoichiometry

You might find it hard to pronounce or spell the word, "Stoichiometry". Try to memorize this word by saying it out loud for several times.

"Stoichiometry", "STOYCHIOMETRY", "STOY-KEE-AHM-EH-TREE".

Good enough?

As you can see, our topic today is "Stoichiometry".

What is Stoichiometry?

Stoichiometry is a Greek word―"Stoichio", meaning element, and "metry",meaning measurement.

Basicly, it is about measuring the amounts of substances involved in a reaction.

Stoichiometry allows you to do many calculations on a chemical reaction using the ratio of moles.

Let's look at an example of caculation using stoichiometry:

Q.When solid Al is heated in presence of oxygen gas, an aluminum oxide, Al₂O₃, is formed. How many moles of aluminum oxide are produced if 32.0g of O₂are heated?

When performing a calculation using stoichiometry, Balanced Chemical Equation is ALWAYS REQUIRED, because that's what tells you the ratio of substances in a system.

So, before starting any kinds of calculations, you must come up with a chemical equation.

４Al + ３O₂→　２Al₂O₃（Don't forget to balance it!）

Now, as you can see, the ratio of moles of O₂to Al₂O₃is 3:2. ( it is called the mole ratio)

using this information, you can find the moles of alminium oxide produced from the reaction.

-convert 32.0g of O₂to moles.

32.0g O₂x 1mole O₂/32.0g O₂= 1mole O₂

-then, using mole ratio, calculate the moles of 　Al₂O₃produced in the reaction.

1 mole O₂x 2moles Al₂O₃/3moles O₂= 0.666 moles Al₂O₃

The answer to this question is, 0.666 moles of Al₂O₃

Using same strategy, you can calculate other quantities.

For example, grams of the substance, moles of the substance, volume of the substance, atoms of substance, etc.)

Here`s another example of stoichiometric calculation!

Q.In a chemical reaction Mg(OH)₂ + 2HCl --> MgCl₂ +2 H2O, 25mLof 3M Magnesium hydroxide, Mg(OH)₂ reacted with enough Hydrochloric acid, HCl to produce Magnesium Chloride, MgCl₂. How many grams of Magnesium Chloride will be produced?