| The Mole |
The mole is a concept introduced by Amedeo Avogadro. How many eggs are there in 1 dozen? You answer 12. How did you know? Because that is what dozen stands for -- 12 of just about anything. How many atoms of carbon are there in 12 grams carbon? Your answer? Oh, well. It is not just that simple. Scientists spend time "counting" these atoms. Until sometime ... TA DAH! they got it. It is equal to 6.02 x 1023 atoms of carbon. Great! The mole is born. Yes, 1 mol is 6.02 x 1023 particles of just about anything too. When we refer to a mole of particles we only write mol. Now, let me ask you again. How many atoms of hydrogen are there in 1 mol of hydrogen? Your answer? Correct! There are 6.02 x 1023 H atoms in 1 mol hydrogen. So basically this is it: When the number of grams of an element is numerically equal to its atomic weight in amu, we have 1 mol of an element and there are 6.02 x 1023 atoms of that element. Try this exercise: The atomic weight of sodium (Na) is 23.0 amu. How many atoms are there in 46.0 grams of Na? Check answer here. We can also relate the mole concept in a molecule. Let's examine methane (CH4). Computing the molecular weight, we have 1(12.0 amu) + 4 (1.0) amu = 16 amu. Therefore, 1 mol methane weighs 16 grams. And in 1 mol CH4, there are 6.02 x 1023 molecules of CH4. Do you get it? Good. How many atoms of C in 1 molecule of CH4? Correct! The answer is 1. What about this question: How many mols of C are there in 1 mol of CH4? Ok. The answer is 1 mol C. Get the idea? How many mols H are there in 1 mol CH4? Now, you're talking! Correct. There are 4 mols H in 1 mol CH4. Let me see if you can get this one: How many atoms of H are there in 1 mol CH4? The answer is: (1 mol CH4) (4 mols H)/(1 mol CH4) x (6.02 x 10 23 atoms H)/ (1 mol H) Here is a good exercise: Butane, C4H10 is one of the common hydrocarbons used as fuel. How many atoms of C are there in 87 grams of butane? Click here for answer. |
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