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How do you work out moles?I need an explanation. My teacher isn't helping me on it...
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How you work out moles depends on the question you are asked. The mole of any element is simply its atomic weight. Thus, one mole of carbon is 12.01 grams because that is the atomic weight of carbon. In one mole of oxygen there is 16.00 grams because that is the atomic weight of oxygen. If you are asked to find out how many moles there are in a given mass you use the equation: number of moles = mass (given)/atomic weight.
Eg: how many moles of carbon is 28 g of carbon ?
To work this out you use the above formula. Mass= 28. Atomic weight = 12.01
= 2.33 moles of carbon.
One mole of any element has 6.022 x 10 to the power of 23 atoms ( Avogadro's number). Thus in one mole fluorine there are 6.022 x 10 to the power of 23 atoms. In one mole of Gold there are 6.022 x 10 to the power of 23 atoms.To find out the number of atoms you use the formula: number of atoms = number of moles x Avogadro's number.
Eg: How many atoms of silver in 2 moles of silver.
Answer: 2 (number of moles) x 6.022 x 10 to the power of 23
Posted by chezmamann on May 29, 2009 at 7:17 PM (Answer #1)
High School Teacher
How many moles of silicon are in 4.60 g of Si? This is the first venture into one of the most common chemical calculations, finding the number of moles present in a given mass of substance. Restate it: 4.60 g Si <=> ? mol Si The atomic mass (you need this for each element in your problems, too) of silicon, 28.09 (rounded from 28.0855), gives us the needed tool, because we know from the definition of the mole that the following is true about silicon. 28.09 g Si <=> 1 mol Si Like any equivalency, this one makes available two conversion factors. One will be the tool we need for our grams-to-mole conversion. 28.09 g Si/1 mol of Si and 1 mol Si/28.09 g Si or:
28.09 g Si and 1 mol Si
1 mol Si 28.09 g Si
Thus if we multiply the given, 4.60 g Si, by the second conversion factor, we will obtain the answer. Solution: We carry out the following calculation. Notice how the units, g Si, cancel to leave the correct unit, mol Si (Draw in the cancel lines yourself).
4.60 g Si x 1 mol Si/28.09 g Si = 0.164 mol Si
In other words, 4.60 g Si <=> 0.164 mol Si. Now, check to see if the answer makes sense. Is its numerical size in the right range? Yes, because we began with 4.60 g Si, clearly less than a whole mole of silicon, so the answer has to reflect this obvious fact. The atomic mass=1 mole.
Posted by amy-lepore on February 4, 2009 at 11:33 PM (Answer #2)
A mole (otherwise known as "Avogadro's Number," first determined by Italian scientist Amadeo Avogadro (1776-1856) ) is a specific, extremely large number, like a million (1 * 10^6) or a billion (1* 10^9). If you count atoms, molecules, marbles, or cars, and have 6.02 * 10^23 of them, you've got a mole. Consider it just like any ordinary number with which you can add, subtract, multiply, or divide. If you take the atomic mass of an element, which is unitless, and specify that atomic mass as a number of grams, by definition, you've got 1 mole of that element. If you've got a solid of so many grams, you can calculate the number of moles by remembering that grams / grams per mole = # of moles. If you've got a gas, the constant to remember is 22.4 liters / mole.
Posted by enotechris on February 5, 2009 at 4:57 AM (Answer #3)
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