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Home :FAQ :The mole conceptPrint | Comment
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How many atoms or moles of an element are in one mole of compound?

I have a question. In KOH, how many ATOMS of K are in the compound? I say that it is 1 divided by 6.022 × 1023 because there are that many atoms in a mole. My teacher says that it is 1. Then in the same day he says that there is 1 MOLE of K in the KOH compound. He agrees that it is quantitively impossible to do it that way, but he still sticks with his answer. Can you help clear it up?
Stephanie 8/26/99

Vocabulary
Avogadro's number*
ionic compound*
empirical formula*
formula unit*
mole*
molecule*
molecular formula*
Stephanie, the question cannot be answered unless an amount of compound is specified. Instead of asking "how many atoms of K are in the compound?" the question probably should be, "how many atoms of K are in 1 mole of the compound?" or perhaps "How many atoms of K are in 1 molecule of the compound?"

How many moles of K are in 1 mole of KOH? The subscripts in the formula indicate moles of each element per mole of compound. KOH contains only one K, so a mole of KOH contains one mole of K.

How many atoms of K are in 1 mole of KOH? There are 6.022 × 1023 atoms of potassium in every mole of potassium. Since one mole of KOH contains one mole of K, the answer is 6.022×1023 atoms of K.

How many atoms of K are in 1 molecule of KOH? Molecules of KOH can exist in the gas phase, but when we're talking about solid KOH we really should say "formula unit" rather than molecule because this is an ionic compound built of K+ and OH- ions packed together in a 1:1 ratio. If KOH is a molecular formula, we can say that there is one atom of K per KOH molecule. If KOH is an empirical formula, there is one atom of K per formula unit of KOH.

How many moles of K are in 1 molecule of KOH?
1 molecule KOH × (1 atom K
1 molecule KOH
) (1 mol K
6.022 × 1023 atoms K
) = 1.661 × 10-24 mol K

Author: Fred Senese senese@antoine.frostburg.edu



General Chemistry Online! How many atoms or moles of an element are in one mole of compound?

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Last Revised 02/15/10.URL: http://antoine.frostburg.edu/chem/senese/101/moles/faq/atoms-in-compound.shtml