One mole of a substance contains Avogadro's number of representative particles:
1.00 mole = 6.02 X 10^23 particles
The chemical formula of a compound tells you how many of each type of atom are in a representative particle. According to the formula FeBr3, one mole of FeBr3 contains 1 mole of iron(III) ions and 3 moles of bromide (Br-) ions. Therefore the number of Br- ions is:
3 X 6.02^23 = 1.81 x10^24 Br- ions
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One mole of a substance contains Avogadro's number of representative particles:
1.00 mole = 6.02 X 10^23 particles
The chemical formula of a compound tells you how many of each type of atom are in a representative particle. According to the formula FeBr3, one mole of FeBr3 contains 1 mole of iron(III) ions and 3 moles of bromide (Br-) ions. Therefore the number of Br- ions is:
3 X 6.02^23 = 1.81 x10^24 Br- ions
A mole is a quantity that's useful when considering atoms and molecules. Atoms combine in small whole-number ratios to form compounds. Since atoms of different elements have different masses, quantities are stated in moles for the purpose of using mathematical relationships in calculations. For example, the ratio of iron(III) ions to bromide ions in FeBr3 is the same as the ratio of moles of iron(III) ions to moles of bromide ions, but it's not the same as the ratio of masses of the two types of ions.
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