# How do you solve or do moles in chemistry?

enotechris | College Teacher | (Level 2) Senior Educator

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A mole is just a number, like a billion or a trillion. So a billion in numeric form looks like 1,000,000,000 and a trillion is the same thing with 3 more zeros, or 1,000,000,000,000.  If you looked at these numbers in scientific notation, they would be 1 x 10^9 and 1 x 10^12, where the exponent is actually the number of zeros in the number.  A mole then, is actually the number 6.02 followed by 23 zeros, or 6.02 x 10^23, which is a huge number, and is used to count particles (atoms, ions, or molecules) since they're so small. To calculate values in chemistry, if you know the number of grams a substance weighs to make a mole of that substance, or grams per mole, and you have a sample of so many grams, you can find out how many moles that sample has, so

weight of a sample in grams / grams per mole  = # moles, or

g(sample) / g/mole = moles, or as my chemistry teacher used to tell me, "grams divided by grams per mole equals moles!"

revolution | College Teacher | (Level 1) Valedictorian

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Let's define what moles means.

Moles is a very big number, and this big sum can be compared to 1 million tonnes of rice. Moles is a quantitative unit, as it is a measurable property. In a mole, there is about 6*10^23 particles, and this is called the Avogadro constant. It will take you 2 million years to count up to that number. The particles present could be atoms, molecules, ions and electrons. Actually, a mole of a substance contains the same number of particles as the number of atoms in 12 g of a carbon-12 atom.

To figure out the moles of a particular type of element, you need to first know the mass of that element and also its molecular mass (Mr) which is at the top of each element in the Periodic Table. Then, you divide the mass with the Mr to get the moles of the chemical element. To put it simply,

Number of moles of an element= (mass of element in grams)/ (relative molecular mass of the element)

Also, you can get the number of moles by dividing the number of particles with the Avogadro's constant (6*10^23). Equal number of moles contain equal number of particles.

gege18 | Student, Grade 11 | eNotes Newbie

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thirdgraderocks | Elementary School Teacher | (Level 1) Honors

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• 1 mole of molecules has a mass equal to the molecular weight in grams.
• examples
• 1 mole H2O is the number of molecules in 18.015 g H2O
• 1 mole H2 is the number of molecules in 2.016 g H2.