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Moles

Moles. Definition. A mole is the mass of a substance which contains the same number of particles as 12 grams of the isotope carbon 12 . These particles could be atoms, ions or molecules. 12 grams of carbon 12 contain 6.02 x10 23 atoms

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Moles

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  1. Moles

  2. Definition • A mole is the mass of a substance which contains the same number of particles as 12 grams of the isotope carbon12. • These particles could be atoms, ions or molecules. • 12 grams of carbon12 contain 6.02 x1023 atoms • This number is the Avogadro Constant, and is given the symbol L.

  3. Eg; One mole is… 16 + 2= 18g ofwater 63.5g of copper 27g ofaluminium

  4. Calculating the number of particles • Number of particles = moles x Avogadro Constant. • Eg; How many particles are there in 0.1moles of hydrogen? • N = 0.1 x 6.02x1023 = 6.02 x 1022molecules.

  5. Calculating the number of moles • Moles = number of particles / Avogadro constant. • Eg; How many moles of methane are there in 3.01 x1023 molecules? • Moles = 3.01x1023 / 6.02x1023 = 0.5 moles.

  6. Calculating the molar mass • One mole of an element has a mass equal to the relative atomic mass in grams. • Eg; the mass of one mole of sodium is 23g. • The mass of one mole of a compound is found by adding together the masses of all its elements in the correct ratio. • Units gmol-1

  7. Eg; What is the molar mass of calcium carbonate? • Write the formula; CaC03. • M = RAMCa+ RAMC + 3xRAMO. • M = 40 + 12 + 3x16 = 100g

  8. Calculating the number of moles • No moles = mass / RAM • Eg; How many moles are there in 4g of calcium. • Look up the mass number of calcium in the periodic table. • The atomic mass is the mass number in grams. • N = 4 / 40 = 0.1 moles

  9. Think of the equation as a triangle Mass (g) m Relative atomic mass RAM n Number of moles

  10. Rearranging; n = m / RAM mass (g) m Number of moles = Relative atomic mass RAM n

  11. Calculating the number of moles of a compound. • No moles = mass / Mr • Eg; How many moles are there in 15g of calcium carbonate? • Look up the Ars, then add them together to find the Mr. • Mr = 40 + 12 + (16 x 3) = 100 • One mole has a mass of 100g. • N = 15 / 100 = 0.15 moles.

  12. Rearranging; m = nRAM mass = m n RAM Number of moles X RAM

  13. Calculating the mass from moles • Mass = No moles X Ar • Eg; What is the mass of 0.75 moles of sodium? • Ar = 23 • Mass = 0.75 x 23 = 17.25g • Similarly for a compound; • Mass = No moles X Mr • Eg; What is the mass of 0.8 moles of sodium chloride? • Mr = 23 + 35.5 = 58.5 • Mass = 0.8 x 58.5 = 46.8g

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