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The Mole

The Mole. -How do we determine the amount of a substance? -Calculating molar mass. The amount of substance. Scientists talk about the ‘amount of substance’ What this means is how many atoms we have in a given amount of a substance. This is given the symbol n and the unit is the mole .

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The Mole

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  1. The Mole -How do we determine the amount of a substance? -Calculating molar mass

  2. The amount of substance • Scientists talk about the ‘amount of substance’ • What this means is how many atoms we have in a given amount of a substance. • This is given the symbol nand the unit is the mole.

  3. The Avagadro Constant • The amount of substance is based on a standard count of atoms called the Avagadro constant- NA • The Avagadro constant is the number of atoms per mole of the carbon-12 isotope. NA= 6.02 x 1023 mol-1

  4. Mass and mole • The mass of one mole of any substance is simply the relative atomic mass in grams. • One mole of H= 1 g • One mole of C= 12 g • One mole of Sn= 118.7 g • Also works for compounds • One mole of H2O= 18 g

  5. Moles are big. • How big is a mole? Some ideas to give you perspective: • Stacked end to end, 1 mole of cereal boxes would stretch from the Sun to Pluto. • One mole of marbles would cover the USA to a depth of four metres. • One mole of red blood cells would be more than the total number of blood cells found in every human on earth. • 7.5 million times.

  6. Using the mole- Molar Mass • Molar mass, M, is the mass per mole of a substance. Measured in grams per mole. • You can find this by adding together all the relative atomic masses for each atom in a molecule. • For oxygen: M(O2)= 16 + 16 = 32 g mol-1 • For methane: M(CH4)= 12 + (4 x 1) = 16 g mol-1

  7. The amount of substance • The amount of substance n, mass m, and molar mass M, are all linked. m M n= number of moles, mol M= molar mass, gmol-1 m= mass, g n= m M n

  8. Examples • In 48 g of C, n(C)= • In 11 g of CO, n(CO)= • In 4 g of CH4, n(CH4) =

  9. Answers • In 48 g of C, n(C) = 48.0/12.0 = 4.00 mol • In 11 g of CO, n(CO) = 11.0/28 = 0.39 mol • In 4 g of CH4, n(CH4) = 4.0/16 = 0.25 mol

  10. More examples • Calculating M and m is also possible: • Calculate the amount in mol of: • 8.00 g of SiO2 • 2.00 g of HCl • 5.00 kg of Na • Calculate the mass in g of: • 4.00 mol of BeF2 • 6.00 mol of NaCl • 0.25 mol of MgO

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