The mole
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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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The mole

The Mole

-How do we determine the amount of a substance?

-Calculating molar mass


The amount of substance

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.


The avagadro constant

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


Mass and mole

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


Moles are big

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.


Using the mole molar mass

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


The amount of substance1

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


Examples

Examples

  • In 48 g of C, n(C)=

  • In 11 g of CO, n(CO)=

  • In 4 g of CH4, n(CH4) =


Answers

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


More examples

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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