# The Mole - PowerPoint PPT Presentation

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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

-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 nand the unit is the mole.

• 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

• 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.

• 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

• 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 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

• In 48 g of C, n(C)=

• In 11 g of CO, n(CO)=

• In 4 g of CH4, n(CH4) =

• 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

• 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