# OCR AS Chemistry Notes- Module 1 to 3

• Created by: elliepin
• Created on: 02-09-17 16:11

AS CHEMISTRY- Module 1 to 3

SUBATOMIC PARTICLE

RELATIVE MASS

RELATIVE CHARGE

PROTON

1

+1

NEUTRON

1

0

ELECTRON

1/2000

-1

MASS NUMBER- NUMBER OF PROTONS AND NEUTRONS

XATOMIC (PROTON) NUMBER- NUMBER OF PROTONS AND THEREFORE ELECTRONS

ISOTOPES-
ISOTOPES OF AN ELEMENT ARE ATOMS WITH THE SAME NUMBER OF PROTONS BUT DIFFERENT NUMBERS OF NEUTRONS.

RELATIVE MASS

RELATIVE ATOMIC MASS
THE WEIGHTED MEAN MASS OF AN ATOM OF AN ELEMENT COMPARED TO 1/12 OF CARBON-12.
The relative atomic mass of each atom is the mass number.

RELATIVE ISOTOPIC MASS

THE MASS OF AN ATOM OF AN ISOTOPE OF AN ELEMENT COMPARED TO 1/12 OF CARBON-12.

CALCULATING RELATIVE ATOMIC MASS

·      Multiply each relative isotopic mass by its isotopic relative abundance and add up the results.

·      Divide by 100

·      EXAMPLE:
(10 X 20.0) + (80.0 X 11.0) = 1080
1080/100 = 10.8
THE RELATIVE ATOMIC MASS OF BORON IS 10.8
Calculating relative abundance using a mass spectra is the same but you divide by the sum of relative abundances (it is not always guaranteed to be 100).

RELATIVE MOLECULAR MASS

THE AVERAGE MASS OF A MOLECULE COMPARED TO 1/12 OF CARBON-12.

RELATIVE FORMULA MASS
AVERAGE MASS OF A FORMULA UNIT COMPARED TO 1/12 OF CARBON-12.
It is used for compounds that are ionic or giant covalent such as SiO2.

THE MOLE
ONE MOLE IS EQUAL TO 6.02 X 1023 (THE AVOGADRO CONSTANT).

Number of moles = Number of particles you have / Number of particles in a mole.

MOLAR MASS
has the same numerical value as he relative molecular mass (Mr). The only difference is that you put ‘g mol-1’for grams per mole on the end.

CALCULATIONS WITH MOLES     How many moles of aluminium oxide are present in 5.1 grams                                          of Al2O3 ?

GAS VOLUMES
If the temperature and pressure stay the same, one mole of gas always has the same volume- this is known as molar gas volume and it has the units of dm3 mol-1.

At room temperature and pressure (298 K and 100 kPa) the molar gas volume is 24 dm3 mol-1 or 24000 cm3 mol-1.

Number of moles = Volume in dm3 / 24

Or

Number of moles = Volume in cm3 / 24000

IDEAL GAS EQUATION

pV = nRT

pressure (Pa) x Volume (m3) = moles (n) x temperature (K) x the gas constant (J k-1 mol-1)

REARRANGING THE IDEAL GAS EQUATION

n = pV / RT

V = nRT / p

What volume would 2.0 moles of argon gas occupy at 27.0 c and 100 kPa?

V = nRT / p                              V = 2.0 x 8.314 x (27.0 +