Summary
Summary AS Unit F321 - Atoms, Bonds and Groups
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A level notes on unit 1 of OCR A Chemistry, made by an A student
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RELATIVE ATOMIC MASSWe can use a mass spectrometer to identify the number of isotopes + abundance of
isotopes. From this we can calculate Ar (relative atomic mass).
Ar = (Mass of isotope x abundance) + (Mass of isotope x abundance) / 100
E.G. (28x92.21) + (29x4.7) + (30x3.09) / 100 = 28.1
204.37 = (20.3 x Y) + (20.5 x (100-y) / 100
1. Multiple by 100
20437 = (203 x Y) + (205 x (100-Y)
2. Multiply by the 100 in the bracket
20437 = 203y + 20500 - 205y
3. Minus the 20,500 from the original number
-63 = 203y - 205y
4. Minus the numbers
-63 = -2y
5. Divide by the y (in this case, 2)
31.5 = Y
Relative atomic mass = The weighted mean mass of an atom of an element compared
1/12th of the mass of carbon12.
Relative isotopic mass = The mass of one isotope compared to one twelfth of the
mass of carbon12.
IONIC EQUATIONS
Spectator ions = A particle that hasn’t changed from left to right.
Ignore spectator ions in ionic equations
ONLY SPLIT IF AQ
E.G. BaCl2 (aq) + 2AgNO3 (aq) -> Ba(NO3)2 (aq) + 2AgCl (s)
Ba 2+ , 2Cl - , 2Ag +, 2NO3-, -> Ba2+ , 2NO3-
2Cl- (aq) + 2Ag(aq) -> 2AgCl (s)
, STOICHIOMETRY
= Mole ratio
E.G. Calculate the mass of aluminum needed to react with 150g of Chlorine.
2Al + 3Cl2 -> 2AlCl3
n Cl2 = m/Mr - 150/71 = 2.11268 moles
Cl2 : Al
3 : 2
n Al = n x Mr = 1.40845 x 27 = 38.0g
MOLES & GASES
Gases take up a specific volume of space at RTP (room temperature & pressure, 25
degrees & 100KPa).
One mole of gas at RTP has a volume of 24dm3.
/
cm3 -> dm3 -> m3
<- <-
x 1000 x 1000
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