Starter - Exam questions feedback
1) Learn precise definitions for masses, and acids and
bases.
2) For concentration calculations, make sure volumes are
converted to dm3 before completing calculations.
3) Practice balancing equations, and predicting salts.
4) Learn how to calculate the relative atomic mass from
percentage abundances.
Calculating the formula of
hydrated salts
C grade – Be able to complete, and explain an
accurate titration experiment
B grade – Be able to use data to calculate the hydrated
formula of a salt
A grade – Conduct a titration experiment accurately,
and use derived data to correctly calculate the formula
of a hydrated salt.
The method
1) Record the mass of the hydrated salt.
2) Record the mass of the anhydrous salt.
3) Calculate the mass of water (subtract
anhydrous from hydrated)
4) Using Mr of salt and water, calculate mole
ratio of salt to water.
Example
Na2SO4.xH20
Calculating hydrated salt formula from
experimental data
For assessment
What is your calculated formula?
What did you do well?
What do you need to improve on before
completing and exam question on hydrated
salts?
Calculating the formula of
hydrated salts
C grade – Be able to complete, and explain an
accurate titration experiment
B grade – Be able to use data to calculate the hydrated
formula of a salt
A grade – Conduct a titration experiment accurately,
and use derived data to correctly calculate the formula
of a hydrated salt.
Plenary
What have you learned about AS
Chemistry exam questions
From GCSE:
What are oxidation and reduction?
Oxidation Number
C grade – Be able to explain reduction and
oxidation in terms of electron transfer
B grade – Be able apply the term oxidation
number
A grade – Be able to identify and calculate
changes in oxidation number during a reaction
OIL RIG
Full equation:
Mg
+
Cl2

Half equations:
Mg 
Cl2
Mg2+ + 2e-
+ 2e-

2Cl-
MgCl2
Oxidising and reducing agents
Oxidising agents accept electrons
Non metals: e.g. F2, Cl2, O2
Reducing agents donate electrons
Metals:
e.g. Na, Fe, Zn
Using oxidation numbers
Oxidation number is similar to the charge from
GCSE.
For example:
Mg2+ has oxidation number
O2- has oxidation number =
= +2
-2
p43
However there are other rules too
Species
Oxidation number
Examples
Uncombined
element
0
Mg, Fe, O2, Cl2
Combined oxygen
(in an oxide)
-2
MgO, H2O
Combined hydrogen
+1
H2O, NH3
Combined fluorine
-1
HF, CaF2
All compounds must be zero overall
CO2
Charged ions must balance to the
charge
2SO4
Using oxidation numbers
Cr2O3(s) + 2Al(s)
 Al2O3(s) + 2Cr(s)
For assessment
Complete oxidation number questions on
worksheet provided.
Oxidation Number
C grade – Be able to explain reduction and
oxidation in terms of electron transfer
B grade – Be able apply the term oxidation
number
A grade – Be able to identify and calculate
changes in oxidation number during a reaction