A2 Salters Chemistry Risk Assessments
Carry out a risk assessment for the sulphuric acid and potassium
manganate (VII) used in this experiment.
A Risk Assessment is an exercise which should be carried out prior to all practical work at
this level. This should ensure that you have considered all the safety implications relating to
the use of any chemical involved. We all want to work in as safe an environment as possible!
For investigation or assessment purposes you usually need to start from scratch and use
Haz-cards – print these off from the internet – sometimes there are both teachers and
students versions.
http://www.cleapss.org.uk/
Secondary
Secondary resources
User Name:
Password:
The following checklist should be used as a guide:
1. Write the chemical name, formula and concentration to be used (in mol dm-3)
2. Read the Haz-cards thoroughly.
3. Record any general hazards e.g. toxic, harmful, corrosive etc.(can you give more
detail e.g. when inhaled, swallowed or by skin absorption)
4. Record any special handling information e.g. wear safety glasses, gloves, stoppers on
bottles of flammable liquids and keep away from naked flames
5. Record any first aid precautions e.g. what to do if the chemical:
a) Gets in your eye
b) Is inhaled
c) Gets in your mouth/is swallowed
d) Gets on your skin
e) Gets spilt on your clothing
6. Record procedures to be employed to deal with:
a) Spillage in the lab
b) Correct disposal of waste chemicals
Irrelevant risks e.g. ones relating to chemicals or concentrations not being used should not
be recorded.
A little book of tips for titrations.
 Calculating the average titre
 Evaluation of results
 Risk assessment

Calculating the average/mean titre:
Titration
Final burette reading/cm3
Initial burette reading/cm3
Titre/cm3
Rough
22.00
0.00
22.00 T
1
43.85
22.00
21.85 √
2
22.95
1.00
21.95 √
3
4
5
Average titre = 21.85 + 21.95 / 2 = 21.90 (quote to 2 decimal places)
Titration
Final burette reading/cm3
Initial burette reading/cm3
Titre/cm3
Rough
22.00
0.00
22.00 T
1
43.85
22.00
21.85 √
2
23.15
1.00
22.15 √
3
44.10
22.15
21.95 √
4
5
Average titre = 21.85 + 22.15 + 21.95 / 3 = 21.98 (there is a rule that you use any titres
within a 0.3cm3 range of the concordant titres to calculate the average)
What is the average titre?
 21.10 + 21.50 + 21.20?
Evaluation has two aspect – evaluation of measurements and
evaluation of procedures (same as GCSE now)
Evaluation of results:
We look at how precise the measurements are. We look at the uncertainty associated with a
measurement (sometimes called the precision error). Then we calculate the percentage
uncertainty (sometimes called the percentage error).
Percentage uncertainty (percentage error) = uncertainty (precision error) x 100
reading
For graduated equipment the uncertainty / precision error is taken to be half a division on
either side of the smallest unit on the scale you are using. For volumetric (or ungraduated)
measuring equipment you use the precision error associated with it.
Using the balance:
The uncertainty associated with a two decimal place balance reading = ±0.005g
The percentage uncertainty associated with a reading of 119.06g = 0.005 x 100 = 0.004%
119.06
The uncertainty associated with the difference between two balance readings = 2 x 0.005 =
±0.010g
The percentage uncertainty in weighing out a mass of 2.56g = 0.010 x 100 = 0.4%
2.56
Using the 250cm3 volumetric flask:
The uncertainty associated with a volumetric flask reading = ±0.2cm 3
The percentage uncertainty associated with volumetric flask reading = 0.2 x 100 = 0.08%
250
Using the 25cm3 pipette:
The uncertainty associated with a pipette reading = ±0.06cm 3
The percentage uncertainty associated with pipette reading = 0.06
25
Using the burette:
The uncertainty associated with a burette readings = ±0.05cm 3
x 100 = 0.2%
The percentage uncertainty associated with a reading of 25.85cm 3 = 0.05 x 100 = 0.2%
25.85
The uncertainty associated with the difference between two burette readings (a titre)
= 2 x 0.05 = ±0.10cm3
The percentage uncertainty in measuring out a volume of 25.85cm 3 = 0.10 x 100 = 0.4%
25.85