AS/A2 Salters Chemistry Risk Assessments



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.

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 |Rough |1 |2 |3 |4 |5 |

|Initial burette reading/cm3 |0.00 |22.00 |1.00 | | | |

Average titre = 21.85 + 21.95 / 2 = 21.90 (quote to 2 decimal places)

Titration |Rough |1 |2 |3 |4 |5 | |Final burette reading/cm3 |22.00 |43.85 |23.15 |44.10 | | | |Initial burette reading/cm3 |0.00 |22.00 |1.00 |22.15 | | | |Titre/cm3 |22.00 T |21.85 √ |22.15 √ |21.95 √ | | | |

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).

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 = ±0.2cm3

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 = ±0.06cm3

The percentage uncertainty associated with pipette reading = 0.06 x 100 = 0.2%

25

Using the burette:

The uncertainty associated with a burette readings = ±0.05cm3

The percentage uncertainty associated with a reading of 25.85cm3 = 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 25.85cm3 = 0.10 x 100 = 0.4%

25.85

-----------------------

Percentage uncertainty (percentage error) = uncertainty (precision error) x 100

reading



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