Uncertainties

Question 1

Readings and measurements

Answer 1

Readings- the values found from a single judgement when using a piece of equipment
Measurements- the values taken as the difference between the judgements of two values

Question 2

Mass balance uncertainty

Answer 2

+/- 0.001g (if 3 d.p balance)

Question 3

Volumetric flask uncertainty

Answer 3

+/- 0.1cm^3

Question 4

25cm^3 pipette

Answer 4

+/- 0.1cm^3

Question 5

Burette uncertainty

Answer 5

+/- 0.10cm^3

Question 6

Formula for calculating % uncertainty

Answer 6

% uncertainty= (uncertainty/ measurement made on apparatus) x100
- for total % uncertainty add all individual equipment uncertainties together

Question 7

How to decrease uncertainty generally

Answer 7

• Either decrease sensitivity, by using apparatus with greater resolution (finer scale decisions)
• Increase size of measurement made

Question 8

Reducing uncertainty in a titration

Answer 8

• Replacing measuring cylinders with pipettes or burettes, as they have lower uncertainties.
• Increase titter volume, maybe by increasing volume and concentration of substances

Question 9

Reducing uncertainty in measuring mass

Answer 9

• Using a balance to more decimal places
  -Using a larger mass
• Weighing a sample before and after addition then calculating difference