5.9 - Evaluating Results

• uncertainty

  amount of error your measurements might have

  half the smallest increment equipment has
• uncertainty reading

  maximum error you could have
• margin of error (±)

  the range in which the true value could lie
• sources of uncertainty in volumetric analysis

  equipment may not have been made accurately

  meniscus may lie between 2 graduation lines so it's hard to determine volume

  material used to prepare standard solution may not be 100% pure

  balance only shows mass to a certain number of decimal places

  hard to make an exact judgement of the end point of a titration
• percentage uncertainty/error

  uncertainty ÷ reading × 100
• minimising percentage uncertainty

  uses the most precise equipment

  plan experiment so you use larger quantities
• method to find total uncertainty in the final result of a titration

  find percentage uncertainties of individual pieces of equipment and ad them together to find percentage uncertainty of final result

  multiply final result by its percentage uncertainty
• random errors

  make results a bit different from each other due to factors out of our control

  if random errors are small results will be closer together so are precise
• random errors in titrations arise by

  judging where bottom of meniscus is

  when judging colour change at the end point
• how to deal with random errors

  repeat experiment and find mean value for results
• systematic errors

  when results differ from the true value by the same amount each time (measurement is biased)
• what can cause systematic errors

  set-up

  equipment used
• how can systematic errors be allowed for

  by calibrating the measuring instruments

  repeating the experiment won't get rid of systematic errors