• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Estimating Errors in Chemistry There are two types of error which occur in measurements

Extracts from this document...

Introduction

Estimating Errors in Chemistry There are two types of error which occur in measurements: 1. Random Errors Random errors or uncertainties cause repeat measurements to vary and be scattered around a mean value. Averaging a number of readings helps to reduce random uncertainties. Precision Precise measurements have a small random uncertainty. Measurements are more precise if the scale used has smaller intervals. e.g. a 50 cm3 measuring cylinder is more precise than a 50 cm3 beaker. A 50 cm3 burette is even more precise. It is possible for a measurement to have great precision but be inaccurate. 2. Systematic Errors Systematic errors affect all the measurements in the same way making them all inaccurate, so they are all lower or higher than the true value. They do not average out so repeating results does not help to eliminate systematic errors. ...read more.

Middle

Absolute uncertainty = Measurement � Uncertainty Absolute Uncertainty Percentage uncertainty = ______________________ x 100 Measurement Mass 1. Consider weighing 1.00g of solid. If you use a two decimal place balance, the mass recorded will be to the nearest 0.01g. The absolute uncertainty is 1.00g � 0.01g 0.01 The percentage error is _____ x 100 = 1% 1.00 2. Consider weighing the same mass of solid on a three decimal place balance. The mass recorded will be to the nearest 0.001g. The absolute uncertainty is 1.00g � 0.001g 0.001 The percentage error is _____ x 100 = 0.1% 1.000 3. Consider weighing 10g of solid on a three decimal place balance. The absolute uncertainty is 10.000g � 0.001 g 0.001 The percentage error is _______ x 100 = 0.01% 10.000 Volume 4. ...read more.

Conclusion

A burette is more accurate still, and you can obtain readings to the nearest 0.05cm3. However there are two uncertainties in the measurement because an initial and a final reading are taken. If 25cm3 is measured, the % error would be: 0.05 _______ x 2 x 100 = 0.4% 25.00 Used well, the burette is very accurate. However the uncertainty increases dramatically for smaller volumes. Time 10. Finally, consider a reaction time of 100s measured on a digital stopwatch. These often show times to the nearest 0.01s. The % error would be: The absolute uncertainty is 100.00 s � 0.01s 0.01 The percentage error is _____ x 100 = 0.01% 100.0 This is wonderful, but how quickly can you stop and start it? The error is really more like 0.2%, and operator incompetence becomes important. Propagating Uncertainty in Equations The overall percentage uncertainty is the sum of all the percentage uncertainties obtained for the different measurements. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our International Baccalaureate Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related International Baccalaureate Chemistry essays

  1. IB Chemistry Kinetics Exam Questions and Answers

    Distribution is shifted towards a higher energy, so that even if the distribution at a higher temperature was the same as at a lower temperature, the number of molecules with Ea would increase. 2) The wider distribution means even more molecules have required activation energy 14.

  2. IB chemistry revision notes

    * The Halogens (Group VII) o As you go down the group, the anionic ionic radius increases. o Anions have a larger atomic radius than the parent atom they come from, because they gain an electron in the outer shell. The electrostatic repulsion makes the outer shell expand.

  1. The chemistry of Alcohols

    The PCl4+ ions and the H+ ion both act as Lewis acids, accepting a lone pair from the oxygen atom in the hydroxyl group on the alcohol molecule. 3i)Pour a little ethanol in to a watch glass and set it on fire using a blue Bunsen burner flame.

  2. The chemistry of atmospheric and water pollution.

    Replace CFCs with compounds which have significantly lower ozone depletion potentials (ODP) such as hyfrochloroflurocarbons (HCFCs). These compounds are effective as they are attacked while in the lower atmosphere thus it does not reach the stratosphere to attack ozone. However these compounds are more expensive and in some cases less effective than CFCs in various applications.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work