BRAINCAKEErrors and Uncertainties
Revision notes for Errors and Uncertainties in Edexcel Chemistry (8CH0). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- Errors vs MistakesIn practical chemistry the words error and mistake mean different things, and exam questions expect you to keep them separate.
- Accuracy and PrecisionAccuracy and precision describe different qualities of results.
- Random Errors and Systematic ErrorsErrors fall into two types, and each one is dealt with differently.
- UncertaintyBecause every measurement has some error, a measured value is really a range.
- Percentage UncertaintyAn uncertainty of ± 0.005 g sounds tiny, but whether it matters depends on how much you are weighing.
- Adding UncertaintiesMany measured quantities come from two readings subtracted from each other: • a titre = final burette reading − initial burette reading • a…
- Adding Percentage UncertaintiesA final result is usually calculated by multiplying or dividing several measurements, for example concentration = moles ÷ volume.
- Minimising Errors and UncertaintiesOnce you know where the uncertainty in an experiment comes from, you can suggest specific improvements.
- Percentage YieldThe theoretical yield is the maximum mass of product that could form, calculated from the mass of the limiting reactant and the balanced equation.
- Atom EconomyAtom economy measures how much of the mass of the reactants ends up in the desired product, rather than in by-products.
- Example Calculation - 1This worked example brings together a mole calculation and a percentage yield.
- Example Calculation - 2This worked example shows why the coefficients in the equation matter in an atom economy calculation.
- Example Calculation - 3This worked example finds the overall percentage uncertainty in a titration result.
- Example Calculation - 4This worked example uses uncertainty to evaluate an experimental result.