BRAINCAKEErrors and Uncertainties
Revision notes for Errors and Uncertainties in Edexcel Chemistry (8CH0). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- 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.