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Amount of Substance and Calculations

Edexcel AS-level ChemistryTopic 8 of 2139 lessons

Revision notes for Amount of Substance and Calculations in Edexcel Chemistry (8CH0). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.

  1. Counting Atoms - The MoleThe easiest way of counting how many particles there are in a substance is to find its mass.
  2. CalculationsThe mass of a sample of substance can be used to count the number of atoms in the sample by using the formula moles = mass &div Mr where Mr is the…
  3. Chemical FormulaeA chemical formula shows the symbols of the elements in a substance and the number of atoms or ions of each.
  4. Balanced EquationsBalanced equations can be used to represent reactions.
  5. Ionic EquationsIonic equations show the ions that react together and not the spectator ions.
  6. Ionic Equations - Question1Question: Write the ionic equation, with state symbols, for the reaction between silver nitrate solution and sodium chloride solution.
  7. Ionic Equations - Question 2Question: Write the ionic equation, with state symbols, for the neutralisation of dilute sulfuric acid by potassium hydroxide solution.
  8. Ionic Equations - Question3Question: Write the ionic equation, with state symbols, for the reaction of solid calcium carbonate with dilute hydrochloric acid.
  9. Ionic Equations - Question 4Question: Zinc powder is added to blue copper(II) sulfate solution.
  10. Calculations of Reacting MassesA balanced equation gives the reacting ratio of moles of reactants and products or stoichiometry of a reaction.
  11. Working out Equations from Reacting MassesIf there are two possible reactions for the same reactants, the reacting masses can be used to identify which reaction has taken place.
  12. Empirical FormulaThe empirical formula is the simplest whole number ratio of atoms of each element in a compound.
  13. Percentage Composition by MassSometimes it is useful to know the percentage composition by mass of an element in a compound.
  14. Combustion AnalysisMany organic compounds contain carbon and hydrogen and when burnt in air produce carbon dioxide and water.
  15. Molecular FormulaThe empirical formula is the simplest whole number ratio of atoms of each element in a compound.
  16. Example Question - 1Question: An oxide of iron contains 70.0% iron and 30.0% oxygen by mass.
  17. Example Question - 2Question: A hydrocarbon contains 85.7% carbon and 14.3% hydrogen by mass.
  18. Example Question - 3Question: 0.46 g of compound X, which contains carbon, hydrogen and oxygen only, is burned completely in oxygen.
  19. Example Question - 4Question: A sample of hydrated magnesium sulfate, MgSO4·xH2O, has a mass of 2.46 g.
  20. Avogadro's LawAvogadro's law states that equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.
  21. Gas Volume Calculation - 1Question: Calcium carbonate decomposes on heating.
  22. Gas Volume Calculation - 2Question: 50 cm3 of propane is burned completely in 300 cm3 of oxygen.
  23. Molar VolumeThe molar gas volume Vm is the volume per mole of gas molecules at a stated temperature and pressure.
  24. Molar Volume Calculation - 1The molar volume is the volume occupied by one mole of any gas.
  25. Molar Volume Calculation - 2Many reactions produce a gas, and the molar volume lets you predict the volume of gas from the mass of a reactant.
  26. Mass ConcentrationThe mass concentration of a solution is the mass of solute in grams dissolved in each 1 dm3.
  27. Molar ConcentrationThe mole concentration of a solution is the amount of solute in moles dissolved in each 1 dm3.
  28. Calculate Concentration - 1Concentration calculations use one equation, rearranged three ways: amount (mol) = concentration (mol dm-3) × volume (dm3) so concentration = amount…
  29. Calculate Concentration - 2Often you know the mass of a solid dissolved, not the number of moles.
  30. Standard SolutionsA standard solution is a solution whose concentration is accurately known.
  31. Making a Standard Solution1.
  32. TitrationsA titration is a method of measuring the volumes of two solutions that react together and using the results to determine the concentration of one of…
  33. The Titration MethodA titration is a method of measuring the volumes of two solutions that react together and using the results to determine the concentration of one of…
  34. IndicatorsThe two indicators most commonly used are methyl orange and phenolphthalein.
  35. Concordant Titres and Mean TitresThe burette reading is read correct to the nearest 0.05cm3 from the bottom of the meniscus.
  36. Calculating ConcentrationOnce a mean titre has been found, the unknown concentration is calculated in three steps.
  37. Titration Calculations - 1Not every titration reaction has a 1 : 1 ratio.
  38. Titration Calculations - 2Sodium carbonate is a common standard solution because it can be weighed accurately as a pure, stable solid.
  39. Titration Calculations - 3Titrations are often used to find the purity of a solid or its Mr.

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