Quantitative chemistry (C3) paper 1

• What is always present when a measurement is made?

  Some uncertainty about the result obtained
• How can students represent the distribution of results?

  By making estimations of uncertainty
• How can the range of a set of measurements be used?

  As a measure of uncertainty
• What unit is used to measure chemical amounts?

  Moles
• What is the symbol for the unit mole?


  mol
• How is the mass of one mole of a substance related to its relative formula mass?

  It is numerically equal to its relative formula mass in grams
• What does one mole of a substance contain?

  The same number of stated particles as one mole of any other substance
• What is the value of the Avogadro constant?


  6.02 x $10^{23}$ per mole
• What can the measurement of amounts in moles apply to?

  Atoms, molecules, ions, electrons, formulae, and equations
• How many atoms are in one mole of carbon?

  The same as the number of molecules in one mole of carbon dioxide
• What are the key skills students should develop regarding measurements and calculations?

  • Recognise and use expressions in decimal form
  • Recognise and use expressions in standard form
  • Use an appropriate number of significant figures
  • Understand and use mathematical symbols
  • Change the subject of an equation
• What are some applications of nanoparticles?

  Medicine, electronics, cosmetics, sun creams, deodorants, and catalysts
• What should students consider regarding the applications of nanoparticulate materials?

  Advantages and disadvantages
• What is the law of conservation of mass?

  No atoms are lost or made during a chemical reaction, so the mass of the products equals the mass of the reactants
• How are chemical reactions represented?

  By balanced symbol equations
• What does the relative formula mass (Mr) of a compound represent?


  The sum of the relative atomic masses of the atoms in the formula
• How can students calculate the percentage by mass in a compound?

  Given the relative formula mass and the relative atomic masses
• Why might some reactions appear to involve a change in mass?

  Because a reactant or product is a gas and its mass has not been taken into account
• What should students be able to explain regarding observed changes in mass in non-enclosed systems?

  These changes in mass can be explained using the balanced symbol equation and the particle model
• How can the masses of reactants and products be calculated?

  From balanced symbol equations
• What does the equation Mg + 2HCl → MgCl2 + H2 represent?

  One mole of magnesium reacts with two moles of hydrochloric acid to produce one mole of magnesium chloride and one mole of hydrogen gas
• How can students calculate the masses of substances shown in a balanced symbol equation?

  By using the balanced symbol equation and the mass of a given reactant or product
• What is the purpose of balancing numbers in a symbol equation?


  To ensure the masses of reactants and products are equal
• What is a limiting reactant?

  The reactant that is completely used up in a chemical reaction
• How does a limiting reactant affect the amount of products?

  It limits the amount of products that can be obtained
• What are the key concepts in quantitative chemistry?

  • Use of quantitative analysis to determine formulae and equations
  • Determining purity of chemical samples
  • Monitoring yield from chemical reactions
  • Classifying different types of chemical reactions
  • Representing chemical reactions with equations
• What are the key skills students should develop regarding chemical equations?

  • Calculate masses of reactants and products
  • Balance equations using masses
  • Change the subject of mathematical equations
  • Substitute numerical values into algebraic equations
• What are the key opportunities for skills development in this study material?

  • Recognise and use expressions in decimal and standard form
  • Use ratios, fractions, and percentages
  • Make estimates of results from simple calculations
• What is the purpose of using an excess of one reactant in a chemical reaction?


  To ensure that all of the other reactant is used
• What is the limiting reactant in a chemical reaction?

  The reactant that is completely used up, limiting the amount of products
• How does a limiting quantity of a reactant affect the amount of products obtained?

  It limits the amount of products that can be formed
• How can the concentration of a solution be measured?

  In mass per given volume of solution, such as grams per dm³ (g/dm³)
• How do you calculate the mass of solute in a given volume of solution with known concentration?

  By using the formula: mass = concentration × volume
• What is the relationship between the mass of a solute, the volume of a solution, and the concentration?

  The mass of the solute and the volume of the solution determine the concentration
• What is the definition of yield in a chemical reaction?

  The amount of a product obtained from a reaction
• Why might the actual yield of a product be less than the theoretical yield?

  Because the reaction may not go to completion, products may be lost, or reactants may react differently
• How is percentage yield calculated?

  % Yield = (Mass of product actually made / Maximum theoretical mass of product) × 100
• How can you calculate the theoretical mass of a product from a given mass of reactant?

  By using the balanced equation for the reaction
• What does atom economy measure?

  The amount of starting materials that end up as useful products
• How is percentage atom economy calculated?

  % Atom Economy = (Relative formula mass of desired product / Sum of relative formula masses of all reactants) × 100