C3 Quantitative Chemistry

• What is relative formula mass denoted as?

  Mr
• How is the relative formula mass of a compound calculated?

  Add relative atomic masses of all atoms
• What is the relative formula mass of MgCl₂?

  95
• Why do you multiply the relative atomic mass of chlorine by 2 in MgCl₂?

  There are two chlorine atoms in MgCl₂
• What is the formula for calculating percentage mass of an element in a compound?

  Ar × number of atoms / Mr × 100
• What is the percentage mass of sodium in sodium carbonate, Na₂CO₃?

  43%
• How do you find the mass of iron in a mixture containing 20% iron ions by mass?

  Calculate 20% of the total mass
• What mass of iron chloride is needed to provide 10 g of iron?

  23 g
• What is the Avogadro constant?

  1. 02 × 10²³
• What does one mole of a substance contain?

  1. 02 × 10²³ particles
• What is the mass of one mole of carbon?

  12 g
• How is the mass of one mole of a substance related to its relative atomic mass?

  It equals the relative atomic mass in grams
• How many moles are in 66 g of carbon dioxide (CO₂)?

  1. 5 mol
• What is the formula to find the number of moles in a given mass?

  Number of moles = mass in g / Mr
• What mass of carbon is there in 4 moles of carbon dioxide?

  48 g
• What happens to mass during a chemical reaction?

  Mass is always conserved
• What does it mean when mass is conserved in a reaction?

  No atoms are created or destroyed
• How can you show that mass is conserved in a reaction?

  Add relative formula masses on both sides
• What happens if the mass seems to change during a reaction?

  Usually a gas is involved
• What happens if the mass increases during a reaction?

  A gas from air is reacting
• What happens if the mass decreases during a reaction?

  A gas is escaping from the vessel
• What are the key points of conservation of mass in chemical reactions?

  • No atoms are created or destroyed
  • Same number and types of atoms on both sides
  • Total Mr of reactants equals total Mr of products
• What are the steps to calculate the percentage mass of an element in a compound?

  1. Find the Ar of the element
  2. Count the number of atoms of that element
  3. Calculate Mr of the compound
  4. Use the formula: (Ar × number of atoms / Mr) × 100
• What are the steps to find the mass of iron chloride needed for a mixture?

  1. Calculate mass of iron in the mixture
  2. Find percentage mass of iron in iron chloride
  3. Use the percentage to find mass of iron chloride
• What is the relationship between moles and mass in chemistry?

  • Moles relate to the amount of substance
  • Mass in grams equals the relative formula mass for one mole
  • Use the formula: Number of moles = mass / Mr
• What are the implications of mass changes in unsealed reaction vessels?

  • Mass increases if a gas reacts
  • Mass decreases if a gas escapes
  • Gases expand to fill containers
• What happens to reactants before a reaction in an open vessel?

  All reactants are contained in the vessel
• What occurs if a gas escapes from an unsealed reaction vessel?

  The total mass inside decreases
• What happens to the mass of the reaction vessel when metal carbonate decomposes?

  It decreases if not sealed
• What does the equation "metal carbonate → metal oxide + carbon dioxide" represent?

  A thermal decomposition reaction
• What do gases do according to the particle model?

  Expand to fill any container
• How can moles be used in chemical reactions?

  To calculate masses in reactions
• What do the big numbers in balanced equations indicate?

  Number of moles of substances
• In the reaction Mg + 2HCl → MgCl₂ + H₂, how many moles of HCl are used?

  2 moles of HCl
• What are the steps to balance equations using reacting masses?

  1. Divide mass by relative formula mass
  2. Divide by smallest number of moles
  3. Multiply to get whole numbers
  4. Write the balanced equation
• What is the first step in balancing a reaction using masses?

  Divide mass by relative formula mass
• What is the relative formula mass of ZnO?

  81
• How do you calculate the number of moles of ZnO from 8.1 g?

  1. 1 ÷ 81 = 0.10 mol
• What is the limiting reactant in a chemical reaction?

  The reactant that gets used up first
• How does the amount of product formed relate to the limiting reactant?

  It is directly proportional to it