C3 - Quantitative Chemistry (Separate)

• What is the relative formula mass (Mr) of a compound?

  It is the sum of the relative atomic masses (Ar) of all the atoms in that compound.
• What does the percentage mass of an element in a compound represent?

  It indicates the proportion of the compound's mass that is due to that element's atoms.
• What is the percentage mass of magnesium in magnesium oxide (MgO) if Mg = 24 and O = 16?

  The percentage mass of magnesium is 60%.
• How do you find the mass of iron chloride in a mixture containing 20% iron ions by mass in 50 g of the mixture?

  First, calculate the mass of iron (10 g), then use the percentage mass of iron in iron chloride to find the mass of iron chloride (22.7 g).
• How is the mass of one mole of a substance related to its relative atomic mass (Ar) or relative formula mass (Mr)?

  The mass in grams of one mole is equal to its relative atomic mass or relative formula mass.
• How many moles are there in 42 g of carbon?

  There are 3.5 moles
• How many moles are there in 66 g of carbon dioxide (CO₂)?

  There are 1.5 moles
• What is the mass of 0.800 moles of sulfuric acid (H₂SO₄)?

  The mass is 78.4 g
• What does the law of conservation of mass state during chemical reactions?

  The total mass of the reactants equals the total mass of the products.
• How can balanced chemical equations demonstrate the conservation of mass?

  By showing that the total relative formula mass of reactants equals that of products.
• How do you calculate the mass of magnesium oxide formed from 6 g of magnesium and 4 g of oxygen?

  The mass of magnesium oxide formed is 10 g
• If 30 g of magnesium oxide is formed from 18 g of magnesium, what mass of oxygen reacted?

  The mass of oxygen that reacted is 12 g.
• Why might the mass of a reaction vessel appear to change during a reaction?

  It can change if gases escape from an unsealed vessel or if gases are involved in the reaction.
• What happens to the mass of a reaction vessel if a gas is produced and escapes?

  The mass appears to decrease because the gas is no longer contained in the vessel.
• What do the big numbers in front of chemical formulae in a balanced equation represent?

  They represent the relative number of moles of each reactant and product involved in the reaction.
• What are the steps to balance a chemical equation using reacting masses?

  1. Divide the mass of each substance by its relative formula mass to find the number of moles.
  2. Divide the number of moles of each substance by the smallest number of moles.
  3. Multiply by the same amount to make all numbers whole if necessary.
  4. Write the balanced symbol equation.
• What is the balanced symbol equation for the reaction of zinc oxide and carbon?

  2ZnO + C → CO₂ + 2Zn
• How do you calculate the number of moles of a substance from its mass?

  Number of moles = mass ÷ relative formula mass
• What is the relative atomic mass of carbon?

  12
• What is the relative atomic mass of oxygen?

  16
• What is the relative atomic mass of zinc?

  65
• What is a limiting reactant?

  A reactant that gets completely used up during a reaction
• How does the limiting reactant affect the amount of product formed?

  It determines the maximum amount of product that can be formed
• What is the definition of concentration in a solution?

  Concentration is the amount of solute dissolved in a solvent.
• What is the relationship between the number of moles of any gas and the volume it occupies at the same temperature and pressure?

  They will occupy the same volume.
• What is the volume occupied by one mole of any gas at 20 °C and 1 atm?

  24 dm³
• How can you calculate the volume of a gas at room temperature and pressure using mass and relative formula mass?

  By using the mass and relative formula mass to find the number of moles, then applying the volume per mole.
• What does it mean to change the subject of an equation?

  It means to rearrange the equation to solve for a different variable.
• How can a balanced chemical equation be used in gas volume calculations?

  It can be used to determine the volumes of gases involved in a reaction based on their mole ratios.
• Why is it important to calculate the correct volume of gas in a car's airbag system?

  • To ensure adequate protection during deployment
  • To avoid burning too much fuel
  • To ensure the airbag inflates properly
• What is a solution in chemistry?

  A mixture containing one substance (the solute) dissolved in another (the solvent).
• What does the state symbol “(aq)” represent?

  It indicates that a substance is dissolved in water, forming an aqueous solution.
• How is concentration defined in terms of solute and solution?

  It is the amount of solute dissolved in a certain volume of solution.
• How does increasing the mass of solute affect the concentration of a solution?

  The concentration increases if the volume remains constant.
• How do you calculate the concentration of a solution in g/dm³?

  Concentration (g/dm³) = mass of solute (g) / volume of solution (dm³).
• What is the concentration of a sodium chloride solution with 30 g dissolved in 0.20 dm³ of water?

  150 g/dm³
• How do you convert 25 cm³ of water to dm³?

  25 cm³ = 0.025 dm³
• What is the concentration of an iron chloride solution with 10 g dissolved in 25 cm³ of water?

  400 g/dm³
• What happens to the concentration if more solvent is added without increasing the solute?

  The concentration decreases.
• What is the formula to find the mass of solute in a solution?

  mass = concentration × volume