C3 -quantitative chemistry

• What is relative formula mass?

  Sum of relative atomic masses in a compound
• How do you find the relative formula mass of MgCl₂?

  Add relative atomic masses of Mg and Cl
• What is the relative formula mass of MgCl₂?

  95
• What is the relative atomic mass of magnesium (Mg)?

  24
• What is the relative atomic mass of chlorine (Cl)?

  35.5
• How do you calculate the percentage mass of an element in a compound?

  Use the formula: (A × number of atoms / M) × 100
• What is the percentage mass of sodium in Na₂CO₂?

  43%
• How do you find the mass of iron chloride needed for 10 g of iron ions in a mixture?

  Calculate using percentage mass of iron
• What mass of iron chloride is needed to provide 10 g of iron ions?

  23 g
• What is Avogadro's constant?

  6.02 x 10²³ particles
• What does one mole of a substance represent?

  Amount containing Avogadro's number of particles
• How does the mass of one mole relate to relative atomic mass?

  Mass in grams equals relative atomic mass
• What is the relative formula mass of carbon dioxide (CO₂)?

  44
• How many moles are in 66 g of carbon dioxide (CO₂)?

  1.5 mol
• How do you calculate the number of moles from mass and relative formula mass?

  Use: moles = mass / M
• What is the mass of 4 moles of carbon?

  48 g
• What is the conservation of mass in a chemical reaction?

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

  Add relative formula masses of reactants and products
• What is the total relative formula mass of the reactants in 2Li + F₂ → 2LiF?

  52
• Why might mass appear to change during a reaction?

  Gas may escape or enter the reaction vessel
• What happens if the mass increases during a reaction?

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

  A gas product escapes from the vessel
• What is the formula to find the number of moles in a given mass?

  Number of moles = mass / M
• How do you balance equations using reacting masses?

  Find moles, divide by smallest, write equation
• What are the steps to calculate the percentage composition by mass of an element in a compound?

  1. Find the relative atomic mass of the element.
  2. Find the relative formula mass of the compound.
  3. Use the formula: (A × number of atoms / M) × 100.
• What are the explanations for mass changes in a reaction vessel?

  • Mass increases if a gas from air is a reactant.
  • Mass decreases if a gas product escapes.
• What is the relationship between moles and mass in chemical reactions?

  • Moles indicate the amount of substance.
  • Balanced equations show mole ratios of reactants and products.
• What is the significance of Avogadro's constant in chemistry?

  • It defines the number of particles in one mole.
  • It relates mass in grams to relative atomic mass.
• What is the importance of conservation of mass in chemical reactions?

  • Ensures no atoms are lost or gained.
  • Total mass of reactants equals total mass of products.
• What do the big numbers in front of chemical formulas indicate?

  They indicate the number of moles.
• What is formed when magnesium reacts with hydrochloric acid?

  Magnesium chloride and hydrogen gas.
• What are the steps to balance equations using reacting masses?

  1. Divide mass by relative formula mass.
  2. Divide by the smallest number of moles.
  3. Multiply to get whole numbers if needed.
  4. Write the balanced symbol equation.
• How do you calculate the relative formula mass of zinc oxide (ZnO)?

  By adding the atomic masses of Zn and O.
• What is the relative formula mass of carbon dioxide (CO₂)?

  44 g/mol.
• How do you determine the number of moles of each substance in a reaction?

  By dividing mass by relative formula mass.
• What is a limiting reactant?

  The reactant that is completely used up first.
• What happens when a limiting reactant is used up?

  The reaction stops.
• What is the relationship between the limiting reactant and the amount of product formed?

  • The amount of product is proportional to the limiting reactant.
  • Halving the limiting reactant halves the product.
  • Doubling the limiting reactant doubles the product.
• How do you calculate the mass of a product formed in a reaction?

  Using the mass of the limiting reactant and the balanced equation.
• What is the balanced equation for the combustion of aluminium?

  4Al + 3O₂ → 2Al₂O₃.