C3

• What is the balanced equation for the formation of hydrochloric acid from hydrogen and chlorine?

  H₂ + Cl₂ → 2HCl
• What is relative atomic mass (A_r)?

  It is the average mass of an atom of an element shown on the periodic table.
• What is relative formula mass (M_r)?

  It is the sum of relative atomic masses of all the atoms in the formula of a compound.
• How do you calculate the relative formula mass of carbon dioxide (CO₂)?

  Mr = 12 + (16 x 2) = 44
• What is percentage yield in a chemical reaction?

  It compares the amount obtained with the amount expected and shows how efficient a reaction is.
• What formula is used to calculate percentage yield?

  Percentage yield = (mass of product obtained / mass of product expected) x 100
• If a reaction was predicted to form 3.5 g of product but only 3.1 g was made, what is the percentage yield?

  Percentage yield = (3.1 / 3.5) x 100 = 88.6%
• What can cause a percentage yield to exceed 100%?

  Improper drying of the product or adding too much reactant can cause this.
• What does atom economy measure?

  It measures the fraction of atoms that end up in the desired product.
• Why is high atom economy desirable?

  It minimizes unwanted waste products.
• How do you calculate atom economy?

  Atom economy = (Mr of desired product / Mr of all reactants) x 100
• What is the atom economy of producing sodium chloride from the reaction NaOH + HCl → NaCl + H₂O?

  Atom economy = (58.5 / (23 + 1 + 35.5 + 1 + 35.5 + 16)) x 100 = 75.5%
• What does the law of conservation of mass state?

  The total mass of the products must equal the total mass of the reactants.
• How does the law of conservation of mass apply to chemical reactions?

  There are the same number of each type of atom present before and after the reaction.
• What happens when metals burn in oxygen?

  The mass of the product is more than that of the starting material due to oxygen combining with the metal.
• What is an example of thermal decomposition?

  CaCO₃(s) → CaO(s) + CO₂(g)
• What is the concentration of a solution?

  It tells you how much of a substance is dissolved in a given volume of solution.
• What is the unit for concentration in solutions?

  g/dm³
• How many grams are in 1 dm³?

  1 dm³ = 1000 cm³, or 1 litre
• How do you convert g/cm³ to g/dm³?

  Multiply by 1000
• How do you convert g/dm³ to g/cm³?

  Divide by 1000
• If 0.5 g of sodium chloride is dissolved in 250 cm³ of water, what is the concentration?

  Concentration = 2 g/dm³
• What is a mole in chemistry?

  A mole is a measure of the amount of substance, equal to 6.02 x 10²³ particles.
• How does the mass of one mole of a substance relate to its relative formula mass?

  The mass of one mole is equal to its relative formula mass in grams.
• How many particles are in one mole of any substance?

  1 mole contains 6.02 x 10²³ particles.
• How do you calculate the mass of a substance using moles?

  Mass = M_r x moles
• What is the concentration in mol/dm³?

  It is the amount of substance dissolved in a given volume of solution.
• How do you find the concentration of a solution with 0.5 mol of H₂SO₄ in 2 dm³?

  Concentration = 0.5 mol / 2 dm³ = 0.25 mol/dm³
• How do you calculate the number of moles in a solution?

  Amount of substance = concentration x volume
• If 20 cm³ of a 1 mol/dm³ solution of HNO₃ reacts with 15 cm³ of NaOH, how do you find the concentration of NaOH?

  Concentration of NaOH = moles / volume = 0.02 / 0.015 = 1.33 mol/dm³
• What is a limiting reactant?

  It is the reacting species that is completely used up during a chemical reaction.
• What does it mean if a reactant is in excess?

  It means there is more of it than is needed to react completely.
• In the reaction NaOH + HCl, if you have 2 moles of NaOH and 1 mole of HCl, how much NaCl and H₂O will be formed?

  1 mole of NaCl and 1 mole of H₂O will be formed.
• How can you determine the reacting masses from a balanced symbol equation?

  By using the multiples that show the ratio of reactants and products.
• What is the balanced equation for the reaction of potassium with water?

  2K + 2H₂O → 2KOH + H₂
• What is the volume occupied by 1 mole of any gas at standard conditions?

  1 mole occupies 24 dm³ at standard conditions.
• How do you calculate the volume of gas produced from moles of gas?

  Gas volume (dm³) = moles of gas x 24
• If 1 mole of N₂ reacts with 3 moles of H₂, what volume of NH₃ is formed?

  Volume = 24 x 2 = 48 dm³
• How many moles are there in 88 g of CO₂?

  2 moles
• How much does 5 mol of NaCl weigh?

  Mass = M_r x moles = 58.5 x 5 = 292.5 g