C4

• What are alkalis?

  Alkalis are soluble bases.
• What does the pH scale range from?

  The pH scale ranges from 0 to 14.
• What do acids form in water?

  Acids form H⁺ ions in water.
• What do alkalis form in water?

  Alkalis form OH⁻ ions in water.
• What are the two ways to measure pH?

  1. Universal Indicator

  • Changes colour based on pH
  • Provides an approximate pH value

  1. pH Probe

  • Gives an accurate pH value
• What is the general equation for neutralisation reactions?

  acid + base → salt + water
• What are the products of neutralisation reactions?

  The products of neutralisation reactions are neutral.
• What is the ionic equation for neutralisation?

  H⁺(aq) + OH⁻(aq) → H₂O(l)
• What are titrations used for?

  • To find the exact volume of acid needed to neutralise a quantity of alkali (or vice versa)
  • Results can be used to calculate acid or alkali concentration
• How do you get the formula of a salt?

  Balance the charge of the ions so the overall charge is neutral.
• What is the reaction of an acid with a metal carbonate?

  acid + metal carbonate → salt + water + carbon dioxide
• What is the reaction of an acid with a metal oxide?

  acid + metal oxide → salt + water
• What is the reaction of an acid with a metal hydroxide?

  acid + metal hydroxide → salt + water
• What salts are produced from common acids?

  • HCl produces chloride
  • H₂SO₄ produces sulfate
  • HNO₃ produces nitrate
• How are soluble salts made?

  • By adding metals or insoluble metal compounds to acids
  • Filter off excess solid
  • Crystallise the remaining salt solution
• What does the first part of a salt’s name indicate?

  The first part of a salt’s name comes from the positive ion in the base, alkali, or carbonate.
• What is a strong acid?

  A strong acid completely ionises in water to produce hydrogen ions.
• What is a weak acid?

  A weak acid partially ionises in water to produce hydrogen ions.
• Give examples of strong acids.

  Hydrochloric acid, sulfuric acid, nitric acid.
• Give examples of weak acids.

  Ethanoic acid, citric acid, carbonic acid.
• What does pH measure?

  pH measures the concentration of H⁺ ions in a solution.
• What happens to H⁺ ion concentration when pH changes?

  When pH changes by X, the H⁺ ion concentration changes by a factor of $10^{-x}$.
• How does acid strength relate to pH?

  As acid strength increases, pH decreases for a given concentration of acid.
• How does the pH of a strong acid compare to a weak acid at the same concentration?

  The pH of a strong acid is always less than that of a weaker acid at the same concentration.
• What is the difference between acid strength and acid concentration?

  • Acid strength: proportion of acid molecules that ionise in water
  • Acid concentration: number of acid molecules in a certain volume of water
• What happens to pH with increasing acid concentration?

  The pH will decrease with increasing acid concentration, regardless of whether it’s a strong or weak acid.
• What is the reactivity series of metals?

  A list that ranks metals based on their ability to form positive ions
• Which metal is at the top of the reactivity series?

  Potassium (K)
• What does it mean for a metal to be very reactive?

  It means the metal easily forms positive ions
• Which metals are considered not very reactive?

  Copper (Cu)
• How are metals extracted from molten compounds?

  Using electrolysis
• What is the reaction of a metal with an acid?

  Metal + acid → salt + hydrogen + water
• What happens to the rate of hydrogen production with increasing metal reactivity?

  The more reactive the metal, the faster bubbles of hydrogen will be produced
• What is a displacement reaction?

  • A more reactive element displaces a less reactive metal from its compound
  • Example: K displacing Cu from CuSO₄
• What is oxidation in terms of redox reactions?

  Oxidation is the gain of oxygen or loss of electrons
• What is reduction in terms of redox reactions?

  Reduction is the loss of oxygen or gain of electrons
• What is a redox reaction?

  A reaction where one substance is reduced and another is oxidised
• In the reaction Fe_(s) + CuSO_(aq) → FeSO_(aq) + Cu_(s), what happens to iron?

  Iron is oxidised
• In the reaction Fe_(s) + CuSO_(aq) → FeSO_(aq) + Cu_(s), what happens to copper?

  Copper is reduced
• What do ionic equations show?

  Ionic equations only show the particles that react and the products they form