C4- Chemical Changes

• What is the general reaction for the formation of metal oxides?

  Metals + oxygen → metal oxides
• Why are oxidation reactions characterized as such?

  Because the metals gain oxygen during the reaction
• What does reduction mean in the context of oxidation reactions?

  Reduction means loss of oxygen
• What does oxidation mean in the context of oxidation reactions?

  Oxidation means gain of oxygen
• How do metal atoms behave when they react with other substances?

  Metal atoms form positive ions
• What is the relationship between a metal's reactivity and its tendency to form positive ions?

  The reactivity of a metal is related to its tendency to form positive ions
• What is the order of reactivity for the metals potassium, sodium, lithium, calcium, magnesium, zinc, iron, and copper when reacting with water and dilute acids?

  • Potassium: violent
  • Sodium: very quick
  • Lithium: quick
  • Calcium: more slow
  • Magnesium: quick with dilute acid
  • Zinc: fairly slow with dilute acid
  • Iron: more slow with dilute acid
  • Copper: very slow with dilute acid
• What happens when a more reactive metal displaces a less reactive metal from a compound?

  A more reactive metal can displace a less reactive metal from a compound
• How is gold typically found in the Earth?

  Gold is found as the metal itself
• What is the extraction process for most metals?

  Most metals are found as compounds that require chemical reactions to extract the metal
• How can metals less reactive than carbon be extracted from their oxides?

  By reduction with carbon
• What does the acronym OIL RIG stand for?

  Oxidation is Loss and Reduction is Gain (of electrons)
• What is the ionic equation for sodium being oxidized?

  Na → Na⁺ + e⁻
• What is the ionic equation for a sodium +1 ion being reduced?

  Na⁺ + e⁻ → Na
• In the reaction 2Na + 2HCl → 2NaCl + H₂, which element is oxidized?

  Sodium is oxidized
• In the reaction 2Na + 2HCl → 2NaCl + H₂, which element is reduced?

  Hydrogen is reduced
• What are the general reactions of acids with metals and their products?

  • Acid + metal → salt + hydrogen
  • These are redox reactions where one substance is reduced and another is oxidised
• What is the ionic equation for magnesium being oxidized in the reaction 2HCl + Mg → MgCl₂ + H₂?

  Mg → Mg²⁺ + 2e⁻
• What is the ionic equation for hydrogen being reduced in the reaction 2HCl + Mg → MgCl₂ + H₂?

  2H⁺ + 2e⁻ → H₂
• What is the neutralization reaction between acids and alkalis or bases?

  • Acid + alkali → salt + water
  • Acid + base → salt + water
  • Acid + metal carbonate → salt + water + carbon dioxide
• What types of salts are produced from different acids?

  • Hydrochloric acid (HCl) produces chlorides (XCl)
  • Nitric acid (HNO₃) produces nitrates (XNO₃)
  • Sulfuric acid (H₂SO₄) produces sulfates (XSO₄)
• What must the charges on the positive ion from the base/alkali/carbonate and the negative ion from the acid do?

  The charges must add up to zero
• What is the salt produced when sodium hydroxide reacts with sulfuric acid?

  Na₂SO₄
• How can soluble salts be made from acids?

  1. Add solid insoluble substance to the acid until it dissolves.
  2. Filter out excess solid.
  3. Evaporate some water and leave to crystallize.
• What ions do acids produce in aqueous solutions?

  H⁺ ions
• What ions do alkalis produce in aqueous solutions?

  OH⁻ ions
• What does the pH scale measure?

  The pH scale measures the acidity or alkalinity of a solution
• What is the pH of a neutral solution?

  pH 7
• What happens to the pH as the acidity increases?

  The pH decreases
• What is the ionic equation for any neutralization reaction?

  H⁺(aq) + OH⁻(aq) → H₂O(l)
• What are the steps to carry out a titration?

  1. Wash burette with dilute hydrochloric acid and water.
  2. Fill burette to 100cm³ with acid.
  3. Use a pipette to add 25cm³ of alkali to a conical flask.
  4. Add a few drops of a suitable indicator.
  5. Add acid from burette to alkali until end-point is reached.
  6. Calculate the titre.
  7. Repeat for precise results.
• What is the volume conversion from cm³ to dm³?

  1 dm³ = 1000 cm³
• How do you calculate the moles of a substance?

  Moles = volume × concentration
• What is the concentration of hydrochloric acid if 25 cm³ is neutralized by 20 cm³ of 0.5 mol/dm³ sodium hydroxide?

  0.4 mol/dm³
• What is the difference between strong and weak acids?

  • Strong acids are completely ionized in aqueous solution (e.g., HCl, HNO₃, H₂SO₄).
  • Weak acids are partially ionized in aqueous solution (e.g., ethanoic, citric, carbonic acids).
• How does the strength of an acid relate to its pH?

  The stronger an acid, the lower the pH
• What happens to the H⁺ concentration as the pH decreases by one unit?

  The H⁺ concentration increases by a factor of 10
• What is the process of electrolysis?

  • Electrolysis is the breakdown of an electrolyte into elements by passing a current through it.
  • Positively charged ions move to the cathode, and negatively charged ions move to the anode.
• What happens to a simple ionic compound like lead bromide during electrolysis?

  The metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode
• How are metals more reactive than carbon extracted?

  By electrolysis of molten compounds