chemical changes

• What does the pH scale measure?

  How acidic or alkaline a solution is
• How can you measure the pH of a solution?

  Using an indicator or a pH probe
• What is an indicator?

  A dye that changes color with pH
• What does a pH probe do?

  Measures pH electronically and displays a value
• What is the pH of an acid?

  Less than seven
• What ions do acids form in water?

  H+ ions
• What is a base?

  A substance that reacts with acid to make salt
• What is an alkali?

  A base that dissolves in water with pH > 7
• What is the reaction between acids and alkalis called?

  Neutralisation
• What are the products of the neutralisation reaction?

  • Salt
  • Water
• What do acids produce in an aqueous solution?

  H+ ions
• How does the pH scale relate to H+ ion concentration?

  Decrease by 1 pH increases H+ by 10x
• What does acid strength indicate?

  Proportion of acid molecules that ionise
• What are some bases made from?

  Metal oxides and metal hydroxides
• What happens when metal oxides dissolve in water?

  They form alkalis
• What are the reactions involving acids and bases?

  1. Acid + Base → Salt + Water
  2. Acid + Metal Oxide → Salt + Water
  3. Acid + Metal Hydroxide → Salt + Water
  4. Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
• What do some metals produce when they react with acids?

  Salt and hydrogen gas
• What do reactive metals produce when they react with water?

  Metal hydroxide and hydrogen
• Why are most metals not found in pure form?

  They react with oxygen to form oxides
• What is oxidation?

  Gain of oxygen
• What is reduction?

  Loss of oxygen
• How can some metals be extracted from their ores?

  By reduction with carbon
• Which metals can be extracted using carbon?

  Metals less reactive than carbon
• What indicates a redox reaction?

  Transfer of electrons
• What does OIL RIG stand for?

  • Oxidation Is Loss
  • Reduction Is Gain
• What happens during redox reactions?

  Oxidation and reduction occur simultaneously
• What type of reactions are all reactions with metals and acids?

  Redox reactions
• What are metal displacement reactions?

  Reactive metal replaces less reactive metal
• What is electrolysis?

  Splitting up with electricity
• What is an electrolyte?

  A molten/dissolved ionic compound
• Why must an electrolyte be molten or dissolved?

  So ions are free to move
• What happens at the cathode during electrolysis?

  Positive ions gain electrons and reduce
• What happens at the anode during electrolysis?

  Negative ions lose electrons and oxidize
• What occurs during electrolysis of molten ionic substances?

  They form elements
• Why can't ionic solids be electrolysed?

  Ions are in a fixed position
• What happens to ions during electrolysis?

  They move towards electrodes and react
• What is required for electrolysis of ionic compounds?

  Free movement of ions to conduct electricity
• What is the cost of extracting metals using electrolysis?

  It is very expensive and energy-intensive
• What happens at the negative electrode during electrolysis?

  Metals form positive ions and reduce
• What happens at the positive electrode during electrolysis?

  Non-metals form negative ions and oxidize