c4

• pH scale

  
• pH scale ranges from 0-14 and shows how acidic or alkaline a solution is
• the lower the pH of a substance, the more acidic it is
• the higher the pH of a substance, the more alkaline it is
• a neutral substance has a pH of 7
• alkalis have a pH above 7
• acids have a pH below 7
• an indicator is a dye that changes colour depending on whether its above or below a certain pH
• an acid is a substance that forms an aqueous solution with a pH of less than 7. Acids form H+ ions in water
• a base is a substance with a pH greater than 7
• an alkali is abase that dissolved in water to form a solution with a pH over 7. Alkalis form OH- ions in water
• Acid + base = salt + water
• reactions between acids and bases is called neutralisation
• strong acids completely ionise in water. All acid particles dissociate to release H+ ions
• weak acids do not fully ionise in solution. Only a small proportion of acid particles dissociate to release H+ ions
• the ionisation of a weak acid is a reversible reaction, which sets up an equilibrium between the undissociated and dissociated
• if the concentration of H+ is higher, the rate of reaction will be faster, so strong acids will be more reactive than weak acids of same concentration
• the pH of am acid or alkali is a measure of the concentration of H+ions in the solution
• for every decrease of 1 on the pH scale, the concentration of H+ ions increases by a factor of 10
• acid strength tells you what proportion of the acid molecules ionise in water
• the concentration of acid measures how much acid is in a volume of water - how watered down your acid is
• the larger amount of acid within a volume, the more concentrated the acid is
• some metal oxides and metal hydroxides dissolve in water, these soluble compounds are called alkalis.
• even bases that wont dissolve in water will still take part in neutralisaton reactions with acids
• acid + metal oxide = salt + water
• acid + metal hydroxide = salt + water
• metal carbonates are also bases, they produce salt, water and carbon dioxide
• acid + metal carbonate = salt + water + carbon dioxide
• reactivity series:

  Potassium

  Sodium

  Lithium

  Calcium

  Magnesium

  Carbon

  Zinc

  Iron

  Hydrogen

  Copper
• the reactivity series lists metals in order of their reactivity towards other substances. Higher in the list = more reactive
• the higher up in the reactivity series means the more easily they form positive ions
• the speed of reaction is indicated y the rate at which bubbles of hydrogen are given off
• the more reactive the metal, the faster the rate of hydrogen given off
• also, the more reactive the metal, the greater the temperature change should be
• metal + water = metal hydroxide +hydrogen
• oxidation means the gain of oxygen
• reduction is the loss of oxygen
• formation of metal ore is called oxidation
• extraction of metal is called reduction
• some metals can be extracted from their ores using carbon