C5 - chemical changes

• what happens chemicals react with oxygen

  Forms metal oxide
• what is gaining oxygen called

  oxidation
• what is reduction

  loosing oxygen - metal oxide back reactants
• Reacting metal with water

  metal + water $\rightarrow$metal hydroxide +hydrogen
• reactivity series of water

  React very rapidly at room temp - potassium, sodium, lithium

  reacts quite rapidly at room temp - calcium

  No reaction at room temp- magnesium, zinc, iron, copper
• Reactivity series with dilute acid

  Potassium - dangerously fast

  Sodium - dangerously fast

  Lithium - dangerously fast

  Calcium - extremely vigorous

  Magnesium - rapid

  zinc - quite rapid

  iron - quite slow

  Copper - none
• which non metals are in the reactivity series

  carbon and hydrogen
• what determines how metals react in the reactivity seies

  • ability to lose electrons and form a positive ion
  • metals at top readily form a positive ion
• what are ores

  unreactive metals found in the earth as the metal itself (gold)
• how is iron oxide and copper oxide formed

  reacted with oxygen to form compounds
• what is displacement

  • a more reactive metal will displace a less reactive element from its compound
  • magnesium + iron oxide $\rightarrow$ magnesium oxide +iron
  • Magnesium is oxidised and iron is reduced
• carbon displacement reaction

  carbon + iron oxide $\rightarrow$ carbon dioxide +iron
• Oxidation and reduction in terms of electrons

  • oxidation is loss of electrons
  • Reduction is gain of electrons
• what do acids produce in aqueous solutions

  hydrogen ions (H+)
• what are bases

  chemicals that neutralise acids producing salt and water usually metal oxides or hydroxides
• what are alkalies

  bases soluble in water - sodium hydroxide
• What ph do acids have

  Between 0 and 6
• what ph is neutral

  7
• alkali ph

  8 and 14
• how to determine ph

  ph probe or universal indicator

  ph probe is electronically

  universal indicator changes colour
• universal indicator colours

  green - neutral

  red - acidic

  purple - alkaline
• what do alkalines produce

  OH-
• neutralisation between acid and alkaline

  • hydrogen ions (acid) react with hydroxide ions (alkaline) to produce water
  • H+ + OH- $\rightarrow$ H2O
• reactivity series and hydrogen

  • all metals more reactive than hydrogen can displace it
• acid and metal reaction

  acid + metal $\rightarrow$ salt + hydrogen
• how does hydrochloric acid react with metals

  produces salts that end in chloride
• how does sulfuric acid react with metals

  Produces salts endino in sulfate
• magnesium reaction with acids

  hydrochloric acid + magnesium $\rightarrow$ magnesium chloride + hydrogen

  Sulphuric acid + magnesium $\rightarrow$ magnesium sulphate + hydrogen

  React rapidly with acids - can easily displace hydrogen
• How does zinc react with acids

  Quite rapidly
• how does iron react with acid

  fairly slow - only slightly more reactive than hydrogen
• how do bases and alkalis react with acid

  • makes a salt and water
  • Salts Contain a positive ion from the base or alkali
  • Also contain a negative ion from the acid
• how do metal carbonates react with acid

  • make a salt, water and carbon dioxide
• Aims of salt practical

  To prepare a pure, dry sample of a soluble salt from an insoluble oxide or carbonate.
• Apparatus for salt practical

  • mixing the solid and acid - beaker and stirring rod
  • filtering the mixture - conical flask, filter paper and filter funnel
  • heating the solution - water bath (beaker of water on a tripod and gauze, heated over a Bunsen burner) and evaporating basin
  • crystallisation - watch glass
• Carrying out salt practical

  1. Add powdered insoluble reactant to acid in a beaker, one spatula at a time, stirring to mix. Continue adding powder until it is in excess (some unreacted powder is left over).
  2. Filter the mixture in the beaker to remove the excess powder. Collect the filtrate.
  3. Pour the filtrate into an evaporating basin. Place on a water bath, and heat until about half the water from the solution has been removed by evaporation. Stop heating when small crystals start to appear around the edge of the evaporating basin.
  4. Pour the remaining solution into a watch glass, and leave in a warm, dry place for crystallisation to occur.
  5. If necessary, dry the crystals by dabbing gently with filter paper
• acids in aqueous solutions

  • acids produce Hydrogen ions in aqueous solutions
  • Acid molecules ionise in aqueous solutions and release H+
• what is a strong acid

  • fully ionise in aqueous solutions
  • arrow goes in one direction only
  • hydrochloric acid, sulphuric acid and nitric acid
• what is a weak acid

  • partially ionise in aqueous solutions
  • shown with reverse reaction arrow
  • carbonic acid, ethanoic acid and citric acid
• how does Ph impact acids

  • gives an indication of concentration of H+ ions
  • strong acids have a lower pH than weak acids
  • as pH scale decreases by one unit the concentration of hydrogen ions increases 10x (orders of magnitude)
• how does concentration of an acid effect pH

  • tells us the amount of acid molecules in a given volume
  • A dilute acid has fewer acid molecules in a given volume than a concentrated, even if the strength is the same