chemical changes

• Metals with oxygen

  • when metals react with Oxygen they become a metal oxide & an oxidation reaction takes place
• Oxidation - gaining oxygen
• Reacting a metal with water produces metal hydroxide & hydrogen gas
• The higher up on the reactivity series the quicker they react with water or acid in which they lose electrons & form positive irons
• Extraction of metal

  • A more reactive element will displace a less reactive element from it’s compound
• Reduction - losing oxygen
• Oxidation - losing electrons
• Reduction- gaining electrons
• neutralisation - a type of chemical reaction in which an acid & a base react to form water & a salt
• the universal indicator is added to the solution it changes to a colour that shows the pH of the solution
• ph scale

  1 to 6 = acid

  7 = neutral

  8 to 14 = alkalis
• Acids - solution that release hydrogen ions in water
• strong acids - are completely ionised in aqueous solution
• weak acids - partially ionised in aqueous solution, usually a reversible reaction
• strong acids

  • hydrochloric acid
  • sulfuric acid
  • nitric acid
• weak acids

  • carbonate acid
  • ethanoic acid
  • citric acid
• redox reactions there is a gain of electrons in one molecule & loss of electrons in another
• soluble salts

  • measure your acid into a measuring cylinder then pour into beaker
  • heat acid gently using a bunser burner
  • add small amounts of the insoluble until there is no more
  • leave to neutralise
  • then filter out excess solid
  • time to evaporate, pour solution into evaporation basin & heat gently over boiling water
  • leave the solution for 24 hours in cool place for crystals to form
  • gently pat the crystals dry
• when an ionic compound is molten (melted to liquid) or aqueous (dissolved in water) the ions are free to move about the liquid or solution. they conduct electricity & called electrolytes
• passing an electric current through electrolytes causes the ions in o move to the electrodes
• electrolysis

  positive charged ions move to negative electrode (the cathode)
• electrolysis

  negatively charged ions move to the positive electrode (the anode)
• electrolysis - ions are discharges at the electrodes producing elements
• a mixture is used as the electrolyte because a mixture of positive & negative ions are needed
• oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide in which gradually burns away. Therefore positive electrodes have to be frequently replaced
• Test for hydrogen

  • uses a burning splint held at the end of a test tub, hydrogen burns rapidly with pop sound
• Test for oxygen

  • used a glowing splint inserted into a test tube of gas. the splint relight is oxygen is present
• Test for chlorine

  • when damp litmus paper is put into chlorine glass, the litmus paper bleaches & turn white
• Test for carbon dioxide

  • use an aqueous solution of calcium hydroxide (limewater) when carbon dioxide is shaken or bubbled with water it tunes milky (cloudy)
• electrolysis is used to extract some metals as they are more reactive than carbon
• electrolysis experiment

  • choose an electrolyte
  • pour out sample of the electrolyte into the solution & place an inverted test tube over each electrode
  • pass current through the electrolyte & collect the gas’s in the inverted test tube
  • use a chemical test to identify the gases
• an exothermic reaction is one that transfers energy to the surroundings so the temperature of the surroundings increase
• an endothermic reactions takes in energy from the surroundings so the temperature of the surroundings decreases
• exothermic use

  • (everyday)self heating cans or hand warmers
  • (in reactions) combustion , many oxidation reactions & neutralisation
• endothermic use

  • (everyday) sport injury packs
  • (reaction) thermal decomposition & the reaction of citric acid & sodium hydrogen carbonate
• reactivity series

  • potassium
  • sodium
  • lithium
  • calcium
  • magnesium
  • carbon
  • iron
  • hydrogen
  • copper
• the closer an element is to the nucleus makes it less reactive as their is a stronger attraction & it’s harder to be reactive and lose electrons
• explain how the reactivity of metals with water or dilute acid is related to the tendency of metals to form positive ions

  When a more reactive metal react with less reactive metal, the more reactive metal atom forms positive as well easily
• The higher up on the reactivity series, the quicker they react with water or dilute to lose electrons and form positive ions
• redox - is wen a reduction & oxidation occurs in the same reaction