paper 1

• Compounds, substances and mixtures:

  • Compound: substance that consists of two or more elements chemically joined together
  • Substances: contain only one element or compound
  • Mixtures: contain different elements and compounds. they are impure substances
• Simple distillation:

  • used to separate a solvent from a solution
  • works because the solute has a much higher boiling point than the solvent

  Method:

  1. solution is heated
  2. solvent boils
  3. solvent vapour passes into condenser
  4. vapour is cooled and condensed back to liquid state by cold water running through space between two tubes in condenser

  • solution becomes more concentrated because the solute stays behind
• Fractional distillation:

  • separate a liquid from a mixture of miscible liquids
  • works because the liquids in the mixture have different boiling points
  • fractionating column has a temperature gradient: hottest at the bottom, coldest at the top

  Method:

  1. mixture boils
  2. hot vapour rises up fractionating column
  3. vapour condenses when it hits cool surface of column and drips back
  4. the fraction with the lowest boiling point reaches 4th top first and passes into the condenser
  5. If you carry on heating, vapours from fractions with higher boiling points pass to condenser
• Filtration:

  • separate an insoluble substance from a liquid or solution in order to:
  • purify a liquid by removing solid impurities from it
  • separate the solid wanted from the liquid its mixed with
  • works because filter paper has tiny pores large enough to let water molecules and dissolved substances through and small enough to stop insoluble solid particles going through
• Crystallisation:

  • produce solid crystals from a solution

  Method:

  1. solution is heated to remove enough solvent to produce a saturated solution
  2. saturated solution is allowed to cool
  3. crystals form in the solution
  4. crystals are separated from the liquid and dried

  • hot water bath gives you more control over heating than a Bunsen Burner
  • works because the solubility of the solute decrease as the saturated solution cools and crystals form from the excess solute
• Drinking water:

  • potable water must have low levels of microbes and contaminating substances

  Stages in water treatment:

  1. sedimentation: large insoluble particles sink to the bottom of the tank
  2. filtration: small insoluble particles are removed by filtering through beds of sand
  3. chlorination: chlorine gas is bubbled through water to kill microbes
• copper sulfate practical:

  • makes pure dry hydrated copper sulfate crystals using copper oxide and sulfuric acid

  method:

  1. add excess base to the acid
  2. filter to remove increased copper oxide
  3. crystallise copper sulfate solution by heating it or leaving it in a warm place
• Titration:

  1. but acid into a burette
  2. use a pipette to put a know volume of alkali into conical flask
  3. put in indicator solution
  4. record the burette start reading
  5. add acid to alkali until colour changes
  6. record burette end reading
• Making a soluble salt from a soluble base:

  1. use titration to find exact volume of soluble base that reacts with the acid
  2. Mix the acid and soluble base in the correct proportions, producing a solution of the salt and water
  3. warm the salt solution to evaporate the water leaving salt crystals behind
• Redox reactions:

  • atoms of the more reactive metal lose electrons- are oxidised
  • metal cations of less reactive metal gain electrons- are reduced
  • less reactive metal is displaced
• Oxidisation is loss of electrons

  Reduction is gain of electrons
• iron extraction:

  • iron is less reactive than carbon so is produced by reducing iron oxide using carbon
  • this happens in a blast furnace
• aluminium extraction:

  • produced by reducing aluminium oxide in an electrolytic cell
• dynamic equilibrium is when the rate of forward and backwards reaction is equal and constant
• the haber process is a reversible reaction between nitrogen and hydrogen to form ammonium
• factors affecting equilibrium:

  • increase in temperature = favours endothermic reaction
  • increase in pressure= favours side with fewest molecules of gas
  • concentration of reacting substance increased = moves direction away from reacting substance
  • catalyst added= speeds up but no change in position of equilibrium
• weak acids partially disassociate

  strong acids fully disassociate

  the ph increases by 1 when the H+ ion concentration decreases by factor of 10
• Bases and alkalis:

  base + acid = salt + water

  metal + acid = salt + hydrogen

  metal carbonate + acid = salt + water + carbon dioxide
• Electrolysis:

  • when current flows through circuit electrodes get a charge
  • ions in compound become attracted to electrode of the opposite charge
  • cations (positive) go to cathode (negative)
  • anions (negative) go to anode (positive)
  • metals or H+ ions will go to cathode
  • non-metals such as Oxygen will go to anode
• The reactivity series:

  potassium

  Sodium

  lithium

  calcium

  magnesium

  Aluminium

  carbon

  zinc

  iron

  tin

  lead

  hydrogen

  copper

  silver

  Gold

  platinum