C6

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  • C6
    • The pH Scale
      • Acids have a pH of less than 7
      • Alkalis have a pH greater than 7
        • Bases are the oxides and hydroxides of metals, soluble ones are called Alkalis
      • Bases are the oxides and hydroxides of metals, soluble ones are called Alkalis
      • Acidic Compounds produce Hydrogen Ions when dissolved in water
      • Alkalis produce Hydroxide Ions when dissolved in water.
        • Acidic Compounds produce Hydrogen Ions when dissolved in water
    • Neutralisation
      • Acid and Base mixed in correct amounts = cancel eachother out (Neutralisation)
        • Acid + Base = Neutral Salt Solution + Water
        • H+ + OH- = H2O
      • Hydrochloric Acid = Chloride salts
      • Sulfuric Acid = Sulfate salts
      • Nitric Acid = Nitrate salts
    • Energy Changes
      • When reactions occur, energy is tranferred to or from the surroundings.
      • Many chemical reactions are accompanied by a temp. change
        • When reactions occur, energy is tranferred to or from the surroundings.
      • Exothermic Reactions
        • They are a RISE in temp.
        • They transfer heat energy to surroundings
          • 'Exo' = Exit?
        • Examples
          • Combustion of Carbon
            • C + O2 = CO2
          • Neutralising Alkalis with Acids
          • Oxidation reactions
        • Products have LESS energy than reactants
      • Endothermic Reactions
        • They have a FALL in temp.
        • They take in heat from surroundings
        • Examples
          • Reaction betwwn Citric Acid + Sodium Hydrogencarbonate
          • Dissolving Ammonium Nitrate crystals in water
          • Thermal Decomposition
        • Products have MORE energy than reactants
      • Very important these changes are managed during Chem Synth. eg nasty accident if too much energy given out
    • Chemical Synthesis
      • Starting minerals react to produce new substances.
      • Greater amount of reactants = greater amount of product
      • Percentage Yeild calculated by comparing actual amount of product with the amount you'd expect to get.
      • 1) Find out reactions needed for product
      • 2) Risk assessment
      • 3) Calculate amount of reactants to use
      • 4) Do reaction under suitable conditions
      • 5) Seperate product from reaction mixture
      • 6) Purify product
      • 7) Measure yeild
      • 8) Check purituy (titration)
        • Titration
          • Calculates concentration of acid - how much alkali needed to neutralise
          • 1) Fill burette with alkali solution and take reading of volume
          • 2) Use pipette to measure 25cm3 of acid and put in conical flask
          • 3) Add a few drops of indicator and put flask under burette
          • 4) Add alkali to acid drop by drop - swirl flask to mix well
          • 5) Keep adding and swirling until acid has been neutralised
          • 6) Record final burette reading.
    • Measuring the Rates of Reaction
      • Chemical reactions only occur when the reacting particles collide with one another with sufficient energy
      • Chemical reactions can happen at different speeds.
      • Weighing reaction mixture
        • Product is gas - mass of mixture will decrease
      • Volume of gas produced
        • Gas syringe to measure volume of gas produced at timed intervals
      • Observing formation of precipitate
        • Watching a cross under flask - see when disappears (time)
        • Colour change using Light Sensor - accurate and reliable results, more data collected.
    • Analysing Rate of Reaction
      • Graphs plotted to show progress
      • Steeper line = faster reaction
      • Reactant used up = reaction stops (flat line)
      • Same amount of product made from same amount of reactant - no matter how fast reaction is
      • Why one reaction is faster than another
        • Surface area of solid reactants is greater
        • Temperature is greater
        • Concentration greater
        • Catalyst used
    • Changing Rate of Reaction
      • 1) Temperature of Reactants
        • Cold reaction mixture = particles move slowly (less kinetic energy)
        • Collide less often, less energy = fwer collisions
        • Hot reaction mixture = paritcles move more quickly (more kinetic energy)
        • Collide more often, greater energy = more successful collisions
      • 2) Concentration of Dissolved Reactants
        • Low concentration = particles spread out so collide successfully less often
        • High concentration = particles close together so collide successfullt more often.
      • 3) Surface Area of Solid Reactants
        • Large particles = small surface area
        • Fewer particles exposed to collisions
        • Collide succeessfully less often - slow rate of reaction
        • Small particles = big surface area
        • More particles exposed to collisions
        • Collide successfully more often - fast rate of reaction
      • 4) Using a Catalyst
        • Substance that increases rate of chemical reaction
        • Hydrogen Peroxide = Water + Oxygen
        • Measure rate of reaction by measuring amount of oxygengiven off at one min. intervals
        • This reaction happens slowly unless catalyst of manganese oxide
        • With a catalyst, plenty of fizzing seen as oxygen id given off
    • Collision Theory
      • Results in more energetic collisions happening more frequently
      • Increasing temp. = increase of kinetic energy of particles
      • Chemical reactions only occur when particles collide with each other with sufficient energy
      • Minimum energy required for a reaction will be achieved more often resulting in a greater rate of reation
      • An increase in concentration of surface area results in more frequent collisions and more collisions that are sufficiently ebergetic for a reaction to occur
    • Controlling a Chemical Reaction
      • Rate of manufacture must be high enough to produce a sufficient daily yeild of product
      • Percentage yield must be high enough to produce sufficient daily yield of product
      • Low percentage yield accepted as long as reaction can be repeated many times with recycled starting materials
      • Optimum conditions should be used that give the lowest cost - rather than fastest reaction or highest % yield
      • Care taken if reactants or products could harm environment
      • Avoid putting any harmful by-products into environment
      • Risk assessment must be carried out and necessary precautions taken
  • Collision Theory
    • Results in more energetic collisions happening more frequently
    • Increasing temp. = increase of kinetic energy of particles
    • Chemical reactions only occur when particles collide with each other with sufficient energy
    • Minimum energy required for a reaction will be achieved more often resulting in a greater rate of reation
    • An increase in concentration of surface area results in more frequent collisions and more collisions that are sufficiently ebergetic for a reaction to occur

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