AQA Chemistry 3

AQA Chemistry 3

The Periodic Table
1. The Early Periodic Table
  1. Newland - Ordered the few elemenets known at the time in order of atomic weight. After Calcium they didnt match the pattern and his ideas weren't accepted.
  2. Mendeleev - Organised by similarities in properties. He left gaps for unknown elements, after these were discovered his predictions were confirmed and they accepted the idea.
  3. Developed by attempts to classify the elements.
2. The Modern Periodic Table
  1. Organised by proton (atomic) number.
  2. Atoms in the same group have similar properties as they have the same number of electrons in their outer shell.
    1. Group number = the amount of electrons in the outer shell.
  3. Trends in reactivity can be explained as we go down a group in terms of:
    1. - the distance between the outermost electrons and the nucleus.
      1. - number of energy levels (shells).
  4. Reactivity of metals increases as we go down the group.
  5. Reactivity of non-metals decreases as we go down the group.
3. Group 1 - The Alkali Metals
  1. React readily with air and water.
  2. Reacts with water to produce Hydrogen Gas and a alkali Metal Hydroxide.
  3. Low melting and boiling points, low density. Soft solids at room temperature.
  4. Form +1 ions (ionic compound).
  5. Reacts with Group 7 to form white salts or colourless crystals.
  6. Reactivity increases as you go down the group.
4. Transition Elements
  1. They are all metals.
  2. Higher melting and boiling points that Group 1.
  3. Malleble.
  4. Good conductors of heat and electricity.
  5. React slowly or not at all with oxygen or water.
  6. Strong and dense, useful as building materials, especially as alloys.
  7. Form positive ions with various charges eg. Fe2+ Fe3+
  8. Compounds of transitions metals are often brightly coloured.
  9. Many work well as catalysts.
5. Group 7 - The Halogens
  1. Non-metals.
  2. Low melting and boiling points that increase further down the group.
  3. Form -1 ionic compounds.
  4. Bond covalently with non metals.
  5. More reacitve halogens can displace a less reactive one from a solution of a halide (halogen) compound.
  6. Reactivity decreases down the group.
Water
1. Hard Water
  1. Uses more soap to produce an effective lather.
  2. Contains dissolved compounds eg. Calcium and Magnesium salts.
    1. These react with the soap to form a precipitate called scum.
  3. Temporary hard water can produce a solid scale when heated, reducing efficiency of appliances.
  4. Better than soft water for maintaining teeth and bones.
  5. Soft water lathers easily.
2. Removing Hardness
  1. Soft water may have dissolved compounds but they don't react to produce scum.
  2. Can be done by removing the dissolved compounds.
  3. Temporary hardness can be removed by heating. Permanent hardness cannot.
  4. Both types can be softened by adding washing soda or by using an ion-exchange resin to remove the calcium and magnesium ions.
3. Water Treatment
  1. Drinking water shouldn't contain any harmful substances and only contain low levels of dissolved substances and microbes.
  2. Water can be made fit to drink by filtering it to remove solids then disinfecting it to kill of any microbes.
  3. Pure water can be made my distillation but this requires a lot of energy, making it expensive.
4. Water Issues
  1. Advantages & Disadvantages of water treatment.
  2. Water can be treated to remove microbes, hardness and improve dental health.
  3. Chlorine is particularly effective at killing microbes but it is poisonous and can produce other toxic compounds. So it must be used carefully.
  4. Fluoride compounds are added to toothpaste to help prevent decay. People say that they should be able to choose to take extra fluoride or not and that it should not be added.
Energy Calculations
1. Comparing Energy Released by Fuels
  1. When fuels and food react with oxygen they release energy in an exothermic reaction.
  2. Calorimeters can compare energy released by different fuels/foods.
    1. Simple Calorimeter: Water in a beaker, burn a substance and temperature rise of water depends on the energy released.
      1. Q= m*c*tempchange
        Q=energy transferred(J)
        c= specific heat capacity
2. Energy Transfers in Solutions
  1. Energy is transferred to or out of the solution.
  2. Measure temperature change then use the equation Q=m*c*temp
  3. Neutralisation and displacement reactions are both examples of reactions where we can use this technique.
3. Energy Level Diagrams
  1. Show the relative different in the energy of reactants and the energy of the products
  2. Catalysts provide a lower activation energy.
  3. Bond breaking, energy taken in - Endothermic.
  4. Bond making, energy given out - Exothermic
4. Calculations Using Bond Energies
  1. Exothermic - Energy released when bonds are formed is greater than the energy absorbed when bonds are broken.
  2. Endothermic - Energy released when new bonds are formed is less then the energy absorbed when the bonds are broken.
Analysis and Synthesis
1. Testing for Positive Ions
  1. Flame Test
    1. Calcium - (Brick) Red
    2. Potassium - Lilac
    3. Lithium - Crimson
    4. Sodium - Yellow
    5. Barium - Green
    6. Burn the substance.
  2. Sodium Hydroxide Solution
    1. Aluminium, Calcium and Magnesium form a white precipitate when NaOH is added to any solution containing them.
      1. Ass excess NaOH to test for Mg (Precipitate will dissolve).
      2. Ca and Mg can be determined using a flame test.
2. Testing for Negative Ions
  1. Carbonate
    1. Two test tubes, one with acid and carbonate, with bung and pipe leading to another test tube with limewater.
      1. Add dilute HCl acid to the substance to see if it fizzes. If it does, the gas turns the lime water cloudy and carbonate ions are present.
  2. Hailde Ions
    1. Add dilute nitric acid then silver nitrate solution and a ppt will form.
      1. Chloride Ions - White ppt.
        Bromide Ions - Cream ppt.
        Iodide Ions - Yellow ppt.
  3. Sulphate Ions
    1. Add dilute HCl acid and then Barium Chloride solution. If a white precipitate forms, sulphate ions are present.
3. Chemical Analysis
  1. Used in environmental, medical and forensic analysis.
  2. Qualitative - Tests if a substance is in a sample.
    1. Quantitative - Test how much of a substance is in a sample.

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