WJEC Chemistry Unit 3

Annotations:

• Spec: http://www.wjec.co.uk/qualifications/science/as-a-level/chemistry-as-a-level-2015/wjec-gce-chemistry-spec-from-2015.pdf?language_id=1#page=30

1. Physical and Inorganic Chemistry
2. 3.1 Redox and standard electrode potential

   Annotations:

   • http://www.wjec.co.uk/qualifications/science/as-a-level/chemistry-as-a-level-2015/wjec-gce-chemistry-spec-from-2015.pdf?language_id=1#page=31
   1. 3.2 Redox reactions

      Annotations:

      • http://www.wjec.co.uk/qualifications/science/as-a-level/chemistry-as-a-level-2015/wjec-gce-chemistry-spec-from-2015.pdf?language_id=1#page=32
      1. 3.3 Chemistry of the p - block

         Annotations:

         • http://www.wjec.co.uk/qualifications/science/as-a-level/chemistry-as-a-level-2015/wjec-gce-chemistry-spec-from-2015.pdf?language_id=1#page=33
         1. 3.4 Chemistry of the d - block transition metals

            Annotations:

            • http://www.wjec.co.uk/qualifications/science/as-a-level/chemistry-as-a-level-2015/wjec-gce-chemistry-spec-from-2015.pdf?language_id=1#page=34
            1. 3.5 Chemical kinetics

               Annotations:

               • http://www.wjec.co.uk/qualifications/science/as-a-level/chemistry-as-a-level-2015/wjec-gce-chemistry-spec-from-2015.pdf?language_id=1#page=35
               1. 3.6 Enthalpy changes for solids and solutions

                  Annotations:

                  • http://www.wjec.co.uk/qualifications/science/as-a-level/chemistry-as-a-level-2015/wjec-gce-chemistry-spec-from-2015.pdf?language_id=1#page=36
                  1. 3.7 Entropy and feasibility of reactions

                     Annotations:

                     • http://www.wjec.co.uk/qualifications/science/as-a-level/chemistry-as-a-level-2015/wjec-gce-chemistry-spec-from-2015.pdf?language_id=1#page=37
                     1. 3.8 Equilibrium constants

                        Annotations:

                        • http://www.wjec.co.uk/qualifications/science/as-a-level/chemistry-as-a-level-2015/wjec-gce-chemistry-spec-from-2015.pdf?language_id=1#page=38
                        1. 3.9 Acid - base equilibria

                           Annotations:

                           • http://www.wjec.co.uk/qualifications/science/as-a-level/chemistry-as-a-level-2015/wjec-gce-chemistry-spec-from-2015.pdf?language_id=1#page=39
         2. Amphoteric means an element can act as either an acid (proton donor) or a base (proton acceptor)
            1. Examples of amphoteric behaviour
            2. The inert pair effect is the tendency of the s2 pair of e- in an atom to remain paired and not get involved in bonding
   2. a) Redox is when both reduction and oxidation happen simultaneously. The oxidising agent gets reduced and vice versa. Always remember OILRIG
      1. b) In an acidic solution
         1. Identify oxidation states, add electrons, balance charges with H+, balance H with H2O
            1. Voltages for half equations cannot be measured directly, however, they can be connected to a "standard" and then compared. (Symbol for SEP is E0)
               1. The standard they are compared to is a hydrogen half-cell with solutions at 1moldm^-3, Gasses at 1atm and temp at 298K
               2. Simple electrochemical cells are formed in two ways depening on the element. Non-metals are bubbled over a Pt electrode in order to conduct. Also metals with two ions such as Fe2+ and Fe3+ use a Pt electrrode because we don't want ions from the electrode interferring with what we're measuring (Fe3+ + e- --> Fe2+)
                  1. Diagram of a standard chemical cell

                     Annotations:

                     • philschatz.com/chemistry-book/resources/CNX_Chem_17_03_GalvanAg.jpg
                  2. Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)

                     Annotations:

                     • Shorthand for metal electrodes
                     1. Pt(s) | H2(g) | 2H+(aq) || Mg2+(aq) | Mg(s)

                        Annotations:

                        • Shorthand for non-metal electrode
                  3. To calculate EMF, reverse the most negative and then add them together
                     1. Ca2+ + 2e- --> Ca = -2.76V
                        1. Pb2+ + 2e- --> Pb = 0.13V
                           1. EMF = 2.76 + (-0.13) = 2.63V
                              1. E.cell = E.reduction + E.oxidation Assuming the oxidation sign is already flipped
                                 1. For a reaction to be feasible EMF must be positive
                     2. An Electrochemical series is half cells with E0 from most negative to most positive. The most negative are good reducing agents and the most positive are good oxidisng agents.
                        1. Hydrogen fuel cells work by hydrogen being ionised, producing electricity. The H+ ions then combine with O- ions to form a harmless biproduct, water.
      2. b) In a basic solution
         1. Balance atom being red/ox, Balance O2 by adding H20, Balance H2 by adding H+, balance charges, convert H+ to H2O by adding OH- to both sides