SECOND TERM OF CHEMISTRY STPM

Second Term

7 Chemical Energetics

7.1 Enthalpy changes of reaction, dH

Candidates should be able to:

(a) explain that most chemical reactions are accompanied by enthalpy changes (exothermic or endothermic);

(b) define enthalpy change of reaction, H, and state the standard conditions;

(c) define enthalpy change of formation, combustion, hydration, solution, neutralisation, atomisation, bond energy, ionisation energy and electron affinity;

(d) calculate the heat energy change from experimental measurements using the relationship: heat change, q mcT or q = mc ;

(e) calculate enthalpy changes from experimental results.

7.2 Hess’ law

Candidates should be able to:

(a) state Hess’ law, and its use to find enthalpy changes that cannot be determined directly, e.g. an enthalpy change of formation from enthalpy changes of combustion;

(b) construct energy level diagrams relating the enthalpy to reaction path and activation energy;

(c) calculate enthalpy changes from energy cycles.

7.3 Born-Haber cycle

Candidates should be able to:

(a) define lattice energy for simple ionic crystals in terms of the change from gaseous ions to solid lattice;

(b) explain qualitatively the effects of ionic charge and ionic radius on the numerical magnitude of lattice energy values;

(c) construct Born-Haber cycle for the formation of simple ionic crystals.

7.4 The solubility of solids in liquids

Candidates should be able to:

(a) construct energy cycles for the formation of aqueous solutions of ionic compounds;

(b) explain qualitatively the influence on solubility of the relationship between enthalpy change of solution, lattice energy of solid and enthalpy change of hydration or other solvent-solute interaction.

8 Electrochemistry

8.1 Half-cell and redox equations

Candidates should be able to:

(a) explain the redox processes and cell diagram (cell notation) of the Daniell cell;

(b) construct redox equations.

8.2 Standard electrode potential

Candidates should be able to:

(a) describe the standard hydrogen electrode;

(b) use the standard hydrogen electrode to determine standard electrode potential (standard reduction potential), Eº;

(c) calculate the standard cell potential using the Eo values, and write the redox equations;

(d) predict the stability of aqueous ions from Eº values;

(e) predict the power of oxidising and reducing agents from Eº values;

(f) predict the feasibility of a reaction from ‘E note cell’ value and from the combination of various electrode potentials: spontaneous and non-spontaneous electrode reactions.

8.3 Non-standard cell potentials

Candidates should be able to:

(a) calculate the non-standard cell potential, Ecell, of a cell using the Nernst equation.

8.4 Fuel cells

Candidates should be able to:

(a) describe the importance of the development of more efficient batteries for electric cars in terms of smaller size, lower mass and higher voltage, as exemplified by hydrogen-oxygen fuel cell.

8.5 Electrolysis

Candidates should be able to:

(a) compare the principles of electrolytic cell to electrochemical cell;

(b) predict the products formed during electrolysis;

(c) state the Faraday’s first and second laws of electrolysis;

(d) state the relationship between the Faraday constant, the Avogadro constant and the electronic charge;

(e) calculate the quantity of electricity used, the mass of material and/ or gas volume liberated during electrolysis.

8.6 Applications of electrochemistry

Candidates should be able to:

(a) explain the principles of electrochemistry in the process and prevention of corrosion (rusting of iron);

(b) describe the extraction of aluminium by electrolysis, and state the advantages of recycling aluminium;

(c) describe the process of anodisation of aluminium to resist corrosion;

(d) describe the diaphragm cell in the manufacture of chlorine from brine;

(e) describe the treatment of industrial effluent by electrolysis to remove Ni2+, Cr3+ and Cd2+;

(f) describe the electroplating of coated plastics.

9 Periodic Table: Periodicity

9.1 Physical properties of elements of Period 2 and Period 3

Candidates should be able to:

(a) interpret and explain the trend and gradation of atomic radius, melting point, boiling point, enthalpy change of vaporisation and electrical conductivity in terms of structure and bonding;

(b) explain the factors influencing ionisation energies;

(c) explain the trend in ionisation energies across Period 2 and Period 3 and down a group;

(d) predict the electronic configuration and position of unknown elements in the Periodic Table from successive values of ionisation energies.

9.2 Reactions of Period 3 elements with oxygen and water

Candidates should be able to:

(a) describe the reactions of Period 3 elements with oxygen and water;

(b) interpret the ability of elements to act as oxidising and reducing agents.

9.3 Acidic and basic properties of oxides and hydrolysis of oxides

Candidates should be able to:

(a) explain the acidic and basic properties of the oxides of Period 3 elements;

(b) describe the reactions of the oxides of Period 3 elements with water;

(c) describe the classification of the oxides of Period 3 elements as basic, amphoteric or acidic based on their reactions with water, acid and alkali;

(d) describe the use of sulphur dioxide in food preservation.

10 Group 2

10.1 Selected Group 2 elements and their compounds

Candidates should be able to:

(a) describe the trends in physical properties of Group 2 elements: Mg, Ca, Sr, Ba;

(b) describe the reactions of Group 2 elements with oxygen and water;

(c) describe the behaviour of the oxides of Group 2 elements with water;

(d) explain qualitatively the thermal decomposition of the nitrates, carbonates and hydroxides of Group 2 elements in terms of the charge density and polarisability of large anions;

(e) explain qualitatively the variation in solubility of sulphate of Group 2 elements in terms of the relative magnitudes of the enthalpy change of hydration for the relevant ions and the corresponding lattice energy.

10.2 Anomalous behaviour of beryllium

Candidates should be able to:

(a) explain the anomalous behaviour of beryllium as exemplified by the formation of covalent compounds;

(b) describe the diagonal relationships between beryllium and aluminium;

(c) explain the similarity of aqueous beryllium salts to aqueous aluminium salts in terms of their acidic property.

10.3 Uses of Group 2 compounds

Candidates should be able to:

(a) state the uses of Group 2 compounds in agriculture, industry and medicine.

11 Group 14

11.1 Physical properties of Group 14 elements

Candidates should be able to:

(a) explain the trends in physical properties (melting points and electrical conductivity) of Group 14 elements: C, Si, Ge, Sn, Pb.

11.2 Tetrachlorides and oxides of Group 14 elements

Candidates should be able to:

(a) explain the bonding and molecular shapes of the tetrachlorides of group 14 elements;

(b) explain the volatility, thermal stability and hydrolysis of tetrachlorides in terms of structure and bonding;

(c) explain the bonding, acid-base nature and the thermal stability of the oxides of oxidation states +2 and +4.

11.3 Relative stability of +2 and +4 oxidation states of Group 14 elements

Candidates should be able to:

(a) explain the relative stability of +2 and +4 oxidation states of the elements in their oxides, chlorides and aqueous cations.

11.4 Silicon, silicone and silicates

Candidates should be able to:

(a) describe the structures of silicone and silicates (pyroxenes and amphiboles), sheets (mica) and framework structure (quartz) (general formulae are not required);

(b) explain the uses of silicon as a semiconductor and silicone as a fluid, elastomer and resin;

(c) describe the uses of silicates as basic materials for cement, glass, ceramics and zeolites.

11.5 Tin alloys

Candidates should be able to:

(a) describe the uses of tin in solder and pewter.

12 Group 17

12.1 Physical properties of selected Group 17 elements

Candidates should be able to:

(a) state that the colour intensity of Group 17 elements: Cl2, Br2, I2, increase down the group;

(b) explain how the volatility of Group 17 elements decreases down the group.

12.2 Reactions of selected Group 17 elements

Candidates should be able to:

(a) deduce and explain the relative reactivities of Group 17 elements as oxidising agents from Eº values;

(b) explain the order of reactivity of F2, Cl2, Br2, I2 with hydrogen, and compare the relative thermal stabilities of the hydrides;

(c) explain the reactions of chlorine with cold and hot aqueous sodium hydroxide.

12.3 Reactions of selected halide ions

Candidates should be able to:

(a) explain and write equations for reactions of Group 17 ions with aqueous silver ions followed by aqueous ammonia;

(b) explain and write equations for reactions of Group 17 ions with concentrated sulphuric acid.

12.4 Industrial applications of halogens and their compounds

Candidates should be able to:

(a) describe the industrial uses of the halogens and their compounds as antiseptic, bleaching agent and in black-and-white photography;

(b) explain the use of chlorine in water treatment.

13 Transition Elements

13.1 Physical properties of first row transition elements

Candidates should be able to:

(a) define a transition element in terms of incomplete d orbitals in at least one of its ions;

(b) describe the similarities in physical properties such as atomic radius, ionic radius and first ionisation energy;

(c) explain the variation in successive ionisation energies;

(d) contrast qualitatively the melting point, density, atomic radius, ionic radius, first ionisation energy and conductivity of the first row transition elements with those of calcium as a typical s-block element.

13.2 Chemical properties of first row transition elements

Candidates should be able to:

(a) explain variable oxidation states in terms of the energies of 3d and 4s orbitals;

(b) explain the colours of transition metal ions in terms of a partially filled 3d orbitals;

(c) state the principal oxidation numbers of these elements in their common cations, oxides and oxo ions;

(d) explain qualitatively the relative stabilities of these oxidation states;

(e) explain the uses of standard reduction potentials in predicting the relative stabilities of aqueous ions;

(f) explain the terms complex ion and ligand;

(g) explain the formation of complex ions and the colour changes by exchange of ligands. (Examples of ligands: water, ammonia, cyanide ions, thiocyanate ions, ethanedioate ions, ethylenediaminetetraethanoate, halide ions; examples of complex ions: [Fe(CN)6]4, [Fe(CN)6]3, [Fe(H2O)5(SCN)]2+);

(h) explain the use of first row transition elements in homogeneous catalysis, as exemplifed by Fe2+ or Fe3+ in the reaction between I and S2O82;

(i) explain the use of first row transition elements in heterogeneous catalysis, as exemplifed by Ni and Pt in the hydrogenation of alkenes.

13.3 Nomenclature and bonding of complexes

Candidates should be able to:

(a) name complexes using International Union of Pure and Applied Chemistry (IUPAC) nomenclature;

(b) discuss coordinate bond formation between ligands and the central metal atom/ion, and state the types of ligands, i.e. monodentate, bidentate and hexadentate.

13.4 Uses of first row transition elements and their compounds

Candidates should be able to:

(a) describe the use of chromium (in stainless steel), cobalt, manganese, titanium (in alloys) and TiO2 (in paints).

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