AQA A Level Chemistry- Inorganic chemistry Questions and Answers

AQA A Level Chemistry- Inorganic chemistry Questions and Answers Periodic table Table that provides chemists with a structural organisation of the known chemical elements that can be used to deduce physical and chemical properties Atomic radius across Period 3 Decreases First ionisation energy across Period 3 Increases Exceptions: Drops at Al and S Melting points across Period 3 Increases from Na to Si Decreases from Si to Ar Small rise at S Explain why the melting point of aluminium is higher than the melting point of sodium Bigger charge (3+ compared to 1+) More free/delocalised electrons Stronger metallic bonding/stronger (electrostatic) attraction between the ions electrons Explain why the melting point of sulfur is higher than the melting point of phosphorus S bigger molecule So more/stronger van der Waals' forces (to be broken or overcome) Atomic radius down Group 2 Increases First ionisation energy down Group 2 Decreases Melting point down Group 2 Decreases Exception Ca which increases Explain the melting point of the elements in terms of the structure and bonding of Group 2 elements Be and Mg have hexagonal close packed structures Ca, Sr and Ba have cubic structures The relative solubilities of the hydroxides, X(OH)2, of the elements Mg-Ba in water Increase down the group The relative solubilities of the sulfates, XSO4, of the elements Mg-Ba in water Decrease down the group The role of magnesium in the extraction of titanium from TiCl4 Mg is used as a reducing agent Mg is oxidised to 2+ in MgO when it is heated with TiCl4 to about 1200C in an inert atmosphere Redox equation of Group 2 elements with water X(s) + 2H2O(l) - X2+(aq) +2OH-(aq) + H2(g) Sparingly soluble Group 2 hydroxide Mg(OH)2 Insoluble Group 2 sulphate BaSO4 The use of acidified BaCl2 solution Test for sulfate ions If Barium Chloride is added to a solution that contains sulphate ions a white precipitate forms (BaSO4) The use of Mg(OH)2 in medicine (in solution as milk of magnesia) to neutralise excess acid in the stomach and to treat constipation The use of BaSO4 in medicine In a 'Barium meal' given to patients who need x-rays of their intestines. The Barium absorbs the x-rays and so the gut shows up on the x-ray image. Even though Barium compounds are toxic it is safe to use here because of its low solubility The use of Ca(OH)2 in agriculture To neutralise acidic soils The use of CaO or CaCO3 to remove SO2 from flue gases Removed by reacting with an alkali such as CaO or CaCO3 slurry (mixed with water) • The process is called wet scrubbing: CaO(s) + 2H2O(l) + SO2(g) - CaSO3(aq) + 2H2O(l) CaCO3(s) + 2H2O(l) + SO2(g) - CaSO3(aq) + 2H2O(l) + CO2(g) Explain the trend in electronegativity down Group 7 Decreases because the attracting power of the nucleus is shielded by the inner electron shells increasingly down the group Explain the trend in the boiling point of the elements in terms of their structure and bonding down Group 7 Increases from F to I, because the larger halogens have greater Van der Waals' forces holding the molecules together, as the relative mass increases down the group Oxidising ability of the halogens down the group Decreases going down the group and the more reactive halogen will displace a less reactive halogen from a solution of its ions Reducing ability of the halide ions Increases as you go down the Group How to identify and distinguish between halide ions Reaction with silver nitrate + dilute nitric acid F- no precipitate Cl- white precipitate Br- very pale cream precipitate I- very pale yellow precipitate The nitric acid reacts with, and removes, other ions that might also give a confusing precipitate with silver nitrate Why ammonia solution is added when testing for halide ions To confirm the precipitate Solubility of the silver halides in ammonia AgCl- precipitate dissolves to give a colourless solution AgBr- precipitate is almost unchanged using dilute ammonia solution, but dissolves in concentrated ammonia solution to give a colourless solution AgI- precipitate is insoluble in ammonia solution of any concentration The reaction of chlorine with water to form chloride ions and chlorate(I) ions Cl2(aq) + H2O(l) - ClO-(aq) + 2H+(aq) + Cl-(aq) The reaction of chlorine with water to form chloride ions and oxygen 2Cl2(aq) + 2H2O(l) - 4HCl + O2 The use of chlorine in water treatment Cl is pumped into the water in the final stage of water treatment This water is stored for about 2 hours to allow disinfection to occur The benefits to health of water treatment by chlorine outweigh its toxic effects The reaction of chlorine with cold, dilute, aqueous NaOH and uses of the solution formed Cl2 + 2NaOH - NaClO + NaCl + H2O Reaction of sodium and water 2Na + 2H2O -- 2NaOH + H2 , pH13 Reaction of magnesium and water Mg + H2O(g) -- MgO +H2 (FAST) Mg + 2H20(l) -- Mg(OH)2 + H2 , pH~12 Reaction of Na with oxygen 2Na + 1/2O2 -- Na2O(s) Vigorous Reaction of Mg with oxygen Mg + 1/2O2 -- MgO(s) Vigorous Reaction of Al with oxygen 2Al + 1.5O2 -- Al2O3(s) Slow Reaction of Si with oxygen Si + O2 -- SiO2(s) Slow Reaction of P with oxygen P4 + 5O2 -- P4O10(s) Spontaneously combusts Reaction of S with oxygen (dioxide) S + O2 -- SO2(g) Burns steadily Melting points of Period 3 oxides Na2O, MgO and Al2O3 have high melting points due to giant ionic lattice structure creating strong forces of attraction between each ion SiO has a higher melting point than other non-metal oxides due to giant macromolecular structure P4O1O and SO3 have low melting points due to simple molecular bonding Reaction of Na2O with water Na2O + H2O -- 2NaOH, pH 12-14 Reaction of MgO with water MgO + H2O -- Mg(OH)2, pH 9-10 Reaction of P4O10 with water P4O10 + 6H2O -- 4H3PO4 (phosphoric(V)acid) Reaction of SO2 with water SO2 + H2O -- H2SO3 (sulphuric(IV)acid) Reaction SO3 with water SO3 + H2O -- H2SO4 (sulphuric(VI)acid) Reaction of Al2O3 with water Insoluble in water but reacts with BOTH acids and bases to form salts - AMPHOTERIC Reaction of sodium oxide and hydrochloric acid Na2O + 2HCl -- 2NaCl + H2O Reaction of magnesium oxide and sulphuric acid MgO + H2SO4 -- MgSO4 + H2O Reaction of magnesium oxide and hydrochloric acid MgO + HCl -- MgCl2 + H2O Reaction of silicon oxide and sodium hydroxide SiO2 + 2NaOH -- Na2SiO3 + H2O Reaction of phosphorus oxide and sodium hydroxide P4O10 + 12NaOH -- 4Na3PO4 + 6H2O Reaction of sulphur dioxide and sodium hydroxide SO2 + 2NaOH -- Na2SO3 + H2O Reaction of sulphur trioxide and sodium hydroxide SO3 + 2NaOH -- Na2SO4 + H2O Reaction of aluminium oxide and hydrochloric acid Al2O3 + 6HCl -- 2AlCl3 + 3H2O Reaction of aluminium oxide and sulphuric acid Al2O3 + 2H2SO4 -- Al2(SO4)3 + 3H2O Reaction of aluminium oxide and sodium hydroxide Al2O3 + 2NaOH + 3H2O -- 2NaAL(OH)4 Cause of transition metal characteristics of elements Ti-Cu An incomplete d sub-level in atoms or ions The characteristic properties of transition metals Period 4 • complex formation • formation of coloured ions • variable oxidation state • catalytic activity Ligand A molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons Complex A central metal atom or ion surrounded by ligands Co-ordination number The number of co-ordinate bonds to the central metal atom or ion Transition metal A metal that can form one or more stable ions with an incomplete d sub-level Monodentate ligands H2O, NH3 (similar in size and are uncharged) and Cl− (larger than the uncharged ligands NH3 and H2O) Exchange of the ligands NH3 and H2O occurs without Change of co-ordination number Exchange of the ligand H2O by Cl- Can involve a change of co-ordination number Types of ligand Monodentate- one coordinate bond Bidentate- two coordinate bonds Multidentate- more than one coordinate bonds Haem An iron(II) complex with a multidentate ligand How oxygen is transported in the blood Oxygen forms a co-ordinate bond to Fe(II) in haemoglobin Carbon monoxide is toxic because It replaces oxygen co-ordinately bonded to Fe(II) in haemoglobin The chelate effect Bidentate and multidentate ligands replace monodentate ligands from complexes An increase in entropy makes the formation of the chelated complex more favourable Cisplatin complex Pt(II) with 2 Cl- and 2 ammonia molecules Square planar Cis/Z isomer Tollen's complex Ag+ Diamminesilver(I) complex Linear complex [Ag(NH3)2]+ Reduction to metallic silver for aldehyde test Transition metal ions commonly form octahedral complexes with Small ligands Transition metal ions commonly form tetrahedral complexes with Larger ligands (eg Cl-) Octahedral complexes can display cis-trans isomerism (a special case of E-Z isomerism) with Monodentate ligands and optical isomerism with bidentate ligands Why transition metal complexes are coloured Colour arises when some of the wavelengths of visible light are absorbed and the remaining wavelengths of light are transmitted or reflected What happens to transition metal ions when light is absorbed d electrons move from the ground state to an excited state The energy difference between the ground state and the excited state of the d electrons in transition metals is given by: ∆E = hν = hc/λ What causes colour change in transition metal ions Changes in oxidation state, co-ordination number and ligand alter ∆E which leads to the change Spectroscopy requires use of Visible light Colorimetry Method used to measure the absorption of light by a sample, the more concentrated it is, the more light will be absorbed Ligand substitution reaction One ligand is swapped for another