Topic 4- INORGANIC AND TESTS

• Why the melting points down group 2 decreases?

  • atomic size increases. The distance between the positive ions and delocalized electrons increases. Therefore the electrostatic attractive forces between the positive ions and the delocalized electrons weaken.
• GROUP 7: trend in m.p increases down group 7 because strength of london foces increases (number of electrons increases down the group); atoms become larger; more energy needed to break london forces.
• GROUP 7: trend in electronegativity decreases down the group (electronegativity is the ability of an atom to attract bonding electrons in a convalent bond). Atomic radii increases, shielding increases, so the nucleus is less able to attract the bonding pair of e-.
• GROUP 7: The reactivity of the halogens decreases down the group as the atoms get bigger, more shielding, so they less easily attract/accept electrons. They therefore form -1 ions less easily down the group
• GROUP 7: A halogen that is a strong oxidising agent will displace a halogen with a lower oxidising agent. oxidising strength decreases down the group. (oxidation agents are electron acceptors. Cl2 WILL DISPLACE Br2 AND I2; Br2 WILL DISPLACE ONLY I2
• GROUP 7: oxidation reactions of halogens with GP1, GP2 metals

  A) oxidation

  B) reduction

  C) I2 is not strong enough oxi.agent

  
• GROUP 7: Oxidation reactions of halide ions

  A) yellow solution

  B) brown solution

  C) no reaction

  D) no reaction

  E) hexane

  F) Cl2 + 2Br- ---2Cl- + Br2

  G) colourless

  H) brown solution

  
• GROUP 7: disproportionation is when the same element simultaneously oxidises and reduces. e.g Cl2 change its oxi. number from 0 to -1 and +1

  A) turn red

  B) HCL + HOCL

  C) pale greenish

  D) turn colourless

  E) water treatment

  
• GROUP 7: reaction with cold alkalis (NaOH)
• GROUP 7: reaction with cold alkalis (NaOH) Cl2(aq) + 2NaOH(aq) ---NaCl (aq) + NaClO (aq) + H2O(l) The mixture of NaCl and NaClO is used as Bleach and to disinfect/ kill bacteria
• GROUP 7: reaction with hot dilute NaOH (alkalis) disproportionation also occurs but the halogen that is oxidised goes to a higher oxidation state. 3Cl2 (aq) + 6 NaOH(aq) --- 5 NaCl (aq) + NaClO3 (aq) + 3H2O (l) ionic eq. 3Cl- + 6OH- ----5Cl- + CIO3 + 3H2O CIO3 has oxidation n^ of +5 -3
• GROUP 7: Reaction of halide salts with conc. sulfuric acid. Halides (lose an electro and so are reducing agents) strength of reducing agent increases going down the group. This is bc going down the gp ionic radius increases, shielding increases, therefore there is less attraction btw nucleus and outer e-, so its easier to remove outer e-. I- is the strongest reducing agent.
• GROUP 7: reaction of halide salts with concentrated sulfuric acid.

  A) steamy fumes

  B) NaHSO4 (S)

  C) evolved

  
• GROUP 7: reaction of halide salts with concentrated sulfuric acid.

  A) red fumes of Br and colourless gas SO2 evolved

  B) Br2 + SO2 + 2H2O

  C) +6 to +4

  
• GROUP 7: reaction of halide salts with concentrated sulfuric acid. KI + H2SO4 ---I2 + S + H2S (+SO2) Observations: White steamy fumes of HI are evolved. Grey solid and purple fumes of Iodine are also evolved. A colourless gas SO2.A yellow solid of Sulphur. Rotten egg smell gas of H2S
• GROUP 7: The reactions of halide ions with silver nitrate. TEST TO IDENTIFY HALIDE IONS PRESENT (colour) ---add dilute HNO3 --add silver nitrate (aq) Ag+ (aq) + Cl- (aq)---AgCl(s)---- + NH3(aq) dil----soluble Ag+ (aq) + Br- (aq)---AgBr(s)---- + NH3(aq) dil----insoluble; BUT SOLUBLE IN CONCENTRATED AMMONIA Ag+ (aq) + I- (aq)---AgI(s) ---- + NH3(aq) diluted OR concentrated----insoluble;

  A) white precipitate

  B) cream precipitate

  C) yellow precipitate

  
• GROUP 7: hydrogen halides + water. HCl (g)+ H2O(l)---H3O+ (aq)+ Cl-(aq)

  A) HCl(g) + NH3(g)--NH4CL(g)

  B) white smoke

  C) ammonia

  D) hydrogen halide

  
• Testing for presence of a carbonate CO3 2- and hydrogencarbonates HCO3 ---Add any dilute acid (HCL) and observe effervescence. Bubble gas test for CO2 – will turn limewater cloudy 2H+ + CO3 2- --- H2O + CO2 H+ + HCO3 - ---H2O + CO2 Fizzing due to CO2 would be observed if a carbonate or a hydrogencarbonate was present
• Testing for presence of a sulfate. --add HCL to remove any carbonate impurities--- add BaCL2 to test for sulfate. Ba2+ (aq) + SO4 2-(aq) ---BaSO4 (s) observations: Barium Chloride bc is insoluble, a white precipitate forms.
• Test for ammonium ion NH4+. ---add warm NaOH(aq) forming NH3. observation: ammonia gas turns damp red litmus paper into blue. NH4+ +OH- ---NH3 + H2O
• GROUP 2: 1st I.E decreases down the group. because the n^ of protons increases, distance inceases, shielding increases and is more important (than n^ of protons), weaker attraction btw nucleus and outer e-, less energy needed to remove outer e-.
• GROUP 2: Reactivity of group 2 metals increases down the group. because down the group the atomic radii increase, shielding increases, The nuclear attraction decreases, so it is easier to remove (outer) electrons and so cations form more easily
• GROUP 2: melting point decreases going down the group because... ionic radius increases (e- are further away from nucleus), more shielding, less attraction btw +ve metal ions and delocalised e-, so less energy needed to overcome this attraction.
• GROUP 2: Reaction with oxygen. 2Mg(s) + O2(g) ---2MgO(s) BUT Ba---BaO2(peroxide) or BaO(oxide). MgO is a white solid, with high m.p due to is ionic bonding.
• GROUP 2: Reaction with chlorine. Mg + Cl2 ---MgCl2(s) Be2+ is very small and therefore very polarising. it would distort the CL- cloud so much that the bonding is mostly convalent.

  A) does not dissolve

  B) ionic

  C) convalent

  
• GROUP 2: reactions with water

  A) cold

  B) steam

  C) GAS

  D) liquid

  E) solid

  F) increases

  G) aqueous

  H) from solid to aqueous going down the group

  
• observations of hydroxides +water

  fizzing, metal dissolving, Ca sa forming a white precipitate
• GROUP 2: Reactions of oxides + water. MgO (s) + H2O (l)----Mg(OH)2 (s) Mg(OH)2 is only slightly soluble in water so fewer free OH- ions are produced and so lower pH. CaO (s) + H2O (l)----Ca(OH)2 (aq)
• GROUP 2: Reactions of the Oxides with Acids. MgO (s) + 2 HCl (aq)---MgCl2 (aq) + H2O (l) Ionic eq. MgO (s) + 2H+(aq) --- Mg2+(aq) + H2O(l)
• GROUP 2: Reactions of the hydroxides with Acids. 2HNO3 (aq) + Mg(OH)2 (aq)---Mg(NO3 )2 (aq) + 2H2O (l)
• GROUP 2: solubility of hydroxides increases down the group. (OH- HAS SINGLE CHARGE SO ITS MORE SOLUBLE DOWN THE GROUP.

  A) INSOLUBLE

  B) 2OH- (aq)

  C) suspension

  D) MgCl2 + H2O

  E) soluble

  F) limewater

  G) cloudy

  H) white precipitate

  I) CaCO3 (s)

  J) dissolves

  K) aq

  
• GROUP 2: solubility of sulfates decreases going down the group. Ba + H2SO4 --- BaSO4 + H2 insoluble barium sulfate produced (white precipitate)
• GROUP 2: Thermal decomposition decreases of carbonates (harder to break). MgCO3 (s)---MgO(s) + CO2 (g)

  A) more

  B) bigger

  C) polarising effect

  D) distort

  E) harder to break

  F) lithium

  G) Li2O (s)

  H) limewater

  I) cloudy

  J) moles

  K) volume

  L) bunsen flame

  
• GROUP 2: Thermal decomposition of nitrates decreses down the group. 2Mg(NO3 )2 → 2MgO + 4NO2 + O2 observe brown gas evolving (NO2 ) and the White nitrate solid goes to a colourless solution. the thermal stability increases gown down the group, because GP2 cations are sufficiently polarising to break N-O bond and form O2-.

  A) smallest

  B) greater charge

  C) polarisation

  D) lithium nitrate

  E) 4NO2

  
• GROUP 1: Lithium nitrate/carbonate decomposes in the same way as group 2 nitrates 4 LiNO3 → 2Li2O + 4NO2 + O2 Li2CO3 (s) -- Li2O(s) + CO2 (g) because Li+ is very small, very polarising, Li+ polarises the N-O bond and break it to form O2-
• THERMAL DECOMP. COMAPARISON GP1 AND 2: GP1 carbonates/nitrates are more thermally stable than GP2. because M2+ are more polaring than M+. going down the group the ionic radius get larger, so less polarising, and thermally stable. M2+ has a higher charge density than M+ and distorts the electron cloud of carbonates/nitrates more than GP1.
• FLAME TESTS: --use a nichrome wire---dip in con. HCL ---dip into sample---heat and observe the colour change. Explanation: heat causes the electron to move to a higher energy level. The electron is unstable at the higher energy level and so drops back down to a lower energy level. energy is emitted in the form of visible light energy with the wavelength of light

  A) red

  B) yellow

  C) lilac

  D) brick red

  E) red

  F) pale green

  G) no flame colour

  
• TESTING FOR THERMAL STABILITY. NITRATES: measure O2 produced--using a gas syringe, relight glowing splint. measure NO2 produced--brown gas(done in fume cupboard-its toxic)---white nitrate solid goes to a colourless solution. CARBONATES: CO2 turns limewater cloudy --use gas syringe. Mg(NO3)2 decomposes the easiest bc Mg2+ ion is smallest and has greater charge density, so more polarising, so distorts NO3- more, so weakens N-O bond.
• GROUP 7: solubility of halogens---more soluble in non-polar organic solvents than in water. solubility in water decreases down the group.
• GROUP 7: tests for chlorine. bleaches damp red litmus paper quickly. (blue in alkali) (red litmus in acid) Cl2 + 2Br- (colourless) --Br2(brown) + 2Cl-