Inorganic Chemistry Flashcards
Groups 1 and 2
All have the highest energy electron in the s subshell
Group 2 reacting with O2
- except Be, they all react vigorously, producing a bright flame
- 2M + O2 -> 2MO
- Ba + O2 -> 2BaO2
- contains a peroxide ion
Peroxide ion
(O2)2-
2Mg + O2 -> 2MgO
- bright white flame
* used in fireworks and flames
Ca + Sr with O2
red flames
Ba + O2 -> 2BaO2
Green flame
Group 2 reactions with water
- less reactive than the corresponding group 1 elements
- Be does not react with steam
- Mg reacts v. slowly w/ cold water and does react w/ steam
- Ca, Sr and Ba all react w/ cold water with increasing vigour
Mg (s) + H2O (g)
-> MgO(s) + H2 (g)
Ca (s) + 2H2O
-> Ca(OH)2 + H2(g)
Calcium hydroxide is only sparingly soluble in water, so a thick white suspension accompanies the effervescence
Sr(s) + 2H2O (l)
-> Sr(OH)2 + H2 (g)
Strontium hydroxide is slightly soluble in water
Ba(s) + 2H2O (l)
-> Ba(OH)2 + H2 (g)
Barium hydroxide is soluble in water
Group 2 reactions with chlorine
All form chlorides
Group 2 oxide reacting with water
- BeO is not attacked by water
* others are ionic; react to form hydroxides
Group 2 oxides reacting with dilute acids
All produce salt and water
Group 2 hydroxides (bases)
React with acids in neutralisation to form salt and water
Group 2 sulphate solubility
Solubility decreases down the group
MgSO4 -> soluble
CaSO4 -> slightly soluble
SrSO4 -> insoluble
BaSO4 -> insoluble
Testing for sulphate ions
- used because BaSO4 is highly insoluble
- if BaCl2 is added to a solution containing sulphate ions, a white ppt is produced
Ba2+(aq) + (SO4)2-(aq) -> BaSO4(s)
Group 2 hydroxide solubility
- solubility increases down the group
- Ca(OH)2 is not very soluble in water; much more soluble than CaCO3
- when CO2 is passed through Ca(OH)2, it forms insoluble CaCO3 suspension, turning limewater cloudy
Indicator of carbonate thermal stability
Time taken for gas evolved to turn limewater cloudy
All group 1 carbonates are…
… thermally stable up to Bunsen temperatures; smaller charge density; lower polarising power
Lithium and group 2 carbonates thermally decompose to form
Metal oxide + CO2
Stability trend down Group 2
- more stable
- charge density decreases
- smaller polarising power
- cannot draw oxygen towards it as easily
- does not distort the C-O bond to the same extent
- need more vibrational energy as the bond has not been as weakened
- harder to release the CO2 and form the metal oxide
All nitrates…
… decompose
Group 1 nitrates except Li
Break down to form
Metal nitrite + oxygen
Lithium and group 2 elements…
… break down to a greater extent (because they have higher polarising power) to form
Metal oxide + nitrogen dioxide + oxygen
Flame test theory
Electrons are pushed to a higher energy level when heated; when they drop back down, they give out their energy in the form of light
Flame colours
Lithium = red Sodium = yellow Potassium = lilac Calcium = brick red Strontium = crimson Barium = apple green
MP and BP trend down halogen group
Don’t confuse with relativity!!!
- increases
- more electrons
- more idids
- more energy needed to overcome the forces
Trend for electronegativity down halogen group
- decreases
- atomic radius increases
- bonding pair is further from nucleus with greater inner shielding
- harder to pull the electron towards the nucleus
Reactivity of the halogens depends upon
How strongly the electron is drawn into the vacant position in their outer-shell
Reactivity trend down halogen group
- decreases
- atomic radius increases
- greater distance and more shielding between incoming electron and the nucleus
- attraction decreases
- illustrated by displacement reactions
Cl2 + 2KBr -> Br2 + 2KCl
Cl2 = chlorine water; colourless 2KBr = potassium bromide; colourless Br2 = bromine water; orange 2KCl = potassium chloride; colourless
Bromine présence is proven by adding an organic solvent into which bromine dissolves preferentially, turning red
Trend in oxidising capacity going down the halogen group
- chlorine is the strongest oxidising agent
- wants to gain electrons!
- smallest atomic radius
- least distance and shielding
- attraction of incoming e-s to the nucleus is greater
As halogens tend to gain electrons (electronegative); they tend to be oxidising agents
Trend in reducing capacity going down the halogen group
- iodine is the best reducing agent
- wants to lose e-
- largest atomic radius
- greatest distance and shielding
- easily loses outer e-
Halogen reactions with metals
- tend to be reactive
- vigour decreases with reduced reactivity
- less exothermic as atomic number increases
Cl2 + H2
-> 2HCl
Explosive in sunlight
Br2 + H2
-> 2HBr
Requires heat + platinum catalyst
I2 + H2
V slow- reaction does not go to completion
Disproportionation of chlorine
Cl2 + H2O <=> HOCl + HCl
Used in water treatment as HOCl contains chlorate(I)ion, which has strong anti-bac action, sterilising the water
Reversible; quantités of chlorate(I)ions are quite small -> it is safe to drink the water
Shifted right by removing acid products, using NaOH alkali
Cl2 + NaOH
Cold!
- -> NaOCl + NaCl
- produces a much higher concentration of chlorate(I)
- used in bleach
3Cl2 + 6NaOH
-> NaOCl3+ 5NaCl + 3H20
• 5 chlorine atoms take an electron to form ions (in NaCl)
• chlorine losing 5 electrons goes to 5+ (in NaClO3)
Iron is a …
… transition metal; can form compounds of iron(II) and iron(III)
Solutions containing iron(II)
Pale green
Solutions containing iron(III)
Yellow
Cl2 + Fe2+
-> 2Cl- + 2Fe2+
Pale green -> yellow
Could also use bromine as oxidising agent, but not iodine
Conc. H2SO4
- oxidising agent
* when added to potassium Hamite, hydrogen halide is formed
KCl(s) + H2SO4 (aq)
-> KHSO4 (aq) + HCl (g)
Steamy white fumes
Effervescence
Wet litmus turns blue -> red
Chloride is not a very strong reducing agent -> holds e-s
KBr (s) + H2SO4 (aq)
-> KHSO4 (aq) + HBr (g)
H2SO4 (aq) + 2HBr (g) -> Br2 (l) + SO2 (g) + 2H2O (l)
KI (s) + H2SO4 (aq)
-> KHSO4 (aq) + HI
H2SO4 (aq) + 2HI (g) -> I2 (s+g) + SO2 + 2H2O
Halide test
1) dissolve in water
2) acidity with dilute HNO3
3) add AgNO3 (aq)
4) identify silver halide precipitate by colour
Ag+ (aq) + X- (aq) -> AgX (s)
Hydrogen halides + water
- soluble
- dissociate into ions, forming acidic solutions
- HX (aq) -> H+ (aq) + X- (aq)
Hydrogen halides + ammonia
- when gaseous hydrogen halides come into contact with gaseous ammonia, ammonium halide (dense white smoke) is produced
- HX (g) + NH3 (g) -> NH4X (g)
Carbonate and hydrogencarbonate chemical test
• adding dilute acid forms CO2 (effervescence)
- (CO3)2- (aq) + 2H+ (aq) -> H2O (l) + CO2 (g)
- HCO3- (aq) + H+ (aq) -> H2O (l) + CO2 (g)
- when CO2 is bubbled through limewater, it goes cloudy due to CaCO3(s) formation
- Ca(OH)2 (aq) + CO2 (g) -> CaCO3(s) + H2O (l)
Sulphate test
- add dilute HCl
- if no reaction, add a few drops of BaCl2 (aq)
- forms a white precipitate
• Ba2+ (aq) + (SO4)2- (aq) -> BaSO4 (s)
Ammonium test
- warm with NaOH(aq) -> produces NH3
- NH3 dissolves
- test w/ damp red litmus
- turns blue
• NH3(g) + H2O(l) -> NH4+ + OH-
Alkali!
