Module 8 Flashcards
Purpose of flame tests
Used to identify presence of certain cations since a distinctive colour is produced when an ionic solution containing that cation is placed into a flame. When solution is placed in flame, metal cations are atomised.
Visible light created when electrons transition to higher energy level due to heating, electrons lose energy and relaxes to original energy level, em radiation in form of visible light is released
Not all metals have a flame test colour in visible range. Colour produced depends on the difference in energy between energy levels
Colours produced by cations
Ba2+: Apple green
Ca2+: Brick-red
Cu2+: Blue-green
Pb2+: light grey (won’t be conducted as burning heavy metals can pose safety risks)
Fe2+: Gold
Fe3+: Orange-brown (lighter than Fe2+)
Mg+: No characteristic flame colour
Ag+: No characteristic flame colour
Problems with fertilisers
Define eutrophication
Fertilisers contain PO4 3- and NO3- ions that promote root and leaf growth in agricultural crops. Over-use or runoff during heavy rain events will cause these ions to build up in waterways. If the water flow is low and there is sufficient sunlight (summer months), algae will bloom in waterways.
Algal bloom
Huge proliferation of algae on water surface
Sunlight blocked from reaching submerged plants
Plant death
Aquatic life death
Algal death
Polluted waterway
Will take 1-15 years to recover reliant on significant rainfall and gradual recovery
The enrichment of waterways with phosphates and/or nitrates.
Problems with decommissioned mining sites
Define bio-accumulation
Old mine sites pose a significant risk to water catchments. A common practice for disused mine
sites was to fill them with water.
The rich mineral ores, containing various metal cations often give the water a beautiful
turquoise colour, however some metals, even at low concentrations pose significant risks to
humans and other organisms when they enter the water catchment.
Pb for example is a bio-accumulative neurotoxin heavy metal that used to be widely
used in industry for its lubrication properties. Once absorbed, Pb cannot be metabolised by the body and builds up to levels that can degrade Central Nervous System function, and in even low levels, cause birth defects in developing babies.
Refers to the buildup of substances, typically heavy metals, in the body at a rate that is faster than they can be metabolised.
How are cations and anions detected
Using flame tests and precipitation tests
Note: Anions cannot be detected with flame test
Order of precipitation tests for cations
Pb2+: Add Cl- (aq); a white PPT forms. Add I-(aq); a yellow PPT forms
Ag+: Add Cl-(aq): a white PPT forms – dissolves if dilute ammonia is added
Ba2+: Add SO4 2−(aq); a white PPT forms – apple green flame test
Ca2+: Add SO4 2−(aq); a white PPT forms – brick-red flame test
Mg2+: Add OH −(aq); a white PPT forms. Does NOT form PPT with SO4 2 −(aq)
Cu2+: Add OH −(aq); a blue PPT forms – blue green flame test
Fe2+: Add OH −(aq); a pale green PPT forms which in time turns brown
Fe3+: Add OH −(aq); a brown PPT forms
Order is important as some cations such as Pb will readily precipitate with almost everything
Order of precipitation tests for anions
CO3 2−: Add H + ions (HNO3) – bubbles of CO2 evolve
OH−: Turns red litmus blue, Add NH4+ and heat, ammonia gas produced
SO4 2−: add Ba(NO3)2; white PPT forms at any pH
PO4 3− Addition Ba(NO3)2 at low pH yields NO PPT; white PPT forms when pH is raised by adding NH3
I−: Add AgNO3 to acidified sample; yellow PPT forms. Does not dissolve in NH3. Add Pb(NO3)2; yellow PPT forms
Cl−: Add AgNO3 to acidified sample; white PPT forms – blackens in sunlight. Add dilute ammonia and PPT dissolves
Br−:Add AgNO3 to acidified sample; cream PPT forms – darkens slowly in sunlight. Add concentrate ammonia and PPT dissolves
CH3COO−:Only forms a PPT with concentrated AgNO3 and no other cations
How to differentiate between silver halides
For complexation reactions, what is in the middle of the complexes
AgI: yellow solution that doesn’t redissolve
AgBr: Cream coloured solution that redissolves in concentrated NH3
AgCl: White solution that redissolves in dilute NH3
Transition metals often reside in the middle of the complexes
Dissolving process is example of complexation reaction as ammonia acts as a ligand where it binds to the solid precipitate where the chemistry further confirms it is either a chloride ion or bromine ion.
AgCl(s) + 2NH3(aq) –> [Ag(NH3)2]+ (aq) + Cl-(aq)
One with square bracket is the complex
What acetates are insoluble and what is the colour of the ppt and soluble in water
Soluble: Barium acetate, calcium acetate, magnesium acetate, copper acetate, iron (II) acetate, iron (III) acetate
Insoluble: Lead acetate (sparingly soluble) white, same with silver acetate
What hydroxides are insoluble and what is the colour of the ppt and soluble in water
Soluble: BaOH
Insoluble: Pb(OH)2 (white), AgOH (brown), Ca(OH)2 (sparingly soluble cloudy white ppt), Mg(OH)2 (white), Cu(OH)2 (blue), Fe(OH)2 (green), Fe(OH)3 (brown)
What carbonates are insoluble and what is the colour of the ppt and soluble in water
Soluble: None
Insoluble: PbCO3 (white), Ag2CO3 (yellow), Ba(CO3) (white), CaCO3 (white), CuCO3 (white), FeCO3 (white), Fe2(CO3)3 (orange-red)
What phosphates are insoluble and what is the colour of the ppt and soluble in water
Soluble: None
Insoluble: Pb3(PO4)2 (white), Ag3(PO4) (yellow), Ba3(PO4)2 (white), Ca3(PO4)2 (white), Mg3(PO4)2 (white), Cu3(PO4)2 (blue-green), Fe3(PO4)2 (brown), FePO4 (brown)
What sulfates are insoluble and what is the colour of the ppt and soluble in water
Soluble: Mg2+, Cu2+, Fe2+, Fe3+
Insoluble: Ca2+, Ba2+, Ag+, Pb2+ are all white
What iodides are insoluble and what is the colour of the ppt and soluble in water
Soluble: Ba2+, Ca2+, Mg2+, Fe2+. Fe3+
Insoluble: Cu2+ (white), Ag+ (yellow), Pb2+ (yellow)
What bromides are insoluble and what is the colour of the ppt and soluble in water
Soluble: Ba2+, Ca2+, Mg2+, Cu2+, Fe2+, Fe3+
Insoluble: Pb2+ (white), silver (cream)
