REQUIRED PRACTICAL 4 - ID tests Flashcards
Calcium Ca2+ flame colour
brick red
Strontium Sr2+ flame colour
Red
Barium Ba2+ flame colour
Pale green
Observation of halides with Acidified silver nitrate
- Flouride = no ppt too soluble
- Chloride = white ppt
- Bromide = cream ppt
- Iodide = yellow ppt
How to test for halides
- Dissolve spatula in measure of sample of dilute HNO3 and add few cm3 of dilute or conc ammonia
Observations of halides with DILUTE ammonia
- Chloride = dissolves to form colourless solution
- Bromide = ppt does not dissolve
- Iodide = ppt does not dissolve
Observations of halides with CONC ammonia
- Chloride dissolves to form colourless solution
- Bromide = dissolves to form colourless solution
- Iodide = ppt does not dissolve
Ionic equations for halides reactions with acidified silver nitrate
- Ag+(aq) + Cl-(aq) —> AgCl(s)
- Ag+(aq) + Br-(aq) —> AgBr(s)
- Ag+(aq) + I-(aq) —> AgI(s)
Why does the silver nitrate solution have to be acidified?
To remove other ions which would interfere with the test like OH- or sulphite ions
Why is HCl acid not used to acidify the AgNO3 reaction
Cl- would react with silver ion Ag+ to form white ppt and form flase positive result
How to get pure dry sample of salt
- Filter to remove the solid from soluble products
- Wash to remove any insoluble purities
- Dry to remove water
Purity test
- Melting point test
- Pure substances melt at fixed melting point
- Impure substances melt over range of temperatures
Trend down group 2 solubility with NaOH
Increases down group 2 (white ppt-> slight white ppt -> colourless solution)
Mg(OH)2 is insoluble
Barium chloride with any amount of NaOH
remains colourless
Magnesium chloride with NaOH
- Colourless to slightly white ppt when limited NaOH used
- Colourless to white ppt when excess used
Calcium bromide with any amount of NaOH
colourless –> slightly white ppt
Strontium chloride with any amount of NaOH
- Colourless to slightly white ppt
Trend down group 2 solubility with H2SO4
- solubility decreases
- BaSO4 is white ppt and solubility increases down the group
Barium chloride with any amount of H2SO4
White ppt
Strontium chloride with any amount of H2SO4
White ppt
Calcium bromide with any amount of H2SO4
Slight white ppt
Magnesium chloride with H2SO4
- With limited H2SO4 slightly white ppt
- With excess remains colourless solution
Test for ammonia solution
- Place ammonium chloride + NaOH + warm releases NH3
- Forms ammonia gas which is a weak base and turns damp red litmus paper blue
Test for strong base (NaOH) and weak base (NH3 solution)
- For both damp red litmus paper goes blue
- Using a pH meter you will get a different reading NaOH = pH 13/14 and NH3 pH = 8-10
Test for carbonate ions CO3(2-) or HCO3-
- Add sample of hydrogen carbonate salt to acid and ensure the gas is bubbled into limewater
- Effervescence and solid disappears
- Turns cloudy if CO2 given off
Test for sulfates
- Dissolve sulfate salt in dilute HNO3 and add few cm3 of barium chloride
- White ppt forms = BaSO4
KCL, KBr and KI with conc sulfuric acid
- KCl effervescence
- KBr effervescence and brown gas produced, solution turns deep brown
- KI solution goes deep brown immediately and brown gas produced
Paper test for KCl
Damp litmus paper turns red
Paper test for KBr
Damp K2Cr2O7 paper orange changes to green in presence of SO2 gas
Paper test for KI
Damp lead nitrate paper turns black in presence of H2S
