Core Practical 7 & 15 Flashcards
How would you test for acid or base character?
Use indicator paper, blue =base, red = acid
How can a flame test be used to identify metal ions?
Dip a nichrome wire in HCl solution. Then into metal ion solution. Hold over blue flame of Bunsen burner and observe the flame colour.
Li+ flame colour
red
K+ flame colour?
lilac
Na+ flame colour?
yellow
Ba2+ flame colour?
green
Ca2+ flame colour?
brick red
Sr2+ flame colour?
crimson
Cs+ flame colour?
Blue
Rb+ flame colour?
Red
Mg2+ flame colour?
No colour
How could you test for CO32- and HCO3- ions?
Add to aqueous acid + collect gas (CO2) formed in gas syringe. Then test gas by using delivery tube & bubbling through limewater. If cloudy = CaCO3 precip formed
How would you test for NH4+ ions ?
Add aqueous ammonia and gently warm the solution. The gas will turn damp red litmus paper blue
How would you test for SO42− ions?
add dilute HCl (removes traces of carbonate ions) followed by BaCl2 = white precip formed(BaSo4)
Test for halides?
Add silver nitrate solution. Cl- = white precip Br- = cream precip and I- = yellow precip
followed by ammonia solution.
Cl- precipitate redissolves, Br- only does in concentrated ammonia solution and I- does NOT
Observation of Mg2+ in NaOH? and then in excess?
NaOH: White suspension
add more NaOH: n/a
Observation of Ca2+ in NaOH? and then in excess?
NaOH: White suspension (but more soluble than Mg(OH)2
add more NaOH: n/a
Observation of Sr2+ and Ba2+ in NaOH? and then in excess?
NaOH:
add more NaOH: n/a
Observation of Zn2+ in NaOH? and then in excess?
NaOH: White ppt Zn(OH)2. soluble in NH3. [Zn(NH3)4] 2+ = colourless solution
add more NaOH: ppt dissolves, colourless solution = [Zn(OH)4] 2-
Observation of Al3+ in NaOH? and then in excess?
NaOH: White ppt Al(OH)3
add more NaOH: ppt dissolves, colourless solution, [Al(OH)4]−
Observation of Ag+ in NaOH? and then in excess?
NaOH: Ag2O dark brown ppt. soluble in NH3, colourless solution [Ag(NH3)2] +
add more NaOH: ppt doesn’t dissolve
Observation of Cu2+ (blue) in NaOH? and then in excess?
NaOH: Blue ppt [Cu(H2O)4(OH)2] soluble in excess NH3 = deep blue solution [Cu(NH3)4]2+
add more NaOH: Ppt doesn’t dissolve
Observation of Fe3+ (yellow) in NaOH? and then in excess?
NaOH: Brown ppt Fe(OH)3
add more NaOH: Ppt doesn’t dissolve
Observation of Fe2+ (green) in NaOH? and then in excess?
NaOH: White/green ppt slowly turning brown in air (oxidation to Fe(OH)3
add more NaOH: Ppt doesn’t dissolve