Chemical tests Flashcards
(12 cards)
1
Q
carbonate test
A
- react with acid (HNO3)
- effervescence
2
Q
sulfate test
A
- add Ba2+(aq) ions
- form a white precipitate (BaSO4 is insoluble)
DONT USE BaCl2 (otherwise you will mess up halide results)
3
Q
halide test equation
A
Ag+(aq) + X-(aq) –> AgX(s)
4
Q
order of tests
A
Carbonate –> no other ion produces effervescence
Sulfate –> must confirm there is no carbonate (or completely react carbonate ions) as BaSO4 also forms a white precipitate which would give a false result (filter our ppt before doing halide test)
Halide test –> Ag2CO3 and Ag2SO4 both form precipitates
5
Q
carbonyl test
A
- 2,4-DNPH
- orange precipitate forms
6
Q
aldehyde or ketone test
A
- mix original sample with Tollens’ reagent
- silver mirror will form if an aldehyde is present
7
Q
Tollens’ reagent formula
A
[Ag(NH3)2]OH
8
Q
Tollens’ reagent equation
A
Ag+ (aq) + e- –> Ag (s)
- Ag forms silver mirror
aldehyde + [O] –> carboxylic acid
9
Q
determine a specific carbonyl
A
- filter, dry and recrystallise the orange precipitate
- find the melting point
- compare value to one in a data book
10
Q
carboxylic acid test
A
- mix with Na2CO3
- effervescence
- only organic compounds acidic enough to react with carbonates
11
Q
ammonium ion test equation
A
NH4+(aq) + OH-(aq) –> NH3(g) + H2O(l)
12
Q
how to differentiate between different halide ppts
A
- AgCl dissolves in dilute NH3
- AgBr dissolves in concentrated NH3
- AgI insoluble in concentrated NH3
