C10: Identification of cations, anions and gases Flashcards
what are the 3 main reagents used when performing tests to identify cations?
- NaOH(aq)
- Aqueous ammonia - NH4OH(aq)
- potassium iodide(KI)
KI(aq) is used to distinguish between these 2 cations:
Pb2+
Al3+
what are the ions present?
A - Al3+
B - Pb2+
C - Zn2+
D - Ca2+
what are the ions present?
A - Cu2+
B - Fe2+
C - Fe3+
when drops of NaOH are added to a clear solution and a white precipitate is formed, the possible cations are (1)___________, (2)_____________, (3) _____________, (4)_____________.
- Al3+
- Pb2+
- Zn2+
- Ca2+
If excess NaOH(aq) is added to a white preciptitate and it dissolves, the possible cations are:
Al3+
Pb2+
Zn2+
If excess NH4+(aq) is added to a white preciptitate and it dissolves, the possible cations are:
Zn2+
when drops of NaOH are added to a clear solution and a white precipitate is formed, the possible cations are (1)___________, (2)_____________, (3) _____________, (4)_____________. If the solution remains clear then the cation present is (5)__________
- Al3+
- Pb2+
- Zn2+
- Ca2+
- NH4+
which of the following cations does NOT form a precipitate when drops of NaOH(aq) are added to its solution
Al3+
Pb2+
Zn2+
Ca2+
NH4+
Fe2+
Fe3+
Cu2+
NH4+
Precipitates of which of the following cations dissolve in excess NaOH(aq) and why
Al3+
Pb2+
Zn2+
Ca2+
NH4+
Fe2+
Fe3+
Cu2+
Al3+, Zn2+, Pb2+,
because they form amphoteric hydroxides which will react with aqueous NaOH(a strong base)
Zn2+ , Pb2+, and Al3+ will form white (1)_________when drops of NaOH are added to their solution because they form hydroxides which are (2)_________, however these salts are (3)_________oxides, so they will react with excess NaOH and dissolve
- precipitates
- insoluble
- amphoteric
the metal cations, except (1)___________ form (2)_____________ metal hydroxides with ammonium hydroxide solution(aqueous ammonia)
- Ca2+
- insoluble
when drops of NH4+ are added to a clear solution and a white precipitate is formed, the possible cations are (1)___________, (2)_____________, (3) _____________.
- Al3+
- Pb2+
- Zn2+
How to distinguish between Al3+ and Pb2+ ions
add a few drops of KI(aq) to solutions of their salts. A bright yellow precipitate of PbCl2 will form. Al3+ will form a soluble salt.
anions are identified by observing the effects of these on their salts:
- heat,
- dilute acid,
- aqueous silver nitrate, and
- barium chloride solution(or barium sulphate
what are the possible anions present in each case below?
A - Carbonate, nitrate
B - Carbonate, sulphate,
C- Chloride, bromide, iodide
D- carbonate, sulphate, sulphite
when a solid is heated a gas is obtained. what are the likely gasses?
CO2
NO2
O2
what anion will give carbon dioxide when heated?
Carbonate ion
what anions gives off O2 when heated?
nitrates of sodium and potassium
what nitrates release nitrogen dioxide when heated?
nitrates of calcium and below
If no gas is released on heating a salt what does this signify?
that the salt is unlikely a carbonate or nitrate i.e. does not contain carbonate or nitrate ions.
dilute HCl or HNO3 is added to a small quantity of an unknown salt in a test tube and a gas evolves. The gas could either be(1)________ or( 2)_________.
- carbon dioxide
- sulphur dioxide
if nothing happens when dilute acid is added to a salt what does this imply:
that the salt is not a carbonate or sulphite but may be a sulphate, nitrate or halide.
when a few drops of conc. sulphuric acid are added to a small quantity of solid in a dry test tube a gas is produced. The gas could be:
carbon dioxide
sulphur dioxide
hydrogen chloride
bromine
iodine
