RP 4

Question 1

Test for group 2 ions method

Answer 1

add 10 drops of metal ion
solution to test tube and then add 10 drops of 0.6M NaOH
(and mix) then add NaOH until it is in excess.

Question 2

results of group 2 test

Answer 2

• MAGNESIUM: white precipitate (sparingly soluble); ~ pH 9
  (some hydroxide ions must have been produced by slight
  dissolving)
• CALCIUM: white precipitate; ~ pH 11 (more soluble and so
  there are more hydroxide ions present)
• STRONTIUM AND BARIUM: no precipitate as they are very
  soluble; the solutions will be highly alkaline; ~ pH 14

Question 3

Other metals:

Answer 3

ALUMINIUM salts form a white precipitate of
aluminium hydroxide which will dissolve in excess NaOH to
form a colourless solution.
* COPPER 2+: blue precipitate
* IRON 2+: green precipitate
* IRON 3+: brown precipitate

Question 4

Test for AMMONIUM ions:

Answer 4

add 10 drops of 0.1M ammonium
chloride to a test tube and add 10 drops of 0.4M NaOH (shake
the mixture)
* Warm gently using a water bath
* Test the fumes by holding a piece of damp red litmus paper in
the mouth of the test tube; turns the litmus paper blue as
ammonia gas is released.

Question 5

Test for sulfate ion:

Answer 5

add BaCl2 with HCl (HCl NEEDED TO REACT
WITH CARBONATE IMPURITIES THAT ARE OFTEN FOUND IN
SALTS WHICH COULD GIVE A FALSE POSITIVE - SULFURIC ACID
CONTAINS SULFATE IONS SO COULD GIVE A FALSE POSITIVE)
* +ve result is a white precipitate of barium sulfate forms

Question 6

Test for halide ions:

Answer 6

add nitric acid (TO REACT WITH ANY
CARBONATES PRESENT TO PREVENT Ag2CO3) then silver nitrate
* CHLORIDES: white ppt (dissolves in DILUTE ammonia)
* BROMIDES: cream ppt (dissolves in CONCENTRATED ammonia)
* IODIDES: yellow ppt (too insoluble to dissolve in ammonia)

Question 7

Test for carbonate ions:

Answer 7

add HCl, bubble gas through
limewater and +ve turns cloudy (as CO2 produced)

Question 8

Test for hydroxide ions:

Answer 8

turn red damp litmus paper blue.