Copper (II) chloride is one of the compounds of copper which can dissolve in water. It is a good electrolyte and it is green in colour. The ions to be analyzed in this compound are copper ions and chloride ions. The methods of identifying copper ions have been discussed in our previous analysis that is in Qualitative analysis of unknown salt(copper (II) tetraoxosulphate VI). In this topic, we will explain how to identify chloride gas and chloride ions.
Chlorine
is a member of group seven elements in the Periodic Table and has seven
valence electrons.
How
to Test for Chloride ion and Chlorine gas
To
an unknown solution of the salt sample, add manganese (VI)oxide and
concentrated tetraoxosulphate (VI) acid, if the gas evolved has greenish-yellow
colour, with a pungent smell, it means that chlorine gas is likely to be the possible
gas. To identify the gas carry out the following tests:
· To
the unknown gas given off from the unknown salt, bring a damp blue litmus paper
closer to the gas, if the litmus paper turns red and bleaches, chlorine gas is likely
to be present.
· The
second test is to bring a damp starch-iodide paper closer to the gas, if the paper
turns dark-blue, then the gas is chlorine.
· Another
test is the reaction of chlorine gas with potassium iodide solution. Bubble the
gas into the solution of potassium iodide, if the gas is chlorine the solution will
turn brown.
Test
for Chloride ion
To
the solution of the unknown substance, add silver trioxonitrate V solution then add
dilute trioxonitrate V acid, if the unknown substance contains chloride ion, it
will form a white precipitate which remains insoluble when dilute trioxonitrate V
acid is added, the white precipitate darken on exposure to sunlight and soluble
to aqueous ammonia solution.
Note:
Silver has two white insoluble salts: silver trioxocarbonate IV and silver chloride, but silver
trioxocarbonate IV is soluble in dilute acid.
Example
Question
X
is an inorganic compound Carry out the following tests and complete the table
below.
|
Test |
Observation |
inference |
A (i) |
X plus 10ml of distilled water and
shake divide into four portions |
Soluble to give a green-coloured
solution |
|
ii |
To the first portion from (i) above,
add dilute NaOH in drops and then excess. |
|
Cu2+ likely present |
iii |
To the second portion add aqueous
ammonia solution in drops and then in excess |
Pale blue gelatinous precipitate but
soluble in excess ammonia solution to give a deep blue solution. |
|
B (i) |
To the third portion add AgNO3
then dilute HNO3 |
|
Chloride ion present. |
ii |
To the mixture above, add aqueous
ammonia solution in excess |
Precipitate dissolves to form a
clear solution |
|
C (i) |
To the fourth portion add MnO2
then a concentrated H2SO4 and heat if necessary |
|
Chlorine gas is likely present |
ii |
Bring damp starch-iodide paper to
the gas given off |
The paper turns black-blue |
|
|
Test |
Observation |
inference |
A (i) |
X plus 10ml of distilled water and
shake divide into four portions |
Soluble to give a green-coloured
solution |
Soluble
ions of transition elements are likely present (Fe2+, Cu2+,
Fe3+). |
ii |
To the first portion from (i) above,
add dilute NaOH in drops and then excess. |
Pale blue precipitate and insoluble
in excess NaOH solution |
Cu2+ likely present |
iii |
To the second portion add aqueous
ammonia solution in drops and then in excess |
Pale blue gelatinous precipitate but
soluble in excess ammonia solution. |
Cu2+ confirmed |
B (i) |
To the third portion add AgNO3
then dilute HNO3 |
A white precipitate formed which
darkens on exposure to sunlight and is insoluble to dilute HNO3 |
Chloride ion present. |
ii |
To the mixture above, add aqueous
ammonia solution in excess |
Precipitate dissolves to form a
clear solution |
Chloride ion confirmed |
C (i) |
To the fourth portion add MnO2
then a concentrated H2SO4 and heat if necessary |
Greenish-yellow gas evolves with pungent
which turns damp blue litmus paper red and bleaches it |
Chlorine gas is likely present |
ii |
Bring damp starch-iodide paper to
the gas given off |
The paper turns black-blue |
Chlorine gas confirmed |
Thank you so much
ReplyDeleteYou are always welcomed
ReplyDelete