Tests for Copper (II) ion – MeitY OLabs

Tests for Copper (II) ion – MeitY OLabs


Tests for Copper (II) ion Copper is a chemical element with the symbol
Cu. It is found in many salts like copper sulphate, copper chloride and copper carbonate
as copper (II) ion. In group II, copper (II) ions are precipitated as their sulphides by
passing hydrogen sulphide gas through their solution.
Our aim here is to test the presence of copper (II) ion in a given salt.
First we look at the preliminary tests of copper (II) ion. Dry Heating Test Materials required: Original salt, test tube, test tube holder
and Bunsen burner. Procedure: Take a small quantity of salt in a test tube.
Heat it over the Bunsen burner. The salt becomes brown on heating, indicates
the presence of copper (II) ion. Charcoal Cavity Test Materials required: Mixture of salt and sodium carbonate, charcoal
piece, distilled water, dropper, tongs, blow pipe and Bunsen burner. Procedure: Take a mixture of small quantity of salt and
double its quantity of sodium carbonate in a watch glass.
Take a charcoal piece with small cavity in it.
Using a spatula, take a small quantity of the mixture and place it in the cavity of
the charcoal piece. Using a dropper, add few drops of distilled
water to the mixture to moisten it. Hold the charcoal piece in front of the reducing
flame of the Bunsen burner using a tongs. Now direct the reducing flame on the cavity
by means of the blow pipe and heat strongly for some time.
Red beads or scales indicate the presence of copper (II) ion. Flame Test Materials required: Original salt, concentrated hydrochloric acid,
dropper, glass rod, platinum wire loop and Bunsen burner. Procedure: Take a small quantity of the salt in a watch
glass. To this, add few drops of concentrated hydrochloric
acid using a dropper. Mix the contents of the watch glass using
a glass rod to make a paste. Take a small amount of the paste on the platinum
wire loop and introduce it into the oxidizing flame of the Bunsen burner.
Bright bluish green flame indicates the presence of copper (II) ion. Borax Bead Test Materials required: Original salt, borax, platinum wire loop and
Bunsen burner. Procedure: Take a small quantity of borax powder in the
loop of platinum wire by dipping it in borax powder.
Heat it in the flame of the Bunsen burner. Borax swells and forms a transparent colourless
glassy bead. Dip the hot bead in the watch glass containing
salt. Heat it again either in the oxidizing flame
or in the reducing flame of the Bunsen burner. In oxidizing flame, the colour of the bead
becomes green when hot and light blue when cold.
In reducing flame, the bead becomes colourless when hot and opaque when cold. Next we look at the Analysis of copper (II)
ion. Materials required: Salt solution in a test tube, dilute hydrochloric
acid, hydrogen sulphide gas, 50% nitric acid, dilute sulphuric acid, distilled water, alcohol
, ammonium hydroxide and water bath. Procedure: Take a small quantity of dilute hydrochloric
acid using a dropper. Add it into the test tube containing a small
volume of salt solution to acidify it. Now pass hydrogen sulphide gas through the
solution. Copper (II) ions present in the salt solution
reacts with hydrogen sulphide to form black precipitate of copper sulphide.
Transfer the precipitate into a centrifuge tube to separate it by centrifugation.
Now, add a small quantity of 50% nitric acid to the precipitate in the test tube and heat
in a water bath. Copper sulphide reacts with nitric acid to
form soluble copper nitrate. To this solution add a small quantity of dilute
sulphuric acid using a dropper. Using another dropper, add a small quantity
of alcohol to the solution. Now, add excess of ammonium hydroxide solution
to it. Copper ions reacts with sulphate ions in the
solution and excess of ammonium hydroxide to form a blue coloured tetramine copper (II)
complex. Finally we look at the confirmatory test of
copper (II) ion. Potassium Ferrocyanide Test Materials required: Solution obtained in the group analysis, acetic
acid, potassium ferrocyanide solution and droppers. Procedure: Take a small quantity of acetic acid using
a dropper. Add it into the test tube containing blue
solution obtained in the group analysis. The tetramine copper (II) complex reacts with
acetic acid to form soluble copper sulphate. Now, using another dropper, add a small quantity
of potassium ferrocyanide solution to the test tube.
The copper sulphate reacts with potassium ferrocyanide to form a chocolate brown precipitate
of copper ferrocyanide.Potassium Iodide Test Materials required: Solution obtained in the group analysis, acetic
acid, potassium iodide solution and droppers. Procedure: Take a small quantity of acetic acid using
a dropper. Add it into the test tube containing blue
solution obtained in the group analysis. The tetramine copper (II) complex reacts with
acetic acid to form soluble copper sulphate. Now using another dropper, add a small quantity
of potassium iodide solution to the test tube. A white precipitate is formed in brown coloured
solution because the copper sulphate reacts with potassium iodide to form white precipitate
of copper iodide and brown solution of iodine.

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