Question

to separate Cu²+ and Cd ²+ ions present in a given mixture using paper chromatography and determine their Rf values. ​

Answer 1

Answer:

Apparatus

Gas jar, glass rod, filter paper strip (What man No. 1 filter paper), jar cover, fine capillary tube.

Chemicals Requirement

Sample solution containing cobalt (II) and nickel (II) ions, acetone, concentrated aqueous ammonia, Rubeanic acid spray reagent.

1. Procedure

Take a What man filter paper strip (20 x 2 cm) and draw a line with pencil above 3 cm from one end. Draw another line lengthwise from the centre of the paper as shown in Fig.

separate-coloured-components-present-mixture-red-blue-inks-ascending-paper-chromatography-1

With the help of fine capillary tube, put a drop of the mixture of red and blue inks at the point P. Let it dry in air. Put another drop on the same spot and dry again. Repeat 2-3 times, so that the spot is rich in mixture.Measure the distance of the two spots from the original line and the distance of the solvent from the original line.

Calculate the Revalues of the blue and red inks by using the formula :

separate-ions-present-given-mixture-using-ascending-paper-chromatography-1Cover the jar and keep it undisturbed. Notice the rising solvent along with the mixture of red and blue inks. After the solvent has risen about 15 cm you will notice two different spots of blue and red colours on the filter paper.

Take the filter paper out of the jar and mark the distance that the solvent has risen on the paper with a pencil. This is called the solvent front.

Dry the paper. Put pencil marks in the centre of the blue and red spots.After elution and drying, place the paper in a large, dry, covered beaker containing a smaller beaker of concentrated aqueous ammonia. After about two minutes, remove the paper and spray it on both sides with rubeanic acid reagent. Allow it to dry. Nickel becomes visible as blue purple band while cobalt becomes visible as yellow orange band. Evaluate Rf values of the two ions.

Observations and Calculations

separate-ions-present-given-mixture-using-ascending-paper-chromatography-3Revalue of Ni2+ =………

Revalue of Con2+ =……..

The above experiment can be carried by using a mixture of

(i) Iron (II) and cobalt (II) (ii) Iron (II) and nickel (II)

(iii) Copper (II) and iron (II) (iv) Copper (II) and nickel (II)

(v) Iron (II) and zinc (II) (vi) Lead (II) and Cadmium (II).

Answer 2

Final answer: The separation of  $Cu^{2+}$ and $Cd^{2+}$ is effected from their differential migration as a liquid mobile phase moves over the stationary phase.

$R_{f} value of Cd^{2+} ions = \frac{distance travelled by the Cd^{2+} ion from the original line}{distance travelled by the solvent front from the origin line in the same time}$

$Rf value of Cu^{2+} ions = \frac{distance travelled by the Cu^{2+} ion from the original line}{distance travelled by the solvent front from the origin line in the same time}$

Given that: We are given mixture containing $Cu^{2+}$ and $Cd^{2+}$ ions.

To find: We have to find, the procedure to separate  $Cu^{2+}$ and $Cd^{2+}$ ions present in a given mixture using paper chromatography and formula for their $R_{f}$ values. ​

Explanation:

• The paper chromatography technique is used to separate components from a mixture and purify compounds efficiently. The separation of component is effected from their differential migration as a liquid mobile phase moves over the stationary phase. This is represented by the $R_{f}$ value.

      $R_{f} =\frac{distance travelled by the component from the original line}{distance travelled by the solvent front from the origin line in the same time}$

• Apparatus require for the paper chromatography consist of a support of the paper, a solvent through an air tight glass cylinder to develop the chromatogram.
• The sample solution containing $Cu^{2+}$ and $Cd^{2+}$ is spotted near the lower edge of paper strip and dried. The paper is then suspended in the glass cylinder with its lower end just dipping in a suitable solvent chosen as the mobile phase, taking care to see that spotted portions are above the solvent level.
• After some time, the paper strip is removed, the solvent front is marked on it, and it is dried.
• The coloured component $Cu^{2+}$ is appeared as coloured spot. The position of colourless $Cd^{2+}$ is determined by spraying the paper with a sensitive reagent such as ammonium sulphide - $(NH_{4})_{2}S$ capable of forming coloured spot.
• Here $acetone-HCl$ mixture as the mobile phase.
• Mark the position of the spot and measure the distance moved by the solvent front and the coloured spots. The distance between the original line and the centre of coloured spots is the shortest distance.
• Record $R_{f}$ value for  $Cu^{2+}$ and $Cd^{2+}$.

$R_{f} value of Cd^{2+} ions = \frac{distance travelled by the Cd^{2+} ion from the original line}{distance travelled by the solvent front from the origin line in the same time}$

$Rf value of Cu^{2+} ions = \frac{distance travelled by the Cu^{2+} ion from the original line}{distance travelled by the solvent front from the origin line in the same time}$

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