Learn about the assay of copper sulphate through a laboratory experiment or practical.
Aim:
Too perform the assay of copper sulphate using standard 0.1 N sodium thiosulphate (Iodometry).
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade sodium thiosulphate (Na2O3S2), potassium iodide (KI), potassium thiocyanate (KSCN), copper sulphate (CuSO4), acetic acid, dilute sulphuric acid (H2SO4) and starch indicator, etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.
Principle of assay of copper sulphate:
Copper sulphate assay is a type of iodometric titration. It is dependent on the instability of cupric iodide, which is formed when copper sulphate and potassium iodate react with the liberation of free iodine. Cupric iodide was formed when copper sulphate was allowed to react with potassium iodide in the presence of acetic acid.
The cupric iodide formed in the reaction is unstable, so it decomposes to give cuprous iodide with the liberation of iodine. The liberated iodine is titrated with 0.1 N sodium thiosulphate using a starch indicator.
The following is the reaction that is involved in this titration.
Preparation and standardization of sodium thiosulphate:
Click here to get the procedure of preparation and standardization of sodium thiosulphate (0.1 N).
Titration procedure:
- All glassware should be cleaned and dried according to standard laboratory procedures.
- Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
- Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
- Remove air bubbles from the burette and adjust the reading to zero.
- Take 01 gm of copper sulphate, pour it into a conical flask and add 50 ml of distilled water.
- After that, add 03 gm potassium iodide and 05 ml acetic acid to the mixture.
- Add few drops of starch indicator.
- Titrate the sample solution with sodium thiosulphate solution. When the solution is swirled for up to 10 seconds, a faint blue color appears and fades, indicates that the endpoint is approaching. The actual endpoint of the titration is indicated by a blue color that lasts longer than 30 seconds.
- To get accurate results, repeat the titration three times.
- Properly record the readings of the burette.
- Take their mean and calculate the molarity of copper sulphate solution.
Observation table:
|
Sr.
No. |
Content in conical flask |
Burette
reading |
Volume
of titrant used (ml) |
|
|
Initial |
Final |
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|
1 |
|
|
|
|
|
2 |
|
|
|
|
|
3 |
|
|
|
|
|
Mean: |
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Calculations:
Percent purity= V x E x AN x 100 / W x RN
Where,
V is a volume of sodium thiosulphate used.
E is an equivalent factor
AN is the actual normality of sodium thiosulphate.
RN is required normality of sodium thiosulphate
W is the weight of the sample
For 1 ml of 0.1 N sodium thiosulphate, the equivalent factor of copper sulphate is 0.02497.
Result:
The percentage purity of the copper sulphate (CuSO4), the sample was found to be_____.
Commonly asked questions on the assay of copper sulphate are as follows.
Why potassium iodide is used in the assay of copper sulphate?
When CuSO4 in aqueous reacts with KI in solid form, cuprous iodide forms as a precipitate liberates iodine gas and forming potassium sulphate in an aqueous state.
Which indicator is used in the estimation of copper sulphate?
The starch indicator is used in the assay of copper sulphate which produces a blue color at the endpoint of the reaction.
Assay of copper sulphate is based on which titration?
The assay of copper sulphate is based on the oxidation-reduction reaction of iodine/thiosulphate.
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