a) Addition of Na2S2O3 to I2+I-->I3 in an aqueous layer will turn the solution clear and colourless. Write an equation explaining this observed colour.
b) Addition of Na2S2O3 to I2+I-->I3 in an varsol layer will turn the solution pink. Write and equation explaining this observed colour.
a) When Na2S2O3 (sodium thiosulfate) is added to a solution containing I2 (iodine) and I- (iodide), the following reaction occurs:
2S2O3^2- + I2 + I- --> 2I3- + S4O6^2-
In this reaction, the iodine molecule (I2) is converted to triiodide ion (I3-). The triiodide ion is colorless, which results in the solution becoming clear and colorless.
b) When Na2S2O3 is added to a varsol layer, which is nonpolar, the following reaction occurs:
2S2O3^2- + I2 + I- --> 2I3- + S4O6^2-
However, since varsol is nonpolar, the triiodide ion (I3-) forms a complex with varsol, resulting in a pink color. The exact mechanism and structure of this complex may vary, but it is responsible for the observed pink coloration in the varsol layer.
a) In an aqueous layer, when Na2S2O3 (sodium thiosulfate) is added to I2 (iodine) and I- (iodide) ion, the following reaction takes place:
2S2O3^2- + I2 + 2I- → 2I3- + S4O6^2-
The addition of Na2S2O3 reduces the iodine (I2) to triiodide (I3-), which is responsible for the observed color change. Iodine is brown in color, whereas the triiodide ion is colorless. Therefore, when the solution turns clear and colorless, it indicates the conversion of iodine to triiodide.
b) In a varsol layer, when Na2S2O3 is added to I2 and I- ions, the reaction is the same as in the aqueous layer:
2S2O3^2- + I2 + 2I- → 2I3- + S4O6^2-
However, in varsol (an organic solvent), the color change is different. Instead of becoming clear and colorless, the solution turns pink. This is due to the formation of an organic complex between triiodide (I3-) and the varsol solvent molecules. The exact structure of this complex depends on the specific composition of varsol, but it is known to have a pink color.
The pink color arises from the interactions between the triiodide and the varsol molecules, leading to a different optical absorption spectrum compared to the colorless solution in the aqueous layer.