Question

5. In a laboratory exercise, students are asked to identify the anion of a colorless solution, which may be X, Y, or Z. Given that students have access to solutions of X, Y, and Z, and data collected above, propose a simple procedure by which students may be able to identify the anion. List the suitable reagent that students should use to complete this procedure on the next page in the space provided. The only restriction in this exercise is that students may only use one of the three solutions of X, Y, or Z. HEXANE + - + UNKNOWN COLOR OF PRODUCT? GREEN BLUE YELLOW ION PRESENT

Answer 1

The question mentions, 'from the data collected above', this probably implies that preliminary tests have been done.
If the salt gives no effervesence with dil. H2SO4, then presence of CO3-2, NO2-, S-2, and SO3-2 is ruled out.
But if halide ions are present , then there would have been some effervesence with conc. H2SO4.
If a colourless gas(HCl) evolves, probably Cl- is present.
If a brownish gas(Br2) evolves, probably Br- is present.
If a violets gas(I2) evolves, probably I- is present
Each of the anions: X-1,Y-1 and Z-1 may be halide ions(each has a -1charge).
For confirmation add Hexane and chlorine water to the aqueous solution of the original salt.
Hexane being less dense than water will float on the top.
[Chlorine water is an oxidising agent and oxidizes the halide ions to the corresponding halogen. Chlorine water can be prepared by adding dil.HCl to KMnO4 solution.]
When the mixture of OS, hexane and Chlorine water is shaken vigourously, we can make the following conclusions from the observations.
Observation: Greenish yellow colour in the hexane layer.
Conclusion: Chlorine is the halogen formed and the original salt contained Cl- ion.   
Observation: Orange yellow colour in the hexane layer.
Conclusion: Bromine is the halogen formed and the original salt contained Br- ion.
Observation: Violet colour in the hexane layer.
Conclusion: Iodine is the halogen formed and the original salt contained I- ion.