A student had taken solutions of KI, H_(2)S, C_(2)H_(5)OH and NaBr in four separate test tube but he forgot to label them. By taking a mall sample of the solution from each of the four test tubes, suggest a method by which he can find out the solution in each test tube by using the same reagent in each of the test tubes. Give the reaction in each case.

A student had taken solutions of KI, H_(2)S, C_(2)H_(5)OH and NaBr in

1.	A student had taken solutions of KI, H_(2)S, C_(2)H_(5)OH and NaBr in four separate test tube but he forgot to label them. By taking a mall sample of the solution from each of the four test tubes, suggest a method by which he can find out the solution in each test tube by using the same reagent in each of the test tubes. Give the reaction in each case.
Answer» Solution :The solution present in each of the four test tubes can be found by adding a mixture of potassium dichromate crystals and concentrated `H_(2)SO_(4)` . A different observation will be noted in different CASES (i) In testcontaining KI, violet vapours of `I_(2)` will appear `K_(2)Cr_(2)O_(7) + 7H_(2)SO_(4) + 6KI rarr 4K_(2)SO_(4) + Cr_(2)(SO_(4))_(3) + underset("violet vapours)")(3I_(2))+7H_(2)O` (ii) In test tube containing `H_(2)S` solution , yellow ppt. of sulphur will appear `K_(2)Cr_(2)O_(7) + 4H_(2)SO_(4) + 3H_(2)S rarr K_(2)SO_(4) +Cr_(2)(SO_(4))_(3)+ 7H_(2)O + underset ("(yellow)")(3S)` (iii) In test tube containing `C_(2)H_(5)OH`, vinegar smell will be noticed due to formation of acetic acid `K_(2)Cr_(2)O_(7) + 4H_(2)SO_(4) rarr K_(2)SO_(4)+Cr_(2)(SO_(4))_(3)+3(O)` `CH_(3)CH_(2)OH+ (O) rarr CH_(3)CHO+ H_(2)O` `CH_(3)CHO+ (O)rarr CH_(3)COOH` (iv) In test tube containing NABR, the colour of the solution will turn BROWN due to formation of `Br_(2)` which dissolves in the solution . Reaction is similarto reaction given in (i) above.