Question

13. What can you say about an unknown compound that gave a pouldve test with 2 hydrazine and a positive test with the Jones Reseat? now compound that gave a pouldve test with 2,4-dinitrophenyl 14 What can you say about sa unknown compound when dissolved in distilled water and tested with peper, pave an estimated pH of about 81. 15. What can you say about an unknown compound that turned a wet plece al blue litmus red? 16. What can you say about an unknown organic compound that gave a positive iodoform test? 17. A positive iodofrom test involved the formation d'a yellow precipitatea the structure of the yellow precipitate? 18. Elghty eight degrees Centigrade (88°C) le- 19. Ietetly twenty millilitera dan unknown liquid compound weighs 273 grama, it density is 20. An unknown alcohol did not react with the Jones repeat, therefore the unknown compound is what type of alcohol? 21. An unknown alcohol did not react with the Lacas reagent, therefore the unknown compound is what type of alcohol? 22. What can you say about an unknown compound that gave a blood red precipitate when reacted with 24-dinitrophenyl hydratino? 23. What can you say about an unknown compound whose sodium fusion filtrate gave a yellow precipitate when reacted with silver nitrate? 24. What can you say about an unknown compound whose sodium fusion filtrate gave a white precipitate when reacted with silver nitrate?

Answer 1

13. 2,4-Dinitrophenyl hydrazine reacts with carbonyl compounds to form 2,4-dinitrophenyl hydrazone which could be yellow, orange or red in colour. Thus a compound which gives a positive test with 2,4-Dinitrophenyl hydrazine must have a ketone (-C=O) or aldehyde group (-CHO).

Jones reagent (a solution of chromium trioxide in dilute sulphuric acid) reacts with primary alcohols to produce corresponding carboxylic acid and with secondary alcohols to produce a ketone. Thus, a compound that gives a positive test with Jones reagent must be a primary or secondary alcohol.

So given compound has both a carbonyl group (either a ketone/aldehyde) and an alcohol group (primary/secondary) as it gives positive test with 2,4-Dinitrophenyl hydrazine and with Jones reagent.

14. A solution with pH<7 is acidic, with pH=7 is neutral and with pH>7 is alkaline. So a compound which when dissolved in distilled water and treated with paper gives an estimated pH=8.1 (>7), must be alkaline in nature.

15. Bases turn red litmus blue and acids turn blue litmus red.

So a compound which turns a wet piece of blue litmus red must be an acid.

16. Methyl ketones (having CH₃CO- group) or alcohols having a structure CH₃CH(OH)- react with iodine in presence of a base like NaOH to form yellow precipitate of iodoform (CHI₃). This is called iodoform test.

So an organic compound which gives a positive iodoform test (formation of yellow precipitate with I₂ in presence of NaOH ) must be a methyl ketone or is an alcohol with CH₃CH(OH)- in its structure.