Q27 of 27 Page 1

(a) An organic compound with the molecular formula C7H6O forms 2,4-DNP derivative, reduces Tollen’s reagent and undergoes Cannizzaro reaction. On oxidation, it gives benzoic acid. Identify the compound and state the reactions involved.

(b) Give chemical tests to distinguish between the following pair of compounds:


(i) Phenol and propanol


(ii) Benzoic acid and benzene


OR


(a) Predict the products of the following:



(b) Arrange the following in increasing order of acidic character: HCOOH, CF3COOH, ClCH2COOH, CCl3COOH


(a) The compound with molecular formula C7H6O forms a 2,4-DNP derivative and reduces Tollen's reagent, so it is an aldehyde. It undergoes Cannizzaro reaction, so the aldehyde group will be directly attached to the benzene ring. On oxidation it gives benzoic acid. So, the compound will be benzaldehyde. The reactions are as follows-


2.4dnp.png


C6H5CHO + 2[Ag(NH3)2]+ + 3OH- → C6H5COO- + 2Ag + 4NH3 + 2H2O


(Benzaldehyde)


2C6H5CHO conc. NaOH→ C6H5COONa + C6H5CH2OH


(Benzaldehyde) (sodium benzoate) (benzyl alcohol)


C6H5CHO (O)→ C6H5COOH


(Benzoic acid)


(b) (i) C6H5OH + FeCl3 → C6H5O-FeCl2


(Phenol) (Violet color complex)


CH3CH2CH2OH + FeCl3 → no reaction


(propanol)


(ii) C6H5COOH + NaHCO3→ C6H5COONa + CO2 + H2O


(benzoic acid) (brisk effervesence)


C6H6 + NaHCO3→ no reaction


(benzene)


OR


(a) A = CH3COOH (oxidation) → acetic acid


B = CH3COCl → acetyl chloride


C= CH3CONH2→ acetamide


D = CH3CONHBr → N- bromoacetamide


(b) Presence of EWG increases the acidity of carboxylic acid by stabilizing the negative charge of conjugate base by –I effect.


Moreover, -I effect of F is greater than that of Cl.


More the no. of EWG, more will be the acidity.


From above points, the increasing order of acidity will be


HCOOH< ClCH2COOH<CCl3COOH< CF3COOH


More from this chapter

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23

(a) Write the names of monomers of following polymer :

(b) What does part 6,6 mean in the polymer Nylon-6,6 ?


(c) Give an example of Biodegradable polymer.


 24

(a) Differentiate between antiseptic and disinfectant. Give one example of each.

(b) Why do we require artificial sweetening agents?


OR


Define the following terms:


(a) Tranquilizers


(b) Ant-acids


(c) Analgesics


 25

(a) A 5% solution (by mass) of cane sugar in water has a freezing point of 271 K. Calculate the freezing point of 5% solution (by mass) of glucose in water. The freezing point of pure water is 273.15 K.

(b) Why is osmotic pressure of 1 M KCl higher than 1 M urea solution?


(c) What type of liquids form ideal solutions?


OR


(a) 1.0 g of a non-electrolyte solute dissolved in 50 g of benzene lowered the freezing point of benzene by 0.40 K. The freezing point depression constant of benzene is 5.12 K kg/mol. Find the molar mass of the solute.


(b) What is the significance of Henry’s law constant, KH?


(c) What leads to anoxia?


 26

A crystalline solid ‘A’ burns in air to form a gas ‘B’ which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolorizes acidified KMnO4 (aq.) solution and reduces Fe3+ to Fe2+. Identify ‘A’ and ‘B’ and write the reactions involved.

OR


Answer the following:


(a) Arrange the following hydrides of Group 16 elements in the decreasing order of their acidic strength: H2O, H2S, H2Se, H2Te


(b) Which one of PCl4+ and PCl4- is not likely to exist and why?


(c) Which allotrope of sulphur is thermally stable at room temperature?


(d) Write the formula of a compound of phosphorus which is obtained when conc. HNO3 oxidizes P4.


(e) Why does PCl3 fume in moisture?