A 0.141g sample of a phosphorus containing compound was digested in a mixture of HNO and

H2S04 which resulted in formation of C02, H20 and H,P04. Addition of ammonium molybdate yielded

a solid having the composition (NH4)3 P04. 12 Mo03. The precipitate was filtered , washed and

dissolved in 50.0 mL of 0,20 M NaOH:

(NH4)3P04. 12 MO03 (S) + 260H" -> HP042" + 12Mo042~ + 14H20 + 3NH3(g)

After boiling the solution to remove the NH3, the excess NaOH was titrated with 14.1 mL of 0.174M

HCl. Calculate the percent of phosphorus in the sample.

Q.10 An accurately weighed 3.15 gm of H2C,04 • 2H20 was dissolved in water to make 500 ml solution. A

warmed 20ml of this solution acidified with H,S04 required 18ml of a KMn04 solution for complete

oxidation. Then 10ml solution containing 1 g ion / litre of Fe2+ & Fe3+ together free from CI ions or other

ions which interfere in KMn04 titration, was diluted 10 fold with water. 20 ml of this diluted solution

required 9.5 ml of the above KMn04 solution for complete oxidation in H,S04 medium. Determine the

amount of Fe3+ ion in gin/litre of original solution.

Q.ll A 1.65 gm sample ofFeS, was oxidized by excess oxygen & the products were SO, and Fe2+, The SO,

gas produced was passed through an acidified solution of 40ml Ba(MnO4)2 produced S04~~ & Mn2+.

The excess permagnate was diluted to 100 ml & 10 ml of it was treated with excess KI & iodine produced req. 0.05 M 5 ml hypo solution producing S4062". In a separate titration the 25 ml of same

solution of permagnate under alkaline condition when treated with KI produced I, that required 20 ml of 0.05 M hypo solution producing S40,2 & Mn6+. Calculate the % of FeS2 in the sample.

Q.12 3 Occ of a solution containing 9.15gm of a salt KxHy (C,0 Jz • nH,0 per litre required 27cc of 0.12 N

NaOH for neutralization. The same quantity of solution was also found to require 36cc of 0.12 N KMn04 solution for complete oxidation. Calculate X, Y, Z and n.

Q.13 Reducing sugars are sometimes characterized by a number RCu, which is defined as the number of mg of

copper reduced by 1 gm of sugar, in which half reaction for the copper is Cu2' + OH > Cu,0 + H20

It is sometimes more convenient to determine the reducing power of a carbohydrate by an indirect method. In this method 43.2 mg of the carbohydrate was oxidized by an excess of K3(Fe(CN)6). The

Fe(CN)64" formed in this reaction required 5.29 ml of0.0345 N CefSO^ for reoxidation to Fe(CN)63.

Determine the RCu value for the sample.

Q.14 12.0 g of an impure sample of arsenious oxide (acting as acidic oxide) was dissolved in water containing 7.5g of sodium bicarbonate and resulting solution was diluted to 250 ml. 25 ml of this solution was completely oxidized by 22.4 ml of a solution of iodine. 25ml of this iodine solution reacted with same volume of a solution containing 24.8g of hydrated sodium thiosulphate (Na2S203-5H,0) in one litre.

Calculate the percentage of arsenious oxide in the sample. Also report the % purity of NaHC03.

EXERCISE II

Q. 1 A 5.0 cm3 solution of HjC^ liberates 0.508g of iodine from an acidified KI solution. Calculate the

strength of H ^ solutionin terms ofvolume strength at STP. [ JEE' 1995 ] Q.2 A 3.00g sample containing Fe304,Fe203 and an inert impure substance, is treated with excessofKI

solution in presence of dilute F^SO^ The entire iron is converted into Fe24 along with the liberation of

iodine. The resulting solution is diluted to 100 ml. A 20 ml of the diluted solution require 11.0 ml of 0.5 M Na^Og solution to reduce the iodine present. A50 ml of the diluted solution, after complete extraction ofthe iodine requires 12.80 ml of 0.25 M KMnG4 solution in dilute F^SC^ medium for the oxidation of

Fe2+. Calculate the percentages of Fe203 and Fe304 in the original sample. [ JEE'96,5 ]

Q.3 The number of moles of KMn04 that will be needed to react completely with one mole of ferrous

oxalate in acid solution is [JEE 1996] (A) 3/5 (B) 2/5 (C) 4/5 (D) 1

Q.4 The number of moles of KMn04 that will be needed to react with one mole of sulphite ions in acidic

solutionis [JEE 1997] (A) 2/5 (B) 3/5 (C) 4/5 (D) 1

Q. 5 One litre of a mixture of 02 and 03 at NTP was allowed to react with an excess of acidified solution of

KI. The iodine liberated required 40 ml of M/l 0 sodium thiosulphate solution for titration. What is the percent of ozone in the mixture? Ultraviolet radiation of wavelength 300 nm can decompose ozone. Assuming that one photon can decompose one ozone molecule, how many photons would have been required for the complete decomposition of ozone in the original mixture? [ JEE' 97,5] Q.6 A sample of hard water contains 96 ppm of SO 4~ and 183 ppm of HC03 , with Ca2+ as the only

cation. How many moles of CaO will be required to remove HCO 3 from 1000 kg of this water? If

1000 kg of this water is treated with the amount of CaO calculate above, what will be the conentration (in ppm) of residual Ca2+ ions (Assume CaC03 to be completely insoluble in water)? If the Ca2+ ions in

one litre of the treated water are completely exchanged with hydrogen ions, what will be its pH (one ppm means one part of the substance in one million part ofwater, weight/ weights)? [JEE' 1997] Q.7 An aqueous solution containing 0.10gKI03 (formulawt. =214.0) was treated with an excessofKI

solution. The solution was acidified with HCl. The liberated ^consumed 45.0 ml of thiosulphate solution to decolourise the blue starch - iodine complex. Calculate the molarity of the sodium thiosulphate

solution. [JEE'1998] Q. 8 How many millilitre of 0.5 M H2S04 are needed to dissolve 0.5 gm of copper II carbonate?

[JEE' 1999] Q.9 The normality of 0.3 M phosphorus acid (H3P03) is [JEE 1999 ]

(A) 0.1 (B) 0.9 (C) 0.3 (D) 0.6

Q.10 One mole of calciums phosphide on reaction with excess of water gives [JEE 1999 ] (A) one mole of phosphine (B) Two moles of phsophoric acid

(C) Two moles of phosphine (D) One mole of phosphorus pentoxide

Q.ll An aqueous solution of 6.3 gm of oxalic acid dihydrate is made upto 250 ml. The volume of 0.1 N NaOH required to completely neutralize 10 ml of this solution is [JEE 2001 ] (A) 40 ml (B) 20 ml (C) 10 ml (D)4ml

Q.12 In the standarization of Na^Og using K2Cr207 by iodometry the equivalent mass of K2Cr207 is

_ s M. Mass _ M. Mass M. Mass

(A) (B) (C) (D) Same as M. Mass. [JEE 2001 ] Q.13 Hydrogen peroxide solution (20 mL) reacts quantitatively with a solution of KMn04 (20 mL) acidified

with dilute L^SC^. The same volume ofthe KMn04 solution is just decolorized by 10mLofMnS04in

neutral medium simultaneously forming a dark brown precipitate of hydrated Mn02. The brown precipitate

is dissolved in 1 OmL of 0.2M sodium oxalate under boiling condition in the presence of dilute HjSO^ Write the balanced equations involved in the reactions and calculate the molarity of H ^ .

[JEE' 2001]

Qi