JEE MANTRAAIPMT2014 / physical chemistry special/paper

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Basic physical chemistry

AVAGADRO HYPOTHESIS

• Equal volume of gases or vapours obeying gas laws under similar conditions of pressure or temperature

explanation

• 1 mole of all gases contain AVAGADROS number

• The volume of one mole of of gas at NTP or STP is 22.4 litre

• NTP or STP refers P = I atm,T=273K

• Molecular weight=twoX Vapour density

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2.Calculate the volume of O2 and volume of air needed for

complete combustion of 1 kg carbon at STP.

SOLUTION;

For the reaction C+O2→CO2

12 Gram c requires O2=22.4litre

1000 gram requires O2=22.4X1000/12

Volume of air=5XVolume of o2

When 22.4 litres of H2(g) is mixed with 11.2 litres ofCl2(g), each at STP, the moles of HCl(g) formed is equalto(1) 1 mol of HCl(g) (2) 2 mol of HCl(g)(3) 0.5 mol of HCl(g) (4) 1.5 mol of HCl(g

In acidic medium, H2O2 changes –2 Cr O2 7 to CrO5which has two (—O—O—) bonds. Oxidation state ofCr in CrO5 is(1) +5 (2) +3(3) +6 (4) –10Answer (3)

1.10 ml mixture of CH4, C2H4 and C3H8 in the ratio 1:1.5:2.5

respectively is burnt in excess of air .calculate the volume of air

used and volume of CO2 Formed after combustion .All

measurements are made at same p and T

Volume of CH4 =10/5= 2 ml

Volume of C2H4-=10X1.5/5= 3ml

Volume of C3H8=2.5X10/5

CH4+ 2O2→CO2 + 2H2O

C2H4 (g) + 3O2 (g) → 2CO2 (g) + 2H2O

C3H8 + 5O2 → 3CO2 +4 H2O

Volume of O2 needed=2x2+2x3+5X5=38ml

V air =38x100/20=190 ml

Volume of Co2=23ml

The reaction of aqueous KMnO4 with H2O2in acidic

conditions gives :(1) Mn4+ and O2 (2) Mn2+ and O2(3) Mn2+ and O3 (4) Mn4+ and MnO2Answer (2)Sol. 2KMnO4+ 5H2

O2+ 3H2SO4 → K2SO4 + 2MnSO4+

8H2O + 5O2

(a) H2O2+ O3 → H2O + 2O2

(b) H2O2+ Ag2O → 2Ag + H2O + O2Role of hydrogen peroxide in the above reactions isrespectively(1) Oxidizing in (a) and reducing in (b)(2) Reducing in (a) and oxidizing in (b)(3) Reducing in (a) and (b)(4) Oxidizing in (a) and (b)Answer (1)Sol. (a) H2O2 is reduced.(b) Ag2O is reduced.

In the Kjeldahl's method for estimation of nitrogenpresent in a soil sample, ammonia evolved from0.75 g of sample neutralized 10 mL of 1 M H2SO4.The percentage of nitrogen in the soil is(1) 37.33 (2) 45.33(3) 35.33 (4) 43.33Answer (1)