# 13 - Atoms and molecules Questions Answers

At 752 mm Hg of total Pressure and 301 K Temperature 150 ml H2 is produced and collected over the water, when current is passed through acidic water for 1 hour. How many Amp. current should have passed? ( at 301 K temperature, The pressure of water is 28 mm Hg )

A) 0.320 A

B) 310 A

C) 321 A

D) 0.305 A

Solution by Joshi sir

by formula PV/T = constant

(752-28)*150/301 = 760*V/273

solve for V, this will be the equivalent volume at STP

now convert this volume in gm by the formula 2V/22400

then finally m = zit, where

z = 1/96500

solve it for i

if there are Three Fe+2  For a Fe+3 in FexO, What is the value of x?

Joshi sir comment

3FeO.1Fe2O3 = Fe5O6 = Fe5/6O

the first line in the balmer series in the hydrogen spectrum will have the frequency

Joshi sir comment

f/c = R[ 1/22 - 1/32 ]

R and f are Rydberg constant and frequency

if radius of first bohr orbit of hydrogen atom is X, then de Broglie wavelength of electron in 4 th orbit is

Joshi sir comment

radius of fourth orbit = 16X

now put 2πr = 4λ

FROM WHERE ELECTRON GET ENERGY
Joshi sir comment

Consider about the amount of energy required. It can gain from its surrounding

A hydrogen like system has ionisation enthalpy 11808KJ/mol. find the no of protons in the nucleus of the system?

Joshi sir comment

A hydrogen like system has ionisation enthalpy 11808KJ/mol

on converting it into eV we get [11808*1000]/[6.023*1023*1.6*10-19]  = 122.53 eV

now formula for this energy is [-Z2/n2]13.6 eV

for n = 1, Z will be 3

the position of both an electron and a helium atom is known within 1nm. further the momentum of the electron is known within 5*10-26 kgm/s. the minimum uncertainity in the measurement of the momentum of the helium atom is

Joshi sir comment

according to Heisenberg principle product of uncertainity in position and momentum of a particle is greater than or equal to h/4π, since uncertanity in position of both the particle are same so same will be the momentum uncertainty minima.

the frequency of radiation emitted when the electron falls n=4 to n=1 in a hydrogen atom will be (given ionisation energy of H =2.18*I0-18 J/atom )

ans=3.08*1015

Joshi sir comment

for n = 1                      E = 2.18*10-18

for n = 4                      E = 2.18*10-18/16

so hν = 15*2.18*10-18/16

so ν = 15*2.18*10-18/16*6.634*10-34

so ν = 3.08*1015

A mixture of FeO and Fe304 when heated in air to constant weight gains 5% in its weight. The % of FeO in the sample

Joshi sir comment

let FeO = x gm and FeO+Fe2O3= y gm so FeO = [72/(72+160)]*y and Fe2O= [160/(160+72)]*y

2FeO + 1/2O2  ---------->  Fe2O3

so amount of Fe2Oformed by x gm FeO  = 160x/144

similarly amount of Fe2Oformed by  [72/(72+160)]*y gm FeO = 160 [72/(72+160)]*y/144

so total Fe2O3 = 160x/144 + 160 [72/(72+160)]*y/144 +  [160/(160+72)]*y = 160x/144 + [160*72/232]y/144 + 160y/232

now according to the given condition {[160x/144 + [160*72/232]y/144 + 160y/232}/{x+y) = 105/100

now solve

what is the relation b/w E1 &E2 whose respective wavelength r 400& 800 Ao . SIR I WANT TO KNOW THE RELATn b/w ENERGY & WAVELENGTH . ARE THEY DIRECTLY PROPTIONAL  ? ANS OF THIS QUES IS E1=2E2