102 - Physical Chemistry Questions Answers

Chemistry >> Physical Chemistry >> Solid State Medical Exam

if all the ions of NaCl str is removed from one of the diagonal plane , then the formula of compd. will be ---- ?

Asked By: SARIKA SHARMA

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Solution by Joshi sir

Normal formula of compound is Na₄Cl₄

now on removing all the atoms from 1 body diagonal,

lost atoms = 4 Cl at corner, 2 Na from edge centre, 2 Cl from face centre, 1 Na from body centre

so loss in Cl = 4*1/8 + 2*1/2 = 1.5

and loss iin Na = 2*1/4 + 1*1 = 1.5

so new formula = Na_2.5Cl_2.5

so formula will remail same

Chemistry >> Physical Chemistry >> Solid State Medical Exam

In FCC unit cell distance b/w centre of two spheres which are touching each other & distance b/w centre of two nearest non touching sphere is

1) (2a)^1/2,, 2a

2)2r, (a+r)

3) a/(2^1/2), a

4) both (2) & (3)

a= edge length. r= radius of atom

Asked By: SARIKA SHARMA

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Joshi sir comment

along diagonal of a face 4r = a√2 or r = a√2/4 so distance b/w centre of two touching spheres is 2r = a√2/2

similarly distance b/w two nearst non touching sphere = a (along edge)

so 3) will be the option

Chemistry >> Physical Chemistry >> Solid State Medical Exam

in a cubic closed packing of mixed oxide, it is found that lattice has O^-2 ion & one half of the octahedral voids are occupied by trivalent cation A⁺³ & ONE EIGHTH of the FORMULA OF COMPOUND IS

1) AB₂O₄

2) A₂B₂O₄

3) A₂BO₄

4)ABO₄

Asked By: SARIKA SHARMA

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Joshi sir comment

the question is incomplete, after ONE EIGHTH, i guess, it will be one eighth of the tetrahedral void are occupied by B

so let no. of O = 1

then no. of octahedral voids = 1 and half of this = 1/2

similarly tetrahedral voids = 2 so 1/8 of it = 2*1/8 = 1/4

so formula = A_.5B_.25O₁ or A₂B₁O₄

if my assumption for question is correct then answer would be 3) here B is divalent positive ion.

Chemistry >> Physical Chemistry >> Solid State Medical Exam

what are d cordination no. of NaCl, ZnS, CsCl, CaF_2,,Li₂O upto four places, is there any trick to remember all these?

Asked By: SARIKA SHARMA

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Joshi sir comment

NaCl fcc structure 6 for Na and 6 for Cl

ZnS In ZnS , S forms the face centered cube and Zn occupies half of the tetrahedral holes..The unit cell can be devided into eight equal small cubes,each with 1 Zn and 4 S ions so the coordination no will be 4 for Zn and 4 for S

CsCl bcc structue 8 for Cs and 8 for Cl

CaF₂ fcc structure of Ca with 100% filled tetrahedral voids by F, so coordination no. of Ca is 8 and that of F is 4

Li₂O anti fluorite structure, fcc structure of O with 100% filled tetrahedral voids by Li so coordination of O is 8 and that of Li is 4

Chemistry >> Physical Chemistry >> Solutions IIT JEE

depression in freezing point of 0.01 molal acetic acid solution is 0.0204 deg.cel. 1molal of this solution freezes at -1.86deg.cel.assuming molality equals molarity find pH of acid A. 2 B. 3 C. 3.2 D. 4.2

Asked By: GAURAV MAHATE

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Joshi sir comment

for 1 molal soln. depression = 2.04 deg. cel.

and normal depression = 1.86

so vant hoff factor = 2.04/1.86 = 102/93 = 34/31

now CH₃COOH ---------> CH₃COO^- + H⁺

let degree of dissociation = α

so concentrations after dissociation will be

1-α α α

so according to these concentrations vant hoff factor = 1+α/1

on comparing 1+α = 34/31 or α = 3/31 so pH = -log3/31

Chemistry >> Physical Chemistry >> Solid State Medical Exam

IF VOLUME OF 1 MOLE OF STRNTIUM CHLORIDE (HAS FLUORITE STR) IS X CM³ & VOL OF UNIT CELL IS Y CM³ D N_A CONSTANT IS GIVEN BY

ANS ( X/Y) X4

Asked By: SARIKA SHARMA

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Joshi sir comment

since 1 unit cell of SrCl₂contains 4 molecules of the same so ratio will be 4X/Y

Chemistry >> Physical Chemistry >> Solid State Medical Exam

IN A FACE CENTRED CUBIC LATTICE A UNIT CELL IS SHARED EQUALLYBY HOW MANY UNIT CELLS

ANS 6

Asked By: SARIKA SHARMA

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Joshi sir comment

due to the reason that a unit cell contribute to 6 of the face attached memers

Chemistry >> Physical Chemistry >> Solid State Medical Exam

IN CRYSTAL OF WHICH ONE OF D FOLLOWING IONIC COMPD. WOULD U EXPECT MAXm DISTANCE B/W CENTRE OF ANION &CATION

1)CsI

2)CsF

3)LiF

4)LiI

Asked By: SARIKA SHARMA

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Joshi sir comment

accordong to my opinion it will be CsI

Chemistry >> Physical Chemistry >> Solid State Medical Exam

C forms ccp, A is at 25%terahedral viod &B is at 50% octahedral viod . if the particles along one of the fce diagonal are removed then formula?

ans A₈B₈C₁₃

Asked By: SARIKA SHARMA

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Joshi sir comment

normal formula has C atom = 1

A atom = 2*1/4 = 1/2

B atom = 1*1/2 = 1/2

so structure = C₂AB = C₄A₂B₂

now we have to remove atoms from one of the face diagonal so

remove 2 corner C, so removed C = 1/8*2 = 1/4 and 1 face centre = 1/2 sum = 3/4

nothing else

so new formula = C_4-3/4A₂B₂ = A₈B₈C₁₃

Chemistry >> Physical Chemistry >> Solid State Medical Exam

if x is length of body diagonal ,then distance b/w 2 nearest cation in rock salt str is

ans x/(6^1/2)

Asked By: SARIKA SHARMA

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Joshi sir comment

two nearest cations will be at corner and face centre so distance between these two will be y = a/2^1/2

here a is side length and according to the given condition x = a3^1/2

so a = x/ 3^1/2

so y = x / 6^1/2

102 - Physical Chemistry Questions Answers

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