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Chemistry >> General Chemistry >> Mole Concept and Stoicheometry IIT JEE

Q. 1.Calculate the number of HCl molecules present in 10ml of 0.1N HCl solution.

Q.2. 4.0g of NaOH are contained in one decilitre of solutions. Calculate mole fraction. Molarity and molality of NaOH. ( Given, density of solution=                                                              1.038g/ cm3)

Q. 3. You are provided with 2 litre each of 0.5 M NaOH and 0.4M of NaOH solutions. What maximum volume of 0.30 M NaOH can be obtained from these solutions without using water at all ?

 

Asked By: HEMA RANI
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Joshi sir comment

1)   no of miligm eq. = 10*0.1 = 1

so no. of gm. eq. = 1/1000

since acid is monobasic so no. of moles = 1/1000

so molecules = 1/1000 * 6.023 * 1023

 

2)     0.1 litre soln. contains              4 gm. NaOH

       so 1 litre contains                      40 gm. NaOH

       so 1 litre soln. contains              40/40 moles of NaOH  = 1 mole so molarity = 1

 

 now 1 litre soln. contains                       40 gm NaOH

so 1*1038 gm soln. contains               40 gm. NaOH                   here 1038 gm/litre is density

so 1038 gm. soln. contains                  40 gm. NaOH

so 1038-40 gm. solvent contains        40 gm. NaOH

so 998 gm. solvent contains                 40 gm. NaOH = 1 mole 

so 0.998 Kg solvent contains                 1 mole NaOH

so molality = 1/0.998 

 

998 gm water contains                   40 gm. NaOH

so 998/18 mole water contains    40/40 mole NaOH

so mole fraction of NaOH = [40/40]/{[40/40]+[998/18]}

 

Third part is irrelevent without using water

 

 

 

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 NA CONSTANT IS GIVEN BY

ANS   ( X/Y) X4

Asked By: SARIKA SHARMA
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Joshi sir comment

since 1 unit cell of SrCl2 contains 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 = C4-3/4A2B2   = 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/(61/2)

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/21/2

here a is side length and according to the given condition x = a31/2  

so a = x/ 31/2   

so  y = x  /  61/2

Chemistry >> Physical Chemistry >> Solid State Medical Exam

in the crystal str of Fe3O4 Fe2+& Fe3+ occupy resp.

50% octatrahedral  &12.5% tetrahedral viods

Asked By: SARIKA SHARMA
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Joshi sir comment

let atom of O = 1

so 50% Fe++ in octahedral void  = 1*1/2 = 1/2

and 12.5 % Fe+++ in tetrahedral voids = 2*1/8 = 1/4

so total Fe = 1/2 + 1/4 = 3/4

so name of the compound = Fe3/4O  = Fe3O4

Chemistry >> Physical Chemistry >> Solid State Medical Exam

d possible types of two dmensional lattice &3 D primitive unit cells are resp.

ans 5& 7

Asked By: SARIKA SHARMA
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Joshi sir comment

and in 3 D these are 7 crystal system, I have given an article for these 7 already

Chemistry >> Physical Chemistry >> Solid State Medical Exam

how many atoms are there in a cubic unitcell having one atom on each corner &two atoms on each body diagonal of cube?

& also if instead 2 there are 3 atoms at body diagonal?

Asked By: SARIKA SHARMA
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Joshi sir comment

corner atoms = 8*1/8 = 1

diagonal atoms = 4*2 = 8

total = 9

in second case calculate similarly

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