VIVA-VOCE

Q.1. What is a double salt ?

Ans. A double salt is a combnation of two different single salts which crvstallise as a single substance uy:
Onie as mo disnct salts on dissohing n water. eg., potash alum.
Q. 2. What is the advantage of double salt over single salt ?
Ans. Double alts are more stable as compared tosingle salts andcan be obtained in a high state of purity.
Q.3. What is crystallisation ?
Ans. Ir s aprress of getting crrstals of a substance by cooling slowly its saturated solution.
What is crystallisation point ?
Ans. It is the stage at which the solution becomes saturated with respect to the solute.
Q. 5. What is seeding ?
Ans. Placing asmall crstal of the substance in the concentrated solution which facilitates crystallisation i:
called seeding
Q. 6. What is mother liquor ?
Ans. The hqudleft after separation of crystals from the saturated solution i called mother liquor.
e. 7. In which ratio are the salts mixed to prepare a double salt ?
Ans. In the rario of their molecular mass
. 8. In which oxidation state iron is in Mohr's salt ?
Ans. In -2axidaion state
Q. 9. Why do we add sulphuric acid be fore adding water for dissolving ferrous sulphate ?
Ans. Sulphunc acid is added to prevent hyàrolysis of iron
Q.10. Why are Mohr's salt crystals washed with alcohol ?
Ans. In order to remve adhering sulphuric acid
Q11. What is the nature of aqueous solution of potash alun?
Ans. Acidic
Q12. What is burnt alum ?
Ans. Anhydrous alum is known as burnt alum
Q13. Why are potash alum crystals washed with cold water ?
Ans.
Potash alum is only slightls soluble in cold water whereas impurities are readily soluble.
Q14 What is the liquid left with the crystals called ?
Ans. Mother hquor.
Q.15. What is the shape of potash alum crystals and Mohr's salt crystals ?
Ans. Potash alum crystals have octahedral shape whereas Mohr's salt crystals have monoclinic shape.
Q16. How does potash alum help in stopping bleeding ?
Ans.
Jions
blod
in potash alum cause coagularion of blood by neutralizing negative charge on the ions present in
Q17. How does alum purify muddy water ?
Ans.
A* ions in alum neutralize the negative charge on mud particles causing their coagulation. These
ultimately settle doWn and are removed
Q.18. Why aqueous potash alum solution is acidic?
Ans.
It is because potash alum in aqueous solution undergoes hy drolysis to form H,SO, which is a strong actd
while base produced is AlOH), which isweak
EVERGREEN CHEMISTRY LAB MANUAL - 12
 Q.19. What is comnon name of potash alum ?
Ans. Phitkari.

Q20. In the preparation of Mohr's salt, water is boiled before using it for making solution, why ?
Ans. To avoid oxidation due to dissolvedO,.
Q.21. What is principle of crystallisation ?
Ans. \When a hot saturated solution of a substance is cooled, the excess of the dissolved substance is thrown out
because solubility ofa solid decreases with decrease in temperature.
Q.22. What is solubility ?
Ans. It isdefined as the amount of the solute dissolved in 100 g of the solvent.
Q.23. VWhy is crystallisation done ?
Ans. () For purificat ion of salts.
(i) For preparation of double salts.
Q.24. What is difference between a erystalline substance and an amorphous substance ?
Ans. In acrystalline substance the constituent particles are arranged in a regular geometric pattern whereas
in amorphous substances it is not so.
Q.25. What is a coordination compound or acomplex compound ?
Ans. It consists of a central metal atom or ion surrounded by a number of ions or neutral molecules called
ligands.
e.g.. [Cu(NH),]SO,
Q.26. What are ligands ?
Ans. The neutral molecules or ions attached to the central metal atom or ion in a coordination compound are
called ligands. They contain a pair of electrons which can be donated to the central metal atom or ion.
Q.27. Name the ligand, central metal ion and coordination number of central metal ion in potassiunm
ferric oxalate.
Ans. Potassium ferrieoxalate = Kz[Fe(C,0)l3H,0.
Ligands = Oxalate, C,0,
Central metal ion = Ferric ion, Fet
C.N. = Six, it contains three bidentate oxalate ligands.
Q.28. Why is the complex K;[Fe(C,O,)]·3H,0, paramagnetic ?
Ans. Due to presence of unpaired electrons im 3d orbitals of iron.
Q.29. What is the geometry of the complex potassium ferric oxalate ?
Ans. Octahedral shape.
Q.30. What is the IUPAC name of the complex potassium ferric oxalate ?
Ans. K [Fe(C,0)3l3H,O
IUPAC name: Potassium trioxalatoferrate (|I) trihydrate.
Q.31. When alum is heated it swells. Why ?
Ans. Upon heating alumn loses its water molecules of crystallisation to form a porous mass which swells 3ndi
known as burnt alum.
Q.32. What is isomnorphism ?
Ans. Diferent crvstalline solids having similar composition and the same erystal structure are called isonmorphous.
This property is called isomorphism.
EVERGREEN CHEMIsTRY LAB MANUAL - 12 83)
Q. 1.
O DISCUSSION QUESTIONS FROM NCERT LAB MANUAL

Why do we take equimolar quantities of the reacting compounds in the preparation of

double salts ?
Ans. It is because double salts contain the constituent salts in equimolar proportions.
Q. 2. What is the di fference between iron compounds, K, [Fe(CN)G] and FeSO4 -(NH4)2 SO4. GH,02
Ans. K4 [Fe(CN)G] is a complex. It ionises in agqueous solution to give K+ and [Fe(CN)G|- ions. It does not give
test for Fet.

FeSO4. (NH)2 SO4 . GH20, it is a double salt. In agueous solution, it ionises into Fe+, SO and NH.t
ions. It gives test for Fet.
Q. 3. What is the action of heat on potash alum ?
Ans. When crystals of potash alum are heated strongly i.e.,above 360 K then a fused mass is obtainedafter the Joss
of all 24molecules of crystallisation. The fused mass obtained is called burnt alum.
Q. 4. Why does an aqueous solution of potash alum turn blue litmus red ?
Ans. Because its aqueous solution is acidic in nature.
Q. 5. What are isomorphous substances ?
Ans. Isomorphous substances have similar composition and same crystal structure.
e.g., All alums are isomorphous.
Q. 6. Givethe name of some of the alums where the cations are other than A3t ?
Ans. Ferric alum : (NH)2 SO4. Fe2 (SO4)3. 24Hz0
Chrome alum : K,S0,. Cr (SO4)3 . 24H,0
Q. 7. What is the difference between a complex compound and a double salt ?
Ans.
A double salt ionises completely in aqueous solution togive all the ions of its constituent simple salts
whereas a complex compound does not furnish all the ions of salts from which it is made.
Q. 8.
What is the coordination number of iron in potassium trioxalatoferrate (III) ?
Ans. Six.
Q. 9. Give two examples of bidentate ligands other than oxalation.
H
Ans. () Ethane-1, 2-diamine (en) : CH, NH, (ii) Glycinato (gly) : CHz N-H
CH, NH, C-0

Q.10. why does the compound, potassium trioxalatoferrate (III) does not give tests for ferric ions ?
Ans. Because it is acomplex and in aqueous solution free Fe* ions are not formed upon jonisation.
K3 [Fe(ox)3] + aq 3K+ (aq) + [Fe (ox)3]3 (aq)
Q11. What are chelates ?
Ans. It is a ring structure formed upon coordination of abidentate or polydentate ligand with same central
metal ion.

84 EVERGREENCHEMISTRY LAB MANUAL -12