viva question answer bsc 1 yearchemistry practical.docx

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1. VIVA QUESTION AND ANSWERS
QUALITATIVE ANALYSIS OF ACIDIC AND BASIC RADICALS
1.What is qualitative analysis ?
Ans. The
type of analysis that deals with the methods which are used to determine the
constituents
of a compound.
2. What is a radical ?
Ans. A
radical may be defined as an atom or group of atoms which carries charge and behaves
as
a single unit in chemical reactions.
3. What are acidic and basic radicals ?
Ans. Radicals
carrying positive charge are called basic radicals and those carrying negative
charge
are called acidic radicals.
4. What type of bond is present in an inorganic salt ?
Ans. Electrovalent
bond.
5. Why do inorganic salts ionise when dissolved in water ?
Ans. Due
to the high dielectric constant of water, the force of attraction holding the two ions in a
salt
decreases. Thus, the two ions separate. The ions are further stabilized by solvation.
6. Give examples of some coloured basic radicals.
Ans.Cu
2+
,Fe
2+
,

 Fe
3+
, Cr
3+
,
Ni
2+
,
Co
2+
 and
Mn
2+
.
7. What is the colour of iron salts ?
Ans. Ferrous
salts are usually light green while ferric salts are generally brown.
8. Name any iron salt which is light green.
Ans. Ferrous
sulphate.
9. What is the colour of nickel salts ?
Ans. Bluish
green or green.
10. What is the colour of manganese salts ?
Ans. Light
pink or flesh colour.
11. Name the basic radicals which are absent, if the given salt is white.
Ans. Cu
2+
,Fe
2+
,

 Fe
3+
, Cr
3+
,
Ni
2+
,
Co
2+
 and
Mn
2+
.
 
12.Why a salt containing lead turn black in colour, when placed for a long time in labora-
tory?
Ans. Due
to the formation of black lead sulphide by the action of H
2S
in atmosphere.
13. Name the salts which produce crackling sound when heated.
Ans. Lead
nitrate, barium nitrate, potassium bromide, sodium chloride.
14. What is sublimation ?
Ans. It
is the process by which a salt directly changes into gaseous phase without melting, when
heated.
On cooling vapours condense back to the solid state.
15. Tell the importance of preliminary tests in qualitative analysis.
Ans. Sometimes,
preliminary tests give authentic information about an ion in the salt. For
example,
golden yellow colour in flame test shows the presence of sodium. In a charcoal cavity
test,
brown residue shows the presence of cadmium in a salt and so on.
16. How is dry heating test performed and what information you get if the residue changes
to yellow when hot ?
Ans. In
dry heating test, the salt is heated in a dry test tube. Yellow residue when hot shows the
presence
of Zn
2+
 ion.
17. What is the expected observation when copper sulphate is heated in a dry test
tube ? Ans. A
white residue is formed and water condenses on the colder walls of the test tube.
18. Name the radical which produces CO2 on heating.
Ans. Carbonate.
19. What is the colour of residue when zinc salt is heated ?
Ans. A
residue yellow when hot and white when cold is formed.
20. What is the colour of residue when cadmium salt is heated ?

2. Ans. A
residue brown when hot, brown when cold.
21. If the residue in dry heating test is white, name the radicals which are absent.
Ans. Cu
2+
,
Mn
2+
,
Co
2+
,
Cr
3+
,
Zn
2+
 and
Pb
2+
.
22. How is charcoal cavity test performed ? Describe the chemistry for the formation of
incrustation as well as metallic bead.
Ans. The
salt is mixed with the double the quantity of sodium carbonate and the mixture is
heated
in the charcoal cavity in luminous flame (reducing flame).
23. Which flame is used in charcoal cavity test ? How is it obtained ?
Ans. A
reducing flame is used in charcoal cavity test. It is obtained by closing the air holes of
the
burner.
24. Why should we avoid excess of cobalt nitrate in cobalt nitrate test ?
Ans. Excess
of cobalt nitrate is avoided because it forms black cobalt oxide in the oxidising
flame.
This colour masks the other colours which might be produced during the test.
25. In the flame test, sodium imparts yellow colour to the flame while magnesium does not
impart any colour. Why ?
Ans. In
case of magnesium, when the excited electron jumps back to the ground state, the
frequency
of radiation emitted does not fall in the visible region.
26. Write the chemistry of flame test.
Ans. In
flame test, the valence electron of the atom gets excited and jumps to the higher level.
When
the electron jumps back to the ground state, the radiation is emitted whose frequency falls
in
the visible region.
27. What is the function of blue glass in flame test ?
Ans. The
blue glass can absorb a part or whole of the coloured light in certain cases. Therefore,
the
flame appears to be of different colour when viewed through blue glass. This helps in
identification
of some basic radicals.
28. Why do we use cone. HCl in preparing a paste of the salt for flame test ?
Ans. In
order to convert metal salts into metal chlorides which are more volatile than other salts.
29. Why can’t we use glass rod instead of platinum wire for performing flame test ?
Ans. This
is because glass contains sodium silicate which imparts its own golden yellow colour
to
the flame.
30. Why is platinum metal preferred to other metals for flame test ?
Ans. Because
platinum does not react with acids and does not itself impart any characteristic
colour
to the flame.
31. Why do barium salts not impart colour to the flame immediately ?
Ans. Because
barium chloride is less volatile, it imparts colour to the flame after some time.
32. Why should we avoid the use of platinum wire for testing lead salts ?
Ans. Because
lead combines with platinum and the wire gets corroded.
33. Why should only a particle or two of the given salt should be touched with the bead in
borax bead test ?
Ans. If
salt is used in excess an opaque bead is formed.
34. Why borax bead test is not applicable in case of white salts ?
Ans. White
salts do not form coloured meta-borates.
35. What is Nessler’s Reagent ?
Ans. It
is a solution of mercuric iodide in potassium iodide. Its formula is
 K2[HgI4].
36. Name the acid radicals detected with dil. H2SO4.
Ans. CO3
2-
,
S
2-
,
SO
3
2-
,
NO
2
–
.
37. Why dil. H2SO4 is preferred while testing acid radicals over dil. HCl ?
Ans. When
the salt is treated with HCl, during reaction HCl gas is also given out along with the
gas
evolved by the salt. So the actual gas cannot be identified whereas with H
2SO4,
no such
problem
arises.
38. Name the acid radicals detected by cone. H2SO4.

3. Ans. Cl
–
,
Br
–
,
I
–
,
NO
3
–
,
CH
3COO
–
.
39. Name the radicals which are tested with the help of water extract.
Ans. NO3
–
,
NO
2
–
 and
CH
3COO
–
.
40. Name the radicals which are confirmed with the help of sodium carbonate extract.
Ans. S
2-
,
Cl
–
,
Br
–
,
I
–
, PO4
3-
,
SO
3
2-
,
SO
4
2-
.
41. How is sodium carbonate extract prepared ?
Ans. The
salt is mixed with double the amount of solid Na
2CO3 and
about 20 ml of distilled
water.
It is then boiled till it is reduced to one-third, and then filtered. The filtrate is sodium
carbonate
extract or (S.E.).
42. What is water extract ?
Ans. The
given salt or mixture is shaken well with distilled water and the solution is filtered.
The
filtrate is water extract or (W.E.).
43. CO2 and SO2 both turn lime water milky. How will you distinguish between them ?
Ans. By
passing through acidified
 K2Cr2O7 solution.
SO
2 turns K2Cr2O7 green
while CO
2 has
no
effect.
44. CO2 and Br2 both are brown in colour. How will you distinguish between them ?
Ans. By
passing through
 FeSO4 solution.
NO
2 turns
FeSO
4 soln.
black while Br
2 has
no effect.
45. How will you test the presence of carbonate ?
Ans. Treat
a small quantity of the mixture with dil. H
2SO4.
CO
2 gas
is evolved. When the gas is
passed
through lime water, it is turned milky.
46. What is lime water ?
Ans. A
solution of Ca(OH)
2 in
water is called lime water.
47. What will happen if excess of CO2 is passed through lime water ?
Ans. The
white ppt. of CaCO
3 changes
into soluble calcium bicarbonate and the milkiness,
therefore,
disappears
48. How do you test for sulphide ?
Ans. Warm
the salt with dil. H
2SO4.
H
2S gas
is evolved. It turns a paper dipped in lead acetate
black.
49. Is there any gas other than CO2 which turns lime water milky ?
Ans. Yes,
it is SO
2 gas.
50. All nitrates on heating with cone. H2SO4 in presence of paper pallet evolve NO2 gas.
What is the function of paper pallet ?
Ans. Paper
pallet (carbon) reduces HNO
3 to
NO
2 
51. How will you test whether the given solution in a bottle is lime water ?
Ans. Take
2 ml of the solution in a test tube and blow into it by means of a glass tubing.
Milkiness
indicates that the solution is lime water.
52. How is ring test performed for nitrates ?
Ans. To
the salt solution, freshly prepared ferrous sulphate solution is added and then sulphuric
acid
(cone.) is added along the walls of the tube. A dark brown ring is formed at the junction of
the
two solutions.
53. Why the hot reaction mixture in case of cone. H2SO4 test is not thrown into the
sink ? Ans. In
order to avoid spurting, due to which H
2SO4 may
fly and spoil clothes and may
result
into serious injuries.
54. What is Tollen’s reagent ?
Ans. Ammonical
AgNO
3 solution
is called Tollen’s reagent.
55. Give formula of Diphenylamine reagent.
Ans. (C6H5)2 NH.
56. Why a dark brown ring is formed at the junction of two layers in ring test for nitrates ?
Ans. H2S04
being heavier forms the lower layer and reacts only with a small amount of nitrate
and
FeS04 at its surface, therefore, a brown ring appears only at the junction of the two layers.
57. Why acetic acid is added before adding lead acetate solution ?

4. Ans. In
order to prevent the hydrolysis of lead acetate which would yield white precipitate of
lead
hydroxide.
58. What is the formula of Sodium nitroprusside ?
Ans. Na2[Fe(CN)5 NO].
59. What is chromyl chloride test ?
Ans. Heat
a small amount of the mixture with cone. H
2SO4 and
solid K
2Cr2O7 in
a dry test tube.
Deep
brownish red vapours of chromyl chloride are formed. Pass these vapours in water. A
yellow
sol. of H
2CrO4 is
formed. Add to this solution NaOH, acetic acid and lead acetate, a
yellow
ppt. confirms chloride in the mixture.
SO4.
H
2S gas
is evolved. It turns a paper dipped in lead acetate black.
60. What is the chemistry of carbon disulphide test for a bromide or iodide ?
Ans. To
a part of the soda extract add dil. HCl. Now to this add small amount of CS
2 and
excess
of
chlorine water and shake the solution well. Chlorine displaces bromine or iodine from the
bromide
or iodide, which dissolves in carbon disulphide to produce orange or violet colouration.
61. Why do bromides and iodides not respond to chromyl chloride test ?
Ans. Because
chromyl bromide (CrO
2Br2)
and chromyl iodide (CrO
2I2)
compounds are not
formed,
instead of these bromine and iodine are evolved.
62. Describe the chemistry of match stick test.
Ans. In
match stick test, the sulphate is reduced to sulphide by carbon of match stick which then
gives
violet colour with sodium nitroprusside solution.
63. Why does iodine give a blue colour with starch solution ?
Ans. The
blue colour is due to the physical adsorption of iodine upon starch.
64. What is Nessler’s Reagent ?
Ans. Nessler’s
reagent is K
2[HgI4],
Potassium tetraiodomercurate (II). It is used for detecting
ammonia
and ammonium ions.
65. Name a cation which is not obtained from a metal.
Ans. Ammonium
ion (NH
4
+
).
66. What is aqua regia ?
Ans. Aqua
regia is a mixture of concentrated HCl and concentrated HNO
3 in
the ratio 3:1 by
volume.
67. What is the name of the product obtained when NH4
+
 ions are reacted with Nessler’s
Reagent ?
Ans. Basic
mercure (II) amido-iodine, HgO . Hg(NH
2)I.
Its common name is iodide of Millon’s
base.
68. Why O.S. is not prepared in cone. HNO3 ?
Ans. HNO3 is
an oxidising agent which on decomposition gives oxygen. A yellow ppt. of
sulphur
is obtained in presence of HNO
3 when
H
2S
is passed.
69. Why is original solution for cations not prepared in concentrated H2SO4 ?
Ans. H2SO4 would
lead to precipitation of cations of group V as sulphates.
70. Name group reagents for different groups.
Ans. Group
I—Dil. HCl.
Group
II—H
2S
in the presence of dil. HCl.
Group
III—NH4OH in presence of NH4Cl.
Group
IV—H2S in presence of NH4OH.
Group
V—(NH
4)2 CO3 in
presence of NH4Cl and NH4OH.
Group
VI—No specific group reagent.
71. Why is it essential to add dil. HCl before proceeding to the test for the basic radicals of
group II ?
Ans. In
the precipitation of group II cations as their sulphides. H
2S
is used in the presence of dil.
HCl.
H
2S
is itself a weak acid and dissociates as follows :
Hydrochloric
acid being a strong acid is largely ionised to H
+
.
Thus, hydrogen ion concentration

5. is
increased and consequently the concentration of sulphide ions produced by the ionisation of
H2S
is sufficiently decreased due to common ion effect. As a result of which the sulphide ion
concentra¬tion
is sufficient only to exceed the solubility product of the sulphides of group II
cations.
Since
the solubility products (Ksp) for the sulphides of groups III and IV cations are very high,
those
cations are not precipitated out under the above conditions.
72. Why is it essential to boil off H2S gas before precipitation of radicals of group III ?
Ans. Before
precipitation of group III cations, the solution is boiled with cone, nitric acid. If H
2S
is
not boiled off then it would react with HNO
3 and
would be oxidized to colloidal sulphur,
which
would interfere with further analysis.
73. Why is the O.S. boiled with cone. HNO3 in III group ?
Ans. In
the presence of NH4Cl,
 Fe(OH)2 is
not completely precipitated because of its high
solubility
product. For this reason Fe
++
 salts
are oxidised to
 Fe
+++ 
salts
by boiling with cone.
HNO3 before
adding NH4Cl and NH4OH ; otherwise Fe
++
 would
not be completely precipitated
in
III group.
74. Why is NH4Cl added along with NH4OH in III group ?
Ans. It
is done in order to decrease the concentration of OH
–
 ions
by suppressing the ionisation
of NH4OH by
common ion effect. If
 NH4OH alone
is used in that case, the concentration of
OH
–
 is
enough to ppt. the hydroxide of IV, V and VI groups.
75. What is blue lake ?
Ans. It
is blue particles, blue litmus adsorbed on white ppt. of Al(OH)3, floating in colourless
solution.
76. H2S gas is passed in presence of NH4OH in group IV. Explain why ?
Ans. When
H
2S
gas is passed in alkaline medium or
 NH4OH,
the H
+
 ions
from the dissociation
of
H
2S
gas combine with hydroxyl ions (OH
–
)
from the dissociation of
 NH4OH to
form nearly
unionised
H
2O.
The
removal of H
+
 ions
from the solution causes more of H
2S
to dissociate, thereby increasing
the
concentration of S
2-
 ions
to such an extent that the ionic product of IV group metal sulphides
exceeds
their solubility product. Hence they are precipitated.
77. Presence of NH4Cl is quite essential before the addition of (NH4)2 COs in group V.
Explain why ?
Ans. Ammonium
chloride suppresses the ionisation of
 NH4OH and
(NH
4)2 CO3 due
to common
ion
effect which results in the decrease in the concentration of OH
–
 and
CO
3
2-
 ions.
So the ionic
product
does not exceed the solubility product of Mg(OH)
2 or
MgCO
3 and
thereby they are not
precipitated
in V group.
78. Why are the group V radicals tested in the order Ba
2+
,  Sr
2+
and Ca
2+ 
?
Ans. Tests
of Sr
2+
 and
Ca
2+
 are
given by Ba
2+
 also.
Similarly tests of Ca
2+
 are
given by Sr
2+
 also.

Therefore
before confirming Sr
2+
 we
have to show absence of Ba
2+
 and
before confirming
Ca
2+
 we
have to show absence of Ba
2+
 and
Sr
2+
.
79.  Na2CO3 cannot be used in place of (NH4)2 CO3 in the group V. Explain why ?
Ans. Na2CO3 is
highly ionised electrolyte, which produces very high cone, of CO
3
2-
 ions.
As a
result
ionic product of MgCO
3 may
increase its Ksp and it may get precipitated along with the
radicals
of V group.
80. How will your prepare chlorine water ?
Ans. Take
cone. HCl in a test tube and add KMnO4
 soln.
dropwise till the pink colour starts
persisting.
Now add a few drops of cone. HCl so that pink colour disappears. The colourless
solution
thus obtained is chlorine water.
81. Can we use ammonium sulphate in place of ammonium chloride in group III
precipitation ?
Ans. No,
ammonium sulphate cannot be used because it would cause precipitation of group V
radicals
as their sulphates in group III.

6. 82. Why does cone. HNO3 kept in a bottle turn yellow in colour ?
Ans. This
is due to formation of NO by decomposition of HNO
3 which
is further oxidized to
NO2.
Yellow colour in due to dissolved to NO2.
Detection of Elements in Organic Compounds
1.Why is sodium metal kept under kerosene oil ?
Ans. Sodium
metal reacts with oxygen and moisture present in air. Kerosene oil prevents the
contact
of air and sodium and thus protects it from the action of moisture and oxygen.
2.Why an organic compound is fused with sodium metal for preparing Lassaigne’s
extract ?
Ans. When
the organic compound is heated with sodium, the elements such as nitrogen, sulphur
and
halogens, if present in the compound, are converted into sodium salts which are soluble in
water.
The aqueous solution is then used to identify these elements.
3.Can we use potassium in place of sodium in Lassaigne’s test ?
Ans. No.
Potassium is too reactive metal and hence dangerous to use.
4. In the Lassaigne’s test for nitrogen what is the bluish green colour due to ?
Ans. It
is due to the formation of ferric ferrocyanide, Fe
4[(FeCN)6]3.
5.During the detection of nitrogen, sometimes a blood red colour is obtained. What is this
due to ?
Ans. The
formation of blood red colour with FeCl
3 solution
shows the presence of both N and S
in
the organic compound. It is due to the formation of Fe(CNS)
3.
6.Why is fresh solution of FeSO4 used in test for nitrogen ?
Ans. On
keeping FeSO
4 solution
for a long time, it gets oxidised to ferric sulphate by
atmospheric
oxygen. So, it will not give the desired reaction.
7. What is the function of the addition of HCl in the detection of nitrogen ?
Ans. The
function of adding HCl is to dissolve green ppt. of Fe(OH)2
 otherwise
it may lead to
wrong
inferences.
8. Why is sodium metal dried up before fusion ?
Ans. It
is done to avoid explosion due to of vapours of kerosene oil during heating.
9. How will you test sulphur by lead acetate solution ?
Ans. A
portion of Lassaigne’s extract is acidified with acetic acid and lead acetate solution is
added
to it. Formation of black ppt. indicates the presence of sulphur
10. Why do we use distilled water for the preparation of Lassaigne’s extract ?
Ans. This
is because tap water contains chloride ions which will give a precipitate of AgCl with
AgNO3 solution
even if the organic compound does not contain chlorine.
11. In the detection of bromine and iodine, why the CS2 layer is coloured and not the
aqueous layer ?
Ans. Because
bromine and iodine are more soluble in CS
2.
12. Why is the sodium extract alkaline in nature ?
Ans. Because
the organic compound is fused with sodium metal and then it is extracted with
water.
The unreacted metal reacts with water and forms an alkaline solution.
13. Why is it necessary to break down red hot ignition tube in distilled water ?
Ans. It
is done to extract all the fused salts viz., NaCN, Na
2S
or NaX with distilled water.
14. What is Beilstein’s test ?
Ans. This
is a test for the detection of halogens. In this test a copper wire is heated till it stops
imparting
blue colour to the flame. Then the compound is touched with wire and again heated. If
it
again imparts blue colour it indicates the presence of some halogen.
15. Why is Beilstein test not sufficient for detection of halogens ?
Ans. This
test does not tell us which particular halogen is present. Moreover, there are many
compounds
which do not contain any halogen but give this test.
Determination of Melting point

7. 1.Define melting point.
Ans. It
is defined as the constant temperature at which the solid and the liquid phases of
sub¬stance
coexist.
2. How is the determination of melting point useful ?
Ans. It
helps us to :
(i)
identify unknown substances ;
(ii)
know whether a compound is pure or not.
3. How does the determination of melting point help us know about the purity of the
compound ?
Ans. Melting
point indicates the purity of a substance. If a substance contains moisture or some
other
impurity, then its melting point is usually lowered. A sharp melting point indicates a pure
substance.
4. What is sharp melting point ?
Ans. Melting
point of a solid is said to be sharp if it melts completely within a range of 1°C.
5. Why do pure solids possess sharp melting point ?
Ans. A
pure solid has same force of attraction between particles at different places and hence
melts
at a constant temperature.
6. What is the effect of impurities on the melting point of solids ?
Ans. Impurities
lower the melting point of a solid.
7. Can we heat the capillary tube directly for the determination of melting point ?
Ans. No,
because direct heating would result in uneven and fast heating.
8. Can any other liquid be used in place of liquid paraffin to determine the melting point ?
Ans. Yes,
concentrated H2S04 or silicone oils can be used to determine the melting point.
9. Why is the melting point of benzamide more than that of acetamide ?
Ans. Benzamide
and acetamide contain same functional group, but the molecular mass of
benzamide
is more than that of acetamide. As a result benzamide has stronger intermolecular
forces
and hence has higher melting point.
10. Why different solids have different melting points ?
Ans. Melting
point depends upon intermolecular forces existing in the solid state. Since
different
solids have intermolecular forces of different strength, their melting points are
different.
Determination of boiling point
1.Define boiling point.
Ans. Boiling
point may be defined as the temperature at which the vapour pressure of the liquid
becomes
equal to the atmospheric pressure.
2. What is the effect of increase of pressure on the boiling point ?
Ans. On
increasing the outside pressure the boiling point of liquid increases.
3. What is the effect of decrease of pressure on the boiling point ?
Ans. On
decreasing the outside pressure the boiling point of liquid decreases.
4. What will happen to the boiling point of the liquid if some non-volatile liquid is added to
it ?
Ans. The
boiling point of the liquid will increase.
5. Why different liquids have different boiling points ?
Ans. Boiling
point depends upon intermolecular forces existing in the liquid. Since different
liquids
have intermolecular forces of different strength therefore their boiling points are
different.

8. 6. Why is food cooked more quickly in a pressure cooker ?
Ans. In
a pressure cooker water boils at a higher temperature and hence cooking takes place at a
higher
temperature.
7. Suppose boiling point of a liquid is 100°C in Delhi. At hill station will it be the same or
different ? Give reasons.
Ans. The
boiling point of the liquid will be less than 100°C at the hill station. Boiling point
decreases
with decrease in atmospheric pressure. At hill stations the atmospheric pressure is less
than
that in plains.
Viva question for viscosity
1.Define
viscosity of a liquid.
Ans.
Frictional drag of a liquid in its subsequent layers
2.What
is coefficient of viscosity of a liquid?
Ans.Tangential
force/unit area required to maintain unit velocity gradient between two
successive
liquid layers at unit distance apart

3. Give the SI unit of coefficient viscosity.
Ans.
N.s.m-2
4.
What is the effect of temperature on viscosity of a liquid?{inversely related}

5. Name the instrument used to determine the viscosity of a liquid.
Ostwald
viscometer
6.
Why the viscometer should be dried before the measurement of viscosity of a liquid?

{If not, water forms emulsion with liquid that may change the rate of flow -of the liquid}

7. Why the viscometer should be cleaned and dried using acetone.

8. How is the viscosity of a liquid related to its mobility.
9.
Why do you record laboratory temperature while calculating viscosity of the liquid?
10.
What is fluidity of a liquid?
{
It is the reciprocal of coefficient of viscosity of a liquid. It is measure of ease with which
liquid
flows.}
11.
Give an example for a liquid with viscosity less and more than water at a given temperature.
12.
Why air bubbles should be avoided during the measurement of viscosity of a liquid? {The
air
bubble hinders the flow of liquid and time of flow gets affected.}

13. Write the formula to find the relative viscosity of a liquid
{
l = [dl tl / dw tw] x w} ῃ ῃ
14.
Name any two factors that influence the coefficient of viscosity of a liquid.

1. Temperature 2.Increase in molar mass 3. Branched chain organiccompounds}

15. Which liquid among acetone and water flows fast in ground when you spill out
Surface
tension
1.
Define Surface tension of a liquid.
{Tangential
cohesive force acting along the unit length of the surface of the liquid} – Formula
used
to determine ST = νl = [dl nw / dw nl] νw}
2.Give
the SI unit for surface tension of a liquid.
{N/m}

3.What
are the forces of cohesion and adhesion.
{The
attractive force between the similar molecules-cohesion, The attractive force between the
dissimilar/unlike
molecules- adhesion}
4.What
is the effect of temperature on the surface tension of a liquid?
{
inversely related}
5.What
are the factors which influences the surface tension of a liquid?
{Nature
of the liqud, nature of the surface in contact, temperature.}
6.The
free surface of water is concave where as that of mercury is convex. Why?

9. {The cohesive force between the water molecules<<< adhesive force between water and glass
molecules
that is why concave where as in mercury the adhesive force between the mercury and
glass
molecules is>>>cohesive force between the mercury molecules.

7. Why the inner surface of the stalagmometer should not oily during the measurement?
{surface
tension of the liquid decreases if it is oily}
8.
Give the two practical applications of surface tension of a liquid.
{1.
free falling liquid drop is spherical 2. cleansing action of soaps and detergents}

9. Liquid drops are spherical in shape. Why?
{
It will try to minimize the surface area so that it can have least surface tension.}
10.
Which instrument is used to determine surface tension of a liquid?
Stagnometer
11.
Which method is used to determine the surface tension of a liquid?
(drop
number)
12.
Why the rate of drop formation is to be controlled?
{surface
tension acting is proper}