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EXPERIMENT 1
AIM: To determine the no. of water molecules of crystallization in Mohr’s
salt provided standard K2Cr2O7 sol (0.1N). Using diphenylamine as
internal indicator.
APPARATUS: Burette, burette stand, pipette, beaker, conical flask, funnel,
measuring cylinder.
CHEMICAL USED: Mohr’s salt, H2SO4, H3PO3, Dipheyl amine, K2Cr2O7
THEORY: This titration is a type of redox reactions. Here, the principle
involved is that ferrous sulphate (FeSO4) present in Mohr’s salt.
[FeSO4(NH4)2 6H2O] is oxidized by potassium dichromate (K2Cr2O7)
to ferric sulphate [Fe2 (SO4)3] in the presence of dil. H2SO4 using
diphenyl amine [(C6H5)2 NH2] as internal indicator. This reaction
involved:
Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O
[Fe2+ → Fe3+ + e-] x 6
--------------------------------------------------------------
Cr2O72- + 14H+ + 6Fe2+ → 2Cr3+ + 6Fe3+ +7H2O
At the end point, all the ferrous ions (Fe2+) present in the solution get
completely oxidized to ferric ions (Fe3+) by chromate ions (Cr2O72-).
As soon as a slight excess of potassium dichromate solution is
added, it brings about the oxidation of diphenylamine resulting in the
formation of a blue coloured complex named diphenyl benzidine. At
the end point a sharp change from colourful solution to deep blue
solution is observed.
H oxidation with N N N Cr2O7
2-
(Colourless) (Blue/Violet)
Diphenylamine Diphenyl benzide
OBSERVTION TABLE:
SNo. Vol. of titrate taken (Mohr’s salt)(ml)
Burette reading (initial)(ml)
Burette reading (final)(ml)
Vol. of titrant (K2Cr2O7) used(ml) (Final-Initial)
1 20ml 5.5 12.8 7.3 2 20ml 12.8 20.3 7.5 3 20ml 20.3 28.6 7.9
CALCULATIONS: Applying law of equivalence,
N1V1 = N2V2 N1= Normality at Mohr’s Salt
N2= Normality of K2Cr2O7
V1= Volume of Mohr’s salt
V2= Volume of K2Cr2O7
N1 x 20 = 110
x V2
N1 = 𝑉2200
= 7.6200
= 0.038
Strength of anhydrated Mohr’s Salt (y) = Normality x eq. wt.
= N1 x 284
= 10.792
Strength of hydrated salt = 20g/l (given)
Strength of hydrated salt
Strength of anhydrated salt =
284 + 18𝑥284
20𝑦
= 284+18𝑥284
18x = 20 x 284
𝑦 – 284
18x = 20 x 28410.79
– 284
x = 13.46
RESULT:
The no. of water molecules of crystallization in Mohr’s Salt is 6.73
EXPERIMENT 2
AIM: Determination of iron content in an iron are by titrating it against
standard K2Cr2O7 solution using potassium ferricyanide [K3Fe(CN)6],
H2SO4, FeSO4 as an external indicator.
APPARATUS: Burette, burette stand, conical flask, white glazed tile, beaker, glass
rod, measuring cylinder, funnel.
CHEMICAL USED: K2Cr2O7, [K3Fe(CN)6], H2SO4, FeSO4
THEORY: This estimation is based on the principle that the solution containing
ferrous ammonium sulphate can be quantitatively titrated against
standard K2Cr2O7 soln in the presence of H2SO4 using potassium
ferrocynide as an external indicator.
Oxides of ferrous sulphate present in Mohr’s salt into ferric
sulphate in the presence of dil H2SO4.[K3Fe(CN)6] is used as an
external indicator gives a greenish blue colour due to formation of
ferro-ferricyanide complex.
OBSERVATION TABLE:
S.No. Vol. of titrate taken (Mohr’s salt)(ml)
Burette reading (initial)(ml)
Burette reading (final)(ml)
Vol. of titrant (K2Cr2O7) used(ml) (Final-Initial)
1 20ml 0 10.1 10.1 2 20ml 10.1 19.9 9.8 3 20ml 19.9 30.2 10.3 CALCULATIONS:
Applying law of chemical equivalence,
N1V1 = N2V2
N1 x 20 = 110
x V2
N1 = 𝑉2200
= 10200
= 0.05
Strength of Fe2+ in the soln = N1 x eq.wt.
= 𝑉2200
x 56
= 120
x 56 = 2.8 g/l
% of Fe = 56 200
x V2 x 100𝑥
(x = 20 given)
= 2.8 x 5 = 14 %
Hence % of iron in iron soln is 14%
RESULT:
The % of iron in iron soln is 14%.
Screw Pinch Cock
B
EXPERIMENT 3
0
20
40
60
80
100
120
140
160
0 50 100
Dro
ps
Composition of A in mixture
Graph
Linear (Graph)
The Redwood viscometer was made by Sir Boverton Redwood in about 1880.
EXPERIMENT 7
AIM:
To determine the type & extent of alkalinity of given water sample.
APPARATUS:
Burette, pipette, conical flask, beaker, measuring flask.
CHEMICALS:
Water sample, V/10 HCl, phenolphthalein and methyl orange
indicator.
THEORY:
Alkalinity of water is mainly due to the presence of the following.
(i) Hydroxides only
(ii) Carbonates only
(iii) Bicarbonates only
(iv) Hydroxides and carbonates
(v) Carbonates & bicarbonates
Since OH- & HCO3- ion cannot co-exist because both combine
together to form carbonates.
OH + HCO3- CO3
2- +H2O
The extent of alkanity present in a water sample is determined by
titrating the water sample (titrate) with a standard acid (titrant) using
phenolphthalein indicator and alkalinity if found out in terms of
CaCO3 equivalent by using normality equation. This is called
phenolphthalein alkalinity (P). At this point, complete neutralization
of hydroxide and conversion carbonate to bicarbonate takes place.
OH- + H+ → H2O -----(i)
CO32- + H+ → HCO3
- -----(ii)
HCO3-+ H+ → H2O + CO2
-----(iii)
Now titrate the same alkality soln using methyl orange indicator &
alkalinity is calculated in terms of caco3 equivalents. This alkalinity is
called mothyl orange alkalinity, alkalinity due to diff. ions can be
calculated. The results are summarized in the following table.
Case I P=O NIL NIL M Case II P=1/2M NIL 2 PORM NIL Case III P<1/2M NIL 2 P (M-2P) Case IV P>1/2M (2P-M) 2 (M-P) NIL Case V P=M P=M NIL NIL
INDICATORS: Phenol phtalien and methyl orange.
END POINTS: Pink to colourless (phenolphthalein),
Yellow to red (methyl orange)
OBSERVATIONS:
(a) Reading using phenolphthalein
S.No. Vol. of soln titrate)token in the titration flask(ml)
Burette reading Vol. of the titration
used(V1-V1)
Initial (V1) Final (V1) Final-Initial 1 20 0 7 7 2 20 11.5 18.2 6.7 3 20 22.5 29.0 6.5
Mean=6.73
(b) Reading using methyl orange
S.No. Vol. Soln taken(ml) Initial Final Final-Initial 1 20 7 11.5 4.5 2 20 18.2 22.5 4.3 3 20 29 33.2 4.2
Mean=4.33
CALCULATIONS:
1. Phenolphthalein alkalinity in terms of CaCO3 equivalent
Acc. to Law of Equivalence,
N1V1 = N2V2
(acid) (water)
1/10(V2-V1) = N2 x 20
N2 = 6.73/200 = 0.03365
Strength in terms of CaCO3 eq. = N2 x eq. wt of CaCO3
= 0.03365 x 50 = 1.6825 g/l
P = 1.6825 x 1000 mg/l = 1682.5 mg/l
= 1.6825 x 1000 ppm = 168.25 ppm
2. Methyl orange alkanity in terms of CaCO3 equivalent
Acc. to Law of Equivalence,
N1’ V1’= N2’ V2’
(acid) (water)
1/10(V3-V1) = N2’ x 20
N2’ = 1/10 x (V3-V1)/20
RESULT:
Phenolphthalein alkalinity (P) = 1682.5ppm of CaCO3
Methyl orange alkalinity (M) = 1082.5 ppm of CaCO3
(To find out the alkalinity in terms of individual fans, find out to which
case the values of P & M falls out from table, calculate the amount of
individual ions as below.)
Alkalinity due to OH- ions = 2P-M = 2282.5 ppm
Alkalinity due to CO32- ions = 2(M-P) = 1200 ppm
Alkalinity due to HCO3- ions = Nil
PRECAUTIONS:
1. Phenolphthalein indicator should be added first & then methyl
orange.
2. The vol. of indicator should be same in all observations.
3. Constant shaking of soln mixture should be done.
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