Titrations class XII
DATE:
EXPERIMENT NO.
AIM : To prepare 250 ml of M/20 standard solution of Mohr’s salt
( Ferrous ammonium sulphate) and determine the molarity & strength of given
KMnO4 solution by titrating it against the standard Mohr’s salt solution prepared.
( Ferrous ammonium sulphate) and determine the molarity & strength of given
KMnO4 solution by titrating it against the standard Mohr’s salt solution prepared.
APPARATUS REQUIRED : Mohr’s salt crystals ,Standard measuring
flask,weighing bottle, funnel,burette,pipette, test
tube, conical flask,weight box,beakers , Dil. H2SO4 &
KMnO4 solution.
THEORY : The reaction between KMnO4 & Mohr’s salt is a Redox reaction &
the titration is called a Redox titration. KMnO4 acts as Oxidising
agent & Mohr’s salt as reducing agent. KMnO4 acts as self
Indicator because in acidic medium it changes from MnO4- ( pink)
to Mn2+ ( colourless) in dilute solution. ( Mn2+ ions are also pink but
appear colourless in dilute solution).
MOLECULAR EQUATION :
2KMnO4 + 8 H2SO4 + 10 FeSO4.(NH4)2SO4.6H2O ------------- K2SO4 + 2MnSO4 + 5Fe2(SO4)3 +68H2O
+10.(NH4)2SO4
IONIC EQUATIONS:
MnO4- + 8H++ 5e- ------------------- Mn2+ + 4H2O
[ Fe2+ ----------------------------- Fe3+ + e- ] X 5
MnO4- + 8H++ 5 Fe2+ ------------------ Mn2+ + 5Fe3+ + 4H2O
CALCULATIONS:
(a). no. of moles of the solute Wsolute / msolute
Molarity = ----------------------------------------- = ----------------------
Volume of solution (in Litres ) 250 / 1000 (L)Wsolute / 392
1 / 20 = --------------------------
250 / 1000
1 X 250 X 392
Wsolute = ----- -- ------------------ = 4.9 grams
20 X 1000
PROCEDURE :
(a). 1. Weigh a clean ,dry weighing bottle.
2. Add calculated weight to the pan containing the weights for the
weighing bottle .
3. Keep adding Mohr’s salt to the weighing bottle till the weight in the pan
is balanced with the weight of the weighing bottle + Mohr’s salt.
4. Transfer Mohr’s salt to the standard measuring flask ,add 1 test tube
of Dil. H2SO4 ( ~ 4N) & approximately 100 ml of water. Shake the flask
thoroughly to dissolve the solid. Add water to make the volume upto 250
ml.
5. Wash the burette with water & rinse it with the given KMnO4 solution.
6. Fill the burette with KMnO4 solution & clamp it. Note down the initial
reading of the burette ( Upper meniscus ).
7. Wash the pipette with water & pipette out 10 ml Mohr’s salt standard
Solution in the conical flask.
8. Add 1 test tube dilute H2SO4 to the conical flask.
9. Run down the solution from the burette to the conical flask till the colour of
the solution changes to light pink.
10. Note down the final reading of the burette. Find out the volume of KMnO4
used by subtracting initial reading from the final reading of the burette.
11. Repeat the experiment to get the concordant readings.
OBSERVATION TABLE :
CONCORDANT READING = -----------
CALCULATIONS (b) :
M KMnO4 X V KMnO4 M Mohr’s salt X V Mohr’s salt
--------------------------- = ---------------------------------
2 10
M Mohr’s salt X V Mohr’s salt X 2
M KMnO4 = ---------------------------------------
10 X V KMnO4
Strength of KMnO4 solution = M KMnO4 X Molar mass of KMnO4 ( i.e.158g)
= _____ g/L
RESULT : (a) 250 ml of M /20 Mohr’s salt standard solution is prepared & used
to determine the molarity & strength of given KMnO4 solution
titration.
(b) The Molarity & Strength of the given KMnO4 solution is _______
& _______ respectively.
PRECAUTIONS :
- There should be no air bubbles in the burette.
- Solution from the burette should be added in drops & should not run too fast.
- Always read the upper meniscus in the case of coloured solution & lower in the case of colourless.
- Titration flask should not be rinsed every time .
---------------------------------------------------------------------------------------------------------------
DATE:
EXPERIMENT NO.
AIM : (a) To prepare 250 ml of M/20 standard solution of Oxalic Acid
( C2H2O4.2H2O )
(b) To determine the molarity & strength of given KMnO4 solution by
titrating it against the standard Oxalic acid solution prepared.
APPARATUS REQUIRED : Oxalic acid , Standard measuring flask , weighing
Bottle , funnel , burette , pipette , test tube, conical
Flask , weight box , beakers , Dil. H2SO4 & KMnO4
solution.
THEORY : The reaction between KMnO4 & Oxalic acid is a Redox reaction &
the titration is called a Redox titration.
KMnO4 acts as Oxidising agent & Oxalic acid as reducing agent.
KMnO4 acts as self Indicator because in acidic medium it changes
from MnO4- ( pink) to Mn2+ ( colourless) in dilute solution. ( Mn2+
ions are also pink but appear colourless in dilute solution).
MOLECULAR EQUATION :
2 KMnO4 + 3 H2SO4 + 5 C2H2O4 ------------- K2SO4 + 2MnSO4 + 10 CO2 + 8 H2O
IONIC EQUATIONS:
[ MnO4- + 8H++ 5e- ------------------- Mn2+ + 4H2O ] X 2
[ C2O42- -------------------- 2 CO2 + 2e- ] X 5
2MnO4- + 16 H++ 5 C2O42- ------------------ 2 Mn2+ + 10 CO2 + 8 H2O
CALCULATIONS:
(a). no. of moles of the solute Wsolute / msolute
Molarity = ----------------------------------------- = ----------------------
Volume of solution (in Litres ) 250 / 1000 (L)
Wsolute / 126
1 / 20 = --------------------------
250 / 1000
1 X 250 X 126
Wsolute = ----- -- ------------------ = 1.575 grams
20 X 1000
PROCEDURE :
(a). 1. Weigh a clean ,dry weighing bottle.
2. Add calculated weight to the pan containing the weights for the
weighing bottle .
3. Keep adding Oxalic acid to the weighing bottle till the weight in the pan is
balanced with the weight of the weighing bottle + Oxalic acid.
4. Transfer Oxalic acid to the standard measuring flask & approximately
100 ml of water. Shake the flask thoroughly to dissolve the solid. Add
water to make the volume upto 250 ml.
5. Wash the burette with water & rinse it with the given KMnO4 solution.
6. Fill the burette with KMnO4 solution & clamp it. Note down the initial
reading of the burette ( Upper meniscus ).
7. Wash the pipette with water & pipette out 10 ml standard Oxalic acid
solution in the conical flask.
8. Add 1 test tube dilute H2SO4 to the conical flask & heat the contents to
60-70 0C.
9. Run down the solution from the burette to the conical flask till the colour of
the solution changes to light pink.
10. Note down the final reading of the burette. Find out the volume of KMnO4
used by subtracting initial reading from the final reading of the burette.
11. Repeat the experiment to get the concordant readings.
OBSERVATION TABLE :
CONCORDANT READING = -----------
CALCULATIONS (b) :
M KMnO4 X V KMnO4 M oxalic acid X V oxalic acid
--------------------------- = ---------------------------------
2 5
M oxalic acid X V oxalic acid X 2
M KMnO4 = ---------------------------------------
5
Strength of KMnO4 solution = M KMnO4 X Molar mass of KMnO4 ( i.e.158g)
= _____ g/L
RESULT : (a) 250 ml of M /20 Oxalic acid standard solution is prepared & used
to determine the molarity & strength of given KMnO4 solution
titration.
(b) The Molarity & Strength of the given KMnO4 solution is _______
& _______ respectively.
PRECAUTIONS :
- There should be no air bubbles in the burette.
- Solution from the burette should be added in drops & should not run too fast.
- Always read the upper meniscus in the case of coloured solution & lower in the case of colourless.
- Titration flask should not be rinsed every time .
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