Acid Base Titrations
Physical Science
Keith Warne
Mole Calculations
GIVEN
ASKED
MASS
VOLUME
MASS
MOLAR
MOLES
RATIO
CONCENTRATION
Number
Of
particles
VOLUME
MOLES
Number CONCENTRATION
Of
particles
Titration Calculations.
(COOH)2.2H2O + 2NaOH --> Na2(COO)2 + 4H2O
OXALIC ACID STANDARD SOLUTION
(COOH)2.2H2O
 Unknown Base (NaOH)
?
………..g
cb = ………….. mol.dm-3
Standard Solution
A standard solution is one for which
the concentration is precisely
known.
Since
c=
n(solute)/v(solution)
= m/
Mass is determined
accurately using an
electronic balance.
1.60g
solute
Mr V
Needed:
•
The number of moles of solute
(Mass)
• The volume of solution.
These values must be accurately
determined.
Volume is measured
using a
Volumetric flask.
• 250 cm3
• 100 cm3
• 200 cm3
250 cm3
Weighing Technique
Procedure - Weighing by difference.
1. Zero scales and clean the pan.
2. Weigh the weighing container.
3. Add (approximately) the
required amount of salt. Take
care not to drop any salt onto
the pan.
4. Transfer the salt to a clean
beaker.
5. Reweigh the weighing
container.
6. Subtract the final mass of the
container from the mass of salt
and container to give the mass
of salt transferred to the beaker.
(COOH)2
2.45g
Mass is determined accurately
using an balance (electronic
or triple beam).
• Possible accuracies of 0.1 0.0001g
Results:
Mass salt + container: …………
Final Mass container: …………
Mass salt transferred:
Making a standard solution.
1.
Rinse a clean & dry 100 cm3 beaker
with a little distilled water.
2.
Transfer the correctly weighed amount
of salt to the beaker. Ensure NO SALT
IS Lost
3.
Add distilled water to the salt and stir
gently with a glass rod until all salt is
dissolved. DO NOT REMOVE THE
ROD FROM THE SOLUTION NOR
ALLOW ANY DROPS OF SOLUTION
TO ESCAPE.
4.
Add ALL the solution to a volumetric
flask via funnel. Ensure glass rod and
beaker are thoroughly rinsed. (Include
rinsings)
5.
Add enough solvent to bring the level
up to the mark.
solute
………..g
Making a standard solution.
1. Use a dropper to bring
the level up to the mark.
Drag here
2. The BOTTOM of the
meniscus must JUST
TOUCH THE LINE of
the flask.
3. The flask should then be
inverted at least 10 times
to ensure thorough
mixing.
The bottom of
the meniscus
must JUST touch
the line!!!
Titration Proceedure.
1.
Rinse# the burette with distilled water and then with small
quantities of the STANDARD ACID solution.
2.
Fill the burette with the standard ACID solution.
3.
Take the zero reading. Does not have to be ZERO.
4.
Rinse # a clean conical flask with DISTILLED WATER.
5.
Rinse # a clean pippette with the unknown base solution.
6.
Pippette 25cm3 of the unknown base solution into the
conical flask.
7.
Add 3-5 drops of a suitable indicator to the conical flask.
8.
Titrate the acid against the base until the FIRST
PERMANENT COLOUR CHANGE.
9.
Note down the volume of acid and repeat this procedure with
a fresh conical flask until CONCORDANT RESULTS are
obtained. ~0.1 cm3.
ACID STANDARD
SOLUTION
unknown BASE
Titration Calculations.
a ACID + b BASE --> salt + water
ACID STANDARD SOLUTION
AT THE END POINT
25cm3
=
0.025dm3
moles ACID = a
moles BASE
b
CaVa = a
CbVb
b
C(mol.dm-3)
V (dm-3)
unknown BASE
Titration Calculations
Conc of acid = ? x
(trying to find)
Volume of acid –
burette = average
titre
CaVa
CbVb
Conc of base= your
standard soln.
Worked out.
=
a
b
Molar ratio from balanced
reaction
a = acid coefficient (2)
b = base coef.
(1)
Vol. of base=
pippette (25cm3)
(1)Na2 CO3 + 2 HCl  2NaCl + H2O + CO2
Solve for x
Determination of unknown base.
A standard oxalic acid solution is made up using 6.4g in 1l.
25cm3 of an unknown sodium hydroxide solution required
22,4 cm3 of the standard acid to reach end point. Calculate
the concentration of the unknown base.
OXALIC ACID (KNOWN/Standard)
 Unknown Base (NaOH)
(COOH)2.2H2O
 Mr = (2(12+32+1)+2(18)= 126 g.mol-1
 6.4g in 1l (1dm3)
 Moles(ACID) = m/Mr
= 6.4/(126)
= 0.051 in 1dm3
 Concentration (ACID) = n/v

= 0.051/1

= 0.051M
Titration Calculations.
(1)(COO)2.2H2O + 2NaOH --> Na2(COO)2 + 4H2O
OXALIC ACID STANDARD SOLUTION
One mole of acid
.: n(acid)
1
 Unknown Base (NaOH)
reacts with
:
:
(COO)2.2H2O
 Mr = (2(12+32+1)+2(18)= 126
 6.4g in 1l (1dm3)
 Moles(ACID) = m/Mr
= 6.4/(126)
= 0.05mol/1dm3
 Concentration (ACID) = 0.05 M
2 moles of base.
n(base)
2
AT THE END POINT
CaVa
=
CbVb
1
2
2 x n(Acid) = n(Base)
2xcava = cbVb
2 x (0.054) (22.4x10-3)=cb(25x10-3)
cb = 0.0038 mol.dm-3
Titration Example
 If 22.3 cm-3 of a standard hydrochloric acid solution were
required to reach end point with 25 cm-3 of an unknown
sodium carbonate solution, what is the concentration of
the sodium carbonate solution?
Titration Example
 If 22.3 cm-3 of a standard hydrochloric acid solution
(0.15 M) was required to reach end point with 25 cm-3 of
an unknown sodium carbonate solution, what is the
concentration of the sodium carbonate solution?
2HCl + Na2CO3  2NaCl + CO2 + H2O
CaVa
CbVb =
1
2
(0.15) (0.0223)
1
=
Cb (0.025)
2
Cb
=
2*(0.15) (0.0223) = 0.268 M
1* (0.025)
Name
of indicator
Methyl Orange
Bromothymol Blue
Phenolphthalein
Colour
acid
Colour
base
pH
range
Red
Yellow
... - ....
Yellow
Blue
.... - ...
Clear
Red
.... - ....
Name
of indicator
Methyl Orange
Bromothymol Blue
Phenolphthalein
Colour
acid
Colour
base
pH
range
Red
Yellow
3-4
Yellow
Blue
6-8
Clear
Red
8 - 10
....
pH ...
0
Amount of ............ added
STRONG
BASE
14
pH 7
STRONG
ACID
0
Amount of BASE added
STRONG ACID WEAK BASE
 The end
END
POINT
STRONG
ACID
WEAK
BASE
point has a
pH lower
than 7
because
the SALT
of a
STRONG
acid and a
weak base
is
ACIDIC!!
WEAK ACID & STRONG BASE
 The pH at
STRONG
BASE
pH at end
point
WEAK
ACID
END
POINT
50.00cm3
the end
point is
HIGHER
than 7
because
the salt of a
weak acid
and
STRONG
base is
BASIC.
WEAK BASE & WEAK ACID
WEAK
BASE
pH at end
point
WEAK
ACID
END
POINT
50.00cm3
 Due to the
gradual
change in pH
the END
POINT is
difficult to
identify.
 These
titrations
have only
limited use.
14
Strong base
Pink
Phenolphthalien
pH 7
Weak acid
STRONG BASE
WEAK ACID
Weak base
Colourless
Blue
Bromothymol blue
Yellow
STRONG BASE
STRONG ACID
WEAK BASE
STRONG ACID
Methyl Orange
Strong acid
0
Red
Moles of base added
Strong acid/strong base
Bromothymol blue
Strong acid/weak base
Methyl orange
Weak acid/strong base
Phenolphthalein