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A. TITLE
Acidi -Alkalimetry
B. DATE OF EXPERIMENT
Tuesday, 22nd November 2011, at 07.30 am
C. FINISH OF EXPERIMENT
Tuesday, 22nd November 2011, at 11.30 am
D. OBJECTIVES
1. Making and determine standarization of base solution.
2. Determine precentage of H2SO4 in accu zuur.
E. BASIC THEORY
Titration is a procedure used to determine the amount of reactant present in a
chemical solution; it is used to cause a reaction in such a way that the reactant is
not in excess.
The kinds of titration :
1. Acid base titration
2. Redox titration
3. Complex formation titration
4. Precipitation titration
Use an indicators in titration
This method relies on observing a color change in the solution. Indicators are
weak organic acids or bases that are different colors in their dissociated and
undissociated states. Because they are used in low concentrations, indicators do
not appreciably alter the equivalence point of a titration. The point at which the
indicator changes color is called the end point.
Table of Commen Acid-Basa Indicators
Indicator pH range Quantity per 10 mL Acid Base
Thymol Blue 1.2-2.8 1-2 drops 0.1% soln. in aq red yellow
Pentamethoxy red 1.2-2.3 1 drop 0.1% soln. in 70%
alc.
red-
violet
Colorles
s
Tropeolin OO 1.3-3.2 1 drop 1% aq. soln. red Yellow
2,4-Dinitrophenol 2.4-4.0 1-2 drops 0.1% soln. in
50% alc.
colorles
s
Yellow
Methyl yellow 2.9-4.0 1 1 drop 0.1% soln. in 90%
alc.
red Red
Methyl orange 3.1-4.4 1 drop 0.1% aq. soln. red
orange
red orange
Bromphenol blue 3.0-4.6 1 drop 0.1% aq. soln. yellow blue-
violet
Tetrabromphenol
blue
3.0-4.6 1 drop 0.1% aq. soln. yellow blue
p-Nitrophenol 5.0-7.0 1-5 drops 0.1% aq. soln. colorles
s
yellow
Azolitmin 5.0-8.0 5 drops 0.5% aq. soln. red yellow
Phenol red 6.4-8.0 1 drop 0.1% aq. soln. yellow red
Neutral red 6.8-8.0 1 drop 0.1% soln. in 70%
alc
red yellow
Rosolic acid 6.8-8.0 1 drop 0.1% soln. in 90%
alc
yellow red
Cresol red 7.2-8.8 1 drop 0.1% aq. soln. yellow red
α-
Naphtholphthalein
7.3-8.7 1-5 drops 0.1% soln. in
70% alc.
rose Green
Tropeolin OOO 7.6-8.9 1 drop 0.1% aq. soln. yellow rose-red
Thymol blue 8.0-9.6 1-5 drops 0.1% aq. soln. yellow Blue
Phenolphthalein 8.0-10.0 1-5 drops 0.1% soln. in
70% alc.
colorles
s
Red
α-Naphtholbenzein 9.0-11.0 1-5 drops 0.1% soln. in
90% alc.
yellow Blue
Thymolphthalein 9.4-10.6 1 drop 0.1% soln. in 90%
alc.
colorles
s
Blue
Nile blue 10.1-
11.1
1 drop 0.1% aq. soln. blue red
Alizarin yellow 10.0-
12.0
1 drop 0.1% aq. soln. yellow Lilac
Salicyl yellow 10.0-
12.0
1-5 drops 0.1% soln. in
90% alc.
yellow orange-
brown
Titrimetric analysis or volumetric analysis is a quantitative analysis by reaction
of a substance to be analyzed with standard solution (standard) which has been
accurately known concentration, and reaction between the substance being analyzed and
the standard solution took place quantitatively.
One of the main group in the classification of titrimetric analysis is the
neutralization reaction or acidimetry and alkalimetry. Alkalimetri acidi method used
to determine the concentration of acid or base number is not known.
Acidimetry a titration technique with acid as titrant, while alkalimetry a titration
with a base as the titrant (Christian 1994). Experiment of acididi-alkalimetry aims is
to determine the concentration of acid or base titrat with previously standardized
base or acid used as titrat. Substances used in the titrimetric must have high
purity. So before use, reagent concentration and volume must be known precisely by
means of standardization (Harjadi 1986).
Standardization is the process by which the concentration of a solution is
accurately. The solution that can use for standardization process called primary
standard. Primary standard should have the following characteristics:
1. It should be readily available in a pure form or in state of known purity at a
reasonable cost. In general, the total amount of impurities should not exceed
0,01 to 0.02%, and it should be possible to test for impurities by qualitative
tests of known sensitivity.
2. The substance should be stable. It should be easy to dry and should not be so
hygroscopic that it takes up water during weighing. It should not lose weight
on exposure to air. Salt hydrates are not normally employed as primary
standards.
3. It is desirable that the primary standard have a reasonably high equivalent
weight in order to minimize the consequences of errors in weighing.
(Underwood )
The formula is
V1 x N1 = V2 x N2
Where:
V1 = Volume of penetration solution (ml)
N1 = Normality of penetration solution (gram equivalents / liter)
V2 = volume of titrated solution (ml)
N2 = Normality of titrated solution (gram equivalents / liter)
End Point titration indicated by the color change indicator, equivalent point
occurs at the trajectory (range) pH indicator. the stoichiometry, acid or hydrogen ions
and base hydroxide ions tepat habis bereaksi at the equivalence point.
H+ + OH- H2O
Acid equivalence = Base equivalence
Phenolphthalein and Methyl Orange Indicators
The well-known indicator phenolphthalein (below) is a diprotic acid and is
colorless. It dissociates first to a colorless form and then, on losing the second
proton, to an ion with a conjugated system; a red color result.
Methyl orange, another widely used indicator, is a base and is yellow in the
molecular form. Addition of a proton gives a cation which is pink in color.
Calculation of Percent Purity
To analyze a sample of unknown purity the analyst weighs accurately a portion
of the sample, dissolves it appropriately, and titrates it with a standard solution. If the
titration reaction is
aA + Tt product
Where a molecules of the analyte, A, react with t molecules of the titrant, T, then at
the equivalence point
t mmol A = a mmol T
mmol A = at
x mmol T
If V and M represent the volume (mL) and molarity (mmol/mL), respectively, of the
titrant, and MWA is the molecular weight of the analyte, then
mmol A = at
x V x M
mg A = at
x V x M x MWA
The precent by weight of A is
% A = mganalytemg sample
x 100
% A = atxV (mL ) x M (mmolmL
x)MW A(mg /mmol)
weight of sample (mg)x 100
F. CHEMICALS AND EQUIPMENT
Chemicals:
1. H2C2O4.2H20 : 0,6008 g
2. Accu Zuur
3. NaOH
4. Phenolphthalein indicators
5. Methyl orange
6. Aquadest
Equipment:
1. Volumetric Flask 100 mL
2. Erlenmeyer 100 mL
3. Graduated Cylinder 10 mL
4. Stative
5. Burette
6. Volumetric Pipette
7. Pipette
8. Spatula
9. Funnel
10. Beaker glass
G. PROCEDURE
Standardization NaOH Solution ± 0,1 N With Oxalate Acid as Primary
Standard.
0,6008 gram H2C2O4.2H2O
Pouring into volumetric flask 100 mlDisolving with aquades and dilute untile boundariesShaking well
Standard solution
Indicator change color
Pipettte 10 mlPouring into conical flaskAdding 25 ml aquadesAdding 3 drops of PP indicatorTitrate with NaOH solution Stop when the changes of indicators colorRead and write the number at initial and end titrationDetermining volume NaOHRepeating until 3 times with the same volume of H2C2O4.2H2OCalculate average concentration of NaOH solution
Determining percentage of H2SO4 in accu zuur
2 ml accu zuur
Dencity of accu zuur
Pouring into piknometer with volumetric pipette 2 mlClose the piknometer soonWeight again piknometer + accu zuur
100 ml aquadest in volumetric flask
Indicator change color
Pouring accu zuur with the funnel Rinse the remnant Dilute until boundariesLet 1-2 our until reach the room temperaturePippete 10 ml solutionPouring into conical flaskAdding drops of metil orange indicatorTitrate with NaOH 0,1 M until there is color changeRepeating until 3 times and calculate amount of H2SO4 in accu zuur
H. EXPERIMENT DATA
Standardization NaOH Solution ± 0,1 N With Oxalate Acid as Basic Solution.
NoScale Volume
NaOH (ml)N NaOH
(eq/L)Titrator
Initial (mL) End (mL)1. 0 8,8 8,8 O,1084 Romadhoni
2. 8,8 17,8 9 0,1060 Nurhalimah
3. 17,9 26,9 9 O,1060 Istiana
Detemining percentage of H2SO4 in accu zuur
NoScale Volume
NaOH (ml)% H2SO4 Titrator
Initial (mL) End (mL)1. 33,3 49,3 16 63,90 Nuurhalimah 2. 31,2 48,9 17,7 70,53 Istiana 3. 16 30,8 14,8 58,99 Romadhoni
I. ANALYSIS
Standardization NaOH Solution ± 0,1 N With Oxalate Acid as Primary
Standard.
Before doing titration Washing burette with NaOH solution in order to make
NaOH concentration is not changed by a drop of water that left.
H2C2O4.2H2O solution is used as the primary standard solution because this
solution is not hygroscopic, so it takes up water during weighing. And it has high
equivalent weight, so minimize the consequences of error in weighing.
In the standardization of NaOH solution, the addition of phenolphthalein
indicators that serve to know the equivalent point titration. Phenolphthalein indicator
is used because this standardization is a weak acid titration (H2C2O4.2H2O) and
strong base (NaOH) so the equivalent point above 7 and in trajectory indicator of
phenolphthalein is 8.0 to 9.6.
Phenolphthalein indicator classified as weak acid, in condition not ionized this
indicator is colorless. So when phenolphthalein indicator was added in H2C2O4.2H2O
solution, there is no changes color. Phenolphthalein indicator in base condition
given light color because of the anion.
The reaction is:
H2C2O4.2H2O (aq) + 2 NaOH (aq) Na2C2O4 (aq) + 4 H2O (l)
In our experiment we get the normality of NaOH when the volume 8,8 mL is
O,1084 eq/L.
Calculation:
m H2C2O4.2H2O = 0,6008 gram
V = 0,1 L
N = 0,6008gram
63gram /eq .0,1L
N = 0,0954 eq/L
V NaOH x N NaOH = V H2C2O4.2H2O x N H2C2O4.2H2O
0,0088 L x N NaOH = 0,01 L x 0,0954 eq/L
N NaOH = 0,1084 eq/L
The normality of NaOH when the volume 9,0 mL is 0,1060 eq/L.
V NaOH x N NaOH = V H2C2O4.2H2O x N H2C2O4.2H2O
0,009 L x N NaOH = 0,01 L x 0,0954 eq/L
N NaOH = 0,1060 eq/L
The normality of NaOH when the volume 9,0 mL is 0,1060 eq/L.
V NaOH x N NaOH = V H2C2O4.2H2O x N H2C2O4.2H2O
0,009 L x N NaOH = 0,01 L x 0,0954 eq/L
N NaOH = 0,1060 eq/L
So the averege normality of NaOH is
Average N NaOH = 0,1084N+0,1060N+0,1060N
3
= 0,1068 eq/L
Determining percentage of H2SO4 in accu zuur
Determining H2SO4 solution in the accu zuur, addition of methyl orange
indicator is to determines the equivalent point in the titration. Methyl orange is used
because for titration H2SO4 with NaOH has a pH below 7 at the equivalent point and
in trajectory methyl orange indicator is 3.1 to 4.4. Methyl orange is the sodium salt
of a sulphonic acid. Anion in alkaline environment gives a yellow color. While in
acid condition methyl orange is a weak base and containing H+ ions, there is a
changes in the structure and gives the red color of the ions.
The reaction is:
H2SO4 (aq) + NaOH (aq) Na2SO4 (aq) + H2O (l)
The mass of sample of H2SO4 is
Dencity = massVolume
= 87,5485g−21,8904 g
50ml
= 1,3132 g/mL
mass of sample = 2 mL x 1,3132 g/mL = 2,6264 g
The percentage H2SO4 when volume of NaOH 16 mL is 63,90%.
V H2SO4 x N H2SO4 = V NaOH x N NaOH
0,01 L x N H2SO4 = 0,016 L x 0,1068 eq/L
N H2SO4 = 0,1709 eq/L
In 100 ml = 2 x 100 x 0,1709
= 34,18 mmol
mmol = mgBM
mg = 34,18 x 49
= 1674,82 = 1,6748 g
% H2SO4 = 1,6748g2,6264 g
x 100
= 63,90 %
The percentage H2SO4 when volume of NaOH 17,7 mL is 70,53 %.
V H2SO4 x N H2SO4 = V NaOH x N NaOH
0,01 L x N H2SO4 = 0,0177 L x 0,1068 eq/L
N H2SO4 = 0,1890 eq/L
In 100 ml = 2 x 100 x 0,1890 N
= 37,80 mmol
mmol = mgBM
mg = 37,80
= 1852,2 = 1,8522 g
% H2SO4 = 1,8522g2,6264 g
x 100
= 70,53 %
The percentage H2SO4 when volume of NaOH 14,8 mL is 58,99 %.
V H2SO4 x N H2SO4 = V NaOH x N NaOH
0,01 L x N H2SO4 = 0,0148 L x 0,1068 eq/L
N H2SO4 = 0,1581 eq/L
In 100 ml = 2 x 100 x 0,1581 N
= 31,62 mmol
mmol = mgBM
mg = 31,62
= 1549,38 = 1,5494 g
% H2SO4 = 1,5494 g2,6264 g
x 100
= 58,99 %
So the averege percentage of H2SO4 is
Average % H2SO4 = 63,90+70,53+58,99
3
= 64,47 %
The percentage of H2SO4 in accu zuur is 64,47%, but we don’t know the percentage
of H2SO4 certain. Because in our accu zuur that we use there is no label of
compotition of accu zuur.
J. DISCUSSION
Application: Determining percentage of H2SO4 in Accu Zuur
In the determining percentage of H2SO4 there is a factor that influence the data
experiment:
There are differences between volume of NaOH that use. In the first experiment
we need NaOH 16 mL. In the second experiment we need NaOH 17,7 mL and in
the third experiment, we need NaOH 14,8 mL. It caused by in the second
experiment, when we add NaOH solution in the analyte the volume is pass the
equivalent point. In the first and second experiment we use NaOH in the bottle 2,
but when we want to continue in the last titration, NaOH solution in bottle 2 is
fresh out. So in a pinch we use NaOH solution in the bottle 3.
K. CONCLUSION
Based on our experiment normality average NaOH solution is 0,1068 eq/L
Based on our experiment percentage of H2SO4 in accu zuur is 64,47%
L. ANSWER OF QUESTION
1. Why in the manufacture of NaOH solution had to use hot water?
Answer:
The aim that have been boiling the water used is to avoid an explosion, because
the reaction of alkali metal (Na) is exothermic and alkali metals are also easily
react with water.
2. What's the difference between:
Answer:
a. Standard solution and primary solution?
Primary solution: where the solution concentration is known from the results
of the weighing and dilution, the concentration is determined from the
calculation
Standard solution: where the solution concentration was determined with
accuracy.
b. Acidimetry and alkalimetri
Acidimetry is a neutralization titration technique with acid as titrant.
Alkalimetri is a neutralization titration with a base as the titrant.
3. Give reasons for the use of indicators in the titration of the above!
Answer:
Phenolphthalein indicator is used because this standardization is a weak acid
titration (H2C2O4.2H2O) and strong base (NaOH) so the equivalent point above 7
and in trajectory indicator of phenolphthalein is 8.0 to 9.6.
Methyl orange is used because for titration H2SO4 with NaOH has a pH below 7 at
the equivalent point and in trajectory methyl orange indicator is 3.1 to 4.4.
4. 1.2 grams NaOH and Na2CO3 dissolve in sample and titrated with 0.5 N HCl
with indicator pp. After addition of 30 mL of HCl solution became
colorless. Then methyl orange indicator was added and titrated again with
HCl. After addition of 5 mL of HCl solution became colorless. How much the
percentage of Na2CO3 and NaOH in the sample?
Answer:
Known :
Mass of NaOH : 1,2 grams
Mass of Na2Co3 : 1,2 grams
N of HCl : 0,5 N
V1 HCl : 30 mL
V2 HCl : 5 mL
Asked :
% Na2CO3…?
% NaOH…?
Solution
% Na2CO3
N Na2CO3 =
mgNa2CO 3
BENa2CO 3 .Volx 1
=
1200mg842x10
= 2,8 N
Equivalence of Na2CO3 = Equivalence HCl
Equivalence of Na2CO3 = NHCl x VHCl
= 2,8 N x 60 mL
= 168 miliequivalence
gram Na2CO3= equivalence x Equivalence Weight x 10
= 168 x 84 / 2 x 10
= 70560 mg
Ratio of Na2CO3 =
70560
1,2x 103100 %
= 58,8
%NaOH :
NNaOH =
mgNaOHBENaOH .Vol
x 1=
1200mg401x10
= 3 N
Equivalence NaOH = Equivalence HCl
Equivalence NaOH = N x V
= 3 N x 60 mL
= 180 miliequivalence
gram NaOH = Equivalence x equivalence Weight x 10
= 180 x 40 / 1 x 10
= 72000 mg
Ratio NaOH =
72000
1,2x 103100 %
= 60 %
4. At which pH can color changes of pp indicators?
At Ph of 8,0-9,6
M. REFERENCES
Day,R.A.,Underwood,A.L.(1991).Quantitative Analysis (Sixth ed).New York:
Prentice Hall.
Tim Penyusun.(2011).Panduan Praktikum Kimia Analitik 1 Dasar-dasar Kimia
Analitik.Surabaya:Jurusan Kimia FMIPA UNESA.
http://chemistry.about.com/od/acidsbases/a/aa082304a.htm.Access at 25nd
November 2011, at 06.30 pm
http://chemistry.about.com/od/acidsbases/a/Acid-Base-Indicators.htm.Access at
25nd November 2011, at 06.30 pm
ATTACHMENT
Picture
TitaratorBefore titration After Titration
H2C2O4.2H2O + Phenolphthalein Indicator
Result experiment 1NaOH + H2C2O4.2H2O + Phenolphthalein Indicator
Rhomadhoni
Result experiment 2NaOH + H2C2O4.2H2O + Phenolphthalein Indicator
Nurhalimah
Result experiment 3NaOH + H2C2O4.2H2O + Phenolphthalein Indicator
Istiana Yuli Purwati
Standardization NaOH Solution ± 0,1 N With Oxalate Acid as Primary Standard
Picture
TitaratorBefore titration After Titration
H2SO4 + Methyl Orange Indicator
Result experiment 1H2SO4 + Methyl Orange
Indicator + NaOH
Nurhalima h
Result experiment 2H2SO4 + Methyl Orange
Indicator + NaOH
Istiana Yuli Purwati
Result experiment 3H2SO4 + Methyl Orange
Indicator + NaOH
Rhomadhoni
Determining Percentage of H2SO4 in Accu Zuur