Conductometric Titrations
Submitted to: • •
Madam Arjumand Madam Aashi
Subject: Applied chemistry lab - II
Date: 8 June 2009
Department of Chemical Engineering University of Engineering and Technology Lahore
Submitted by: 1.
Muhammad Usman
2.
T A H IR
(08 - Chem-02-B)
Mehmood
(08 - Chem-16-B)
3.
SAQIB
4.
Sameullah
5.
Allah Ditta Khizar
6.
Faraz Naeem
(08 -Chem-118-B)
7.
Syed M. Hanan
(0 8- Chem-84- B)
8.
LIAQUAT ALI
9.
S H O A Ib H A Meed (08- Chem-122-B)
10. Ronald
R A O U F (08 - Chem-26-B)
Ojiambo
(08 - Chem-30-B) (0 8- Chem-42- B)
(08- Chem - 22-B)
(08- Chem-146-B)
Contents Submitted by:.......................................................... by:................................................................................................... .................................................. .........2 2 History.....................................................................................................................6
Types of titrations................................. titrations............................................................ ...................................................... ....................................... ............7 7 •
Acid-base titrations............................... titrations.......................................................... ...................................................... .................................7 ......7
•
Redox titrations............................. titrations........................................................ ................................................................... ........................................7 7
•
Complexometric Complexometric titrations................................ titrations........................................................... .......................................... .....................7 ......7 1.
PH indicato indicator.... r......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .............. ...............8 ......8
2.
Redox Redox indicato indicators.. rs....... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ..........8 .....8
4.
PH meter... meter........ .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ............. .................... ......................8 ..........8
5.
Conducta Conductance:. nce:...... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ............. .................... ......................8 ..........8
Explanation:.............................. Explanation:......................................................... ...................................................... ................................................9 .....................9 6.
Colour Colour change:.. change:....... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ........... .................. .....................9 .........9
7.
Precipita Precipitation: tion:..... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ................. ......................9 ..........9
8.
Thermom Thermometric etric titrimetr titrimetry:... y:........ .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ............... ...........9 .9
9.
Spectros Spectroscopy copy:..... :.......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ...........9 ......9
10.
Amperom Amperometry. etry...... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ............ ................... ..................10 ......10
Experiment:.............................................................................................................10 Conductance:.............................. Conductance:......................................................... ...................................................... ...............................................10 ....................10 CONDUCTOMETRIC TITRATION:.............................................................................................11 Theory:......................................... Theory:.................................................................... ...................................................... .................................................11 ......................11 GRAPHICAL
REPRESENTATION :.............................................................................................14
ALTERNATIVE 1.
METHODS OF DETERMINING THE ACID STRENGTH.......................................................16
By volumetr volumetric ic analysis analysis:.... :......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .........16 ....16
Procedure:............................................................................................................16 Calculations:.........................................................................................................16 2.
By pH method:... method:........ .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ........17 ...17
Works Cited.......................................... Cited..................................................................... ...................................................... .........................................18 ..............18 Error: Reference source not found
Summary: Titration is the method in which we determine the strength of an unknown solution by reacting it with a solution of known strength. In the late 18th century French chemists were using this technique.
Francois Francois Antoine Henri Descroizilles Descroizilles invented the 1st burette. The other important important names in Gay-Lussac . the history of titration are Karl Friedrich Mohr, Joseph Louis Gay-Lussac.
Titrations are of many types… some of the important types are… Acid base titration, redox titration, Complexometric titration etc Ther here are are many any metho ethods ds of det determ ermini ining the the end end poi point of a tit titrati ration on.. A metho ethod d is the point where reaction is completed Conductometric method. In this method we determine the point with with the help of a conduct conductome ometer ter that measur measures es the changes changes in conduc conductanc tancee of solutio solution n produced by the ions in the solution. Conductometer works on the principle of ohm’s law. If we are to find the strength of a acid then we take that acid into a beaker and dip the electrode of conductometer into the acid solution. This measures the conductance of acid. Now, we titrate this acid solution against the base of known molarity, the conductance starts decreasing. This is due to the binding of H+ ions of acid with the OH- of Base until a point is reached where conductance is minimum. When we move forward the conductance starts increasing again. This is now due to the free ions of Base present in solution. This point at which this transition occurs is called Equivalence point . At Equivalence point we measure the volume of base used to neutralize the acid ions completely in the solution. Putting these values in formula we can get the strength of acid. Alternate method to calculate the strength of acid is the simple volumetric analysis . Acid base are reacted in the presence of a pH indicator that changes its color at the completion of reaction. Again we can get the strength of acid when we know the Molarity of Base and the Volume of Base used. Another alternate method of doing this thing is the pH method. We measure the pH of acid so can calculate the concentration of positive and negative ions. At a specific temperature we already know the dissociation constant of an acid. So we can calculate the strength of acid very easily.
They ask thee about the (final) Hour― when will be its appointed time? Say: "The knowledge thereof is with my Lord (alone): none but He can reveal as to when it will occur. Heavy were its burden through the heavens and the earth. Only, all of a sudden will it come to you. They ask thee as if thou wert eager in search thereof: Say: "The knowledge thereof is with Allah (alone), but most men know not." (Al-Araf [7:187])
History The word "titration" comes from the Latin word “titulus” , meaning inscription or title. The French word titre, also from this origin, means rank . Titration , by definition, is the determination of rank or concentration of a solution with respect to water with a pH of 7 (which is the pH of pure H 2O under standard conditions).
The origins of volumetric analysis are in late-18th-century French chemistry.
1st burette: Francois Antoine Henri Descroizilles developed the first burette (which looked more like a graduated cylinder) in 1791.
Joseph Louis Gay-Lussac Developed an improved version of the burette that included a side arm, and coined the terms " pipette pipette"" and " burette burette"" in an 1824 paper on the standardization of indigo solutions
Karl Friedrich Mohr, A major breakthrough in the methodology and popularization of volumetric analysis was due to Karl Friedrich Mohr , who redesigned the burette by placing a clamp and a tip at the bottom, and wrote the first textbook on the topic1
Types of titrations Titrations can be classified by the type of reaction. Different types of titration reaction include: •
Acid-base titrations are based on the neutralization reaction between the analyte and an acidic or basic titrant. These most commonly use a pH indicator, a pH meter, or a conductance conductance meter to determine the endpoint.
•
Redox titrations are based on an oxidation-reduction reaction between the analyte and titrant. These most commonly use a potentiometer or a redox indicator to determine the endpoint.
•
Complexometric titrations are based on the formation of a complex between the analyte and the titrant. The chelating agent EDTA is very commonly used to titrate metal ions in solution.
1 Lehrbuch der chemisch-analytischen Titrirmethode (Textbook of analytical-chemical titration methods), methods), published in 1855
Measuring the Endpoint of A Titration Different methods to determine the endpoint include: indicator: This is a substance that changes color in response to a chemical change. 1. PH indicator: Example:
An acid-base indicator (e.g., phenolphthalein (e.g., phenolphthalein)) changes color depending on the pH the pH.. 2.
Redox indicators A drop of indicator solution is added to the titration at the start; when the color changes the endpoint has been reached.
Potentiometer:: 3. . Potentiometer
This is an instrument that measures the electrode potential of the solution. Example:
These are used for titrations based on a redox reaction; the potential of the working electrode will suddenly change as the endpoint is reached. meter: This is a potentiometer that uses an electrode whose potential depends on 4. PH meter: the amount of H+ ion present in the solution.
Explanation:
(This is an example of an ion-selective electrode.) electrode.) This allows the pH of the solution to be measured throughout the titration. At the endpoint, there will be a sudden change in the measured pH. It can be more accurate than the indicator method, and is very easily automated. 5. Conductance:
The conductivity of a solution depends on the ions that are present in it. During many titrations, the conductivity changes significantly. Explanation:
This changes the conductivity of the solution.) The total conductance of the solution depends also on the other ions present p resent in the solution (such as counter ions). Not all ions contribute equally to the conductivity; this also depends on the mobility of each ion and on the total concentration of ions (ionic (ionic strength). strength). Thus, predicting the change in conductivity is harder than measuring it.
Example:
For instance, during an acid-base titration, the H+ and OH- ions react to form neutral H2O. 6. Colour change:
In some reactions, the solution changes color without any added indicator. Example:
This is often seen in redox titrations, for instance, when the different oxidation states of the product and reactant produce different colours. 7. Precipitation:
If the reaction forms a solid, then a precipitate a precipitate will form during the titration. Example:
A classic example is the reaction between Ag+ and Cl- to form the very insoluble salt AgCl. An isothermal titration calorimeter uses calorimeter uses the heat produced or consumed by the reaction to determine the endpoint. This is important in biochemical in biochemical titrations, such as the determination of how substrates substrates bind bind to enzymes enzymes.. 8. Thermometric titrimetry: titrimetry:
change. Instead, the endpoint is determined by the rate of temperature change. 9. Spectroscopy Spectroscopy::
It can be used to measure the absorption of light by the solution during the titration, if the spectrum of the reactant, titrant or product is known. The relative amounts of the product and reactant can be used to determine the endpoint. 10.Amperometry
Current due to the oxidation or o r reduction of either the reactants or products p roducts at a working electrode will depend on the concentration of that species in solution. The endpoint can then be detected as a change in the current. Example:
This method is most useful when the excess titrant can be reduced, as in the titration of halides with Ag+. (This is handy also in that it ignores precipitates.)
Experiment:
To find the Strength of an acid using conductivity
method
Principle: conductivity of a solution when no. Basic principle is the changes in conductivity of ions that are the responsible for the conduction of electricity is changing.
Explanation: Conductance: This is the method in which the capability of analyte to conduct an
electrical current is monitored from ohm’s law.
Ohm’s law says that…
V = IR V = VOLTAGE I = ELECTRIC CURRENT R = ELECTRICAL RESISTANCE
CONDUCTOMETRIC
TITRATION :
The The conduc conductan tance ce method method can be employ employed ed to follow follow the cours course e of a titrat titration ion,, provided that there is a significant difference in conductance between the original solution and the reagent of the product of reaction. It is not necessary to know the cell constants, since relative values are sufficient to permit locating the equivalence point. The The conduc conductan tance ce produc produced ed by an ion ion is propor proportio tional nal to its concen concentra tratio tion n (at constant temperature), but the conductance of a particular solution will in general not vary linearly with added reagent, because of the dilution effect of water being added along with reagent added. Hydrolysis of reactants or products, or partially solubility of a precipitated product, will also cause departures from linearity.
The shape of the titration curve can be predicted easily. The concentration of each ion at any any point point in the titratio titration n is calcul calculate ated d by the usual usual method methods s based based on stoichometry, stoichometry, equilibria, and dilution.
Theory: The conductance of the solution mainly depends on two factors
1. Size Size of th the e ion ions s The conducti conductivity vity of the solution solution is inversely inversely proport proportiona ionall to the size of the ions .if the size of the ions is increasing increasing then the conductivity conductivity of the solution will decrease because the mobility mobility of the ions will decrease by increasing increasing the size of the ions. So the mobility of the hydrogen ions will be greater then the sodium ions so the conductance of the solution containing sodium ions will be less than the solution containing hydrogen ions. same principal is used here in this experiment ,initially solution contain the hydrogen ions when this solution is titrated against the base solution ,the base reacts with the acid and the number number of of the hydrogen ions go on decreasing. Finally a stag stage e reac reache hes s when when ther there e is no hydr hydrog ogen en ion ion in the the solu soluti tion on so the the conductivity decreased and remains constant. If further base is added then the number of negative ions increases and the conductivity go on increasing. The point at which the conductivity becomes constant is the equivalence point. The volume of base used at equalance point is used to calculate the molarity of acid and then the strength of acid. Consider a solution of a strong acid, hydrochloric acid, HCl for instance, to which a solution of a strong base, sodium hydroxide NaOH, is added. The reaction occurs. For each amount of NaOH added equivalent amount of hydrogen ions is removed. Effectively, the faster moving H+ cation is replaced by the slower moving Na+ ion, and the conductivity of the titrated solution as well as the measured conductance of the cell fall. This continues until the equivalence point is reached, at which we have have a solu soluti tion on of sodi sodium um chlo chlori ride de,, NaCl NaCl.. If more more base base is adde added d an increase in conductivity or conductance is observed, since more ions are bein being g adde added d and and the the neut neutra rali liza zati tion on reac reacti tion on no long longer er remo remove ves s an appreciable number any of them. Consequently, in the titration of a strong acid with a strong base, the conductance has a minimum at the equivalence point. This minimum can be used instead of an indicator dye to determine the endpoint of the titration. Conductometric titration curve that is a plot of the measured measured conductance conductance or conductiv conductivity ity values values against against the number number of milliliters of NaOH solution
2. Temperatu Temperature: re:
By increasing the temperature, the mobility of the ions in the solution will increase. So temperature has a direct effect on conductance of solution. E.g. by increasing the temperature the conductance will increase and vice versa.
Procedure: 1. 2. 3. 4. 5. 6.
100 Ml Ml of acid acid was was taken taken in beak beaker. er. Solution Solution was was kept at room room temperatur temperature e for at least least 10 minutes. minutes. Then Dip Dip the electr electrode ode of conduc conductome tometer ter in solutio solution. n. Measure Measure the the initial initial conduc conductanc tance e of solution solution.. First First reading reading of of conduct conductomet ometer er was was noted. noted. Then this solution was titrated titrated against against the Base Base solution solution of known strength strength using burette. 7. Observe the the change in conductance conductance of acid solution solution after every 5 ml addition addition of base. 8. Plot these these values values to to find the equiva equivalenc lence e point. point. 9. Volume Volume of base used used till the the equivalenc equivalence e point is the the volume which which is required to fully neutralize the acid.
Calculations:
Acid
Base
M1 V1 = M2 V2 M=molarity v=volume used M1=M2V2V1
Volume of Base used (mL)
Conductance
0
28.2
5
28
10
27.7
15
27.2
20
26.6
25
21.8
30
20.6
35
19.4
40
18.6
45
17.6
55
16.6
65
13.6
75
12
85
10.6
95
9
105
7.8
110
7.2
115
6.6
120
6
130
5
135
5.1
140
5.3
150
5.9
160
6.3
170
6.8
185
7.4
M1=M2V2V1 M1=0.1×130100 M M1=0.13 M
Strength of acid = molarity x molecular wt. =0.13 X 36.5= 4.745 g/mL
GRAPHICAL
REPRESENTATION :
APPLICATIONS OF CONDUCTOMETRIC TITRATIONS Acid-base titrations redox titrations are known to us in which commonly indicators are used to locate the end point e.g., methyl orange, phenolphlthalene for acid base titrations and starch solutions for iodemetry type redox process. How ever electrical conductance conductance measurement can be used as a tool to locate the end point. 1. This method can be used with much diluted solutions 2. This method can be used with colored or turbid solutions in which end point can not Be seen by eye 3. This method can be used in which there is no suitable indicator 4. has many applications, i.e. it can be used for acid base, redox, precipitation, or complex titrations
a. Determin Determination ation of sulphur sulphur dioxide dioxide in air polluti pollution on studies studies b. Deter Determin minati ation on of soap soap in oil oil c. Determin Determination ation of accel accelerato erators rs in rubber rubber d. Determin Determination ation of total total soap in in latex latex e. Specif Specific ic conduc conductanc tance e of water water
ALTERNATIVE
METHODS OF DETERMINING THE ACID STRENGTH
1. By volumet volumetric ric analysi analysis: s: Experiment: To determine the strength of an acid
Principle: It is an acid base titration.
Apparatus: 1. Bure Burett tte e 2. Conica Conicall Flask Flask
3. Pipe Pipett tte e 4. Burett Burette e Stand Stand
Indicator: 1-2 drops of Phenolphthalein
Chemical reaction: HCL+NaOH→NaCL+H2O
End point: Light pink color
Procedure: 1. 2. 3. 4. 5.
Take 10ml 10ml of acid acid in the conic conical al flask flask with the the help of a pipette pipette.. Add 1-2 drops drops of indicato indicatorr in it. Solution’s Solution’s color color was was changed changed to pink. Take the the base base of known known molarit molarity y in buret burette. te. Titrate Titrate the acid acid solution solution against against the the base of known known molarity. molarity. Calcul Calculate ate the volum volume e of base base used used to neutr neutrali alize ze the acid as we see see that that end point is reached. 6. Perform Perform following following calcula calculation tions s to calculate calculate the strength strength of acid…
Calculations: Acid M1 V1 = M2 V2 M=molarity v=volume used
Base
M1=M2V2V1
1. By pH pH metho method: d: Experiment: To determine the strength of an acid
Principle: Strength of acid is calculated from the pH of solution.
Chemicals and apparatus: 1. PH meter meter 2. Pipe Pipett tte e solutions (acid & base)
3. Therm Thermome ometer ter 4. Chem Chemic ical al
Procedure: As we know that Ka=H+A-HA K a has a fixed value at a given temperature that is given in literature. H+ Can be measured by using ph apparatus Also A- can be found as For monobasic acid H+=ASo initial concentration of acid can be calculated as HA=H+A-Ka
Works Cited Board, p. T. (2009). Chemistry I. punjab Text Book Board. encyclopedia Britinica. Britinica . (n.d.). Retrieved 10 2009, from http://www.britannica.com/EBc http://www.britannica.com/EBchecked/topic/13169 hecked/topic/131698/conductometr 8/conductometry y ewing, g. w. Instrumental Instrumental Methods of Chemical Analysis. Mcgrawhil publisher. Ewing, G. W. Instrumental Instrumental Methods of Chemical Analysis. McGrawhill Publisher. J.Welehor, F. Standard Methods of Chemical Analysis. D.VAN Nostrand company, INC. www.wikipedia.org. www.wikipedia.org. (n.d.). Retrieved 10 8, 2009, from wikipedia the free encyclopedia: http://en.wikipedia.org/wiki/Titratio http://en.wikipedia.org/wiki/Titration n
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