Introduction to titration MANIK

1. Introduction to Titration
Course Code: PHARM 1206
Prepared By
Md. Imran Nur Manik
Lecturer
Department of Pharmacy
Northern University Bangladesh

2. Key Concepts: Titration (Volumetric analysis)
Volumetric analysis is also referred to as titrimetric analysis.
Volumetric analysis refers to a quantitative chemical analysis of a solution using accurate volumes.
Volumetric analysis requires:
(i) Extremely clean glassware
(ii) Great care in taking and recording measurements
To be used in volumetric analysis, a reaction must:
a) be a simple reaction which can be expressed by a chemical equation (that is, there must be simple stoichiometric, or
mole, ratio of reactants and products so that the equivalence point of the reaction can be determined)
b) be instantaneous
c)show a marked change in some chemical or physical property of the solution at the equivalence point (an indicator can
be used to indicate the end point of the reaction by changing color as close as possible to the equivalence point of the
reaction)
Volumetric glassware to be used:
(i) Volumetric flask: used to prepare and store a standard solution of known concentration.
(ii) Pipette: used to deliver an accurate volume (aliquot) of solution.
(iii) Burette (buret): used to deliver and measure the volume of a solution.
 Aliquot: an accurately known volume of solution (delivered by pipette).
 Titration: the process of adding one solution to another until the reaction is just completed.
 Titrant: solution of known concentration.
 Titrate: solution being titrated in order to determine its concentration.
 Titre: total volume of solution delivered by the burette (buret) to reach the end point of the titration.
 Concordant titres: The volumes of three or more titres lie within 0.05 mL (or 1 drop) of each other.
Introduction to the Glassware
There are two types of glassware you will be using:
Volumetric glassware: glassware calibrated to either contain an accurate volume of solution or to deliver an accurate volume
of solution.
Non-volumetric glassware: glassware that has not been calibrated to contain or deliver a volume of solution.
Volumetric Glassware (Glassware that has been calibrated.)
Volumetric flask: Flat-bottomed, pear-shaped flask with a single calibration mark etched onto its long neck and calibrated
to contain an accurate volume of solution1
when filled to the mark. The volume of solution is only accurate at the
temperature printed on the flask.
Pipette: Long narrow tube with a cylindrical bulb in the middle with one calibration mark etched onto the tube and
calibrated to deliver an accurate volume of solution when filled to the mark. The volume of solution is only accurate at the
temperature printed on the pipette.
Burette (buret): Long cylindrical tube with graduation marks along its length, closed at the bottom by a stopcock and
calibrated to deliver a volume of solution with accuracy from one graduation mark to another. The volume of solution is
only accurate at the temperature printed on the burette.
Non-volumetric Glassware (Glassware that has NOT been calibrated.)
Glass funnel: Used to facilitate pouring of solution into the burette.
Beaker: Used to facilitate the acquisition of an aliquot of solution using the pipette, and, helps prevent possible
contamination of stock solution.
Conical flask (erlenmeyer flask): Used to contain the reaction mixture (the initial pipetted aliquot of solution plus the
addition of solution from the burette.
1.1: Preparing the Glassware
Before using any glassware for a volumetric analysis, it is essential that the glassware be clean.
 Test for the cleanliness of glassware by adding distilled water to it, then allowing the water to drain out.
 If the glassware is clean, the water will leave an unbroken film.
 If the glassware is dirty, the water will form droplets and the thin film will have crinkly edges.
 Dirty glassware will need to be cleaned using a suitable detergent and water before it can be used for volumetric
analysis.
Only clean glassware should be used for volumetric analysis.
Before being used for volumetric analysis, the clean glassware is then prepared by rinsing with a suitable solution.
Md.
Imran
Nur
Manik

3. Glassware Use Rinsed with Reason
Beaker
To store solution from the
volumetric flask, preventing
contamination of solution in
volumetric flask.
Solution
to be
used.
Rinsing with solvent, e.g. water would dilute the solution so its
concentration would no longer be known accurately. Rinsing with
solution to be used ensures removal of any moisture adhering to
glass.
Pipette
To deliver an accurate
volume (aliquot) of solution
from the beaker.
Solution
to be
used.
Rinsing with solvent, e.g. water would dilute the solution so its
concentration would no longer be known accurately.
Rinsing with solution to be used ensures removal of any moisture
adhering to glass.
Burette
(buret)
To deliver an accurate
volume (titre) of solution.
Solution
to be
used.
Rinsing with solvent, e.g. water would dilute the solution so its
concentration would no longer be known accurately.
Rinsing with solution to be used ensures removal of any moisture
adhering to glass.
Conical
flask
(erlenmeyer
flask)
To contain the reaction
mixture.
Solvent
(e.g.
water)
Rinsing with the solution to be added from the pipette would
increase the moles of substance used in the reaction, so the titre
volume would be greater than it should be.
Rinsing with the solution from the burette (buret) would cause
some of the titrant to react before the volume of the titre is
recorded so the value of the titre would be less than it should be.
1.2: Preparing the burette (buret):
a) Once the burette has been rinsed, insert the glass funnel into the burette leaving an air gap between the
neck of the funnel and the sides of the burette.
b) With the burette's stopcock in the closed position, pour some solution in to the funnel and allow it to
drain down into the burette until the volume of solution is well above the 0.00 mL mark etched onto
the side of the burette.
c) Remove the funnel.
d) Position the burette over a waste receptacle such as a beaker, or the sink.
e) Gently, partially open the burette's stopcock and allow some of the solution to flow through slowly,
until the bottom of the meniscus sits exactly on the 0.00 mL graduation mark etched on the side of the
burette when viewed at eye level, and close the stopcock.
f) Discard the solution collected in the waste receptacle appropriately.
1.3: Preparing the conical (erlenmeyer) flask:
a) Use an aspirette (pipette filler or bulb) attached to the clean, rinsed pipette to draw up a volume of
solution from the beaker to a point above the calibration mark etched on the pipette.
b) Position the pipette over a waste receptacle such as another beaker or the sink.
c) Very slowly and carefully, allow solution to escape from the pipette drop by drop until the bottom
of the meniscus sits exactly on the calibration mark when viewed at eye level. (Discard the solution
in the waste receptacle appropriately.)
d) Position the pipette containing the solution within the confines of the clean, rinsed conical flask,
touching an internal wall of the flask at an angle.
e) Allow the solution to run freely through the pipette.
f) When the solution is no longer flowing, that is, the meniscus comes to rest; remove the pipette from
the conical flask.
g) DO NOT attempt to remove the small amount of solution still in the pipette; the pipette has been
calibrated to take this small amount of solution into account.
h) If required, a drop of indicator could now be added to the solution in the conical flask.
i) The conical flask with its solution is now placed under the burette containing its solution. It is best to position the
burette within the confines of the neck of the conical flask to ensure all the drops of solution from the solution go
straight down into the flask.
j) Prepare three Erlenmeyers.
The next step is to
conduct the titration.
Md.
Imran
Nur
Manik

4. 1.4: Performing the Titration
The equipment that will be used for each titration should now be set up as shown in the diagram on
the right.
1. It is usual to place a white tile, or even a piece of white paper, under the conical flask so that
it is easier to see any color changes that occur in the conical (erlenmeyer) flask.
2. It is also good practice to position your burette against a contrasting background so that the
bottom of the meniscus is easier to read.
3. This can be done by holding a piece of paper behind the burette whenever you take a
reading, or, by cutting 2 parallel slits, a few centimeters apart, in a piece of plain paper (or
filter paper) and sliding this over the burette so that it can slide up and down the burette
giving you a contrasting background wherever you need it.
Follow these steps:
1. Clean and rinse the burette. ( See section 1.1 for details)
2. Fill a burette with the standard solution. Run a little through the tap to make sure that no air is
trapped. The zero line is at the top of the burette. Ensure that the bottom of the meniscus is level
with the zero line.( See section 1.2 for details)
3. Record the initial volume of solution in the burette. Remember to read the volume at eye level
and from the bottom of the meniscus.
4. Use a pipette to exactly measure the acid (secondary standard substance) of unknown
concentration and place this into a conical flask.
5. Add two drops of a suitable indicator (e.g. phenolphthalein or methyl orange). The indicator will show its acidic color.
6. Open the burette's stopcock and allow solution to run down into the conical (erlenmeyer) flask.
7. Swirl the conical flask while adding solution from the burette.
8. When you are close to (say within 80% of) the expected end point based on the rough titration,
then close the stopcock.
9. Note: Don’t want to overshoot the end point, so don't try to get too close on this first careful
titration. Partially open the stopcock so that solution falls drop by drop into the conical flask.
Continue swirling the flask.
10. When you are very close to the end point, a drop of solution from the burette will change the
color of the solution, but when you swirl the flask, this color will disappear.
11. At this point, close the stopcock, and then only open the stopcock enough to allow one drop at a time to fall from the
burette.
12. The end point of the titration has been reached when 1 drop changes the color of the solution in the conical flask, and,
swirling the flask does not cause this color to disappear.(Referred to as a "permanent color change")
13. Close the stopcock as soon as the reaction reaches its equivalence point. When the indicator changes color
permanently, the end point has been reached.
14. Record the final volume (of alkali used to neutralise the acid) as shown on the burette. Remember to read the volume at
eye level and from the bottom of the meniscus.
15. Calculate the titre (the volume of solution added to the conical flask from the burette:
titre = final burette reading - initial burette reading
16. Clean and rinse your conical (erlenmeyer) flask, add another aliquot of solution and indicator, refill the burette (buret)
if required, then repeat this titration.
17. Rinse out the conical flask, top up the alkali in the burette and then repeat steps 3 to 15 (at least two times) to ensure
that the results are reliable.
To ensure Success
• Save time and NaOH: Don’t refill your buret to 0.00 each time. Read the initial and final values for each trial
• Don’t overshoot your endpoint!! Patience is key.
• Use a funnel to fill your buret, fill over sink if necessary
• Use a waste beaker for NaOH rinses and titrated acid
Md.
Imran
Nur
Manik

5. GLP Good Laboratory Practice - is now a widely recognized term, covering standards of working practice which are required
by law in many laboratories and demanded by clients in many others.
General aspects which should be considered in a GLP program are:
1. Safety and Cleanliness
•The laboratory and the apparatus in it must be clean and this is absolutely essential for trace analysis it will also be a safe
laboratory, and accidents will be rare.
• Labeling of all containers is a MUST. Clean the outside of the bottles as well as the inside, and have only ONE label! Either use
a glass marking felt tip pen or a sticky label.
• The method of cleaning will depend on what was in the article before, and what the article is made of. If it is only dilute
inorganic reagents then a simple rinse with dilute nitric acid followed by several rinses with water and finally one rinse with
deionized water will suffice.
For organic or concentrated reagents detergents are usually good enough; especially when helped by brushing. All apparatus must
then be rinsed very thoroughly. It is not always necessary to dry apparatus but when it is, glassware may be dried in the oven.
Rinsing with solvents may leave residues and costs moneys and there is a disposal problem.
2. Records
• A laboratory notebook must be used at all times. No scribbling pads or loose pieces of papers with instrument readings or
weighing! Record all relevant data. Use a duplicate book. Hand in the copy at the end of the practical.
• Record the date and the experiment name on each page. Use the notebook also for rough calculations, for example, at working
out how much of chemical is needed for preparing a solution.
3. Good Housekeeping
• You will be working in a busy laboratory shared with many other people, and often you will be using shared equipment. Co-
operation is the only solution. Think about the consequences for other people when you do something for yourself.
• Wash up regularly and tidy away clean apparatus. Clean the bench and the shelves where you work.
• Put waste chemicals and solvents in clearly marked Waste bottles for safe disposal. Label all bottles correctly and clearly.
• Keep instruction books beside instruments.
4. Cost and efficiency
Chemicals cost money - look at the price of a bottle of solvent or acid. Scaling down will save on cost and also on the disposal
problem when you have finished.
The Analytical Balance
Most of the necessary precautions are the same as those we had to observe with mechanical balances. Thus, a balance must be
placed away from windows, to protect it from sunlight and draughts, and it should be kept away from air ducts or fans, and from
lights. The room temperature should be kept as constant as possible, and so should the humidity. The weighing table should not
transmit vibrations, should have no deflection when it is worked on, be made of antimagnetic materials, and be protected against
static charges. Balances must be calibrated regularly, at the location where they are used, against a standard mass.
The other points to note are under your control:
• Check that the balance is level, and adjust if necessary.
• Press the bar to switch on and zero the balance.
• Before opening the weighing chamber, check to make sure that the display is indicating exactly zero.
• Touch the container as little as possible, to avoid transfer of heat and humidity.
• Open the weighing chamber only long enough to put the vessel on the pan. As far as possible, keep
your hands out of the chamber.
• Place the vessel in the middle of the pan.
• Take the reading as soon as the display stabilizes, then remove the vessel.
• Keep the weighing chamber and pan clean. Only use clean containers for weighing.
• Do not use any plastic containers for weighing, because they are very susceptible to developing a
static charge, which could cause wrong weights to be obtained. Glass vessels may cause problems too if the humidity is low.
• Objects should only be weighed when they are at the same temperature as the air in the balance room. Allow warm objects to
cool and cold objects to warm up before weighing.
• Chemicals should NEVER be weighed directly on the pan, but should always be placed in a vessel, preferably a weighing bottle.
• "Weighing by difference" should be the normal practice. That is, place the chemical in the weighing bottle, put the bottle on the
balance and record the weight. Tip a suitable quantity into the destination container OUTSIDE the balance case, and then reweigh
the bottle.
[It is normal practice to use the rough balance on the laboratory side-benches to get approximately the correct amount of chemical
into the bottle at the start.]
NEVER attempt to add a chemical to a vessel inside the weighing chamber
References:
1. Handbook: Good Laboratory Practice (GLP): Quality Practices for Regulated Non-clinical Research and Development;
World Health Organization, 2010.
2. Good Laboratory Practice Standards: Applications for Field and Laboratory Studies; American Chemical Society, 1992
3. Jürg P. Seiler: Good Laboratory Practice: The Why and the How; Springer Science & Business Media, 2012
Md.
Imran
Nur
Manik

6. What method of measuring should you use?
Method Typical volumes Accuracy
Pasteur pipette 1-5 mL Low
Beaker / flask 25-5000 mL Very Low
Measuring cylinder 5-2000 mL Medium
Volumetric flask 5-2000 mL high
Burette 1-100 mL high
Glass pipette 1-100 mL high
Weighing ---------- Very high
Pipette Filler Instructions
Use this rubber bulb pipette filler to safely fill glass and plastic pipettes. The three‐valve design allows you to
release air, draw liquid into the pipette, and accurately release liquid. It works with all sizes of Mohrs,
serological, or volumetric pipettes, except for 1ml and smaller plastic pipettes.
1. Release air from the pipette filler by squeezing valve “A” on the top of the pipette filler while
simultaneously squeezing the bulb. The amount of air you release is dependent on the size of the pipette
you are using release more air for larger volume pipettes. Release control pad (A); bulb remains
depressed.
2. Insert the tip of the pipette into the liquid to be dispensed. Siphon liquid into the pipette to the desired
level by squeezing valve “S” on the bottom of the pipette filler. This uses the vacuum created in the bulb
to draw liquid into the pipette. Be careful not to draw liquid into the pipette filler.
3. Empty the pipette by squeezing valve “E” on the side‐tube. This allows you to release liquid at the
desired rate and to the desired level.
4. To dispense under pressure, squeeze pad (A), allowing the bulb to re-inflate, then press pad (S) while
squeezing bulb to dispense.
It works best to fill the pipette past the zero mark on step 2(valve “S”) and then draw the level down to
the zero mark on step 3 (valve “E”). Once the pipette is filled to the level desired the contents can be
dispensed using valve “E”.
Md.
Imran
Nur
Manik