NEUTRALIZATION TITRATIONS
NEUTRALIZATION TITRATIONS
The reaction between an acid and a base is called as neutralization
reaction.
A titration is a laboratory technique that measures the concentration of an
analyte using reaction between analyte and standard solution (solution of
known concentration).
Acid-base titrations is also called neutralization titrations.
Acidimetry is the determination of concentration of acidic substances by
titrating with a standard base solution, and alkalimetry is the measurement
of concentration of basic substances by titrating with a standard acid solution.
The end-point (equivalence point) of acid-base reactions are observed by using
indicators which are substances that changes colors near their pKa. Therefore a
suitable indicator should be selected for acids and bases that are reacted.
A titration curve is a plot of pH vs. the amount of titrant added. Shape of titration
curves differ for weak and strong acid-bases or for polyprotic acids and bases.
A titration of a polyprotic acid (H3PO4) with a strong base (NaOH)
Indicators having pKa in the range of end-points on the titration curves are suitable for
that titrations. End-points can also be determined by some other methods such as
potentiometry, conductometry, amperometry, spectrophotometry.
TIPS FOR TITRATION
1) Solutions must be shaken well before starting.
2) First, a known volume of the analyte is placed in a flask, and a few
drops of an acid-base indicator, such as phenolphthalein, are added.
3) Next, the standard solution is placed into a buret. This solution is also
called as titrant.
4) Then, the titrant is added drop by drop to the analyte while swirling
the flask. Titration must be performed slowly and always hold
stopcock one hand while swirling the flask with other hand.
Check the tip of the buret for leak or air bubble. To remove an air
bubble, whack the side of the buret tip while solution is flowing. If an
air bubble is present during a titration, volume readings may be in
error. If there is a leak, assemble the stopcock properly.
Standardization of 0.1 N NaOH solution
•
Carefully weigh 0.1-0.2 gram of oxalic acid (H2C2O4.2H2O) and note the exact
amount. This should be done by taking required amount of oxalic acid from the
stock of oxalic acid on the balance and transferring it to an erlenmeyer flask.
•
Dissolve oxalic acid by adding 50 mL of water into the erlenmeyer flask.
•
Add 1-2 drops of phenolphthalein to the erlenmeyer flask.
•
Fill a buret with NaOH solution that you want to standardize.
Check for leak and bubbles. Read the bottom of the meniscus.
•
Deliver solution drop by drop to the erlenmeyer flask by turning the stopcock while
swirling the flask. Continue to the titration until the color of the solution in the flask
turns to light pink.
CALCULATIONS
meq NaOH = meq H2C2O4 . 2H2O
VNaOH x N
(126.1 / 2)
NaOH
= miligram of Oxalic acid (weighed) / equivalent amount of oxalic acid
Calculate NNaOH and report it to your TA with other results in your bench.
A white paper under the erlenmeyer flask may help you to
determine the end-point.
HOW TO WEIGH OXALIC ACID
• Take the crucible having oxalic acid in it from desicator and put it onto a balance.
Take a note of the amount on the screen (For example 30.100 g).
For taking 0.1 - 0.2 g of oxalic acid
30.100 – 0.2 = 29.900
30.100 – 0.1 = 30.000
We need to take an amount of oxalic acid that the remaining amount must be in
betweeen 29.900 g – 30.000 g
• Then, by using a spatula, take required amount of oxalic acid and transfer it to the
flask and keep the spatula in the flask for flushing the oxalic acid sticked on the
surface of the spatula.
• If the final amount of remaining oxalic acid is 29,980 then we took
•
30.100 – 29.980 = 0.120 gram
Primer Standards for Acids
• Na2CO3 (sodium carbonate)
• TlCO3(talium carbonate)
• KHCO3 (potassium bicarbonate)
Primer Standards for Bases
• H2C2O4.2H2O (oxalic acid dihydrate)
• KHC8H4O4 (potassium biphthalate)
• HC7H5O2 (benzoic acid)
Standardization of 0.1 N HCl solution
• Pour 10 mL HCl into a erlenmeyer flask and add 1-2 drops of
phenolphthalein.
• Fill a buret with NaOH solution that you already standardized
• Titrate until light pink color
CALCULATION
meqHCl = meq NaOH
V HCl x NHCl = VNaOH x NNaOH
Calculate NNaOH and report it to your TA with other results in your
bench.
REFERENCES
Analitik Kimya Pratikleri – Kantitatif Analiz (Ed. Feyyaz ONUR), 2014