NEUTRALIZATION TITRATIONS

NEUTRALIZATION TITRATIONS

Standardization of HCl and NaOH solutions

NEUTRALIZATION

NEUTRALIZATION TITRATION TITRATION S S

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 are also called neutralization titrations.

Acidimetry is the determination of concentration of basic substances by

titration with a standard acid solution, and alkalimetry is the measurement of

concentration of acidic substances by titration with a standard base 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 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 holding

stopcock with 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 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

A white paper under the erlenmeyer flask may help you to

determine the end-point.

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HOW TO WEIGH OXALIC ACID 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

•Na

CO

(sodium carbonate)

•TlCO

(talium carbonate)

•KHCO

(potassium bicarbonate)

Primer Standards for Bases

•H

C

O

.2H

O (oxalic acid dihydrate)

•KHC

H

O

(potassium biphthalate)

•HC

H

O

(benzoic acid)

Standardization of 0.1 N HCl solution 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

HCl + NaOH → NaCl + H₂O (mole ratio 1:1) n_HCl = n _NaOH

V _HCl x M_HCl = V_NaOH x M_NaOH

Calculate M_HCl and report it to your TA with other results in your bench.

REFERENCES

Analitik Kimya Pratikleri – Kantitatif Analiz (Ed. Feyyaz ONUR), 2014