ACID BASE TITRATION PART -3-Application and Question With Answer

The application of acid base titrations are :-

  1. Determination of barbiturates
  2. Determination of nicotinic acid
  3. Determination of amino acid
  4. Determination of aspirin
  5. Assay of benzoic acid

 

  1. Determination of barbiturates :-  

    Sample is dissolved in (Methanol + water) mixture + indicator is added. This solutions is titrated with NaOH solutions.

  2. Determination of nicotinic acid :-

    Nicotinic acid is titrated with NaOH using phenolphthaein as indicator.

  3. Determination of aspirin :- 

    Sample + ethanol+ 2-3 drops of phenolphthaelin. this solution is titrated with NaOH solutions.

Estimation of sodium benzoate :-

Sodium benzoate (C7H5NaO2, m. wt.= 144.1) is a white, crystalline or granular powder or flakes. It is slightly hygroscopic, freely soluble in water, and sparingly soluble in alcohol. The powder when dried contains not less than 99 % of sodium benzoate.
Sodium benzoate has antibacterial and antifungal properties. It is used as a preservative in pharmaceutical formulations including oral preparations in concentrations up to 0.5 %. Sodium benzoate is also a common ingredient of cough preparations.

Sodium benzoate is a salt derived from a weak acid and a strong base, so its aqueous solution is alkaline. Therefore, solutions containing sodium benzoate are assayed using a standard N2 hydrochloric acid solution in an acid- base titration.

Procedure :-
• wash the burette with the D. W. and the titrant (HCl)
• fill the burette with N/2 HCI to a level (adjust it)
• put 10 mL or an unknown sodium benzoate solution in a
clean conical flask
• add 25mLof D.W.and I5mLof ether
• add 6 drops of bromophenol blue
• start titration by adding HCl drop wise with shaking the
aqueous and ethereal layers until a light green colour
persists in the aqueous layer (end point)
• record the volume of HCl used

CALCULATION :

calculate the chemical factor:-
(each 1 mL or N/2 hydrochloric acid is equivalent to 0.07205 g of C7HNaO2)

correct the volume of HCI solution used into N/2 volume
> calculate the quantity of sodium benzoate present in your sample
calculate the percentage w/v of you sodium benzoate sample

 

MCQ 

1.Which of the following is responsible for the acidic pH of normal rainwater

A.CO2

B.NO2

C.SO2

D.NH3

2. Which of the following is a general property of base

A. Taste Sour

B.Turn litums red

C.Conduct electric current in solution

D.Concentration of h3o is greater than concen. of oh.

 3.A solution of known concentration is the definition of a 

A. Buffer solution

B. Standard solution

C. Neutral solutions

D. Standard solutions

4.pH of 7 is shown through a color of 

A.Red

B.Blue

C.Green

D.Yellow

5. Which one of the following indicators would be most suitable for this titration?
A. Any acid/base indicator is suitable
B.Phenolphthalein (pKa = 9.6)
C. Cresol red (pKa = 8.3)
D. Methyl red (pKa = 5.1)

6. Which is correct sequence of assay of barbiturates ?

A. Barbiturates + methanol +water +indicator + NaOH solution

B.Barbiturates + indicator + methanol +water + NaOH solution

C.Barbiturates + NaOH solutions +water +methanol

D. None of the above

7. Which is correct sequence of assay of aspirin ?

A. Aspirin+ 2-3 drops of phenolphthalin  +NaOH solutions +ethanol

B. Aspirin+NaOH solutions +ethanol  +2-3 drops of phenolphthalin

C. Aspirin +ethanol +2-3 drops of phenolphthalin + NaOH solutions

D. Aspirin+NaOH solutions +ethanol  +2-3 drops of phenolphthalin

ANSWER KEY

1.A

2.C

3.B

4.C

5.D

6.A

7.C

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REFERENCE :-

VOGEL′S TEXT BOOK OF QUANTITATIVE CHEMICAL ANALYSIS FIFTH EDITION BY G.H.JEFERY, J.BASSETT (PG.NO. 262-278)

 

 

 

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