Page 62 - PC 101 practical notes 24-25..

MANSOURA NATIONAL UNIVERSIY
PHARM D- CLINICAL PHARMACY LEVEL I PHARM. ANAL. CHEM. I (PC 101)

2) The concentration of borax can be calculated from either E.P 1 or E.P 2.

3) Borax is considered a sodium salt of boric acid and the reaction between

HCl & borax is an example of displacement titration where HCl (strong

acid) displaces boric acid (very weak acid) in its salts.

Na 2B 4O 7 + 7 H 2O → 2 NaOH + 4 H 3BO 3

2 NaOH + 2 HCl → 2 NaCl + 2 H 2O
.
by summation: Na 2B 4O 7 + 5 H 2O + 2 HCl → 4 H 3BO 3 + 2 NaCl

Important Question :

As we discussed before, borax can be determined through its NaOH

content by titration against 0.1 N HCl (E.P 1) and then it can be again

determined through its boric acid content by adding glycerol to the above

titrated solution and then titration against 0.1 N NaOH (E.P 2).

Q1- What is the relation between E.P 1 and E.P 2 ?

Answer: E.P 2 = 2 E.P 1 ............... as mentioned before

Q2- If the same volume of borax sample is treated directly with glycerol:

a- Will the resulting solution be acidic or basic ?

b- If this solution is titrated against a suitable titrant having the same

normality (0.1 N) as the above mentioned titrants. What will be

the relation between the observed end point (E.P 3) and (E.P 1 or E.P 2)?

Answer:

Na 2B 4O 7 + 7 H 2O → 2 NaOH + 4 H 3BO 3

+ glycerol

reaction between 4 Glyceroboric acid

them leaving

2 glyceroboric acid
only

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