Page 24 - PC 101 Interactive practical book

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

M Ma ai in n s st te ep ps s o of f t th he e c ca al lc cu ul la at ti io on ns s

At the beginning of calculations, you should write “balanced” chemical

equations that represent the reactions of the experiment and from these

equations find the relation between the sample and the standard.

Then the concentration of the sample can be calculated by making the

2 following steps:

1 1s st t S St te ep p: : C Ca al lc cu ul la at ti io on n o of f E Eq qu ui iv va al le en nc ce e F Fa ac ct to or r ( (F F) )

D De ef fi in ni it ti io on n o of f e eq qu ui iv va al le en nc ce e f fa ac ct to or r: :

It is the weight of the sample that is equivalent to 1 mL of the standard.

(F) is written as follows:

a x M.W. of sample x N of standard
each ml of (x) N standard ≡
b x 1000

≡ (F) g sample

≡ (F x 1000) mg sample

Where:

a = no. of moles of the sample equivalent to 1 mole of the standard.

i.e. 1 standard ≡ a sample ………… {from the reaction equations}

b = differs according to the type of the reaction:
-
+
1) In acid-base titration: b = no. of replaceable H or OH present in or
react with ONE molecule of the standard. (ex.: for H 2SO 4 → b =2).

2) In precipitation titration: b = no. of univalent cation atoms present in or
equivalent to ONE molecule of the standard.
(ex.: for AgNO 3 → b =1, Hg(NO 3) 2 → b =2).

3) In complexometric titration: b is absent as we use molar concentrations.

4) In redox titration: b = electron transfer or no. of electrons lost or
gained by ONE molecule of the standard. (ex.: for KMnO 4 → b = 5).

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