Page 27 - Phytochemistry -1 (PG404) / Clinical Pharmacy 2nd level students ( 2019 )

Clinical pharmacy PharmD program Third level Phytochemistry-1 (PG-504)

• 10 ml Fehling's solution contains 0.11 gm cupric oxide which is able to

oxidize 0.05 gm of glucose.

Linge's Indicator

• It is an external indicator and could replace M.B.

• It consists of:

• 1 gm ferrous ammonium sulfate Fe (NH 4) 2(SO 4) 2
• 1.5 gm ammonium sulfocyanide

• dissolved in a mix of 10 ml water + 2.5 ml conc HCI
• The solution is decolorized before use by adding few pieces of zinc

granules.

• When a drop of cupric salt is brought in contact with this indicator in a

porcelain lab, oxidation of ferrous salt occurs with immediate production
of red color of ferric thiocyanate.

• For the use of Ling's indicator in the process of titration apply the

followings:

When the blue color of the solution has disappeared and precipitation of

Cu 2O is complete, a drop of sol. is brought in contact with indicator, E.P
is reached. When color of mixture ceases to give red color.

Calculations

The sugar solution taken (in ml) which reduces 10 ml Fehling's solution
contain 0.05 gm of any of the reducing hexoses (e.g glucose, fructose, ….

etc.). In case of reducing disaccharides (e.g maltose or lactose) each 10
ml of Fehling's solution is equivalent to 0.08 gm of maltose or lactose.

(i.e.):

A. For monosaccharide

0.05 x 100

% of glucose =

ml of sugar solution taken (E.P) - 0.2
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