Question

This is the determination of zinc in cold relief lozenge by complexometric titration

1. Discuss the role of pH in your determination and why experiment was run at ph 5.5 rather than at ph 10 which is typical for complexometric titration with EDTA for calcium ion or magnesium ion

2. Discuss chemical form of zinc ion present in the cold relief lozenge

3. Discuss role of indicator used in chemical terms

4. How come when edta reacted with zinc ion you get 1:1 mole

5. Why edta is used in complexometric titration

Answer 1

1) EDTA is insoluble in water at low pH because H4Y is predominant in that pH (less than 2). With increasing the pH, each hydrogen ion in the carboxyl groups of EDTA will start to dissociate. ... As we need Y4- to react with the metal ions present in the titration solution, we use pH 10 buffer such as ammonium chloride.

2) cold relief lozenge mean duration of zinc-treated colds was 3.9 days, and 10.8 days for placebo-treated
colds (difference ¼ 7 days, p < 0.0001) These lozenges contained no carbohydrates
and were not bitter, rather they were chalky and bland in taste.
The Al-Nakib et al. [3] ZG lozenges studied at the British MRC Common Cold
Unit in Salisbury, England, also contained 23 mg of zinc, which released 16.56 mg iZn.
Daily iZn was 149 mg. The formulation was a wet-granulated fructose-based com-
pressed tablet made by RBS Pharma, Milan, Italy (now part of Rhone-Poulenc ^
Pharma). The lozenges were used against human rhinovirus-2 induced colds. The
lozenges dissolved in 20 min and were used every two wakeful hours (9 per day) for 6
days. The loading dose on the first day when viruses were most prevalent as used by Eby
et al. [2] was not used. Total scores over the six-day trial of physician-observed com-
mon cold symptoms were 41.0 in the placebo-treated group and 27.2 in the zinc-treated
group (p < 0.05) The average number of tissue papers used was 21.7 in the placebo-
treated group and 14.3 in the zinc-treated group (p < 0.01) Nasal secretions averaged
51.4 g in the placebo-treated group and 22.0 g in the zinc-treated group (p < 0.05).
Re-analysis of the MRC Figs. 1 and 2 demonstrated a 4.8 day mean difference between
the zinc- and placebo-treated colds [4]. These lozenges were formulated with fructose
and were not bitter, rather they were sweet, highly flavored and chalky in taste.
Smith et al. [20], using extremely bitter ZG lozenges (11.5 mg zinc—half the
amount planned) in sucrose, mannitol and sorbitol lozenges and 11 other con-
founding ingredients, found no significant difference in median or mean duration of
colds using lozenges nine times per day, although 12.6% fewer subjects using zinc on
days 5 through 7 were sick (p ¼ 0.09), and severity was reduced on days 5 through 7
(p ¼ 0.02). Daily iZn was 74.5 mg. Similarly, with low dose, bitter ZG maltitol
hard-boiled candy (4.5 mg zinc) lozenges.

3) Chemical indicator, any substance that gives a visible sign, usually by a colour change, of the presence or absence of a threshold concentration of a chemical species, such as an acid or an alkali in a solution. An example is the substance called methyl yellow, which imparts a yellow colour to an alkaline solution. If acid is slowly added, the solution remains yellow until all the alkali has been neutralized, whereupon the colour suddenly changes to red.

4)For 0.01 M titrant and assuming 50 mL burette, aliquot taken for titration should contain about 0.35-0.45 millimoles of zinc (23-29 mg). If preparation of such sample is difficult, we can use different EDTA concentration.

5)Indicators. Titra To carry out metal cation titrations using EDTA, it is almost always necessary to use acomplexometric indicator to determine when the end point has been reached. ... Thus, the free indicator (rather than the metal complex) serves as the endpoint indicator.