B.pharm 1st semester pharmaceutical analysis topic- Estimation of calcium gluconate

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    ✯Pharmaceutical analysis✯

◍ Estimation of calcium gluconate ; 

✷ Principle;

• Complexometric titration is a form of volumetric analysis in which the formation of a coloured complex is used to indicate the end point of a titration. Complexometric Titrations are particularly useful for the determination of a mixture of different metal ion in solution.
   

               ( Principle same as record)



◍ Procedure ; 

1. Standardisation of EDTA ;

✷ Pipette out 20 ml of calcium gluconate solution, add 10ml of ammonia , ammonium chloride solution or ammonium buffer solution. Titrate against EDTA using mordant black 2nd mixture till the colour changes from red to blue.

2. Assay of calcium gluconate;

✷ Weigh 0.5g calcium gluconate, add 50ml distilled water, add 10ml of ammonia , ammonium chloride solution or ammonium buffer solution. Titrate against EDTA using mordant black 2nd till the colour change from red to blue.

☆calculation;

Each ml of 0.05M EDTA = 0.02242g of calcium gluconate.

◍ Estimation of magnesium sulphate;

✷ Principle;

• Complexometric titration is a form of volumetric analysis in which the formation of a coloured complex is used to indicate the end point of a titration.
 Complexometric titration are useful for the determination of a mixture of different metal ion in solution.
Magnesium can be easily determined by EDTA titration in the pH10 against Eriochrome black T
If the solution initially contain also different metal ions , they should be removed or masked , as EDTA react easily with most cation.




✯Calculation;

Each ml of 0.05M EDTA = 0.01232g of magnesium sulphate.

◍Indicators;

✷ "An indicator is a substance which show characteristics change in its colour when comes in contact with acid or base" and thus it is used to determine dictators the degree of acidity or basicity of any solution. 
For example; litmus solution or litmus paper.
• Role of indicators in chemistry is very important. They are also used to find out the end point in a titration.
• In acid base titration. Organic substances ( weak acid or weak base ) are generally used in indicators.
 

✯Theory of indicators: Ostwald's theory ✯

✷ An indicator is a substance which is used to determine the end point in a titration. In acid- base titration, organic substances ( weak acid or weak base ) are generally used as indicator .
They change their colour within a certain pH range. The colour change and the pH range of some common indicators are tabulated;

Indicator.            pH range.        Colour change

Methyl orange.      3.2- 4.5.           Pink to yellow

Methyl red.             4.4- 6.5.           Red to yellow

Litmus.                     5.5-7.5.            Red to blue

Phenol red.              6.8 - 8.4.          Yellow to red

Phenolphthalein.    8.3- 10.5.    Colourless to pink

There are two theories which explain the change of colour indicators with change in pH.

 According to Ostwald's theory;

✷ The colour change of any indicator is due to its ionisation. The unionised form of indicators has different colour than its ionised form.

✷ An indicator is either a Weak acid or weak base . So it's ionisation is highly affected in acids and base.
If an indicator is weak acid ,it's ionisation would be very much low in acid due to common H+ ions while it's fairly ionised in alkalies .
In the same way , if the indicator is a weak base , it's ionisation is large in acid and low in alkalies due to common OH ions.

Example— phenolphthalein( weak acid), methyl orange( weak base).


1. Phenolphthalein;

• It's represented as HPh. This indicator being a weak acid ionises in solution to a small extent as follows:

        HPh         🔁       Hydrogen + Ph -

Colourless.                                         Pink 

Applying law of mass action, we get
K= [H+] [Ph-] / [ HPh]

✷ The undissocited molecules of phenolphthalein are colourless while the Ph- ions are pink in colour.

In presence of an acid , ionisation of HPh is practically negligible as the equilibrium shift to the solution would remain colourless.

On addition of alkali , hydrogen ions are removed by OH - ions in the form of water molecules and the equilibrium shift to right hand side .

Thus, the concerntration of Ph- ions increase in solution and they impart pink colour to the solution.
  

2. Methyl orange;

• It is a very weak base and can be represented as MeOH. Its ionised in solution to give Me+ and OH- ions.

     MeOH           🔁.        Me+.     +     OH - 

     Yellow.                          Red

Applying law of mass action, 
K= [Me+][OH-] / [ MeOH]

✷ in presence of an acid OH- ions  ions are removed in the form of water molecules.

Thus, sufficient Me+ ions  are produced which impart red  colour to the solution, on addition of alkali.

 the concentration of OH- ions increase in the solution.the isolation of MeOH is practically negligible the solution requires the colour of unionised  methyl orange molecule.

According to quinonoid theory;

✷ According to this theory , an acid and base indicator exist in two tautomeric forms having different structure,which are in equilibrium. One form is termed benzenoid form and the other quinonoid forms .



Thankyou,
































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