Determination of Calcium Ions in Milk Using Titration Essay Example

complexes.

This diagram shows the six points of attachment in red and green. Ca 2+ + EDTA 4- CaEDTA 2- This equation shows that the EDTA reacts with the metal ion, which in this case is calcium on a 1:1 ratio, therefore it can be worked out however many moles of EDTA is used the calcium will be the same. To work this obviously needs an indicator to show when all of the free ions in the milk have reacted with the EDTA solution. The one chosen here is eriochrome black T. This works by initially forming weak complexes with the calcium and magnesium in the milk solution, which shows as a reddy/pink colour. Then as the EDTA is titrated in the Eriochrome black T becomes free ions which changes the colour of the solution to a lilac/blue colour.

Thus enabling us to see the end point of the reaction. This picture showing a CaEDTA2- complex. So as previously mentioned the amount of calcium in a given solution can be determined by titration with EDTA. This reaction needs to have a buffer solution with a pH in the range of 10-11, which then allows the indicator (eriochrome black t) to change colour when it forms disassociated ions. So 1M sodium hydroxide has been chosen. For our titrant we are using the 0. 01M EDTA solution. This is placed in the burette using a funnel below eye level to ensure it does not splash into our faces.

Then it is allowed to run through into an empty beaker or flask to ensure the air from the tip of the burette is purged. To

make our aliquot we firstly, using a pipette, place15ml of milk in a flask, which is then diluted to approximately 100ml using distilled water. Then 10ml of the 1M sodium hydroxide solution is added to provide the pH range necessary. Next added is 3 to 4 drops of the indictor. Then this solution is ready to titrate with the EDTA. Starting at a red colour and ending at a lilac colour as the end point is reached.