Aa – alphabetical list

Eriochrome black-T -  making a solution

A.DRY SOLUTION. Eriochrome black-T[3200-25g] for EDTA titrations. Add 1g of eriochrome black-T to 200-500g of potassium chloride [4170.1-500g] or sodium chloride [4650.1-500g]. Use an AR grade to avoid metallic contamination. Grind the mixture well in a pestle and mortar. Keep in a dry tightly sealed container. Sprinkle a small amount into the test solution.

B. Liquid solution: Dissolve 0.2g of the eriochrome black-T[3200-25g] in 15 ml of triethanolamine [5330.8-500ml]. add 5ml of absolute ethanol [2292.1-2.5L] to reduce viscosity. The reagent is stable for several months.

C. Methanol solution: Dissolve 0.4% of the eriochrome black-T in methanol [cat# H409-2.5L]

Nutrient Agar :-Add 1 tablespoon/15g of marmite and 15g of glucose[cat# 2530.1-500g] to enough agar [cat#1100.1-500g] to make 50 plates of media.

Skincare formula - download file

Soap Making - download file

Starch solution

Make a paste of 1g of  soluble starch 5070.1-500g,or 5070.8-500g undenatured starch, with a little water and pour the paste with constant stirring into 100ml of boiling water. Boil for a minute (3 min for undenatured starch), allow the solution to cool and add 2-3g of potassium iodide. The addition of 5mg of mercuric iodide [313-100g] will preserve the solution for several months.

Vitamin C   -

1. Qualitative test for vitamin C 

2. Quantitative test for vitamin C

1.Qualitative test for vitamin C  using 2,6-dichlorophenolindophenol, sodium salt (DCPIP)

DCPIP can also be used as an indicator for Vitamin C. If vitamin C, which is a good reducing agent, is present, the blue dye, which turns pink in acid conditions, is reduced to a colorless compound by ascorbic acid.

1. Add 10ml of 10% acetic acid to 30-50 ml water.

2.Add the DCPIP indicator until a pink colour is obtained.

3. Add the measured amount of vitamin C solution. The solution will turn  clear.If you just need an indication of vitamin C being present, you can stop here. If the red colour disappears, that is a positive result.

4.To make this quantitative, titrate with your oxidiser to colourless.

DCPIP (blue) + H⁺ ----------> DCPIPH (pink)

DCPIPH (pink) + VitC ----------> DCPIPH2 (colorless)

C₆H₈O₆ + C₁₂H₇NCl₂O₂ ----------> C₆H₆O₆ + C₁₂H₉NCl₂O₂

In a titration,eg with potassium dichromate, when all the ascorbic acid in the solution has been used up, there will not be any electrons available to reduce the DCPIPH and the solution will remain pink due to the DCPIPH. The end point is a pink color that persists for 10 seconds or more.

Vitamin C determined with Iodine titration.

One way to determine the amount of vitamin C in food is to use a redox titration.

Iodine is relatively insoluble, but this can be improved by complexing the iodine with iodide to form triiodide:

I₂ + I^- <--> I₃^-

Triiodide oxidizes vitamin C to form dehydroascorbic acid:

C₆H₈O₆ + I₃^- + H₂O --> C₆H₆O₆ + 3I^- + 2H⁺

As long as vitamin C is present in the solution, the triiodide is converted to the iodide ion very quickly. However, when the all the vitamin C is oxidized, iodine and triiodide will be present, which react with starch to form a blue-black complex. The blue-black color is the endpoint of the titration.

Preparing Solutions

1% Starch Indicator Solution

1.    Add 0.50 g soluble starch to 50 near-boiling distilled water.

2.    Mix well and allow to cool before use. (doesn't have to be 1%; 0.5% is fine)

Iodine Solution

1.    Dissolve 5.00 g potassium iodide (KI) and 0.268 g potassium iodate (KIO₃) in 200 ml of distilled water.

2.    Add 30 ml of 3 M sulfuric acid.

3.    Pour this solution into a 500 ml graduated cylinder and dilute it to a final volume of 500 ml with distilled water.

4.    Mix the solution.

5.    Transfer the solution to a 600 ml beaker. Label the beaker as your iodine solution.

Vitamin C Standard Solution

1.    Dissolve 0.250 g vitamin C (ascorbic acid) in 100 ml distilled water.

2.    Dilute to 250 ml with distilled water in a volumetric flask. Label the flask as your vitamin C standard solution.

Standardizing Solutions

1.    Add 25.00 ml of vitamin C standard solution to a 125 ml Erlenmeyer flask.

2.    Add 10 drops of 1% starch solution.

3.    Rinse your burette with a small volume of the iodine solution and then fill it. Record the initial volume.

4.    Titrate the solution until the endpoint is reached. This will be when you see the first sign of blue color that persists after 20 seconds of swirling the solution.

5.    Record the final volume of iodine solution. The volume that was required is the starting volume minus the final volume.

6.    Repeat the titration at least twice more. The results should agree within 0.1 ml

You titrate samples exactly the same as you did your standard. Record the initial and final volume of iodine solution required to produce the color change at the endpoint.

Titrating Juice Samples

1.    Add 25.00 ml of juice sample to a 125 ml Erlenmeyer flask.

2.    Titrate until the endpoint is reached. (Add iodine solution until you get a color that persists longer than 20 seconds.)

3.    Repeat the titration until you have at least three measurements that agree to within 0.1 ml.

Titration Calculations

1.    Calculate the ml of titrant used for each flask. Take the measurements you obtained and average them.

average volume = total volume / number of trials

2.    Determine how much titrant was required for your standard.

If you needed an average of 10.00 ml of iodine solution to react 0.250 grams of vitamin C, then you can determine how much vitamin C was in a sample. For example, if you needed 6.00 ml to react your juice (a made-up value - don't worry if you get something totally different):

10.00 ml iodine solution / 0.250 g Vit C = 6.00 ml iodine solution / X ml Vit C

40.00 X = 6.00

X = 0.15 g Vit C in that sample

3.    Keep in mind the volume of your sample, so you can make other calculations, such as grams per liter. For a 25 ml juice sample, for example:

0.15 g / 25 ml = 0.15 g / 0.025 L = 6.00 g/L of vitamin C in that sample