|
|
Vitamin C
indicator
use
2613-100g, Hydroxy Naphthol Blue or
655-1g, DCPIP
Making an Iodine
solution
Dissolve 20g of potassium iodide [2396-500g or
410-500g] and 10g of iodine [267-100g or 268-100g] in 1litre of water. Keep in a
stoppered conatiner in the dark
.
Making an eriochrome black-T
solution
A.DRY SOLUTION. Eriochrome
black-T[3200-25g] for EDTA titrations. Add 1g of eriochrome black-T to 200-500g
of potassium chloride [383-500g] or sodium chloride [465-500g]. Use the UNIVAR
grades 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: Disolve 0.2g of the eriochrome black-T[3200-25g] in 15 ml of triethanolamine [787-500ml]. add 5ml of absolute ethanol [214-500ml] to reduce viscosity. The reagent is stable for several months. C. Methanol solution: Disolve 0.4% of the eriochrome black-T in methanol [cat# 318 ] Water glass or sodium silicate
solution
Dissolve 250g of sodium metasilicate
[707-500g] in 1L of water.
Or, dissolve 100g of sodium
metasilicate [707-500g] and 64g of silica [438-500g] in 173 g of hot water.
Stirr.Make up weight loss back to 337g with water. This will
make a solution containing 8.55% Na2O and 27.45% of SiO2.
Chromic acid for glassware cleaning
To make chromic acid, add 7.25g of
sodium dichromate [1227-500g] to 500ml of sulphuric acid concentrate [cat# 534
or 1599 or 1598]. Stirr until disolved
Nutrient agar
Add 1 tablespoon/15g of
marmite and 15g of glucose[cat# 783] to enough agar [cat#863] to make 50 plates
of media.
Benedicts Solution
Benedict's Solution (also
called Benedict's reagent or Benedict's test) is a named after an American
chemist, Stanley Rossiter Benedict . It is used as a test for the presence of
reducing sugars such as glucose , fructose , and maltose . or more generally for
the presence of aldehydes , (except aromatic ones). It is often used in place of
Fehling's solution.Benedict's reagent contains blue copper(II) sulfate CuSO4) which is
reduced to red copper(I) oxide (Cu2O) by aldehydes, also oxidizing them to
carboxylic acids .The copper (I) oxide is insoluble in water and so
precipitates.
Benedict's reagent can be made from 100 g sodium carbonate and 173 g
sodium citrate dissolved in 850 mL water, to which a solution of 17.3 g
copper(II) sulfate in 100 mL of water is slowly added, and the overall reagent
made up to 1 litre.
Chemical test
To test for the presence of reducing sugars in food, the food sample is dissolved in water and about 5ml of the sample solution is added to 5ml of Benedict's reagent. The mixture is placed in a boiling water bath for 5 minutes and any precipitate formed is recorded as a positive result for the presence of reducing sugars in the food. Sucrose (household sugar) is a non-reducing sugar and thus does not react with Benedict's reagent. Sucrose can produce positive results with Benedict's reagent if heated with dilute hydrochloric acid prior to the test. Doing so hydrolyses the glycosidic bond to give the monosaccharides glucose and fructose. Benedict's reagent can be used to test for the presence of glucose in urine . Glucose found to be present in urine is an indication of diabetes 5ml of Benedict's reagent is mixed with 0.5ml of urine and the mixture is put in a boiling water bath for 5 minutes. The results are recorded like this: no precipitate- Green - a trace Yellow + Orange ++ Red +++ Once a reducing sugar is detected in urine, further tests have to be undergone in order to ascertain which sugar is present. Only glucose is indicative of diabetes. Making a starch
solution
Make a paste of 1g of soluble starch
1254-500g,or 1534-500g potato starch, with a little water and pour the paste
with constant stirring into 100ml of boiling water. Boil for a minute (3 min for
potato 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.
Vitex starch is also available [#620]. THis does
not require the high heat for dissolution.
Common pH Indicators and their transition
range
|
|
||||
