Preparation of organic reagents
Ammoniacal silver nitrate.
(Tollens reagent)
Solution A. (3g. of silver nitrate in 30ml. of water)
Solution B. (3g. of NaOH in 30ml. of water)
Mix equal volumes of A and B (1ml) and add dilute ammonia solution drop by drop until the silver oxide is just redissolved. Use this as the reagent.
Barfoed's reagent
To 100 ml of dilute acetic acid , add 6.5 g of cupric acetate.
Bial's reagent
Bial's reagent consists of 0.4 g orcinol, 200 ml of concentrated hydrochloric acid and 0.5 ml of a 10% solution of
ferric chloride. Bial's test
is used to distinguish pentoses from hexoses; this distinction is based on the color that develops in the presence
of orcinol and iron (III) chloride
Benedicts reagent.
Solution A: Dissolve 8.65g of CuSO4.5H2O in 75 ml of H2O.
Solution B: Dissolve 86.5 g of sodium citrate and 50 g of anhydrous Na2CO3 in 400 ml H2O.
Pour Solution A slowly into Solution B and make up the volume to 500 ml . Mix well.
Bradys reagent (2,4 DNPH)
(Method 1. Suspend 2.0g. of 2:4 dinitrophenylhydrazine in 100ml. of methanol. Cautiously and slowly add 4.0ml. of conc. Sulphuric acid. Filter if nessary.)
Method 2. Dissolve 0.25g. of the reagent in a mixture of 42ml. conc.HCl and 50ml. of water by warming on a water bath; dilute to 50 ml. with distilled water.This reagert is more suitable for water soluble aldehydes and ketones since alcohol is abscent.
Fehlings solution
Solution no. 1. Dissolve 34.64g. of AR copper sulphate crystals in water containing a few drops of dilute sulphuric acid and dilute to 600ml.)
Solution no. 2. Dissolve 60g. of NaOH and 173g. of sodium potassium tartrate in water and dilute to 500ml.
Keep the two solutions separately in tightly stoppered bottles and mix exactly equal volumes immediately before use.
Ferric chloride (Neutral)
Dissolve FeCl3 in water. Add NH4OH dropwise till there is a start of precipitation. Filter. Use filterate as neutral FeCl3 solution.
Precipitation indicates that HCl produced by hydrolysis of FeCl3 has been neutralized and added ammonium hydroxide is reacting with FeCl3 to precipitate Fe(OH)3)
Iodine reagent.
Dissolve 20g KI and 10g iodine crystals in 100ml water.
Jones reagent.
The Jones Reagent is a mixture of chromic trioxide or sodium dichromate in diluted sulfuric acid, which forms chromic acid in situ.
The unknown is first dissolved in acetone and the reagent added to the mixture.
Mix 25g of chromium trioxide (chromic anhydride CrO3) with conc. sulphuric acid to a paste (use ice bath), then dilute with water to 75mls to make the regent.
1. Dissolve 10 mg (solid) or 2 drops (liquid) of the unknown substance in 0.8 mL to 1 mL of pure acetone.
2. Add 1 drop of Jones reagent and shake.
3. Look for a color change from orange-yellow to green.
Molischs reagent.
20% soln. in naphthol. Dissolve 20g of 1-naphthol in 100ml ethanol.
Nesseler's reagent .
Dissolve 5g of KI in minimum amount of water. To it add saturated solution of HgCl2 till a faint permanent red precipitate is formed.
Mix it with 40 ml of 50% aqueous KOH solution. Allow the precipitate to settle. Dilute to 100 ml with water. Allow it to stand overnight and filter. Filterate is nesseler's reagent.
Ninhydrin solution.
Dissolve 0.2 g of ninhydrin in 100 ml of rectified spirit (alcohol).
Schiff's reagent.
Method (1) Dissolve 0.2g. of pure p-rosaniline hydrochloride in 20ml. freshly prepared saturated aqueous solution of solphur dioxide. Dilute to 200ml. and keep in tightly stoppered bottle.
Method (2) Add 2g. of sodium bisulphite to a solution of 0.2g.of p-rosaniline hydrochloride and 2ml. of conc. HCl in 200ml. of water.
Tollens reagent.
Add sodium hydroxide soln. to silver nitrate soln. to form a ppt. then add dilute ammonia soln. until ppt. dissolves.
