Practicals Flashcards
State the procedure for the starch/ iodine test
To 1 cubic centimeter of solution in a test tube was added 3 drops of iodine solution.
What can you conclude about a starch test in which a colorless/ turbid solution turned to a pale brown solution?
Starch absent
What is the observation of a starch test in which little starch was present?
A turbid/ colorless solution turned to a pale blue black solution/ brown solution with black specks.
What can you conclude about a starch test in which a colorless/ turbid solution turned to a blue-black solution?
Much starch present
What is the procedure for the Reducing sugars/ Benedict’s test?
To 1 cubic centimeter of solution in a test tube was added 1 cubic centimeter of Benedict’s solution and boiled
What is the preferred boiling duration for the Benedict’s test and non-reducing sugars test?
About 2 minutes
State the color changes for the reducing sugars test from absence to very much present.
A colorless/ turbid solution turned to a:
-Pale blue solution which persisted on boiled (reducing sugars absent)
-Pale blue solution then to a green solution on boiling (little reducing sugars present)
-Pale blue solution then to a green solution and finally to a yellow precipitate (moderate amount of reducing sugars present)
-Pale blue solution then to a green solution, then to a yellow precipitate and finally to an orange precipitate (much reducing sugars present)
-Pale blue solution then to a green solution, then to a yellow precipitate, then to an orange precipitate and finally a brown precipitate (very much reducing sugars present)
State the procedure for the non-reducing sugars test
To 1 cubic centimeter of solution in a test tube was added 1 cubic centimeter of dilute hydrochloric acid , boiled and then cooled.
2 cubic centimeters of dilute sodium hydroxide were added followed by 1 cubic centimeter of Benedict’s solution and boiled.
What is the significance of adding hydrochloric acid in the non-reducing sugars test?
To hydrolyze non-reducing sugars to reducing sugars
What is the significance of adding sodium hydroxide to the non-reducing sugars test?
To neutralize excess hydrochloric acid
What is the sequence of color changes of the non-reducing sugars test (from absence to much present)?
Pale blue solution (persisted) > Green solution > Yellow precipitate > Orange precipitate
What is the procedure of the protein test?
To 1 cubic centimeter of solution in a test tube was added 1 cubic centimeter of dilute sodium hydroxide solution followed by 2 drops of copper(II) sulphate solution
What are the three expected color outcomes of the protein test?
Turbid / colorless solution turned to a pale blue solution
(Proteins absent)
Turbid / colorless solution turned to a pale purple solution
(Little proteins present)
Turbid / colorless solution turned to an intense purple solution
(Much proteins present)
When incubating test solutions in a beaker, which is added first; hot or cold water? And why?
Cold water; it is easier to regulate the initial temperature this way :)
(Cold water added until slightly above level of contents and little hot water is added until optimum temperature is reached + stirred)
