NCERT Class 9 Science Lab Manual – Food Sample Test for Starch and Adulteration
- The presence of starch in the given food sample
- The presence of adulterant metanil yellow in dal
- Carbohydrates: The energy-giving food, that contains carbon, oxygen,and hydrogen.
- Glucose: It is the simplest form of carbohydrate, formula: C6H12O6. It instantly gives energy on oxidation during respiration.
- Starch: The long chain of glucose forms starch, e.g., rice, potato.
- Iodine: It is a halogen, brown coloured liquid solution present in lab used for starch test.
Iodine + Starch \(\longrightarrow \) Blue black colour.
- When food is mixed with undesirable substances which can cause harm to our body, this is called adulteration.
- Long time consumption of adulterated food causes severe health problems which may lead to cancer, stomach ulcers, brain damage, etc.
- Adulterant: Any substance that is added to the food and degrades the quality of food material is called an adulterant.
- Adulteration of food affects the health of the people.
- Foodstaff and their common adulterants
Harmful effects of Adulteration on health:
- Mixing of argemone oil in mustard oil results in dropsy, gastrointestinal disturbances, swelling of limbs etc. Dropsy has also caused death in some cases.
- Mixing of Kesari dal in Arhar dal causes crippling of lower limbs.
- Mixing of lead chromate in turmeric causes paralysis, mental retardation, brain damage and stiffening of limbs.
- Mixing of artificial colour (coal tar) in tea leaves causes cancer.
Diseses caused by adulterants :
- It is a yellow colour dye, generally used for colouring food material. For e.g., starch when dyed with metanil yellow looks like turmeric. Poor quality dal when dyed with metanil yellow looks superior quality dal.
- Test for Metanil Yellow: On addition of hydrochloric acid, the metanil yellow solution turns into pink colour.
- Disease caused by metanil yellow consumption: Paralysis, brain damage, anaemia and abortion.
- Prevention of Food Adulteration (PFA): It is an act passed by Government of India to check the adulteration in food.
- Food articles with “Agmark” and FPO (Food Products Order) label are safe with unadulterated food in it.
(A) To test the presence of starch in the given food sample.
Test tube, test tube stand, dropper.
Given food sample, Iodine solution.
- Take a clean test tube and add a little given food sample and water in it.
- Add few drops of iodine solution in the given food sample. Shake the contents of the test tube. Observe the change in colour.
The colour of the given food sample changes to blue-black on adding iodine solution to it.
The given sample of food contains starch (only if iodine changes its colour to blue-black).
Given food sample + Iodine solution \(\longrightarrow \) Blue-black colour
(B)To test the presence of the adulterant metanil yellow in dal.
Test tubes, test tube holder, test tube stand, dropper.
Any yellow dal (arhar), cone, hydrochloric acid
- Take any yellow dal in a test tube in powdered form. Add 2-3 mL of water and shake well.
- Add 2-3 drops of concentrated hydrochloric acid in the test tube, shake the contents.
Record your observation.
A pink colour solution appears in the test tube.
The given sample of dal contains metanil yellow adulteration.
- Use clean and dry test tubes.
- Handle concentrated HC1 carefully.
- Use chemical judiciously. Do not waste unnecessarily.
Name the polymer of glucose.
Name the main source of starch.
In which form food is stored in animals?
Name the adulterant present in turmeric and yellow dal.
Name the acid used to test the metanil yellow in dal.
Name the solution used to test the presence of starch.
Give the full form of FPO and Agmark.
FPO \(\longrightarrow\) Food Products Order.
Agmark \(\longrightarrow\) Agricultural Marketing.
PRACTICAL BASED QUESTIONS
What is the difference between starch and carbohydrate?
Starch is a stored food under the nutritional group—carbohydrates.
What is adulteration?
The addition of cheaper food material in better quality food is called adulteration.
Starch is a polymer of glucose, will glucose turn blue-black with brown iodine solution?
No, glucose is a simplest sugar.
NCERT LAB MANUAL QUESTIONS
In what form the food is stored in plants?
Food is stored in the form of starch.
Which is the common adulterant of arhar dal?
What are the effects of adulteration of food items?
Adulterants make the food very attractive and colorful but it also makes the food toxic and dangerous for consumption.
Why do the old stock of potato taste sweet?
Starch present in the potatoes undergoes a chemical change over a long period of time and break down to form simple sugars due to which it tastes sweet.
What are the different adulterants commonly used in foods?
The commonly used adulterants in food are:
- Black pepper: dry seeds of papaya
- Honey: jaggery
- Red chilli powder: red brick powder
- Mustard seed: argemone seeds
MULTIPLE CHOICE QUESTIONS (MCQs)
Questions based on Procedural and Manipulative Skills
(d) all of these.
Acid used to test the presence of metanil yellow in dal is
(a) nitric acid
(b) sulphuric acid
(c) hydrochloric acid
(d) carbonic acid.
The cheaper materials which are added to superior food items for profit is called
(c) metanil yellow
Meenu was trying to test the presence of starch in potato tuber. She forgot the reagent with which the starch gives blue colour. Help her to select the correct stain from the following
(b) Methylene blue
The following statements describe the steps to detect the presence of metanil yellow in dal. One of the four statements given below is incorrect.
(a)Take 2 mL of potato extract
(b) Grind 3-5 g of dal and prepare solution
(c) Filter the contents and collect the filtrate
(d) Add 2-3 drops of concentrated hydrochloric acid.
The incorrect statement is
In a school laboratory most commonly used chemical to test the presence of metanil yellow in a dal is
(a) iodine solution
(b) cone. HCl
Metanil yellow is used as an adulterant for
(c) yellow dal
(d) yellow dal and turmeric powder.
Institute set up by Govt, for setting food standard
(d) all of the above
The food in plants is stored in the form of
(d) none of the above
The commonly found adulterant in chilli powder is
(a) chalk powder
(c) brick powder
Questions based on Observational Skills
When iodine solution is added into starch solution the colour obtained is
The colour obtained on addition of HCl to metanil yellow is
The test tubes A, B and C are taken with food samples of dal, mustard and rice respectively in powdered form. On adding iodine solution the blue-black colour is observed in
(a) Test tube A
(b) Test tube B
(c) Test tube C
(d) None of these.
Four test tubes P, Q, R and S shown below contain the following:
Sugar solution on adding 2 drops of iodine to each test tube, which will show blue-black solution?
(a) P and Q
(b) Q and R
(c) R and S
When iodine solutions is added to starch solution, the colour produced is
Questions based on Reporting and Interpretation Skills
Starch is present in
(d) all of these.
Which one of the following food material will not give blue-black colour on the addition of iodine?
Arun wanted to test the adulteration of arhar dal. He washed a few grains of dal with water which turned yellow. He then added a few drops of HCl. The yellow water turned pink in colour. This showed that the dal was adulterated with:
(a) Metanil yellow
(b) Crimson yellow
(c) methylene yellow
(d) Methyl yellow.
Substance ‘X’ was added to a test tube containing water and grinded arhar dal to test the presence of metanil yellow. The colour of the solution changed to pink. Identify ‘X’.
Filtrate of a food product is taken in four test tubes marked A, B, C and D. Few drops of the following is added to the test tubes to test the presence of starch.
(A) sulphuric acid to test tube A
(B) iodine solution to test tube B
(C) chlorine solution to test tube C
(D) sodium hydroxide to test tube D
Blue black colour will appear in the test tube
When 2-4 drops of cone, hydrochloric acid are added to the given sample of arhar dal, the pink colour is due to
(a) metanil yellow
(c) turmeric powder
(d) chalk powder
Iodine solution was added to four samples of food I, II, III, IV. Which will develop blue-black colour?
I. boiled rice
II. crushed potatoes
III. boiled arhar dal
IV. powdered arhar dal
(a) I, II
(b) I, II, III
(c) I, II, IV
(d) I, III, IV
Which of the under-mentioned food groups will not turn blue black when treated with iodine? –
(a) rice, potato, bread
(b) bread, wheat, com flour
(c) rice water, boiled potato, com starch
(d) dal, fish, meat.
Students were instructed to add a few drops of iodine solution to each of the following samples.
The content turned blue-black in:
(a) A and B
(b) B and C
(c) C and D
(d) D and A
Four students A, B, C and D carried out test for the adulteration of metanil yellow in arhar dal and recorded their observations as given below. The procedure followed correctly is that of student:
A food sample turned blue-black after addition of a few drops of iodine solution. This sample contains
While doing an experiment with a potato, a student accidently dropped a liquid on it, which made the potato slice blue-black. The liquid that got dropped may be
(a) sulphuric acid
(b) hydrochloric acid
(c) Benedict’s solution
(d) Iodine solution
Metanil yellow, an adulterant used in arhar dal is basically
(a) an acid
(b) a detergent
(c) a dye
(d) none of the above.
SCORING KEY WITH EXPLANATION
- (d) Carbohydrates are the compounds of carbon, hydrogen and oxygen.
- (c) Metanil yellow colour changes to pink when heated with hydrochloric acid.
- (d) Adulterant are cheap substances added to food for profit and are very dangerous to health.
- (c) Starch test is done with iodine solution, it turns blue black when added to starch.
- (a) For testing metanil yellow adulterant potato is not required.
- (b) Metanil yellow colour changes to pink when heated with hydrochloric acid.
- (d) Metanil yellow is added as an adulterant to any food substance that is yellow in colour.
- (d) All these are Indian Standard Institutes for testing and setting food standard and quality.
- (b) Plants store the food in the form of starch.
- (c) Chilli powder is red in colour hence brick powder (red in colour) is added as an adulterant.
- (c) Iodine solution is used for starch test, it gives blue-black colour in the presence of starch.
- (c) Metanil yellow tolour changes to pink when heated with hydrochloric acid.
- (c) Test tube C contains rice and rice is rich in carbohydrtaes.
- (c) Both rice and potato contain starch and the iodine solution will turn blue-black when added to these food items.
- (c) Iodine gives blue-black colouration with starch solutions.
- (d) Starch is complex carbohydrate and is present in rice, wheat ( bread), potato.
- (b) All rice, wheat and potato contain starch but sugar does not contain starch. Iodine turns blue-black in presence of starch only. .
- (a) Metanil yellow colour changes to pink when heated with hydrochloric acid.
- (d) Metanil yellow colour changes to pink when heated with hydrochloric acid. Hence the substance X added to yellow dal is HCl.
- (b) Starch test is done with iodine solution, it turns blue- black when added to starch.
- (a) Metanil yellow colour changes to pink when heated with hydrochloric acid. Hence the substance X added to yellow dal is HCl.
- (a) Rice and potato contain starch in it but yellow dal does not contain starch.
- (d) Dal, fish and meat are rich in proteins but do not contain any starch in it.
- (a) Idly is made from rice which contains starch but talcum powder and glucose does not contain any starch.
- (b) On taking dal + water + dil. HCl, the solution turns pink due to metanil yellow.
- (c) Only starch turns blue-black with iodine solution.
- (d) Iodine solution is used for starch test, it gives blue-black colour in presence of starch.
- (c) Metanil yellow is used in dal as an adulterant for colouring. Its presence can be tested in dal by adding a few drops of HCl to a test sample, if the solution turns pink in colour, it indicates the presence of metanil yellow.