CBSE Class 9 Science Practical Skills – Food Sample Test for Starch and Adulteration

CBSE Class 9 Science Practical Skills – Food Sample Test for Starch and Adulteration

EXPERIMENT

AIM
To test

1. the presence of starch in the given food sample
2. the presence of the adulterant metanil yellow in dal.

(1) To test starch in the given food sample.

MATERIALS REQUIRED
Samples of food material (boiled rice or boiled potato), test tubes, test tube holder, iodine solution, distilled water.

THEORY
Starch is a complex carbohydrate which consists of many glucose molecules. It gives blue-black colour with iodine solution.

PROCEDURE, OBSERVATION AND INFERENCE

RESULT
The given food sample (rice/potato) contains starch.

PRECAUTIONS

1. Use reagents/chemicals judiciously.
2. Always use a clean test tube.

(2) To test the presence of the adulterant metanil yellow in dal.

MATERIALS REQUIRED
Dal, cone. HCl, distilled water, test tubes, test-tube holder, test-tube stand.

THEORY
Metanil yellow is a synthetic dye which is not permitted to use as food colour. However, it is extensively used to give yellow colour to dal and turmeric. It is toxic in nature and it has adverse effects on liver, intestine and brain. Presence of metanil yellow can be tested in dal by adding few drops of hydrochloric acid to a test sample. If the test solution turns pink in colour, it indicates presence of metanil yellow.

PROCEDURE, OBSERVATION AND INFERENCE

RESULT
Metanil yellow is present as adulterant in dal.

PRECAUTIONS

1. Use chemicals judiciously.
2. Hold test tubes with test-tube holder while adding HC1.

INTERACTIVE SESSION

Examiner:
Name blood sugar in humans. Write the most important function of sugars?
Examinee:
Glucose is blood sugar in humans. Sugars are energy-giving foods.

Examiner:
In what form are carbohydrates stored in plants and animals?
Examinee:
Plants – Starch; Animals – Glycogen.

Examiner:
On the basis of physical property how would you distinguish between glucose and starch?
Examinee:
Glucose is soluble in water while starch is not.

Examiner:
What do you mean by adulteration?
Examinee:
Addition or mixing of undesirable materials with foodstuffs is called adulteration.

Examiner:
Name the disease caused by consumption of Arhar dal adulterated by Khesari dal.
Examinee:
Lathyrism.

Examiner:
How does Lathyrism affect our body?
Examinee:
In Lathyrism, lesions develop in the lower spinal cord which causes paralysis.

Examiner:
What is metanil yellow? Why is it added to dal?
Examinee:
Metanil yellow is toxic yellow dye which is added to foodstuffs to improve their colour and appearance.

Examiner:
What is Dropsy?
Examinee:
Dropsy is an epidemic caused by consumption of mustard oil mixed with adulterant argemone oil.

NCERT LAB MANUAL QUESTIONS

Question 1:
Which is the common adulterant of Arhar dal?
Answer:
Metanil yellow

Question 2:
What are the effects of adulteration of food items?
Answer:

1. They become toxic.
2. Adulterants are added to enhance appearance and weight of food items.

Question 3:
Why do the old stock of potato taste sweet?
Answer:
When potatoes are kept for long, starch present in them breaks down into simple sugars which imparts sweet taste.

Question 4:
What are the different adulterants commonly used in foods?
Answer:

1. Papaya seeds in black pepper.
2. Cow dung in coriander powder.
3. Brick powder in red chilli powder.
4. Khesari dal and metanil yellow in Arhar dal.

PRACTICAL BASED QUESTIONS
Multiple Choice Questions/VSA

Question 1:
To observe, starch granules in potato under a microscope, a fresly cut surface of potato was pressed on a slide. The stain that will show starch granules clearly is
(a) methylene blue
(b) iodine
(c) safranin
(d) eosin.

Question 2:
Metanil yellow added to foodstuffs as
(a) vitamin
(b) adulterant
(c) flavouring agent
(d) preservative

Question 3:
Which one of the following can be used for test of starch?
(a) Lemon
(b) Albumin
(c) Papaya
(d) Potato

Question 4:
Common table sugar used is
(o) fructose
(b) glucose
(c) sucrose
(d) maltose

Question 5:
Epidemic Dropsy is caused by
(a) vegetable oil in desi ghee.
(b) argemone oil in mustard oil.
(c) coconut oil in mustard oil.
(d) none of the above.

Question 6:
Seema bought arhar dal (tuar dal) from the market. On adding water to the dal, the water became yellow in colour. She took a sample of this yellow water to the laboratory and added a few drops of HCl. The sample became pink. This confirmed that the adulterant added to the dal was
(a) turmeric
(b) metanil yellow
(c) potassium dichromate
(d) yellow dye.

Question 7:
A student took 5 g of powdered arhar dal in a test tube and added 5 ml water into it. She shook the test tube vigorously. After adding a few drops of HCl she observed that the dal tested positive for adulteration with metanil yellow. The observation she noted was:
(а) the water turned brown.
(b) there was no colour change in the water.
(c) the water turned pink.
(d) the water turned blue-black.

Question 8:
While doing an experiment with a potato, a student accidently dropped a liquid on it, which turned the potato slice blue-black. The liquid that got dropped may be was
(a) sulphuric acid
(b) hydrochloric acid
(c) benedict’s solution
(d) iodine solution.

Question 9:
The teacher asked the students to correctly record results of the experiment done to detect presence of metanil yellow in an adulterated arhar dal sample that was provided to them.

Question 10:
Four test tubes P, Q, R, S shown below contain the following:

On adding 2 drops of idione to each test tube which will show blue-black solution?
(a) P and Q
(b) Q and R
(c) R and S
(d) all the test tubes

Question 11:
A science teacher soaked arhar dal in water for few hours and put 2 ml of solution into four test tubes each and asked four students to test it for the presence of adulterant metanil yellow. Student A put water into it, student B put HCl into it, student C put NaOH into it and student D put alcohol into it. The student who would get the correct result is
(a) student A
(b) student B
(c) student C
(d) student D.

Question 12:
A student added only two drops of iodine to a rice extract in test tube A. Another student added a little rice extract to iodine solution in test tube B. They would then observe
(a) a change of colour to blue-black in test tube A but not in test tube B.
(b) a change of colour to blue-black in test tube B but not in test tube A.
(c) a change of colour to blue-black in both test tubes A and B.
(d) no change of colour in any test tube.

Question 13:
Paul was rushing with a bottle of tincture iodine. Some iodine solution splashed on his yellow coloured cotton shirt and also on the white table cloth. The stain on the table cloth was yellowish brown while that on his shirt was blue-black. The most plausible scientific reason for this is that the ‘
(а) shirt was dyed with metanil yellow.
(б) shirt was starched after washing.
(c) table cloth was starched but not the shirt.
(d) shirt had absorbed sweat.

Question 14:

The food extract has
(a) sugars
(b) starch
(c) proteins
(d) fats

Question 15:
Substance ‘X’ was added to a test tube containing water and grounded arhar dal to test the presence of metanil yellow. The colour of solution changed to pink. Identify ‘X’.
(a) H₂0
(b) NaOH
(c) H₂C0₃
(d) HCl

ANSWER KEY
Multiple Choice Questions/VSA

1. (b)
2. (b)
3. (d)
4. (c)
5. (b)
6. (b)
7. (c)
8. (d)
9. (b)
10. (c)
11. (b)
12. (c)
13. (b)
14. (b)
15. (d)

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