14. Substances in Common Use

Question 1:  Fill in the blanks.

a. The number of molecules of water of crystallization in washing soda is 10.
b. The chemical name of baking soda is sodium bicarbonate.
c. Iodine 123 is used in treatment of hyperthyroidism.
d. The chemical name of Teflon is polytetrafluoroethene.

Question 2: Match the pairs

                        Group A                                                                            Group B

1. Saturated brine                                                                   c. crystallization of salt
2. Fused salt                                                                             a. sodium metal freed
3. CaOCl2                                                                                   d. oxidation of colour
4. NaHCO3                                                                                b. basic salt

Question 3: Write answers to the following

a. What is meant by radioactivity?

Ans. The property of spontaneously emitting invisible, highly penetrating and high energy radiation is called radioactivity.

Examples: Elements having high mass number, such as : uranium, thorium, radium.

b. When is said to be the nucleus unstable?

Ans. The nucleus of a radioactive elements such as uranium, thorium and radium have a property of spontaneously emitting invisible highly penetrating and high energy radiation. This is due to the unstable nucleus of these elements that undergo spontaneous decay by emission of either alpha, beta or gamma radiations to form a more stable nucleus.

c. Which diseases are caused by artificial food colours ?

Ans. Diseases like ADHD (Attention Deficit Hyperactivity Disorder) can affect children
due to excessive consumption of foods with added food colours.

d. Where in the industrial field is radioactivity used?

​Ans. Radioactivity has various industrial application:
1. Radiography – Internal cracks and voids in cast iron articles and iron solder can be detected with the help of gramma rays. For this purpose, isotopes like cobalt-60, iridium-192 are used in the radiography camera. This technique is used for detecting flaws in metal work.
2. Measurement of thickness, density and level – It is necessary to maintain the required thickness in the manufacture of aluminium, plastic, iron sheets of differing thickness. In the manufacturing process, a radioactive substance is placed on one side and an instrument to measure radiation on the other. The radiation read by the measuring instrument varies with the thickness of the sheet.
3. Material inside a packing can also be examined by the same technique.
4. Luminescent paint and radioluminescence – The radioactive substances radium, promethium, tritium with some phosphor are used to make certain objects visible in the dark, for example, the hands of a clock, and certain other objects. Krypton-85 is used in HID (High Intensity Discharge) lamps while promethium-147 is used in portable X-ray units as the source of beta rays.
5. Use in Ceramic articles – Luminous colours are used to decorate ceramic tiles, utensils, plates, etc. Earlier uranium oxide was used in these paints.

e. Write down properties of teflon.

Ans. Teflon has the following properties:
(i) The atmosphere and chemical substances have no effect on Teflon.
(ii) Neither water nor oil will stick to Teflon coated articles.
(iii) High temperatures do not affect Teflon as its melting point is 327 C.
(iv) Teflon coated articles are easy to clean.

f. What type of colours will you use to celebrate ecofriendly Rang Panchami? Why?

Ans. (i) We should use eco-friendly colors for Rang Panchami and avoid the artificial colors.
(ii) Eco-friendly colors can be prepared from natural resources such as beet root, flowers of flame of forest, spinach, flame tree (gulmohar).
(iii) We can protect our health by using such eco-friendly colors.
(iv) This is because, the red color used for Rang Panchami is very dangerous. It contains a high proportion of mercury in it. This poses risks like blindness, skin cancer, asthma, itching of the skin, permanent blocking of sweat pores etc. Therefore, it is necessary that artificial colours are used cautiously.

g. Why has the use of methods like Teflon coating become more common?

Ans. The following properties of Teflon are reasons for the wide use of Teflon coating:
1. The atmosphere and chemical substances have no effect on Teflon.
2. Neither water nor oil will stick to Teflon coated articles.
3. High temperatures do not affect Teflon as its melting point is 327 C.
4. Teflon coated articles are easy to clean.

Question 4: Give scientific explanation

a. Bleaching powder has the odour of chlorine.

Ans. (i) As bleaching powder undergoes slow decomposition due to the carbon dioxide in air and chlorine gas is released.
Reaction:  CaOCl2 + CO2 ——–> CaCO3 + Cl2­­­­­­­­­­­­­
(ii) It is because of this release of chlorine gas the baking powder has the odour of chlorine.

b. The hard water of a well becomes soft on adding washing soda to it.

Ans. (i) The hard water from a well or a bore-well becomes soft on adding washing soda
and we come to know this from the lather formed on it.
(ii) The hardness of water is due to the presence of chlorides and sulphates of calcium and magnesium in it. Na2CO3 is added to it to soften such water and make it suitable for use.
(iii) The reaction with Na2CO3 causes the formation of insoluble carbonate salts of magnesium and calcium.
Reaction: MgCl 2 (aq)+ Na 2 CO 3 (s) ——–> MgCO 3 (s) + 2 NaCl (s)

c. Soap forms a precipitate in hard water.

Ans. When soap is mixed with hard water calcium and magnesium salts
of fatty acids are formed. These being water insoluble they form a precipitate and that is
why lather is not formed.

d. The particles of powder are given an electric charge while spraying them to form the powder coating.

Ans. The particles of powder are given an electric charge while spraying them to form the powder coating, because the electrostatic charge on the particles causes a uniform layer of powder to stick on the metal surface to avoid rusting.

e. The aluminium article is used as an anode in the anodising process.

Ans. (i) In the anodizing process a protective layer is formed naturally on the surface of aluminium metal by reaction with oxygen in air. This layer can be made of the desired thickness.
(ii) Anodizing is done by electrolysis. Dilute acid is taken in the electrolytic cell and the aluminium article is dipped in it as the anode. When an electric current is passed hydrogen gas is released at the cathode and oxygen gas at the anode.
(iii) A reaction with oxygen occurs and a layer of hydrated aluminium oxide is formed on the anode, i.e. the iron article.
Hence aluminium article is used as an anode in the anodising process.

f. When the radiation coming out from certain radioactive substance is passed through an electric field, marks are found at three places on the photographic plate placed in its path.

Ans. (i) When the radiation coming out from certain radioactive substance is passed through an electric field, marks are found at three places on the photographic plate placed in its path.
(ii) These three marks represent the three kind of rays which are emitted by the radioactive substances. One type of radiation deviated slightly towards the negatively charged plate and were called alpha rays. The second type of radiation deviated substantially towards the positively charged plate and was called the beta rays. The third type of radiation did not deviate at all and was called the gamma rays.
Hence marks are found at three places on the photographic plate.

g. A certain type of ceramic tiles are fixed on the outer layer of a space shuttle.

Ans. The ceramics have special properties like:
(i) Ceramics can withstand high temperatures without decomposing.
(ii) Ceramic is brittle, water resistant and an electrical insulator. Therefore, it is used in electrical instruments, for coating the interior of a kiln, the outer surfaces of ships and blades of jet engines.
Thus to sustain the high stresses of contraction and expansion of its skin while launch and reentry, the space shuttle it is covered with a certain type of ceramic tiles.

Question 5. Write answers to the following

a. Write about artificial food colours, the substances used in them and their harmful effects.

Ans. (i) Food colours are mixed in most soft drinks and foodstuffs available in the market. These food colours are in the form of powders, gels and pastes.
(ii) Food colours are used in domestic as well as commercial products. Certain colours and essences are added to ice cream, ice candies, sauce, fruit juices, cold drinks, pickles, jams and jelly.
(iii) Food colors are often found to be added to packaged meat (chicken, mutton), chilli powder, turmeric, sweets and other similar substances so as to give
them a good colour.
(iv) Food colours are natural as well as artificial. The food colours prepared from
seeds, beetroot, flowers and fruit concentrate are natural.
(v) Tetrazene, sunset yellow are artificial food colours used extensively. However, over-consumption of artificial food colours can be detrimental to health.

Harmful effects of artificial food colours:

(i) Food colours added to pickles, jam and sauce contain small quantities of lead and
mercury. These can be harmful for those who consume these products on a regular
basis.
(ii). Diseases like ADHD (Attention Deficit Hyperactivity Disorder) can affect children
due to excessive consumption of foods with added food colours.

b. What is meant by water of crystallization? Give examples of salts with water of crystallization, and their uses.

Ans. (i) Ionic compounds are crystalline in nature. These crystals are formed as a result of definite arrangement of ions. In the crystals of some compounds water molecules are also included in this arrangement. That is the water of crystallization.
(ii) The water of crystallization is present in a definite proportion of the chemical formula of the compound.
(iii) Some substances in our daily use which contain water of crystallization
1. Alum (Potash alum – K2SO4.Al2(SO4)3 .24H2O )
2. Borax (Na2B4O7.10H2O)
3. Epsom salt (Magnesium sulphate MgSO4.7H2O)
4. Barium chloride (BaCl2.2H2O)
5. Sodium sulphate (Glauber’s salt Na2SO4.10 H2O)

Uses of substances which contain water of crystallization:

1. Alum (Potash alum – K2SO4.Al2(SO4)3 .24H2O )

(i) Alum is used in the process of water purification. Because of property of coagulation, the solid impurities in water come together, become heavy and settle to the bottom. As a result, the water above becomes clear.
(ii) as a mordant in dyeing, and in tanning.
(iii) It is still widely used in cosmetics (in deodorant),
(iv) in food preparation in baking powder and pickling
(v) making of fire-proof paper and cloth.

2. Borax (Na2B4O7.10H2O)

(i) Borax is a common component of many detergents, cosmetics, and enamel glazes.
(ii) Used to make buffer solutions in biochemistry,
(iii) as a fire retardant,
(iii) as an anti-fungal compound,
(iv) in the manufacture of fiberglass,
(v) useful as an insecticide.

3. Epsom salt (Magnesium sulphate MgSO4.7H2O)

(i) Epsom salt has been traditionally used as a component of bath salts for relaxing.
(ii) Used as a beauty product.
(iii) Gardeners use it to improve growth of crops.
(iv) Use is effective in the removal of splinters.

4. Barium chloride (BaCl2.2H2O)

(i) In industries, barium chloride is used in the purification of brine solution in caustic chlorine plants
(ii) used in the manufacture of heat treatment salts,
(iii) used case hardening of steel.
(iv) used in manufacture of other barium salts.

5. Sodium sulphate (Glauber’s salt Na2SO4.10 H2O)

(i) The largest use of Sodium sulphate is as filler in powdered home laundry detergents.
(ii)  Used as a diluent for food colours.
(iii) Used as a fining agent, to help remove small air bubbles from molten glass.
(iv) Used as drying agent for organic liquids.

c. Write briefly about the three methods of electrolysis of sodium chloride.

Ans. (i) When an electric current is passed through a saturated solution of sodium chloride (brine) it is electrolysed and hydrogen gas is released at the cathode while
chlorine gas is released at the anode. This method is used for production of chlorine gas. In this method an important basic compound NaOH is formed in the cell.
Reaction : 2NaCl + 2H2O  ——->  2NaOH + Cl2 + H2
(ii) Dilute aqueous sodium chloride solution when electrolysed produces hydrogen at the cathode and oxygen at the anode.
(ii) When the salt of sodium chloride is heated to a high temperature (about 800 0C), it melts. This is called the fused state of the salt. When fused salt is electrolysed, chlorine gas is released at the anode and liquid sodium metal, at the cathode.

Question 6: Write the uses.

a. Anodizing

(i) It is used for iron surfaces to protect them from rusting.
(ii) It is used in the manufacturing of anodized utensils like griddles and cookers.

b. Powder coating

(i) Powder coating is done to avoid rusting of iron objects
(ii) It is slao done on plastic and fibre (MDF) materials to make them durable and attractive.

c. Radioactive substances

(i) Used as a fuel in nuclear reactors for  power generation.
(ii) Used in the manufacturing of luminescent paints and objects that show radioluminance.
(iii) Used in ceramics, utensils, plates etc. to obtain luminous colours.
(iv) In medical science, it is used for detection of cancer, treatment of hyperthyroidism and bone cancer.
(v) In agriculture, they are used in food preservation, prevention of sprouting in onions and potatoes etc.

d. Ceramic

(i) Ceramics are brittle, water resistant, electrical insulators and can withstand high temperatures without decomposing therefore, used in electrical instruments,
for coating the interior of a kiln, the outer surfaces of ships and blades of jet engines.
(ii) Also a certain type of ceramic tiles are fixed on the outer layer of a space shuttle.
(iii) Some types of ceramics are used as superconductors.

7. Write the harmful effects

a. Artificial dye

(i) Dyeing hair can have adverse effects like hair fall, damage to hair texture, burning of skin, adverse effect on eyes, etc.
(ii) Lipstick contains a dye named carmine. It does not affect lips but causes stomach disorders.
(iii) Excessive use of plants for making natural dyes results in deterioration of the environment.

b. Artificial food colour

(i) Food colours added to pickles, jam and sauce contain small quantities of lead and
mercury. These can be harmful for those who consume these products on a regular
basis.
(ii) Diseases like ADHD (Attention Deficit Hyperactivity Disorder) can affect children
due to excessive consumption of foods with added food colours.

c. Radioactive substances

(i) The central nervous system is affected by radioactive radiations.
(ii) Hereditary defects are generated by bombardment of radiation on D.N.A in the body.
(iii) Radioactive radiation can penetrate the skin, and causes diseases like skin cancer,
leukemia.
(iv) The radiative pollutants created due to explosions enter the body through air and it is difficult to control them.
(v) The radioactive pollutants released in the sea enter the bodies of fishes and through
them enter the human body.
(vi) The radioactive paint on the watch can cause cancer.
(vii) The radioactive isotopes strontium-90 can enter the body through plants, fruits,
flowers, cereals, milk, etc. and cause diseases like bone cancer, leukemia.

d. Deodorant

(i) Aluminium – Zirconium compounds are the most harmful chemicals in the deodorant.
Disorders like headache, asthma, respiratory disorders, heart disease are likely to occur
without our knowledge.
(ii) There is a possibility of various skin disorders and also skin cancer due to the aluminium chlorohydrates.

8. Write the chemical formula :

  • Bleaching powder : Calcium oxychloride CaOCl2
  • Common salt : NaCl
  • Baking soda : Sodium bicarbonate NaHCO3
  • Washing soda : Na2CO3.H2O

9. Explain what you see in the following picture :

14-01

The above picture shows the process of powder coating. The process of powder coatg can be explained as follows:
(i) Powder coating is a method of applying a layer harder than paint on
the surface of an iron object to prevent rusting.
(ii) In this method, a polymer resin, a pigment and some other ingredients are melt mixed, cooled and ground into a uniform powder.
(iii) This powder is sprayed on the polished metal surface by electrostatic spray deposition (ESD).
(iv) In this method, the particles of the powder are given an electrostatic charge due to which a uniform layer of the powder sticks to the metal surface. Then the object is heated in the over along with the coating.
(v) A chemical reaction occurs in the layer, resulting in the formation of long cross-linked polymeric chains. This powder coating is highly durable, hard and attractive.
(vi) Powder coating can be done on plastic and medium density fibre (MDF) board in day to day use as well.

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