Chapter 14 - Substances in Common Use
1. Fill in the blanks.
a. The number of molecules of water of crystallization in washing soda is _______
Ans: 10
b.The chemical name of baking soda is _______
Ans: Sodium bicarbonate
c. _______ is used in treatment of hyperthyroidism.
Ans: Iodine-123
d. The chemical name of Teflon is _______
Ans: Polytetra
2. Match the pairs.
| A | B |
|---|---|
1. Saturated brine | a. sodium metal freed |
2. Fused salt | b. basic salt |
3. CaOCl₂ | c. crystallization of salt |
4. NaHCO₃ | d. oxidation of colour |
Ans:
| A | 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 |
3. Write answers to the following
a. What is meant by radioactivity?
Ans:
(i) Elements with a high atomic number such as uranium, thorium, radium have a property of spontaneously emitting invisible, highly penetrating and high energy radiation.This property is called radioactivity.
(ii) A substance having this property is called a radioactive substance.
b. When is the nucleus said to be unstable?
Ans:
(i) It is the balance of protons and neutrons in a nucleus which determines whether a nucleus will be stable or unstable.
(ii) Too many neutrons or protons upset this balance disrupting the binding energy from the strong nuclear forces making the nucleus unstable.
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 is used in industrial fields in the following areas:
(A) Radiography:
(i) Internal cracks and voids in cast iron articles and iron solder can be detected with the help of gamma rays.
(ii) For this purpose, isotopes like cobalt-60 and iridium-192 are used in radiography cameras.
(iii) This technique is used for detecting flaws in metal work.
(B) Measurement of thickness, density, and level:
(i) It is necessary to maintain the required thickness in the manufacture of aluminium, plastic, and iron sheets of differing thicknesses.
(ii) In the manufacturing process, a radioactive substance is placed on one side and an instrument to measure radiation on the other.
(iii) The radiation read by the measuring instrument varies with the thickness of the sheet.
(iv) Material inside a package can also be examined by the same technique.
(C) Luminescent paint and radioluminescence:
(i) The radioactive substances radium, promethium, and tritium with some phosphorus are used to make certain objects visible in the dark, for example, the hands of a clock and certain other objects.
(ii) 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.
(D) Use in ceramic articles:
(i) Luminous colours are used to decorate ceramic tiles, utensils, plates, etc.
(ii) Earlier, uranium oxide was used in these paints.
e. Write down properties of teflon.
Ans: Properties of teflon:
(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 regularly use artificial colours on Rang Panchami.
(ii) The red colour used on Rang Panchami is very dangerous. It contains a high proportion of mercury.
(iii) This poses risks like blindness, skin cancer, asthma, itching of the skin, permanent blocking of sweat pores, etc.
(iv) Therefore, it is necessary to use eco-friendly colours.
(v) We should prepare the colours for Rang Panchami from natural resources such as beet root, flowers of the forest flame, spinach, and flame tree (gulmohar), and protect our health.
g. Why has the use of methods like Teflon coating become more common?
Ans: The use of methods like Teflon coating became more common because of the following properties of Teflon:
(i) The atmosphere, rainwater, 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.
(v) Teflon is a poor conductor of electricity.
4. Give scientific explanation
a. Bleaching powder has the odour of chlorine.
Ans:
(i) When exposed to air, bleaching powder reacts with carbon dioxide in air to produce calcium carbonate and chlorine.
(ii) Thus, it smells of chlorine.
(iii) Chemical Equation:
CaOCI₂ + CO₂ → CaCO₃ + Cl₂↑
Bleaching Carbon Calcium Chlorine
Powder Dioxide Carbonate
b. The hard water of a well becomes soft on adding washing soda to it.
Ans:
(i) The hardness of hard water is due to the presence of chlorides and sulphates of calcium and magnesium in it.
(ii) NaCl is added to it to soften the water and make it suitable for use.
(iii) The reaction with Na, CO, causes the formation of insoluble carbonate salts of magnesium and calcium.
(iv) This changes the hard water into soft water, which makes it suitable for use.
MgCl2 (4) +Na₂CO3 (8) MgCO3(s) +2 NaCl (s)
(iii) Chemical Equation:
MgCI₂ + Na₂CO₃ → MgCO₃ + 2NaCl
Magnesium Sodium Magnesium Sodium
Chloride Carbonate Carbonate Chloride
c. Soap forms a precipitate in hard water.
Ans:
(i) When soap is mixed with hard water, calcium and magnesium salts of fatty acids are formed.
(ii) 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:
(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.
(v) Then the object is heated in the oven along with the coating.
(vi) A chemical reaction occurs in the layer, resulting in the formation of long cross-linked polymeric chains.
e. The aluminium article is used as an anode in the anodising process.
Ans:
(i) A protective layer is formed naturally on the surface of aluminium metal by reaction with oxygen in air.
(ii) In the anodizing process, this layer is made of the desired thickness. Anodizing is done by electrolysis.
(iii) Dilute Sulphuric acid is taken in the electrolytic cell and the aluminium article is dipped in it as the anode.
(iv) When an electric current is passed, hydrogen gas is released at the cathode and oxygen gas at the anode.
(v) A reaction with oxygen occurs and a layer of hydrated aluminium oxide is formed on the anode. Therefore, aluminium article is used as an anode in the anodizing 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. This is because the radiation coming out from radioactive substance are of three types Alpha rays, Beta rays and Gamma rays.
(ii) The rays which get deviated slightly towards negatively charged plate are called alpha rays. They get deviated towards negatively charged plate because they are made of positively charged particles called as alpha particles (He⁺⁺)
(iii) The rays which get deviated substantially towards the positively charged plate are called beta rays. They get deviated towards positively charged plate because they are made of negatively charged particles called as beta particles (e⁻).
(iv) The rays which do not deviate at all are called gamma rays. They are uncharged electromagnetic radiation. 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:
(i) Each shuttle is covered by more than 24,000 of the six- by six-inch advance ceramic tiles. This tiles withstand high temperatures without decomposing. They are brittle, water resistant and electrical insulator. Most of the tiles are made of silica fibres, which are produced from high-grade sand (SiO₂).
(ii) Silica is an excellent insulator because it transports heat slowly. When the outer portion of a tile gets hot, the heat takes a long time to work its way down through the rest of the tile to the shuttle’s skin. The tiles keep the orbiter’s aluminum skin at 350 degrees or less.
(iii) The silica fibers are mixed with water and chemicals, and the mixture is poured into molds, which are zapped in microwave ovens at 2,350 degrees to fuse the silica fibres. Tiles are too brittle to attach to the orbiter directly.
(iv) The shuttle’s skin contracts slightly while in orbit, then expands during re-entry.
(v) In addition, the stresses of launch and re-entry cause the skin to flex and bend. Such motions. could easily crack the tiles or shake them off. To keep them in place, workers glue the tiles to flexible felt-like pads, then glue the pads to the orbiter.
5. Write answers to the following
a. Write about artificial food colours, the substances used in them and their harmful effects.
Ans:
(a) Artificial food colour and substances in them
(i) Food colours are mixed in most soft drinks and foodstuffs available in the market.
(ii) These food colours are in the form of powders, gels and pastes.
(iii) Food colours are used in domestic as well as commercial products.
(iv) Certain colours and essences are added to ice cream, ice candies, sauce, fruit juices, cold drinks, pickles, jams and jelly.
(v) Food colours 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.
(vi) Tetrazene, sunset yellow are artificial food colours used extensively.
(b) 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:
The exact number of water molecules that are chemically bonded to a molecule of a salt within a hydrated crystalline compound is called “water of crystallization.” Some substances we use daily that contain water for crystallisation are:
(i) Alum (Potash alum: K₂ SO₄ • AL₂ (SO₄)₃ • 24H₂O)
(ii) Borax (Na₂B₄O₇ • 10H₂O)
(iii) Epsom salt (Magnesium sulfate, MgSO₄ • 7H₂O)
(iv) Barium chloride (BaCl₂ • 2H₂O)
(v) Sodium sulphate (Glauber’s salt, Na₂SO₄ • 10 H₂O)
(vi) Blue vitriol (copper sulfate, CuSO₄ • 5H₂O)
Uses of these salts are as given below:
(i) Alum (Potash alum: K₂ SO₄ • AL₂ (SO₄)₃ • 24H₂O)
(a) Alum is used in the process of water purification. Because of the property of coagulation, the solid impurities in water come together, become heavy, and settle to the bottom. As a result, the impure water or muddy water above becomes clear.
(b) Alum powder, found in the spice section of many grocery stores, may be used in pickling recipes as a preservative to maintain the crispness of fruits and vegetables.
(c) Alum is used as the acidic component of some commercial baking powders.
(d) Alum has been used as an after-shave treatment.
(ii) Borax (Na₂B₄O₇ • 10H₂O)
(a) Borax today is used for many cleaning purposes. (b) It is used to make homemade laundry detergent.
(c) It is added as a cleaning boost to any other detergent.
(d) It even keeps ants and other pests away.
(iii) Epsom salt (Magnesium sulfate, MgSO₄ • 7H₂O)
(a) Epsom salt is used as a relaxing magnesium bath soak.
(b) To grow better vegetables, add a tablespoon of Epsom salt to the soil below a vegetable plant to boost growth.
(iv) Barium chloride (BaCl₂ • 2H₂O)
(a) In industry, barium chloride is mainly used in the purification of brine solution in caustic chlorine plants.
(b) It is also used in the manufacture of heat treatment salts.
(c) It is used in hardening steel.
(d) It is used in the manufacture of pigments.
(v) Sodium sulphate (Glauber’s salt, Na₂SO₄ • 10 H₂O)
(a) In the laboratory, anhydrous sodium sulphate is widely used as an inert drying agent for removing traces of water from organic solutions.
(b) Glauber’s salt, the decahydrate, is used as a laxative.
(vi) Blue vitriol (copper sulfate, CuSO₄ • 5H₂O)
(a) Blue vitriol is used in the blood test for diagnosing anaemia.
(b) Slaked lime is used with blue vitriol in the Bordeaux mixture, which is used as a fungicide on fruits like grapes and musk melons.
c. Write briefly about the three methods of electrolysis of sodium chloride.
Ans:
Electrolysis of a sodium chloride solution with inert electrodes can be done by chemical electrolysis, producing different sets of products by providing different experimental conditions.
(i) Solid sodium chloride melts at just over 800⁰ C, and electrolysis of molten sodium chloride yields sodium metal at the cathode and chlorine gas at the anode.
(ii) A concentrated aqueous sodium chloride solution with a mercury cathode produces a solution of sodium metal in mercury (“sodium amalgam”) and chlorine at the anode.
(iii) A diluted aqueous sodium chloride solution produces hydrogen at the cathode and oxygen at the anode.
(iv) A concentrated aqueous sodium chloride solution produces hydrogen at the cathode and chlorine at the anode.
Sodium metal and chlorine gas can be obtained with the electrolysis of molten sodium chloride. Electrolysis of aqueous sodium chloride yields hydrogen and chlorine, with aqueous sodium hydroxide remaining in solution. The reason for the difference is that the reduction of Na⁺ (E° = –2.7v) is energetically more difficult than the reduction of water (–1.23v).
6. Write the uses.
a. Anodizing
Ans:
(i) It is used for iron surfaces to protect them fom rusting.
(ii) It is used in the manufacturing of anodized utensils like griddles and cookers.
b. Powder coating
Ans:
(i) It makes painted architectural steel parts resistant to heat damage, cold damage and even corrosion.
(ii) Most of metal products designed to be used outdoors are finished using the powder coating method.
c. Radioactive substances
Ans:
(i) It is used as a fuel in nuclear reactors to generate power.
(ii) It is used in controlling the thickness of paper, plastic and metal sheets during their manufacturing.
(iii) It is used in the manufacturing of luminescent paints and objects which show radioluminance. For example, substances such as radium, promethium etc. are used to make objects which glow in the dark like hands of clock. Similarly, krypton-85 is used in high intensity discharge lamps.
(iv) Radioactive substances are used in ceramics, utensils, plates etc. to obtain luminous colours.
(v) In medical science, it can be used for detection of cancer, treatment of hyperthyroidism and bone cancer.
(vi) In agricultural field they are used in food preservation, prevention of sprouting in onions and potatoes etc.
d. Ceramic
Ans:
(i) They are used in making roofing tiles, construction bricks, pottery, terracotta etc.
(ii) Special type of ceramics are used in outer surfaces of ships and blades of jet engines.
(iii) They are also used on the outer surfaces of space shuttles.
7. Write the harmful effects
a. Artificial dye
Ans:
(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 the lips but causes stomach disorders.
(iii) Excessive use of plants for making natural dyes results in deterioration of the environment.
b. Artificial food colour
Ans:
(i) Food colours added to pickles, jams, and sauces contain small quantities of lead and mercury. These can be harmful to those who consume them 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
Ans:
(i) The central nervous system is affected by radioactive radiation.
(ii) Hereditary defects are generated by bombarding DNA with radiation.
(iii) Radioactive radiation can penetrate the skin and cause diseases like skin cancer and leukemia.
(iv) The radioactive pollutants created by explosions enter the body through the air, and it is difficult to control them.
(v) The radioactive pollutants released in the sea enter the bodies of fish and, through them, enter the human body.
(vi) The radioactive paint on the watch can cause cancer.
(vii) The radioactive isotope strontium-90 can enter the body through plants, fruits, flowers, cereals, milk, etc. and cause diseases like bone cancer and leukemia.
d. Deodorant
Ans:
(i) Aluminium-Zirconium compounds are the most harmful chemicals in the deodorant. Disorders like headache, asthma, respiratory disorders, and 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, common salt, baking soda, washing soda
Ans:
a.Bleaching powder – CaOCl₂
b. common salt – NaCl
c. baking soda – NahCO₃
d. washing soda – Na₂CO₃•10H₂0
9. Explain what you see in the following picture.
Ans:
(i) This picture shows the powder coating of the given object. Powder coating is a method of applying a layer harder than paint on the surface of an iron object to prevent rusting.
(ii) A polymer resin, a pigment, and some other ingredients are melted, mixed, cooled, and ground into a uniform powder.
(iii) This powder is sprayed on the polished metal surface by electrostatic spray deposition (a method in which the particles of powder are given an electric charge) that makes a uniform coating on the substance.
(iv) Once completely coated, the object is then heated, which results in the formation of long, cross-linked polymeric chains.
(v) This coating is highly durable, hard, and attractive.
(vi) It can be done on plastic and medium-density fiberboard as well.