Substances in Common Use Class 9 Science Notes Maharashtra Board

Substances in Common Use Class 9 Science Notes Maharashtra State Board

We use various substances in day-to-day life. We have previously learned in some detail about a few of them, their uses and constituents, and the method of their preparation.

Important Salts in Daily Life
The ionic compounds that do not contain H+ and OH ions and contain only one kind of cation and anion are called simple salts. For example, Na2SO4, K3PO4, CaCl2. Inorganic substances occur naturally in the form of salts rather than acids or bases. About 80 million tons of salt are added every year to seawater. Therefore, the sea is said to be a rich source of salt. The sea is a rich source of several salts of various elements such as chlorine, sodium, magnesium, potassium, calcium, and bromine. However, we also use other salts apart from these in day-to-day life. The important salts found in seawater are

  • Sodium chloride
  • Magnesium chloride
  • Magnesium sulphate
  • Potassium chloride
  • Calcium carbonate
  • Magnesium bromide

We have seen in the previous lesson that salt is neutral when its pH value is 7. Such a salt is made from a strong acid and a strong base. The pH value of a salt made from a strong acid and a weak base is less than 7 and it is acidic. On the other hand, the pH value of a salt made from a weak acid and strong base is more than 7 and it is basic. Let us now learn about some salts of everyday use.

Substances in Common Use Class 9 Science Notes Maharashtra Board

Sodium Chloride (Table Salt – NaCl)
Table salt, or common salt, which gives a salty taste to food, is the most used of all salts. Its chemical name is sodium chloride. Sodium chloride is formed by a neutralization reaction between sodium hydroxide and hydrochloric acid. We have already seen that this is a neutral salt and that the pH value of its aqueous solution is 7.
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Properties and Uses:

  • Common salt is a colorless and crystalline ionic compound. There is no water of crystallization in its crystalline structure.
  • It is a neutral salt, salty.
  • This compound is used for the production of salts like Na2CO3, and NaHCO3.
  • When an electric current is passed through a saturated solution of sodium chloride (brine) it is electrolyzed and hydrogen gas is released at the cathode while chlorine gas is released at the anode. This method is used for the production of chlorine gas. In this method, an important basic compound NaOH is formed in the cell.
    2NaCl + 2H2O → 2NaOH + Cl2 ↑+ H2
  • When salt is heated to a high temperature (about 800°C), it melts. This is called the fused state of the salt.
  • When fused salt is electrolyzed, chlorine gas is released at the anode and liquid sodium metal, at the cathode.

Salt is also obtained from a certain type of rock. This salt is called rock salt. The mineral halite and Himalayan rock salt are some examples of rock salt. This salt is used to treat many diseases. The 25% aqueous solution of salt is called saturated brine. When \(\frac{1}{5}\) of this solution is evaporated the dissolved salt gets crystallized and salt gets separated from the solution.
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Sodium Bicarbonate (Baking Soda – NaHCO3)
Your mother brings cake on your birthday or makes it at home. She also makes crisp bhaji. Have you ever asked your mother what makes the cake porous or the bhaji crisp? Mother adds baking soda to the batter. Baking soda is a white noncrystalline powder. Its chemical name is sodium hydrogen carbonate or sodium bicarbonate and its molecular formula is NaHCO3.

Properties and Uses:

  • NaHCO3 reacts with moist litmus paper and red litmus turns blue which means that it is basic.
  • It is used to make bread, cake, and dhokla.
  • Being basic it is used to reduce acidity in the stomach.
  • NaHCO3 is used to make the active substance CO2 in the fire extinguisher.
  • Baking soda is used to clean an oven.

Bleaching Powder (Calcium Oxychloride CaOCl2)
Tap water has a typically strong odor in the rainy season. Have you experienced it? Water in a swimming pool also has the same odor. It is the odor of the chlorine gas used to destroy the microbes in the water. Chlorine gas is a strong oxidizing agent and therefore, it has a strong disinfecting as well as bleaching action.
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Chlorine is inconvenient to handle because of its gaseous state. Instead, the solid bleaching powder which has the same effect is more convenient to use. Bleaching powder undergoes slow decomposition due to the carbon dioxide in the air and chlorine gas is released. Bleaching powder gets its property because of this release of chlorine gas.
CaOCl2 + CO2 → CaCO3 + Cl2
Bleaching powder is obtained by the reaction of chlorine gas with slaked lime.
Ca(OH)2 + Cl2 → CaOCl2 + H2O

Substances in Common Use Class 9 Science Notes Maharashtra Board

Properties and Uses:

  • Bleaching powder is a yellowish-white colored solid substance.
  • Its chemical name is calcium oxychloride.
  • It has a strong odor of chlorine gas.
  • It is used for disinfection of drinking water at the water works and the water in the swimming pool.
  • It is used for the bleaching of cloth.
  • It is used for disinfection by the roadside and garbage sites.
  • Dilute sulphuric acid and dilute hydrochloric acid react rapidly with bleaching powder to release chlorine gas completely.
    CaOCl2 + H2SO4 → CaSO4 + Cl2 ↑+ H2O
  • Calcium oxychloride reacts slowly with carbon dioxide to form calcium carbonate and chlorine.

Washing Soda (Na2CO3.H2O)
Procedure: Take a sample of water from a well or a bore-well, in a beaker, add some soap to it, and stir. Then take another sample, add one spoonful of washing soda, and stir; then add some soap and stir again. Observe the changes that take place. Which changes did occur? Why do they occur? 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. 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. The reaction with Na2CO3 causes the formation of insoluble carbonate salts of magnesium and calcium.
MgCl2 (aq) + Na2CO3 (s) → MgCO3 (s) + 2NaCl (s)
Sodium carbonate is a water-soluble salt of sodium. Crystalline sodium carbonate on keeping, loses its water of crystallization readily and a white powder is obtained. This powder is called washing soda.
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Properties and Uses:

  • Washing soda is a whitish and odorless powder at room temperature.
  • Litmus has a blue color in its aqueous solution.
  • It is hygroscopic, that is, it absorbs moisture if left exposed to air.
  • It is used mainly for washing clothes.
  • Sodium carbonate is used in the glass and paper industry and also in the refining of petrol.

Some Crystalline Salts
You have learned about water crystallization in the previous chapter. We use various salts which contain water for crystallization. Some substances in our daily use that contain water for crystallization

  • Alum (Potash Alum – K2SO4.Al2(SO4)3.24H2O)
  • Borax (Na2B4O7.10H2O)
  • Epsom Salt (Magnesium Sulphate – MgSO4.7H2O)
  • Barium Chloride (BaCl2.2H2O)
  • Sodium Sulphate (Glauber’s Salt – Na2SO4.10H2O)

Collect more information on the properties and uses of the substances listed above. You have learned that 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 water above becomes clear. Blue vitriol is used in the blood test for diagnosing anemia. In the Bordeaux mixture which is used as a fungicide on fruits like grapes, musk melon, and slaked lime it is used with blue vitriol.

When oil or animal fat is boiled with an aqueous solution of sodium or potassium hydroxide, sodium or potassium salts of carboxylic acids (fatty acids) are formed. These salts are called soap. 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.

Radioactive Substances
Elements with a high atomic number such as uranium, thorium, and radium have the property of spontaneously emitting invisible, highly penetrating, and high-energy radiation. This property is called radioactivity. A substance having this property is called a radioactive substance. The nucleus of radioactive elements is unstable. Radiation occurs from an unstable nucleus. Radioactive substances are relevant to our day-to-day life. However, before going further, let us learn something more about these substances. Three types of radiation are given out by radioactive substances. These are alpha, beta, and gamma rays.

Substances in Common Use Class 9 Science Notes Maharashtra Board

The French scientist Henry Becquerel was studying pitchblende, a compound of uranium. He had kept some unused photographic plates in a cardboard box in a drawer. A key was lying on the box. He happened to leave the uranium compounds on it. After a few days, he washed the plates only to find that the plates were cloudy and showed the shape of the key. As this incident occurred in the dark, Becquerel inferred that the uranium compounds might be emitting from their interior, rays like x-rays which penetrate substances. These rays were called Becquerel rays. After a few days, Madame Curie discovered similar properties in compounds of thorium.

Nature of Radioactive Radiation
In 1889 Rutherford discovered that the radiations emitted by radium were of two types. They are called alpha and beta radiation. Willard discovered the third type namely gamma radiation. When these rays are allowed to pass through two oppositely charged plates they get separated. This method was introduced by Rutherford in 1902. Rutherford and Willard studied the radiation emitted by radioactive substances. For this purpose, the rays were allowed to pass through an electrical field and a photographic plate was held in their path. It was found that the radiation was divided into three types.
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One type of radiation deviated slightly toward the negatively charged plate, while the second type of radiation deviated substantially toward the positively charged plate. However, the third type of radiation did not deviate at all in the electrical field. The rays that deviate slightly toward the negatively charged plate are called alpha rays, those that deviate substantially toward the positively charged plate are called beta rays, and those that do not deviate at all are called gamma rays.

Ernest Rutherford (1871-1937), a scientist from New Zealand did research on radioactivity under the guidance of J.J. Thomson at the Cavendish Laboratory at Cambridge and McGill University, Canada. He showed that the nitrogen atom could be split by bombarding it with alpha particles. This experiment ushered in a new era in the field of Physics.
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Characteristics of Alpha, Beta, and Gamma Rays

Property Alpha Rays (α) Beta Rays (β) Gamma Rays (γ)
1. Nature The current of Alpha (He++) Particles The current of Beta (e) Particles Electromagnetic Radiation
2. Mass 4.0028 u 0.000548 u No Mass
3. Charge +2 -1 Electrically Neutral
4. Velocity 1/5 to 1/20 times the velocity of light 1/5 to 9/10 times the velocity of light Same as the velocity of light
5. Deviation in the Electric Field Attracted toward the negatively charged plate Attracted toward the positively charged plate Not deviated
6. Penetrating Power Can penetrate an aluminum sheet of thickness < 0.02 mm. Can penetrate an aluminum sheet of thickness 2 mm, which is 100 times the penetration of alpha particles. Can penetrate a 15 cm thick lead screen which is 10,000 times the penetration of alpha particles.
7. Ionization Power Very High Low Very Low
8. Power to Produce Fluorescence Very High Very Low Low

Uses of Radioactive Isotopes:
It is a misconception that radioactive elements are used only for making an atomic bomb. Radioactive isotopes are used in various fields such as scientific research, agriculture, industry, medicine, etc. Radioactive substances are used in two ways.

  • By using the radiation alone.
  • By using the radioactive element itself.

Natural Radioactivity:
Generally, the elements with atomic numbers from 82 to 92 are found to radiate spontaneously in nature. These are called natural radioactive elements.
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Artificial Radioactive Elements:
The couple Fredric Joliot Curie and Irene Joliot Curie first invented induced radioactivity. The radioactive elements produced in the nuclear fission processes brought about in the laboratory by the bombardment of particles are called artificial radioactive elements. They were awarded the Nobel Prize in 1935 for this invention.

Substances in Common Use Class 9 Science Notes Maharashtra Board

Radioactive isotopes are used in various fields as follows.
1. Industrial Field

  • Radiography: Internal cracks and voids in cast iron articles and iron solder can be detected with the help of gamma rays. For this purpose, isotopes like cobalt-60, and iridium-192 are used in the radiography camera. This technique is used for detecting flaws in metalwork.
  • Measurement of thickness, density, and level: It is necessary to maintain the required thickness in the manufacture of aluminum, plastic, and 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. Material inside a packing can also be examined by the same technique.
  • Luminescent paint and radioluminescence: The radioactive substances radium, promethium, and 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.
  • Use in Ceramic Articles: Luminous colors are used to decorate ceramic tiles, utensils, plates, etc. Earlier uranium oxide was used in these paints.

2. Field of Agriculture

  • The genes and chromosomes that give seeds properties like fast growth, higher productivity, etc. can be modified by employing radiation.
  • The radioactive isotope cobalt-60 is used for food preservation.
  • Onions and potatoes are irradiated with gamma rays from cobalt-60 to prevent their sprouting.
  • Strontium-90 is used as a tracer in the research on various crops.

3. Medical Science

  • Polycythemia: The red blood cell count increases in the disease polycythemia. Phosphorus-32 is used in its treatment.
  • Bone Cancer: Strontium-89, strontium-90, samarium-153, and radium-223 are used in the treatment of bone cancer.
  • Hyperthyroidism: Enlargement of the thyroid gland, weight loss despite appetite, and insomnia are the symptoms of hyperthyroidism. It occurs due to overproduction of hormones by the thyroid gland. Iodine-123 is used in the treatment of hyperthyroidism.
  • Tumour Detection: Boron-10, iodine-131, and cobalt-60 are used in the treatment of brain tumors, while arsenic-74 is used in the detection of small tumors in the body.

Hazards of Radioactive Substances and Radiation

  • The central nervous system is affected by radioactive radiation.
  • Hereditary defects are generated by the bombardment of radiation on D.N.A. in the body.
  • Radioactive radiation can penetrate the skin and cause diseases like skin cancer, and leukemia.
  • The radiative pollutants created due to explosions enter the body through air and it is difficult to control them.
  • The radioactive pollutants released in the sea enter the bodies of fish and through them enter the human body.
  • The radioactive paint on the watch can cause cancer.
  • The radioactive isotope strontium-90 can enter the body through plants, fruits, flowers, cereals, milk, etc., and cause diseases like bone cancer, and leukemia.

Chernobyl Disaster:
On 26th April 1986, the graphite reactor in the Chornobyl atomic power plant exploded, and suddenly the radioactive isotopes and radiation came out. Due to this episode radioactive isotopes entered the human body through water and land and caused genetic disorders. These got carried further into the next generation. Thyroid disorders increased in children as well as adults. As a result, the incidence of throat diseases is greater there than in other places.

Some Chemical Substances in Day-to-Day Life: The food that we eat, and objects like clothes, utensils, watches, medicines, and other objects are made from various kinds of matter. These affect our health directly or indirectly.

Substances in Common Use Class 9 Science Notes Maharashtra Board

Food Colours and Essences
Food colors are mixed in most soft drinks and foodstuffs available in the market. These food colors are in the form of powders, gels, and pastes. Food colors are used in domestic as well as commercial products. Certain colors and essences are added to ice cream, ice candies, sauce, fruit juices, cold drinks, pickles, jams, and jelly. Food colors are often found to be added to packaged meat (chicken, mutton), chili powder, turmeric, sweets, and other similar substances to give them a good color.
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Harmful Effects of Artificial Food Colours

  • Food colors added to pickles, jam, and sauce contain small quantities of lead and mercury. These can be harmful to those who consume these products regularly.
  • Diseases like ADHD (Attention Deficit Hyperactivity Disorder) can affect children due to excessive consumption of foods with added food colors.

Food colors are natural as well as artificial. The food colors prepared from seeds, beetroot, flowers, and fruit concentrate are natural. Tetrazene and sunset yellow are artificial food colors used extensively. However, over-consumption of artificial food colors can be detrimental to health. Therefore, the usage of natural food colors is always good.

The colored substance that on applied to an article, imparts that color to the article, is called a dye. Generally, a dye is soluble in water and insoluble in oil. Often a mordant has to be used to fix the colour after dying a cloth. Plants are the main source of color for preparing a natural dye. Roots, leaves, flowers, bark, fruits, seeds, fungus, and pistil are used for making dyes. In Kashmir, a very good dye is made from saffron, which is used to dye fibers from which saris, shawls, and dresses are made. These are very costly. Many people are engaged in this occupation as their means of earning a livelihood. The use of henna leaves to color hair is safe for health. William Henry Perkin invented an artificial dye in 1856. Artificial dyes are classified into many types based on chemical properties and solubility. Petroleum products and minerals are used in these dyes.


  • They are used for coloring cloth and hair.
  • Fluorescent colors are used to make street boards that are visible at night.
  • Dyes are used to polish leather shoes, purses, and chappals.

Adverse Effects:

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

Substances in Common Use Class 9 Science Notes Maharashtra Board

Artificial Colours
We regularly use artificial colors on Rang Panchami, decorating the house by painting. The red color used on 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, artificial colors must be used cautiously.
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Body odor is caused by the bacterial decomposition of the sweat. A deodorant is used to prevent this odor. Everybody likes a fragrant deodorant to remain fresh the whole day. School children use deo on a large scale. This large-scale use of deo in adolescents is a result of the advertisements shown on television. Deodorants contain parabens (methyl, ethyl, propyl, benzyl, and butyl) and also alcohol in large proportions. Aluminum compounds and silica are also used.

  • Ordinary Deo: It contains a smaller proportion of aluminum. It decreases the odor of the sweat.
  • Antiperspirant Deo: This decreases the extent of sweating. It contains about 15% of aluminum chlorohydrate. It clogs the sweat pores on the skin.
  • Clinical Deo: Some people sweat heavily and it has harmful effects on the skin. Clinical deo is meant for such people. It contains 20 to 25% aluminum. It is used during the night.

Harmful Effects:

  • Aluminum: Zirconium compounds are the most harmful chemicals in the deodorant.
  • Disorders like headaches, asthma, respiratory disorders, and heart disease are likely to occur without our knowledge.
  • There is a possibility of various skin disorders and also skin cancer due to the aluminum chlorohydrates.

Teflon is used for coating cooking utensils and industrial equipment to avoid sticking. It is the polymer of tetrafluoroethylene. Roy J. Plunkett discovered it in 1938. Its chemical name is polytetrafluoroethene (C2F4)n.
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  • The atmosphere and chemical substances do not affect Teflon.
  • Neither water nor oil will stick to Teflon-coated articles.
  • High temperatures do not affect Teflon as its melting point is 327°C.
  • Teflon-coated articles are easy to clean.


  • Teflon is a poor conductor of electricity. Therefore, Teflon cladded wires and parts are used in high-technology electronic instruments.
  • It is used for making non-stick kitchenware.
  • The colored metal sheets of two-wheelers and four-wheelers are given a Teflon coating to protect them from damage due to high temperatures and rain.

Powder Coating:
Powder coating is a method of applying a layer harder than paint on the surface of an iron object to prevent rusting. In this method, a polymer resin, a pigment, and some other ingredients are melted mixed, cooled, and ground into a uniform powder. This powder is sprayed on the polished metal surface by electrostatic spray deposition (ESD). 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. 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. Powder coating can be done on plastic and medium-density fiber (MDF) boards for day-to-day use as well.

A protective layer is formed naturally on the surface of aluminum metal by reaction with oxygen in air. In the anodizing process, this layer can be made of the desired thickness. Anodizing is done by electrolysis. Dilute acid is taken in the electrolytic cell and the aluminum 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. A reaction with oxygen occurs and a layer of hydrated aluminum oxide is formed on the anode, i.e. the iron article. This layer can be made attractive by adding color to the cell during electrolysis. We use anodized cooking utensils like griddles and cookers. Why?

Substances in Common Use Class 9 Science Notes Maharashtra Board

Ceramic is a heat-resistant substance formed by kneading an inorganic substance in water and then shaping it and hardening it by heating. Pots made by a potter, Mangalore roofing tiles, construction bricks, pottery, and terracotta articles are some examples of common ceramic articles that we see around.
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This is how a ceramic article is made: When clay is kneaded in water, shaped, and then fired in a kiln at a temperature of 1000 to 1150°C, a porous ceramic is formed. To overcome the porosity the fired object is covered with finely ground glass powder suspended in water (glaze) and is then fired again. As a result, the surface of the ceramic becomes shiny and its porosity disappears

This is a hard, translucent, and white-colored ceramic. It is made by using the white clay called kaolin, found in China. Glass, granite, and the mineral feldspar are mixed with kaolin and kneaded with water. The resulting mixture is shaped and fired in a kiln at a temperature of 1200 to 1450°C. On firing again after glazing, beautiful articles of porcelain are obtained. Which porcelain vessels are used in the laboratory?

Bone China:
Bone china is made by adding some ash of animal bones in a mixture of china clay, feldspar, and fine silica while making porcelain. This ceramic is harder than porcelain.

Advanced Ceramics:
Oxides like Alumina (Al2O3), Zirconia (ZrO2) Silica (SiO2), and some other compounds like silicon carbide (SiC), boron carbide (B4C) are used instead of clay for making advanced ceramic. This ceramic requires a temperature of 1600 to 1800°C and an oxygen-free atmosphere for firing. This process is called sintering.

Substances in Common Use Class 9 Science Notes Maharashtra Board

Ceramics can withstand high temperatures without decomposing. 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. A certain type of ceramic tile is fixed on the outer layer of a space shuttle. Some types of ceramics are used as superconductors.

Maharashtra State Board Class 9 Science Notes Substances in Common Use can be used for revisiting and reinforcing previously learned content.

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