The Class 9 is an important year in a student’s life and Maharashtra State Board Science is one of the subjects that require dedication, hard work, and practice. It’s a subject where you can score well if you are well-versed with the concepts, remember the important formulas and solving methods, and have done an ample amount of practice. Worry not! Home Revise is here to make your Class 9 journey even easier. It’s essential for students to have the right study material and notes to prepare for their board examinations, and through Home Revise, you can cover all the fundamental topics in the subject and the complete Maharashtra State Board Class 9 Science Book syllabus.
1) Why are carbon and its compounds used as fuels?
Answer: The reasons why carbon and its compounds are used as fuels are given below:
1) Carbon and its compounds produces a lot of heat and light when burnt in air, as it contains large amounts of carbon and hydrogen
2) Saturated hydrocarbons do not produce any smoke and burns with a clean flame
3) Carbons that are used as fuels has the optimum ignition temperature
4) Carbon used as fuel have high calorific value
5) Combustion can be easily controlled
2. In which compound forms does carbon occur?
Answer: Carbon in free state is found as Diamond and Graphite. Meanwhile, Carbon is found in the combined state in the following compounds:
1. As carbon dioxide (CO2 ) and in the form of carbonates such as calcium carbonate, marble, calamine (ZnCO3 )
2. Coal, Petroleum and Natural gas used as fossil fuels
3. Carbohydrates, Proteins and Fats used as Carbonaceous nutrients
4. Cotton, Wool and Silk as Natural fibres
3. Write the uses of diamond.
Answer: Given below are certain uses for diamond:
4. Difference between Diamond and Graphite.
Answer: Every carbon atom in diamond forms covalent bonds with four of its neighbouring atoms. So, diamond has a tetragonal three dimensional structure that makes it very hard. Meanwhile, every carbon atom in graphite bonds to three other carbon atoms to form a hexagonal layered structure. Graphite crystal is made of several sheets or layers of carbon atoms, which slip over others if pressure is applied. One layer of graphite is known as graphene.
5.What are the differences between crystalline and non-crystalline forms of carbon?
Answer: In the crystalline form of carbon, the atoms are arranged in a regular and definite manner. The melting and boiling points are pretty high for these. These also have definite geometrical shapes and have sharp edges and plane surfaces. There are three crystalline allotropes for carbon-Diamond, Graphite and Fullerene. Meanwhile, the arrangement of carbon atoms in non-crystalline forms of carbon is not regular. The non-crystalline forms of carbon include coal, charcoal, coke and so on.
6. Graphite is a conductor of electricity. State a scientific reason for this.
Answer: Inside each layer of graphite, free electrons move continuously within the entire layer. This is the reason why graphite is a good conductor of electricity.
7. Limewater turns milky when CO2 is passed through it. Give a scientific explanation.
Answer: Limewater turns milky when CO2 is passed through it, due to the formation of calcium carbonate.
8. Diamond, graphite and fullerenes are crystalline forms of carbon. Explain.
Answer: Allotropy is the property of the element, when the element occurs in nature in more than one form with same chemical properties but different physical properties. Diamond, graphite and fullerenes are the three crystalline allotropes of carbon. All three allotropes have a definite geometrical shape with sharp edges and plane surfaces.
9. Methane is called marsh gas. Explain.
Answer: Since, it is normally found at the surface of marshy places, methane is also known as marsh gas.
10. Petrol, diesel, coal are fossil fuels. Explain.
Answer: Petrol, diesel and coal are all obtained from the fossils or the remains of the living organisms, both living and aquatic as well as from dead plants, all of which have been buried underground for millions of years. Hence, they came to be called fossil fuels.
11. Explain the use of CO2 in fire extinguishers.
Answer: The CO2 that is obtained by chemical reaction or kept under pressure is used in fire extinguishers. CO2 based fire extinguishers are not that corrosive and are non-conductors of electricity. Hence, these are used when electrical and electronic equipment catches fire. These fire extinguishers are also used to put out small fires and they do not have the capacity to tackle big fires. The liquid and solid CO2 is filled under pressure in modern extinguishers. If the pressure is reduced, it becomes gaseous and bursts out through the horn-like hose pipe.
12. What are the practical uses of CO2 ?
Answer: Some of the practical uses of Carbon dioxide is given below:
1. Used to make aerated drinks
2. Used in cold storage
3. Helps to keep milk and milk products and frozen substances cool during transport
4. Used for getting special effects of a mist in dramas and movies
5. Used in fire extinguishers
6. Liquified CO2 helps to remove caffeine from coffee
5. Liquid CO2 is a solvent in modern eco-friendly dry cleaning
13. Give two physical properties of Diamond.
Answer: Brilliant and pure diamond is the hardest natural substance. Given here are two physical properties of Diamond:
1. The density of diamond is 3.5 g/cm3 with melting point at 35000 C
2. Diamond does not dissolve in any solvent nor do acids and bases have any effect on it
14. Mention two physical properties of Graphite.
Answer: A black, soft, brittle and slippery product, Graphite has some properties, two of which are mentioned below:
1. Graphite can be used for writing on paper because of its layered structure
2. The density of graphite is 1.9 to 2.3 g/cm3 and it is a good conductor of electricity
15. What are the physical properties of fullerene?
Answer: Given here are the physical properties of fullerene:
1. Molecules of fullerenes are found in the form of buckyballs and buckytubes
2. One molecule of fullerene consists of 30 to 900 carbon atoms
3. Fullerenes are soluble in organic solvents such as carbon disulphide, chlorobenzene
16. What are the different types of coal? What are their uses?
Answer: Coal, the fossil fuel are of four types. There are Peat, Lignite, Bituminous and Anthracite.
a. Formation of Peat is the first step in the formation of coal. Peat contains a high proportion of water and less than 60% Carbon, so not much heat can be obtained from this.
b. During the second step of formation of coal, Peat is transformed into Lignite as a result of increased pressure and temperature inside the earth. It contains 60 to 70% of carbon.
c. Then, in the third step of formation of coal, the Bituminous coal is formed, which contains 70 to 90% of carbon.
d. Finally, Anthracite, also called pure form of coal is hard and contains about 95% of carbon.
17. What is the electron configuration and valency of carbon?
Answer: The electron configuration of carbon is 2, 4 and the valency of carbon is 4.
18. What are organic and inorganic compounds?
Answer: Organic compounds are those obtained directly or indirectly from plants and animals, while the compounds obtained from minerals are known as inorganic compounds.
19. How is carbon in marine water converted into calcium carbonate?
Answer: Some types of plants that grow on the ocean floor convert carbon in marine water into calcium carbonate.
20. Which are some of the elements that exhibit allotropy?
Answer: Elements like carbon, sulphur and phosphorus, all exhibit allotropy.
21. Where are diamonds normally found?
Answer: Diamonds are mainly found in India in Golconda (Karnatak) and Panna (Madhya Pradesh) and also in Brazil, Russia, South Africa, Belgium and America.
22. Why are diamonds considered as bad conductors of electricity?
Answer: Diamond is known as a bad conductor of electricity as it does not have free electrons.
23. Where are graphites found?
Answer: Graphite is found in the natural state in India, Russia, America and New Zealand.
24. How is the lead in pencil made? Who discovered the process?
Answer: The lead used in pencils is made by mixing graphite with clay. In 1795, Nicholas Jacques Conte discovered this process.
25. What are the main uses of graphites?
Answer: Given below are the uses of graphites:
1. Used to make lubricants
2. To make carbon electrodes
3. Used in pencils for writing
4. Used in paints and polish
5. Used in arc lamps that give a very bright light
26. What are the uses of fullerenes?
Answer: We have given here the uses of fullerene:
1. Useful as insulators
2. Used as a catalyst in water purification
3. At a certain temperature fullerene exhibits superconductivity
27. What are the uses of coal?
Answer: Coal is used as a fuel in the factories and at home. Coke, coal gas and coal tar are also obtained from it. Finally, it is also used in thermal plants to generate electricity.
28. What is coke? What are its uses?
Answer: Coke is the pure coal that remains when coal gas is taken away from coal. Coke is used as a domestic fuel and as a reducing agent. Coke is used in formation of water gas (CO +H2 ) and producer gas (CO+H2 +CO2 + N2 ).
29. How is a methane molecule CH4 formed?
Answer: A methane CH4 molecule is formed when a carbon atom shares one electron each with four hydrogen atoms to form four C-H bonds.
30. What are the properties of covalent bonds?
Answer: Covalent bonds with low melting and boiling points are also poor conductors of heat and electricity. They are also insoluble in water and soluble in organic solvents.
31. What are saturated hydrocarbons? Give examples.
Answer: The hydrocarbons that have only single bonds between carbon atoms are saturated hydrocarbons. Examples are ethane (C2 H6 ) which is (CH3 -CH3 ) and propane (CH3 -CH2 -CH3 ).
32. What are unsaturated hydrocarbons?
Answer: Some hydrocarbons may have multiple bonds such as a double bond or a triple bond between two carbon atoms. A hydrocarbon that has at least one multiple bond is known as unsaturated hydrocarbon.
33. What are two physical properties of Methane?
Answer: Methane is a colourless gas, sparingly soluble in water and highly solvent in organic solvents such as gasoline, ether and alcohol. At room temperature, methane remains in its gaseous state. Meanwhile, the liquid methane is less dense than water.
34. What is chlorination?
Answer: In the presence of ultraviolet light and at a temperature of 2500 C to 4000 C, Methane and chlorine gases react with each other to form mainly methyl chloride (chloromethane) and hydrogen chloride.This reaction is called chlorination of methane.
35. What is a biogas?
Answer: The microbes in a biogas plant decompose the animal dung, dry leaves and wet garbage to produce methane gas, also known as biogas. This biogas is a cheap option for fuel and meets the demand for cooking gas as well as is used in production of electricity. Biogas consists of 55% to 60% methane and rest carbon dioxide. Biogas is a convenient fuel to use and as a side product of the process, very good manure is also made.
36. Explain the biogas production process.
Answer: An anaerobic process, the production of biogas occurs in two stages -1) the production of acids and 2) methane gas production. In the first stage, the microbes act on the biodegradable complex organic compound to produce organic acids, while in the second stage, the methanogenic bacteria acts on the organic acids, thus producing methane gas.