Occurrence of Carbon and its Allotropic Forms Class-8th Goyal Brothers ICSE Chemistry Solutions Ch-9 (Carbon and its Compounds) Unit-1 (Occurrence of Carbon and its Allotropic Forms). We Provide Step by Step Answers of MCQs, True and False, Incorrect and Correct, Definitions, Match the followings and Short/Long Question Type answers of Ch-9 (Carbon and its Compounds) Unit-1(Occurrence of Carbon and its Allotropic Forms). Visit official Website CISCE for detail information about ICSE Board Class-8.
Occurrence of Carbon and its Allotropic Forms Class-8th Goyal Brothers ICSE Chemistry Solutions Ch-9 Unit-1
| Board | ICSE |
| Class | 8th |
| Subject | Chemistry |
| Book Name | Goyal Brothers |
| Chapter-9 | Carbon and its Compounds |
| Unit-1 | Occurrence of Carbon and its Allotropic Forms |
| Topic | Solution of exercise questions |
| Session | 2023-24 |
OBJECTIVE TYPE QUESTIONS
Occurrence of Carbon and its Allotropic Forms Class-8th Goyal Brothers ICSE Chemistry Solutions Ch-9 Unit-1
Que: A. Fill in the blank spaces by choosing the correct words from the given list:
List: allotropy, conductors, graphite, carat, diamonds
1. Black diamonds are used for cutting and polishing other __diamonds__.
2. The phenomenon, due to which an element exhibits different physical forms, which have same chemical properties is known as __allotropy__.
3. The weight of diamond is measured in __carat__.
4. Some fullerenes are super __conductors__ of electricity.
5. __diamonds__ is the only crystalline form of carbon which is a good conductor of electricity.
Que: B. Statements given below are incorrect. Write the correct statements:
Question: 1. Black diamond is not very hard and is used for making cheap jewellery.
Answer: Black diamond is very hard metal and is used for making cheap jewellery.
Question: 2. Graphite is good conductor of heat and bad conductor of electricity.
Answer: Graphite is good conductor of heat and electricity.
Question: 3. Pure diamond is transparent to visible light, but not to X-rays.
Answer: Pure diamond is transparent to X-ray and the visible light.
Question: 4. In Buckminsterfullerene, each molecule has sixty atoms arranged in rectangles and triangles.
Answer: In Buckminsterfullerene, each molecule has sixty atoms arranged in hexagons and pentagons.
Question: 5. Graphite is used in nuclear reactors to speed up the excess neutrons.
Answer: Graphite has been used as a moderator and reflector of neutrons in nuclear power plants.
Que: C. Match the statements in Column A, with those in Column B:
| Column A | Column B |
| 1. A free state of carbon. | (a) Petroleum |
| 2. A combined state of carbon. | (b) Buckminsterfullerene |
| 3. A form of carbon which is a good conductor of heat and electricity. | (c) Allotropy |
| 4. A free form of carbon whose one molecule has 60 carbon atoms. | (d) Graphite |
| 5. Name of various physical form of elements having same chemical properties. | (e) Diamond |
Answer:
| Column A | Column B |
| 1. A free state of carbon. | (a) Diamond |
| 2. A combined state of carbon. | (b) Petroleum |
| 3. A form of carbon which is a good conductor of heat and electricity. | (c) Graphite |
| 4. A free form of carbon whose one molecule has 60 carbon atoms. | (d) Buckminsterfullerene |
| 5. Name of various physical form of elements having same chemical properties. | (e) Allotropy |
Que: D. Write ‘True’ or ‘False’ for the following statements:
| Statements | True/False |
| 1. All compounds of carbon are called hydrocarbons. | F |
| 2. Carbon is an organogen element. | T |
| 3. Diamond is purest form of carbon. | T |
| 4. Zinc is found in traces in all plants and animals and hence is an organogen. | F |
| 5. Graphite is used as dry lubricant in high speed machinery. | T |
Que: E. Tick (√) the most appropriate answer:
1. When diamond is heated in vacuum for a very long time, it changes into:
(a) graphite
(b) charcoal
(c) lampblack
(d) carbon dioxide
Answer: option (a) graphite is correct.
2. fullerene molecule [C60] is named after:
(a) H.W. Kroto
(b) R.F. Curl
(c) R.B. Fuller
(d) R.E. Samalley
Answer: option (c) R.B. Fuller is correct.
3. Graphite is used as a lubricant because it is:
(a) good conductor of heat
(b) good conductor of electricity
(c) very soft and slippery
(d) soluble in oil
Answer: option (c) very soft and slippery is correct.
4. The property due to which, the gases and the liquids accumulate on the outer surface of solid is called:
(a) adhesion
(b) cohesion
(c) adsorption
(d) absorption
Answer: option (c) adsorption is correct.
5. The property due to which and element exhibits various physical forms which has same chemical properties is called
(a) isotopy
(b) allotropy
(c) atomicity
(d) none of these
Answer: option (b) allotropy is correct.
STUDY QUESTIONS
Occurrence of Carbon and its Allotropic Forms Class-8th Goyal Brothers ICSE Chemistry Solutions Ch-9 Unit-1
Question: 1. What do you understand by the term organogens? Name four elements which constitute organogens.
Answer: Organogen (plural organogens) (chemistry, dated) Any of the four elements — carbon, hydrogen, oxygen, and nitrogen — that are especially characteristic of organic compounds. (chemistry, dated) Any of certain other elements sometimes found in organic compounds, such as sulphur and phosphorus.
Question: 2. Name two substances in which element carbon occurs in:
(a) free state
(b) combined solid state
(c) combined liquid state
(d) combined gaseous state
Answer: It occurs as diamond, graphite in impure form as coal, in the free state. It occurs as carbon dioxide in the atmosphere, hydrocarbon as natural gas, petroleum, cellulose in wood and limestone in combined states.
(b)Combined State (solid) – CaCO3 and CaC2
(c) Combined state (liquid) – CS2 and CCl4
(d) Combined state (gas) – CO2 and CH4
3. (a) What do you understand by the following terms:
(i) allotropy
(ii) allotropic forms
Answer: (i) The ability of an element to exist in more than one physical form having the same physical state is called allotropy.
(ii) The various existing forms of an element bonded to each other in a different manner, exhibiting identical chemical properties but different physical properties are called allotropic forms.
(b) Name three crystalline allotropes of carbon.
Answer: Diamond, Graphite and Fullerene.
(c) Name four amorphous forms of carbon.
Answer: Charcoal, coal, soot, gas carbon, and coke.
Question: 4. (a) How are diamonds formed in nature?
Answer: Diamonds were formed over 3 billion years ago deep within the Earth’s crust under conditions of intense heat and pressure that cause carbon atoms to crystallise forming diamonds. Diamonds are found at a depth of approx. 150-200 km below the surface of the Earth.
(b) Describe the structure of a diamond molecule.
Answer: A crystal of diamond is a molecule of carbon atoms in which each carbon atom is connected to four other carbon atoms by strong covalent bond forming a regular tetrahedron shape.
(c) What factors determine the value of a diamond?
Answer: Carat Weight, Clarity, Cut, & Color All Determine a Diamond’s Value. As we have demonstrated, there are many factors that determine a diamond’s value. Carat weight, cut, clarity, and color are all components that a skilled GIA grader uses when a diamond gets it’s grade.
Question: 5. State six physical properties of a diamond.
Answer: State six physical properties of a diamond:
1. It is the hardest naturally occurring solid. Amongst the diamonds, the black diamonds are the hardest.
2. A pure diamond is a (i) colourless, (ii) transparent, and (iii) brittle solid.
3. A pure diamond is transparent to X-ray and the visible light.
4. The density of pure diamond is 3.5 gcm-3.
5. It is a very poor conductor of heat and electricity.
6. It is insoluble in all solvents.
Question: 6. State five uses of black diamonds.
Answer: Used of Black diamonds:
- Due to their hardness, black diamonds are used in various cutting tools.
- Coal is known as Black Diamond.
- This is because coal is used for a variety of purposes, such as:
- A source of fuel in the kitchen.
- As a raw material in industries.
Question: 7. (a) What is graphite?
Answer: Graphite is an opaque, non-metallic carbon polymorph that is blackish silver in colour and metallic to dull in sheen.
(b) Describe the structure of graphite.
Answer: Graphite is composed of layers of carbon atoms that are arranged in 6-membered, hexagonal rings. These rings are attached to one another on their edges. Layers of fused rings can be modeled as an infinite series of fused benzene rings (without the hydrogen atoms).
(c) How is graphite artificially manufactured?
Answer: Graphite can be prepared artificially by heating Anthracite coal with small amount of Iron oxide (FeO ) or Silica (SiO2 ) as a catalyst in an electric furnace.
Question: 8. (a) State five physical properties of graphite.
Answer: Five physical Properties of Graphite:
- A greyish black, opaque substance.
- Lighter than diamond, smooth and slippery to touch.
- A good conductor of electricity( Due to the presence of free electrons) and good conductor of heat.
- A crystalline solid.
- Very soapy to touch.
(b) State five uses of graphite.
Answer: Five Uses of Graphite:
- Writing Materials.
- Lubricants.
- Refractory.
- Nuclear Reactors.
- Batteries.
Question: 9. What is a fullerene? How many carbon atoms are in Buckminsterfullerene? How are these atoms arranged?
Answer: Crystalline forms of carbon having 30 to 960 atoms in their molecules are called Fullerenes. Buckminsterfullerene is a spherical molecule in which 60 carbon atoms are arranged in interlocking hexagonal and pentagonal rings of carbon atoms.
Question: 10. Water has two more physical forms, i.e., ice and steam. Why are ice and steam not called allotropes of water?
Answer: Allotropes are different forms of an element and they differ in the way the atoms are bonded. Diamond and graphite are allotropes of carbon. In diamond each carbon is bonded to 4 other carbon atoms while in graphite each carbon is bonded to 3 other carbon atoms. The bonding between hydrogen and oxygen in ice and steam are the same. These two only differ in the state, ice is solid while steam is a gas.
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