ICSE Chemistry Class 8 Notes Chapter 9 Carbon and Its Compounds
→ \({ }_{12}^{6}\)C has atomic number 6 and mass number 12 covalent, valency 4 is a constituent of all plants and animals.
→ Organic chemistry is a branch of science which deals with the study of organic compounds made up of mainly carbon, hydrogen and oxygen.
→ Inorganic chemistry is a branch of science which deals with the study of inorganic compounds made up of oxides of carbon, carbonates, bicarbonates, metallic carbides.
→ Allotropy : “Existence of an element in more than one physical form having different physical properties but same graded chemical properties.” “It is due to – difference in atomic arrangement.”
→ Two crystalline forms of carbon are :
- Diamond.
- Graphite.
And amorphous forms are :
- Coal
- Coke
- Lamp black
- Wood charcoal
→ Structure of diamond – is tetrahedron. Carbon – Carbon covalent bond and is hardest substance. The structure is such that it has no free electron and is bad conductor of electricity. Is chemically very inert – does not react with most of chemicals as structure is compact.
→ Structure of graphite is hexagonal rings parallel layers of carbon atoms held together by weak VANDER WAALS forces which slide over one another – is soft and greasy feel, forms lubricant for heavy machiness that run fast.
Open structure – slightly more reactive than diamond.
→ Coal is formed by the bacterial decomposition of vegetable
matter (plants) under the influence of heat, pressure and limited air over millions of years.
→ Types of coal depends on the % of carbon in it. Worst type is peat [60%C] best is anthracite [90%C, bituminous [85%C] and lignite [65%C].
→ USES OF COAL as a cheap fuel, in manufacture of coke, coal gas and synthetic petroleum.
→ USES OF COKE as a reducing agent in iron and steel production, fuel in the manfacture of water gas and producer gas.
→ Uses of lamp black : In making – printers ink, typewriter ribbons, black shoe polish, black paints. It is also used as a – filer in rubber tyres.
→ Wood charcoal : Is obtained as residue on – distructive distillation of wood.
→ The products of destructive distillation of wood are :
- wood gas
- wood charcoal
- pyroligneous acid and wood tar.
→ Adsorption : It is property due to which a substance accumulates – gases or liquids on its outer surface – adsorption is a surface phenomenon.
→ Heating wood charcoal in a retort around 900°C and passing steam over it. The impurities on the surface get removed and adsorption capacity increases 100 times.
→ Wood charcoal is used as:
(i) Reducing agent
(ii) as house hold fuel
(iii) decolourising agent
(iv) in making gas masks, during indigestion, sewers.
→ Dil. sulphuric acid is not used to prepare CO2 gas from marble chips as it forms CaSO4 which is insoluble and the reaction stops soon.
→ Dry ice : CO2liquefied at about 70 atmospheres pressure at ordinary temperature and solidifies on cooling at -78°C to form a white solid known as dry ice.
→ CO2 gas is colourless, odourless, slightly sour taste non-
poisonous, does not bum, does not help in burning, turns lime water [Ca(OH)2] milky, acidic in nature i.e., changes moist blue litmus paper to red.
→ Uses of CO2 : Is used by plants to prepare their food, dry ice is used as refrigerant, in fire fighting, in cold drinks, in baking powder.
→ CO is produced by burning carbon or its compound – in a limited supply of oxygen.
→ When CO monoxide is formed and it comes in contact of more of air, CO2 is formed.
→ CO is highly poisonous gas, it combines with haemoglobin present in blood or R.B.C. it form carboxyl-haemoglobin and reduces oxygen carrying capacity of blood. The person dies due to lack of oxygen [asphyxia is an extreme condition caused by lack of oxygen which results in unconsciousness and then death.
→ CO2gas and SO2 gas both turn lime water milky but SO2 turns potassium permanganate paper from purple to colourless whereas CO2 does not.
→ Burning of any thing first produces CO which bums with blue flame but when this CO come in contact with more of air or oxygen CO2 is formed.
Check Your Progress (Page 117)
Answer these questions.
Question 1.
Name the three crystalline allotropes of carbon.
Answer:
Diamond, graphite and fiillerene are the three crystalline allotropes of carbon.
Question 2.
Which is the purest form of carbon?
Answer:
Diamond is the purest form of carbon.
Question 3.
Which type of bond joins the carbon atoms in a diamond?
Answer:
Each carbon atom in diamond is joined to four other carbon atoms by covalent bonds.
Question 4.
Name an allotrope of carbon that is a good conductor of electricity.
Answer:
Graphite is a good conductor of electricity.
Question 5.
How many carbon atoms can fullerenes have?
Answer:
A molecule of fullerenes can have about 30 to 900 atoms of carbon.