Balbharti Maharashtra State Board Class 9 Science Solutions Chapter 13 Carbon: An Important Element Notes, Textbook Exercise Important Questions and Answers.
Class 9 Science Chapter 13 Carbon: An Important Element Textbook Questions and Answers
1. Select the proper option and complete the statements
(single, all, double, ionic, carbon, give and take, hydrogen, multiple, share, most, covalent)
a. A carbon atom forms a ….……………. bond with other atoms. In this bond the two atoms ….electrons.
Answer:
covalent, share
b. All the carbon bonds in a saturated hydrocarbon ….……………. electrons.
Answer:
share
c. At least one carbon bond in an unsaturated hydrocarbon is ….…………… .
Answer:
multiple
d. ….……………. is the essential element in all the organic compounds.
Answer:
Carbon
e. The element hydrogen is present in ….. organic compound.
Answer:
all
2. Answer the following questions
a. Why are carbon and its compounds used as fuels?
Answer:
(i) The name ‘carbon’ is derived from Latin word ‘carbo’meaning coal. In the earth’s crust, carbon is present to an extent of approximately 0.27% in the form of carbonate, coal and petroleum. One of the non-crystalline and amorphous form of carbon is coal. Coal is a fossil fuel.
(ii) Peat, lignite, bituminous and anthracite are the four types of coal in the increasing order of their carbon content and heat produced respectively. Charcoal and coke are the other amorphous forms of carbon used as fuel.
(iii) Compounds of carbon such as hydrocarbons consist of carbon and hydrogen and they are easily combustible. For example, methane (CH4) which occurs in natural gas is highly inflammable. It bums by reacting with oxygen to give a bluish flame. In this reaction, 213 Kcal/mol of heat is given out. Methane bums completely.
Chemical reaction:
CH4 + 2O2 → CO2 + 2H2O + Heat
(iv) Thus when hydrocarbons are burnt in air, large amount of heat is evolved with formation of carbon dioxide (CO2) and water (H2O). Due to evolution of heat on combustion, carbon and its compounds are used as fuels.
b. In which compound forms does carbon occur?
Answer:
Carbon in its combined state exists as various compounds such as:
c. Write the uses of the diamond.
Answer:
Uses of diamonds are:
3. Explain the difference:
a. Diamond and graphite.
Answer:
| Diamond | Graphite |
| (i) Diamond is a brilliant, hard and crystalline allotrope of carbon. | (i) Graphite is a black, soft, brittle and slippery crystalline allotrope of carbon. |
| (ii) In diamonds, every carbon atom is bonded to four neighbouring atoms by covalent bonds forming tetragonal three dimensional structure which makes it very hard. | (ii) In graphite, every carbon atom is bonded to three other carbon atoms by covalent bonds in such a way that a hexagonal layered structure is formed. A graphite crystal is made of many such layers of carbon atoms. These layers slip over each other on applying pressure. |
| (iii) Density of diamond is 3.5 g/cm3. | (iii) Density of graphite is 1.9 to 2.3 g/cm3. |
| (iv) Diamond is a bad conductor of electricity as it does not have free electrons. | (iv) Inside each layer of graphite, free electrons move continuously within the entire layer. Hence, graphite is a good conductor of electricity. |
b. Crystalline and non-crystalline forms of carbon.
Answer:
| Crystalline forms of carbon | Non-crystalline forms of carbon |
| (i) A crystalline form has a regular and definite arrangement of atoms. (ii) They have high melting points and boiling points. (iii) A crystalline form has a definite geometrical shape, sharp edges and plane surfaces. (iv) Diamond, graphite and fullerene are different crystalline forms of carbon. |
(i) A non-crystalline form does not have a regular and definite arrangement of atoms. (ii) They have low melting points and boiling points. (iii) They are amorphous, hence, they do not have definite geometrical shape. (iv) Coal, charcoal and coke are different noncrystalline/amorphous forms of carbon. |
4. Write scientific reasons
a. Graphite is a conductor of electricity.
Answer:
b. Graphite is not used in ornaments.
Answer:
c. Limewater turns milky when CO2 is passed through it.
Answer:
d. Biogas is an eco-friendly fuel.
Answer:
5. Explain the following.
a. Diamond, graphite and fullerenes are crystalline forms of carbon.
Answer:
b. Methane is called marsh gas.
Answer:
c. Petrol, diesel, coal are fossil fuels.
Answer:
(i) A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms. Fossil fuels contain high percentage of carbon. The word carbon is derived from the Latin word ‘Carbo’ meaning coal.
(ii) Coal is formed from the remains of trees and other vegetation. Approximately 350 million years ago, these remains were trapped on the bottom of swamps, accumulating layer after layer and creating a dense material called peat. As this peat was buried under more and more ground, the high temperature and pressure transformed it into coal.
(iii) Petrol and diesel are obtained from mineral oil. Mineral oil also called as crude oil or petroleum oil is formed from the remains of plants and animals that lived in the seas millions of years ago. This plant and animal matter has been drawn down and subjected to extremes of temperature and pressure over millions of years ago.
(iv) Mineral oil is commonly formed in rocks under the sea bed. The word petroleum is derived from Latin word ‘Rock oil’. Petrol and Diesel are obtained from mineral oil by the process called as fractional distillation.
Thus petrol, diesel and coal are fossil fuels.
d. Uses of various allotropes of carbon.
e. Use of CO2 in fire extinguisher.
Answer:
f. Practical uses of CO2.
Answer:
Practical uses of CO2 are:
6. Write two physical properties each.
a. Diamond
Answer:
Properties of diamond are:
b. Charcoal
Answer:
c. Fullerene
Answer:
Properties of fullerenes are:
7. Complete the following Chemical reactions.
1. ………………..+………………..→ CO + 2H2O + Heat
2. ………………..+………………..→ HCl + Cl + HCl
3. 2 NaOH + CO2 →………………..+………………..
Answer:
8. Write answers to the following in detail.
a. What are the different types of coal? What are their uses?
Answer:
Coal is a fossil fuel. It contains carbon, hydrogen and oxygen. It also contains nitrogen, phosphorus and sulphur. It occurs in the solid state. It is of four types.
Uses of coal:
b. How will you prove experimentally that graphite is good conductor of electricity?
Answer:
Apparatus required: Lead pendi, electrical wires, battery/cell, small bulb, etc.
Step-I: Remove the lead from a pencil and assemble the apparatus as shown in the diagram.
Step-II:
c. Explain the properties of carbon.
Answer:
Allotropic nature of Carbon: Some elements occur in nature in more than one form. The chemical properties of these different forms are the same but their physical properties are different. This property of elements is called allotropy. Carbon shows the property of allotropy.
Carbon allotropes are of two types:
(A) Crystalline forms:
Carbon has three crystalline allotropes: Diamond, Graphite and Fullerene. Properties of crystalline forms of carbon are as follows:
(B) Amorphous forms or non-crystalline forms: Coal, charcoal, coke are the non-crystalline forms of carbon.
Properties of non-crystalline forms of carbon are as follows:
d. Classify carbon.
Answer:
Carbon is classified as follows:
9. How will you verify the properties of carbon dioxide?
Answer:
Properties of carbon dioxide can be verified in the following ways:
Class 9 Science Chapter 13 Carbon: An Important Element Intext Questions and Answers
Can you recall?
Question 1.
Whatremains behind on complete combustion of any organic compound?
Answer:
A black colour substance ‘Carbon’ remains behind on complete combustion of any organic compound.
Question 2.
What type of element is carbon? Give some information about it.
Answer:
Question 3.
What is an element? What are the different types of elements.
Answer:
Answer the following questions:
Question 1.
Does an electric charge form on atoms when a covalent bond is formed between them? Why is a single bond between two carbon atoms strong and stable?
Answer:
Question 2.
In which of the solvents – water, kerosene and cooking oil does the coal powder dissolve?
Answer:
Solvents such as water, kerosene and cooking oil do not dissolve coal powder in them.
Question 3.
What inference will you draw about the solubility of carbon?
Answer:
Carbon is insoluble in water, kerosene and cooking oil.
Question 4.
Is the density of CO2 more or less than that of air?
Answer:
Question 5.
What is a compound? How are compounds formed?
Answer:
Class 9 Science Chapter 13 Carbon: An Important Element Additional Important Questions and Answers
Choose and write the correct option:
Question 1.
The organic compound having double or triple bond in them is termed as
(a) unsaturated
(b) inorganic
(c) saturated
(d) complete
Answer:
(a) Unsaturated hydrocarbon
Question 2.
Covalent compounds are generally soluble in solvents.
(a) inorganic
(b) organic
(c) mixed
(d) mineral
Answer:
(b) organic
Question 3.
Methane is also called as
(a) maha gas
(b) mar’s gas
(c) Anthracite
(d) marsh gas
Answer:
(d) Marsh gas
Question 4.
is an alio trope of carbon used to make ornaments.
Answer:
Diamond
Question 5.
The number of valence electrons in carbon is
(a) 4
(b) 5
(c) 6
(d) 3
Answer:
(a) 4
Question 6.
In saturated hydrocarbons, two carbon atoms are linked by
(a) double bond
(b) triple bond
(c) multiple bond
(d) single bond
Answer:
(d) single bond
Question 7.
Carbon has 4 valence electrons in its outermost shell, hence, it is
(a) divalent
(b) tetravalent
(c) trivalent
(d) pentavalent
Answer:
(b) tetravalent
Question 8.
Methanogenic bacteria act on the organic acids to produce
(a) oxygen gas
(b) nitrogen gas
(c) methane gas
(d) carbon dioxide gas
Answer:
(c) Methane gas
Question 9.
is used to remove caffeine from coffee.
(a) liquefied O2
(b) liquefied N2
(c) liquefied CO2
(d) liquefied CH4
Answer:
(c) Liquified CO2
Question 10.
Exhaled air contains about CO2.
(a) 4%
(b) 3%
(c) 5%
(d) 6%
Answer:
(a) 4%
Question 11.
Electronic configuration of carbon is
(a) (2, 2)
(b) (2,4)
(c) (2, 5,4)
(d) (2, 6)
Answer:
(b) 2, 4
Question 12.
Molecular formula of ethane is
(a) C3H4
(b) C2H4
(c) C2H6
(d) C2H2
Answer:
(c) C2H6
Question 13.
Molecular mass of carbon dioxide is
(a) 28
(b) 22
(c) 56
(d) 44
Answer:
(d) 44
Question 14.
On heating a mixture of hydrogen and carbon monoxide gases at 300°C in the presence of nickel (catalyst) is formed.
(a) carbon dioxide gas
(b) oxygen gas
(c) methane gas
(d) ethylene gas
Answer:
(c) methane gas
Question 15.
Ethane with molecular formula C2H6 has covalent bonds.
(a) six
(b) seven
(c) eight
(d) nine
Answer:
(b) seven
Question 15.
Weight of Kohinoor Diamond was
(a) 186 carats
(b) 27 carats
(c) 252 carats
(d) 23 carats
Answer:
(a) 186 carats
Question 16.
Covalent compounds have
(a) high melting point
(b) low melting point
(c) moderate melting point
(d) very high melting point
Answer:
(b) low melting point
Question 17.
Methane is
(a) C2H6
(b) C3H8
(C) CH2
(d) CH4
Answer:
(d) CH4
Question 18.
Wohler, a German scientist synthesized the compound from an inorganic compound ammonium cyanate.
(a) methane
(b) ethylene
(c) urea
(d) acetic acid
Answer:
(c) urea
Question 19.
Molecular mass of methane is
(a) 19
(b) 16
(c) 17
(d) 18
Answer:
(b) 16
Question 20.
coal contains highest percentage of carbon.
(a) Bituminous
(b) Peat
(c) Anthracite
(d) Lignite
Answer:
(c) Anthracite
Question 21.
H2C = CH2 is ……………………… .
(a) Propane
(b) Ethyne
(c) Ethane
(d) Ethene
Answer:
(d) Ethene
Question 22.
CH3 – C = CH is ……………………… .
(a) Propene
(b) Propyne
(c) Ethyne
(d) Ethene
Answer:
(b) Propyne
Question 23.
Carbon dioxide gas is not used in
(a) photosynthesis
(b) aerated drinks
(c) glass cutting
(d) fire extinguishers
Answer:
(c) glass cutting
Question 24.
Melting point of diamond is
(a) 3700 °C
(b) 3500 °C
(c) 4000 °C
(d) 2500 °C
Answer:
(b) 3500 °C
Question 25.
Melting point of C02 is
(a) 26 °C
(b) 56 °C
(c)-56.6°C
(d)-98°C
Answer:
(c) -56.6 °C
Question 26.
Melting point o* methane is
(a) -182.5 °C
(b) -161.5 °C
(c) 182.5 °C
(d) 161.5 °C
Answer:
(a) -182.5 °C
Question 27.
Biogas contains about methane.
(a) 55% to 60%
(b) 20% to 25%
(c) 90% to 95%
(d) 40% to 45%
Answer:
(a) 55% to 60%
Question 28.
is not a property of carbon dioxide gas.
(a) Supporting combustion
(b) Odourless
(c) Colourless
(d) Turns blue litmus red
Answer:
(a) Supporting combustion
Name the following:
Question 1.
Industries that use methane in the form of natural gas.
Answer:
Fabric mills, paper mills, food processing industry, petrol purification.
Question 2.
Organic compounds prepared from methane.
Answer:
Ethanol, methyl chloride, methylene chloride, acetylene.
Question 3.
Chemicals used in regular fire extinguisher.
Answer:
Sodium bicarbonate and dilute sulphuric acid.
Question 4.
Components of biogas
Answer:
Methane, carbon dioxide
Question 5.
Organic solvents is which fullerenes are soluble.
Answer:
Carbon disulfide, chlorobenzene.
Question 6.
Use of carbon dioxide is dramas and movies
Answer:
The special effect of mist.
Match the columns:
Question 1.
| Column ‘A’ | Column ‘B’ |
| (1) Diamond (2) Fullerenes (3) Graphite |
(a) Hexagonal layered structure (b) Tetragonal three-dimensional structure (c) Geodesic dome |
Answer:
(1-b),
(2- c),
(3 – a)
Question 2.
| Column ‘A’ | Column ‘B’ |
| (1) Peat (2) Lignite (3) Bituminous (4) Anthracite |
(a) 60-70% of Carbon (b) 95% of Carbon (c) less than 60% of Carbon (d) 70 – 90% of Carbon |
Answer:
(1 – c),
(2 – a),
(3 – d),
(4 – b)
Question 3.
| Column ‘A’ | Column ‘B’ |
| (1) Propyne (2) Propene (3) Propane |
(a) CH3 – CH2 – CH3 (b) CH3 – C = CH (c) CH3 – CH = CH2 |
Answer:
(1 – b),
(2 – c),
(3 – a)
Question 4.
| Column ‘A’ | Column ‘B’ |
| (1) Fullerene (2) Diamond (3) Graphite |
(a) Lubricants (b) Insulator (c) Ornaments |
Answer:
(1 – b),
(2 – c),
(3 – a)
Question 5.
| Column ‘A | Column ‘B’ |
| (1) Water gas (2) Methane gas (3) Producer gas (4) Carbon dioxide gas |
(a) CH4 (b) CO + H2 (c) CO2 (d) CO + H2 + CO2 + N2 |
Answer:
(1 – b),
(2 – a),
(3 – d),
(4 – c)
State whether the following statements are true or false. Correct the false statement.
(1) Study of organic compounds is called as organic chemistry.
(2) Hydrocarbons with double bonds are called as saturated hydrocarbons.
(3) Ethene is saturated hydrocarbon.
(4) Covalent compounds are good conductor of electricity.
(5) Methane is a covalent compound.
(6) Covalent compounds are soluble in organic solvents.
(7) Graphite is used in making lubricants and lead pencils.
(8) The density of diamond is 9.8 g/cm3.
(9) Diamond knives are used in eye surgery.
(10) Fullerenes are used as insulators.
(11) Coke is used in production of water gas i.e. (CO2 + H2O).
(12) Structural formula of propyne is CH3 – C = CH.
(13) COz is used to make aerated drinks.
(14) Methane gas is black in colour.
(15) Production of biogas is aerobic process.
Answer:
(1) True
(2) False. Hydrocarbons with double bonds are called as Unsaturated hydrocarbons.
(3) False. Ethene is Unsaturated hydrocarbon.
(4) False. Covalent compounds are bad conductor of electricity.
(5) True
(6) True
(7) True
(8) False: The density of diamond is 3.5 g/cm3.
(9) True
(10) True
(11) False. Coke is used in production of water gas i.e. (CO + H2).
(12) False. Structural formula of propyne is CH3 – C = CH.
(13) True
(14) False. Methane gas is colourless.
(15) False. Production of biogas is anaerobic process.
Find the odd man out:
Question 1.
Propane, Methane, Ethene, Pentane.
Answer:
Ethene. It is an unsaturated hydrocarbon with double bond between two carbon atoms while rest are saturated hydrocarbons with single bond between two carbon atoms.
Question 2.
CH4, C2H6, C3H8, CaCO3.
Answer:
CaCO3. It is a salt which is an inorganic’ compound, while rest are hydrocarbon compounds, i.e. organic compounds.
Question 3.
C2H2, C3H8, C2H6, CH4.
Answer:
C2H2. It is an unsaturated hydrocarbon with triple bonds while rest are saturated hydrocarbons with single bonds between two carbon atoms.
Question 4.
Diamond, Fullerene, Graphite, Methane.
Answer:
Methane. It is a marsh gas while rest are allotropes of carbon.
Question 5.
Coal, Petroleum, Natural gas, Cotton
Answer:
Cotton. Cotton is a natural fibre while rest all are fossil fuels.
Question 6.
Cotton, Silk, Proteins, Wool
Answer:
Proteins. Proteins are carbonaceous nutrients while rest all are natural fibres.
Question 7.
Carbohydrates, Coal, Proteins, Fats
Answer:
Coal. Coal is a fossil fuel while rest all are carbonaceous nutrients.
Question 8.
Peat, Charcoal, Lignite, Bituminous
Answer:
Charcoal. Charcoal is a non-crystalline form of carbon while rest all are types of coal.
Question 9.
Lubricants, Electrodes, Ornaments, Arc Lamps
Answer:
Ornaments. Ornaments are made from diamonds while rest all are made from graphite.
Write the correlated terms:
(1) Propene : Double bond :: Propyne : ……………………. .
(2) Ethane : CH3 – CH3 :: Ethene : ……………………. .
(3) Hydrogen : Monovalent :: Carbon : ……………………. .
(4) Methane : Low melting point i.e. -182.5°C Diamond : ……………………. .
(5) Graphite : Hexagonal structure :: Diamond : ……………………. .
(6) Density of Diamond : 3.5 g/cm3 :: Density of Graphite : ……………………. .
(7) Peat: 60% of carbon :: Anthracite : ……………………. .
(8) Melting point of CO2: -56.6°C :: Melting point of CH4: ……………………. .
Answer:
(1) Triple Bond
(2) CH2 = CH2
(3) Tetravalent
(4) High melting point i.e. 3500°C
(5) Tetragonal structure
(6) 1.9 to 2.3 g/cm3
(7) 95% of carbon
(8) -182.5 °C
Give scientific reasons:
Question 1.
Covalent compounds have low melting and boiling points.
Answer:
Question 2.
Graphite is a good conductor of electricity whereas diamond is a non-conductor of electricity.
Answer:
Question 3.
Graphite is used as a lubricant.
Answer:
Question 4.
Methane is used as a domestic fuel.
Answer:
Answer in short:
Question 1.
What was the contribution of chemist Wohier in organic chemistry?
Answer:
Question 2.
With neat diagram explain the structure of diamond.
Ans.
Question 3.
With neat diagram explain the structure of graphite?
Answer:
Question 4.
Give the properties of graphite.
Answer:
Properties of graphite are:
Question 5.
Give the uses of graphite.
Answer:
Uses of graphite are:
Question 6.
Give the uses of fullerenes.
Answer:
Uses of Fullerenes are:
Question 7.
What is Coal?
Answer:
Question 8.
What is Coke?
Answer:
The pure coal that remains when coal gas has been taken away from coal, is called coke.
Question 9.
Give the uses of Coal.
Answer:
Uses of Coal are:
Question 10.
Give the uses of Coke.
Answer:
Uses of Coke are:
Question 11.
Name the types of coal and give the differences in them.
Answer:
The four types of coal are Peat, Lignite, Bituminous and Anthracite.
Question 12.
Give the properties of covalent compounds.
Answer:
Properties of covalent compounds:
Question 13.
What are saturated hydrocarbons? Give examples.
Answer:
Question 14.
What are unsaturated hydrocarbons? Give examples.
Answer:
Question 15.
Give the following information of carbon dioxide: Molecular formula, Molecular mass, Melting point, Percentage occurrence in air.
Answer:
Molecular formula – CO2, Molecular mass – 44, Melting point -56.6 °C Percentage occurrence in air – 0.03%.
Question 16.
Give the physical and chemical properties of carbon dioxide.
Answer:
Physical properties of carbon dioxide are:
Chemical properties of carbon dioxide are:
Question 17.
Give the uses of Carbon dioxide.
Answer:
Uses of Carbon dioxide are:
Question 18.
Give the occurrence of methane.
Answer:
The occurrence of methane is as follows:
Question 19.
Give the physical properties of methane.
Answer:
Physical properties of methane are:
Question 20.
Give the uses of methane.
Answer:
Uses of methane are:
Question 21.
How is methane formed? Give structural formula and electron dot model of methane.
Answer:
Question 22.
What are organic and inorganic compounds?
Answer:
Compounds obtained directly or indirectly from plants and animals are called organic compounds and compounds obtained from minerals are called inorganic compounds.
Question 23.
What is allotropy?
Answer:
Question 24.
What are basic organic compounds? What are they also called as?
Answer:
Write a balanced chemical equation and explain the following chemical reactions.
Question 1.
Preparation of urea from Ammonium cyanate:
Answer:
Organic compound Urea can be synthesized from an inorganic compound Ammonium cyanate.
Question 2.
Coal when burnt in air
Answer:
When coal is burnt in air, the carbon present in coal combines with oxygen present in air to form carbon dioxide gas.
Question 3.
Calcium carbonate reacts with dilute hydrochloric acid:
Answer:
When Calcium carbonate reacts with dilute hydrochloric add it forms Caldum chloride, water and Carbon dioxide gas is evolved.
Question 4.
Carbon dioxide is passed through an aqueous solution of Sodium hydroxide:
Answer:
When Carbon dioxide gas is passed through an aqueous solution of Sodium hydroxide it forms Sodium carbonate and Water.
Question 5.
Carbon dioxide is passed through an aqueous solution of Sodium carbonate:
Answer:
When carbon dioxide is passed through an aqueous solution of Sodium carbonate, it forms Sodium bicarbonate.
Question 6.
Carbon dioxide is passed through freshly prepared lime water for a short duration and then for longer duration:
Answer:
When Carbon dioxide is passed through freshly prepared lime water, it forms water and white precipitate of Calcium carbonate because of which lime water turns milky.
When Carbon dioxide is continuously passed through milky lime water, it forms Calcium bicarbonate which is soluble in water and therefore, water once again turns colourless.
Question 7.
Carbon dioxide gas is dissolved in water.
Answer:
Carboh dioxide gas is fairly soluble in water, it dissolves in water under pressure to form Carbonic acid.
Question 8.
Sodium bicarbonate reacts with dilute Sulphuric acid, (reaction in fire extinguisher):
Answer:
When Sodium bicarbonate reacts with dilute Sulphuric acid it forms Sodium sulphate, water and Carbon dioxide gas.
Question 9.
Methane gas is burnt in air:
Answer:
Methane is highly inflammable, it burns in air with a bluish flame and combines with oxygen present in air to form Carbon dioxide and water. In these reaction 213 kcal/mol of heat is given out.
Question 10.
Methane and Chlorine gases react with each other.
Answer:
Methane and chlorine gases react with each other at the temperature of 250 °C to 400 °C in presence of ultra voilet light and form mainly Methyl chloride (Chloromethane and ‘ Hydrogen chloride)
This reaction is called Chlorination of methane.
Question 11.
Production of methane gas in biogas plant.
Answer:
In biogas plant, microbes act on the bio-degradable complex organic compounds and produce organic acids.
The methanogenic bacteria act on the organic acids to produce Methane gas and Carbon dioxide gas.
Question 12.
Production of water gas:
Answer:
When super heated steam is passed over red hot coke at high temperature, it forms carbon monoxide gas and hydrogen gas.
This gaseous product of carbon monoxide gas and hydrogen gas together is called as water gas.
With the help of ne abelled diagram explain the following:
Question 1.
Regular fire extinguisher.
Answer:
Question 2.
Biogas plant.
Answer:
Chemical reaction:
Answer the following
Question 1.
What happens when substances like milk, sugar, wool, dry leaves, hair and seeds are heated strongly in hard glass test tube?Answer:
When milk, sugar, wool, dry leaves, hair and seeds are heated strongly in hard glass test tube, they get charred and a black substance is left behind. This black substance is carbon.
Answer the following questions:
Question 1.
Take some milk in an evaporating dish. Heat the evaporating dish on a bunsen burner. What remains behind at the bottom of an evaporating dish on complete evaporation of the milk?
Answer:
Question 2.
Take small samples of sugar, wool, dry leaves, hair, seeds, split pulses and plastic in separate test tubes. Heat each test tube and observe the changes taking place in the substances. What does the black substance in each test tube indicate?
Answer:
Question 3.
Apparatus : Coal, match box, moist litmus paper, etc.
Procedure : Ignite the coal. Hold the moist blue litmus paper over the gas released on igniting the coal. Note the observation.
(a) With which gas in the air does the coal react on igniting?
Answer:
Coal reacts with oxygen gas present in the air, on igniting.
(b) What is the substance formed?
Answer:
The substance formed is carbon dioxide.
(c) What change takes place in the litmus paper?
Answer:
The moist blue litmus paper turns red.
(d) Write down the chemical reaction taking place in the above procedure.
Answer:
(i) Carbon combines with oxygen to form Carbon dioxide gas.
(ii) This C02 combines with water present on moist blue litmus paper to form Carbonic acid which turns blue litmus to red.
Question 4.
Apparatus : Pencil, electrical wires, battery/ cell, small bulb, water, kerosene, test tube, lead pencils, etc.
Procedure : Remove the lead from a pencil and arrange the apparatus as shown in the above diagram. Note your observations for the following.
(a) What is the colour of lead in the pencil? .
Answer:
The colour of the lead in the pencil is black as it is made from graphite which is an allotrophic form of carbon.
(b) Try to break lead with your hand.
Answer:
The lead breaks easily as it is made up of graphite which is brittle in nature.
(c) Start the electric current in the circuit and observe. What did you find?
Answer:
When we start the electric current in the circuit, the bulb in the circuit glows, indicating that the lead in the pencil is a good conductor of electricity.
(d) Take some water in a test tube. Take some kerosene in another test tube. Put lead dust in both the test tube. What did you observe?
Answer:
(i) Lead dust does not dissolve in water nor in kerosene.
(ii) It remains insoluble in both the test tubes.
Question 5.
Apparatus : Test tube, straw, lime water, etc.
Procedure: Take freshly prepared lime water in a test tube. Blow air in it for some time through the straw and observe the lime water. Note the observation.
(a) What did you see?
Answer:
When we blow air through the straw in freshly prepared lime water, it turns milky.
(b) What might be the reason behind the change?
Answer:
Freshly prepared lime water is obtained by dissolving lime (CaO) in water (H2O).
When we blow air through the straw in lime water, carbon dioxide (CO2) present in the air reacts with lime water to form white precipitate (insoluble substance) of Calcium Carbonate (CaCO3) due to which lime water turns milky.
Question 6.
With the help of a neat labelled diagram explain the laboratory preparation of Carbon dioxide gas.
Answer:
The laboratory preparation of Carbon dioxide gas is as follows:
Apparatus : Retort stand, round bottom flask, thistle funnel, gas delivery tube, gas jars.
Chemicals : Calcium carbonate (Pieces of Shahabad tiles/marble pieces/limestone), dilute hydrochloric acid.
Procedure: