Kerala SSLC Class 9 Solutions for Physical Sciences – The World of Carbon

Kerala SSLC Class 9 Solutions for Physical Sciences – The World of Carbon (English Medium) Part-2

Page No.139:

Question 1.
Sometimes, while cooking, food gets charred when overheated. What other things get charred when heated?
Solution:
Materials such as paper, sugar, wool, silk, jute get charred on heating.

Question 2.
Take some sugar in a steel spoon and heat it. Watch the changes. What is the substance that you get in the end?
Solution:
Sugar gets charred on heating and a brownish black sticky mass is obtained. Carbon and water are formed on heating the sugar.
The blackish mass obtained in the end is carbon.

Question 3.
How are wood charcoal and coconut shell charcoal made?
Solution:
Wood charcoal and coconut shell charcoal are made by heating wood and coconut shell respectively in the absence of air.

Question 4.
Food articles, wood, paper, wool, silk, jute etc. get charred when heated. Why does this happen?
Solution:
Substances which do not vaporise during burning do not form flames and get charred. Thus, the carbon containing materials such as food articles, wood, paper, wool, silk, jute gets charred when heated.

Question 5.
What happens when CaCO₃ is heated? Do you get charcoal?
Solution:
On heating CaCO_3, calcium oxide and carbon dioxide are formed. We do not get charcoal.

Question 6.
Which is the gas whose quantity is mainly determined during emission test in motor vehicles?
Solution:
The quantity of carbon monoxide gas is mainly determined during emission test in motor vehicles.

Question 7.
What are the other materials containing carbon known to you? List them.

• Wax
• Marble
• Kerosene
• Methane
• ……………….
• ……………….
• From the list, identify the organic compounds or materials containing them.
• Which are the inorganic compounds or materials containing them?

Solution:
The following materials contain carbon in them:

• Wax
• Marble
• Kerosene
• Methane
• Diesel
• Petrol
• Rubber
• Cotton
• Nylon
• Polyester
• LPG
• CNG
• Paper
• Plastic
• Dyes
• Sugar
• Graphite
• Diamond
• Charcoal
• Wool
• Silk
• Jute
• From the list,Wax, kerosene, methane, diesel, petrol, rubber, cotton, nylon, polyester, LPG, CNG, paper, plastic, sugar, wool, silk, jute are organic compounds or materials.

• Marble, dyes, graphite, diamond, charcoal are the inorganic compounds or materials.

Question 8.
Locate carbon in the periodic table. Find out the following and complete table given below and make a record of it in your science diary.

Mass number
Atomic number
Electronic configuration
Period
Group
Valency
Metal/Non-metal
Family
Metals in the group
Metalloids in the group

Solution:
Carbon atom is present in the fourteenth group and second period of the periodic table.

Mass number	12
Atomic number	6
Electronic configuration	2, 4
Period	2nd period
Group	14th group
Valency	4
Metal/Non-metal	Non-metal
Family	Carbon family
Metals in the group	Tin, Lead
Metalloids in the group	Germanium, Silicon

Page No.140:

Question 1.
What are the forms of carbon that you are familiar with? List them.

• Wood charcoal
• Coal
• …………….
• …………….
• …………….
• …………….

Solution:
List of the forms of carbon atom is as follows:

• Wood charcoal
• Coal
• Coke
• Diamond
• Graphite
• Petroleum
• Lamp black
• Bone Charcoal
• Coconut shell charcoal
• Wood charcoal

Question 2.
What could be the reasons for using diamond in ornaments? Make a note in the science diary.
Solution:
Diamond is used in the preparation of ornaments because

• It is transparent, shiny and crystalline in nature.
• It gets an attractive lustre when reflected by light.
• It is the hardest substance in nature.

Question 3.
You might have heard of the use of diamond for cutting glass. Which quality of diamond is put to use here?
Solution:
Diamonds are the hardest substance in nature. This property of hardness is put in use while cutting glass.

Question 4.
What are the reasons for using graphite for making pencils? Write a note in the science diary.

• Ash colour
• ……………………..
• ……………………..

Solution:
The reasons for using graphite to make pencils are

• Ash in colour
• Soft and smooth
• Ability to make a mark on paper, hence can stay for long period of time.
• More adhesion force on paper
• Lubricant in nature

Therefore graphite is used to make lead pencil.

Question 5.
Connect pencil lead into a circuit as shown in figure given below.

• What do you observe?
• Which characteristic property of graphite could you find out from this?
• Is this not the reason for using graphite for making electrodes?

Solution:

• We observe that

1. Current passes through the circuit and the bulb glows.
2. The black central portion of the pencil is graphite.
3. Graphite is a good conductor of electricity.

• It is a good conductor of electricity.
• Yes, this is the reason for using graphite for making electrodes.

Page No. 141:

Question 1:

• Which is the main carbon compound in the atmosphere?
• What is the main compound formed when carbon or carbon containing substances burn in air?
• You have already learned the activity of heating a shell. Put a piece of shell in a test tube. Add dilute HCl to it.
  Insert a burning splinter into the test tube and watch. What happened to the flame? What is the reason?
• Which gas was produced as a result of the chemical reaction?
• Complete the equation of this chemical reaction.
  CaCO₃ + 2HCl → CaCl₂ + H₂O + …………….

Solution :

• Carbon dioxide is the main carbon compound in the atmosphere.
• Carbon dioxide is the main compound formed when carbon or carbon containing substances are burnt in air.
• Flame goes off because carbon dioxide gas is not a supporter of combustion. It is not a combustible gas.
• Carbon dioxide gas (CO₂) was produced as a result of the chemical reaction.
• CaCO₃ + 2HCl → CaCl₂ + H₂O + CO_2(g)↑

Question 2:
Will the result be the same if the experiment is done with other carbonates? Try it out with sodium carbonate and potassium carbonate.
Solution :
All carbonates except sodium carbonate and potassium carbonate decompose to give CO₂ on heating.
When carbonates react with acids, CO₂ gas is produced.
Carbon dioxide gas can be prepared by arranging the apparatus as shown in the figure given below.

Activiy: Let us perform an activity to study the reaction between sodium carbonate or (potassium carbonate) and hydrochloric acid
Procedure:
Take about 0.5 gram of sodium carbonate in a test tube and clamp it to the stand.
Add about 2 millilitre (ml) of dilute hydrochloric acid in it.
Close the test tube with the rubber cork of the glass delivery tube. Dip the lower end of the delivery tube in a test tube containing lime water.
Observation:
We will observe brisk effervescence of a gas. This gas reacts with lime water, making it milky.
Reaction:
Sodium carbonate reacts with dilutehydrochloric acid to give sodium chloride, carbon dioxide and water

Question 3:

• Pass CO₂ gas through clear lime water in a test tube and through water in another test tube. Lime water is calcium hydroxide [Ca (OH)₂] solution.
• What happened to the limewater?
• What could be the reason for this?
  Analyse the equation for this chemical reaction to find out the reason.
  Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
• Haven’t you identified the substance which gave milky colour to the solution? Write the chemical name of this substance.

Solution :

• The lime water turned milky.
• On passing CO₂ through limewater, it dissolves in it to form carbonic acid. The lime water turns milky because of the formation of undissolved calcium carbonate in the solution.Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
• The substance which gave milky colour to the solution is calcium carbonate.

Page No. 142:

Question 1:

• How will you find out whether a given substance is carbonate or not? Add dilute HC1 to various carbonates.
• Introduce a glass rod dipped in clear lime water into the gas coming out. Record the findings in the science diary.
• Now, using litmus, test the water through which carbon dioxide has been passed.

Solution :

• Lime water turns milky.
• Carbon dioxide dissolves in water to form carbonic acid and thus, making the solution acidic in nature. Due to this, the blue litmus paper turns red when passed through that water.

Question 2:
The chemical formula of carbonic acid can be found out by completing the following equation.
H₂O + CO₂ → …………….
Solution :

The complete reaction is given as
H₂O + CO₂ → H₂CO₃
Carbonic acid

Question 3:
Activity
Place lighted candles of different heights in a trough as shown in the given figure. Using a delivery tube, pass CO₂ gas into the trough.

• What happened?
• What is the reason for the candle flame getting extinguished?
• Which was the first candle to be put out?
• Can you find the reason for the tallest candle to be the last to get extinguished?
• What can be guessed about the density of CO₂ gas? Less or more than that of air?

Solution :

• All the candles get extinguished when CO₂ gas is passed into the trough.
• CO₂ is not a supporter of combustion. Hence, when the CO₂ gas is passed into the trough, all the candle flame extinguishes.
• The smallest candle will be put out first.
• The level of CO₂ reaches the flame of the tallest candle only at the end when the CO₂ gas is passed into the trough.
• The weight and density of CO₂ gas is more than that of air. The density of CO₂ is 22 and that of air is 14.4.

Page No. 143:

Question 1:
Making a Fire Extinguisher
Take 20ml baking soda (sodium bicarbonate) solution in a wash bottle. Take a little vinegar in a small test tube and suspend it in the wash bottle, as shown in figure given below. Close the wash bottle. Hold the bottle tilted and observe.

• What do you see?
• Direct the gas coming out of the tube towards a lighted candle. What happened?
• What features of CO₂ gas enable it to function as a fire extinguisher? Think it over.
  1. Not a supporter of combustion
  2. ………………………………………
  3.  ………………………………………

Solution :

• The foam containing carbon dioxide gas comes out through the tube.
• The flame of the lighted candle gets extinguished.
• The following features enable carbon dioxide gas to function as a fire extinguisher:
  1. Not a supporter of combustion. When carbon dioxide gas is released through a jet it spreads like a thick sheet and hence fire does not spread.

Question 2:
Is CO₂ the only product obtained when carbon reacts with oxygen?
Solution :
Yes, carbon combines with oxygen to only to form CO₂ gas.

Page No. 144:

Question 1:
CO readily reacts with the haemoglobin in blood and a compound carboxyhaemoglobin is formed. Due to this, blood loses its ability to carry oxygen.
What would be the consequence?
Solution :
The reaction of carbon monoxide with the haemoglobin forms carboxyhaemoglobin which leads to lack of oxygen in blood. This can cause death of the person.

Question 2:
What are the possibilities of CO being formed in the following real life situations?

• At home ………………………….
• In vehicles ………………………….
• In factories ………………………….

Solution :

• At home:Carbon monoxide is produced by devices that burn fuels. Therefore, any fuel-burning appliance in our homes is a potential source of carbon monoxide gas.Common sources of CO include the wood, oil or gas fuelled appliances such as Boilers, room heaters, furnaces, charcoal grills, water heaters, fireplaces, portable generators, wood burning stoves.
  Improperly operating or improperly vented appliances can produce fatal carbon monoxide concentrations in our homes. Using kerosene heaters or charcoal grills indoors can cause levels high enough to result in CO poisoning.
• In vehicles:Vehicles emit gases like carbon monoxide and hydrocarbons. They spread in the atmosphere and pollute the air.  Car idling in garage releases high amount of carbon monoxide gas into the atmosphere.
• In factories:Combustion of substances in various factories produces carbon monoxide which is highly poisonous to animals and man.

Question 3:
It is dangerous to start and keep idling vehicles in closed garages. Find out the reason and note it in the science diary.
Solution :
When the vehicles kept in closed garages are started the smoke emitted by them accumulates in the garage. This smoke contains carbon monoxide which is highly poisonous. Inhaling of this gas can cause suffocation and may even cause death.

Page No. 145:

Question 1:
Look at the figure given below depicting the cyclic changes of carbon on the earth in different ways. This is the carbon cycle.

• Analyse the carbon cycle
• Which is the compound that plays a major role in the cyclic changes of carbon?
• What are the main processes through which the cyclic transformation of carbon takes place?

Solution :

• Carbon Cycle:Atmosphere contains about 0.03% carbon dioxide by volume. It is an important constituent of all the organic compounds. From atmosphere, the carbon dioxide moves to green plants which by the process of photosynthesis transform it into carbohydrates. From the producers it goes to the consumers and finally to microorganisms like bacteria and fungi (decomposers). By the decomposition of dead organic matter, it is returned to the atmosphere. In aquatic ecosystem, carbon dioxide reaches the atmosphere from the lime deposits. Some part of the green plants goes into the formation of coal deposits, rocks. This is due to weathering and combustion that carbon dioxide is given back to atmosphere. Respiration by animals and plants also returns free carbon dioxide to atmosphere.
• Carbon dioxide plays a major role in the cyclic change of carbon.
• The main processes through which the cyclic transformation of carbon takes place are
  Photosynthesis
  Respiration
  Decomposition
  Thermal decomposition
  Combustion

Question 2:
What is the activity in which the CO₂ in the atmosphere is made use of?
Solution :
The CO₂ in the atmosphere is made use by the plants for the process of photosynthesis.  In this process, green plants use sunlight to synthesize nutrients and carbohydrates from carbon dioxide and water.

Question 3:
What are the activities which increase the quantity of CO₂ in the atmosphere?
Solution :
Activities such as burning of fuels, deforestation and wildfire, increasing number of factories, emission of smoke from automobiles and vehicles increase the quantity of CO₂ in the atmosphere.

Question 4:
If the amount of CO₂ increases in the atmospheric beyond a limit, is it a welcome change?
Solution :
No. The amount of CO₂ increases in the atmospheric beyond a limit is not a welcome change.

Question 5:
If the proportion of CO₂ increases, more infrared rays will be retained. What will be the result of such an event?
Solution :
If the proportion of CO₂ increases, more infrared rays will be retained. Due to this, the atmospheric temperature will increase and it will ultimately lead to global warming.

Question 6:
What are the possible repercussions of global warming?
Solution :
The possible repercussions of global warming are

• Big natural calamities
• Rise in sea level due to melting of polar ice caps and glaciers
• Abnormal weather conditions
• Flooding and submergence of coastal regions
• Damage to our eco-system

Page No. 146:

Question 1:
Why are these compounds called hydrocarbons?
Solution :
Compounds containing carbon and hydrogen are called hydrocarbons.

Page No. 147:

Question 1:
With how many other atoms has one carbon atom in the given compounds combined? What is the valency of carbon?

Solution :
In CH4 (methane), one carbon atom combines with 4 hydrogen atoms.
In C2H6 (ethane), 2 carbon atoms combine with 6 hydrogen atoms.
Valency of carbon is 4.

Question 2:
Is the bonding seen in these compounds ionic or covalent?
Solution :
The bonding seen in these compounds is covalent.

Question 3:
In the listed compounds, what is the type of covalent bond between the carbon atoms? (✓) the correct one (single bond / double bond / triple bond).
Solution :
Single bond

Page No. 148:

Question 1:
How does the number of hydrogen atoms change, when the number of carbon atoms increases in the alkanes?
Solution :
In alkanes, as the number of carbon atoms increase the number of hydrogen atoms also increase.

Question 2:
Is it possible to indicate alkanes by a general formula? Complete the following table and make an attempt.

Name of alkane	Chemical formula	No. of carbon atoms	No. of hydrogen atoms
Methane	CH4	1	2 × 1 + 2 = 4
Ethane	C2H6	2	2 × 2 + 2 = 6
Propane	C3H8	3	————-
Butane	————-	4	————-

Solution :

Name of alkane	Chemical formula	No. of carbon atoms	No. of hydrogen atoms
Methane	CH4	1	2 × 1 + 2 = 4
Ethane	C2H6	2	2 × 2 + 2 = 6
Propane	C3H8	3	2 × 3 + 2 = 8
Butane	C4H10	4	2 × 4 + 2 = 10
Pentane	C5H12	5	2 × 5 + 2 = 12
Hexane	C6H14	6	2 × 6 + 2 = 14

Question 3:
What will be the general formula of alkanes if the number of carbon atoms is ‘n’?
Solution :
C_nH_2n+2 is the general formula of alkanes where n = number of carbon atoms.

Question 4:
Look at the structure of some other hydrocarbons in the given figure.

• In these compounds, is the carbon-carbon bond the same as that in alkanes?
• What is the ratio of the number of carbon atoms and hydrogen atoms?
Solution :
No. The carbon-carbon bond is not the same as that in alkanes.
The ratio of the number of carbon atoms and hydrogen atoms is 1 : 2.

Page No. 149:

Question 1:
Complete the table given below.

Solution :

Question 2:
Can you indicate alkenes by a general formula?
Solution :
The general formula of alkenes is C_nH_2n.

Page No. 150:

Question 1:
Complete the table given below

Solution :

Question 2:
Find out the general formula for alkynes:
Solution :
The general formula of alkynes is C_nH_2n-2.

Question 3:
How are the hydrocarbons classified based on the bonding between carbon atoms?

Solution :
The Hydrocarbons are classified as alkanes, alkenes and alkynes on the basis of the bonding present between the carbon atoms.
The carbon atoms linked with each other through single bonds are called alkanes.
The carbon atoms linked with each other through double bonds are called alkenes.
The carbon atoms linked with each other through triple bonds are called alkynes.

Question 4:
Is there any connection between the names of the hydrocarbons and the chemical bonding between the carbon atoms? Try to find out.
Solution :
Yes. The second part of the name of the members of hydrocarbons (alkane, alkene and alkyne) denotes the nature of chemical bond.

Type of bond	Suffix	Hydrocarbon
Single bond	-ane	Alkane
Double bond	– ene	Alkene
Triple bond	– yne	Alkyne

Page No. 151:

Question 1:
Open chain and ring, Look at the structures of hydrocarbons given below:

How are the compounds on the left and right sides different from each other? Write down the carbon chain excluding all hydrogen atoms.
Solution :
The compounds on the left side are in the open chain form and those on the right side are in the form of closed chain (Cyclic).
The carbon chain structure excluding all hydrogen atoms of the given compounds is

Question 2:
What difference do you find? Is it not possible to classify hydrocarbons on the basis of carbon chain too? How is it done?
Solution :
The Classification of Hydrocarbons