Kerala SSLC Class 9 Solutions for Physical Sciences – Some Non-Metals in Nature (English Medium) Part-2
Page No. 129:
Question 1:
What are the ways in which trees support human life?
Solution :
Trees support human life by
- Purifying air
- Providing food and wood
- Preventing soil erosion
- Contributing to climate control
Question 2:
What is the role of plants in providing oxygen and food? Do you know the chemical process behind this?
Solution :
The green plants acts as the basic energy source for all the living beings on Earth. They convert solar energy from the Sun into chemical energy and synthesize carbohydrates using chlorophyll, present on the cells of the leaves, carbon dioxide and water. This process is known as photosynthesis.
During photosynthesis, carbohydrates get synthesized to form starch which acts as a source of food and indicates the occurrence of photosynthesis on leaves.
Green plants play an important role in maintaining the oxygen content in the atmosphere. They release oxygen as a byproduct during photosynthesis which is used by all living beings for respiration.
For respiration, oxygen is taken in and carbon dioxide is given out by the living beings. Plants use this carbon dioxide for photosynthesis and gives out oxygen. For plants, water is their source of oxygen.
Thus, plants help in maintaining the oxygen level in the atmosphere. The chemical equation for photosynthesis is
Page No. 130:
Question 1:
There are metallic and non-metallic elements among these. Identify them.
Solution :
Metallic elements – Mg, Ca, Na, K, Fe Non metallic elements – C, H, O, N, CI, P, S
Question 2:
As you know water and air have a major role in sustaining life. What are their constituents?
Solution :
Hydrogen and oxygen are the constituent elements of water.
Question 3:
Now take a look at the components of the atmosphere.
Which among them are compounds?
- Note down their constituent elements.
- Which component of air is essential for respiration?
- How many compounds of oxygen are known to you?
Solution :
- Carbon dioxide is a compound composed of carbon and oxygen.
- Constituent elements of carbon dioxide are carbon (C) and oxygen (O).
- Oxygen is essential for respiration.
- Compounds of oxygen are
- Water
- Calcium carbonate
- Carbon dioxide
- Potassium chlorate
- Silicon dioxide
- Carbohydrate
- Nitrogen dioxide
- Nitric oxide
- Nitrous oxide
- Potassium nitrate
- Sodium hydroxide
- Sodium carbonate
- Sodium bicarbonate
- Potassium sulphate
- Potassium nitrite
Question 4:
Oxygen exists in nature in the free state as well as in the combined state.
- How is free oxygen represented? Write down its chemical formula.
- To which of the following categories does oxygen molecule belong? (Monoatomic, Diatomic, Polyatomic)
- How is ozone represented?
- Write down the characteristic features of ozone you know.
Solution :
- The chemical formula of the free oxygen is O.
- Oxygen molecule (O2) is diatomic. Oxygen is also found in the atmosphere in a triatomic form called ozone (O3).
- Ozone is represented as O3. Characteristic features of ozone are
-
- Ozone is a light bluish and a poisonous gas with a chlorine-like odour found in the upper layer of the atmosphere called stratosphere..
- It is formed by the action of ultraviolet rays from the Sun on atmospheric oxygen.3O2 → 2O3
(Oxygen) (Ozone) - The ozone layer acts as a blanket in the atmosphere at a height of 16 km above the Earth’s surface.
- It absorbs harmful ultraviolet rays (UV radiations) coming from the Sun and prevents them from reaching the surface of the Earth.
Question 5:
Millions of living beings, animals and plants use oxygen every minute for respiration. Will this not lead to the exhaustion of oxygen in the atmosphere?
Solution :
No. Plants do not use oxygen for respiration. They give out oxygen as a byproduct of photosynthesis. This oxygen which gets spread in the atmosphere is then used by other living beings for respiration. The living beings then release carbon dioxide as the byproduct of respiration. The plants then make use of this carbon dioxide for photosynthesis. This will help in maintaining the oxygen level in the atmosphere and will not lead to the exhaustion of oxygen in the atmosphere.
Page No. 131:
Question 1:
Prepare a note explaining the role of green vegetation in maintaining the quantity of oxygen in the atmosphere.
Solution :
Green plants perform important functions which help in sustaining life on Earth. While preparing food for them, the green plants give out a lot of oxygen. All living things need oxygen for respiration. No form of life can exist without oxygen. They act as gas plants and produce life supporting oxygen. Thus the green plants replenish the atmospheric oxygen and maintain life.
Question 2:
Is it possible to prepare oxygen in your laboratory?
Solution :
Yes. It is possible to prepare oxygen in the laboratory.
We can prepare oxygen in by the following ways:
- Laboratory preparation of oxygen from hydrogen peroxide H2O2.
Equation:
Hydrogen peroxide is decomposed using manganese oxide to give water release oxygen
Reactants:
Hydrogen peroxide
Manganese dioxide (Catalyst)
Apparatus:
Thistle funnel
Flat bottom flask
Procedure:
Hydrogen peroxide is added drop-by-drop from the thistle funnel to manganese dioxide in the flat bottom flask.
Observation:
Brisk effervescence is observed due to liberation of oxygen gas.
Collection of the gas:
The gas is collected by the downward displacement of water through the delivery tube. Oxygen gas is slightly soluble in water.
- Laboratory preparation of oxygen from potassium chlorate KClO3
Equation:
Procedure:
Potassium chlorate and manganese dioxide are heated strongly in a hard glass test tube kept in an inclined position.
Observation:
Brisk effervescence is observed due to liberation of oxygen gas.
Collection of the gas:
The gas is collected by the downward displacement of water through the delivery tube. Oxygen gas is slightly soluble in water.
Role of the catalyst:
- Alters the rate of the reaction.
- The evolution of oxygen gas is more rapid.
- It does not undergo any change by chemically or by mass.
Question 3:
Notice the balanced equation for the reaction taking place, when powdered potassium permanganate is heated in a test tube.
2 KMnO4 + Heat → K2MnO4 + MnO2 + O2
What happens if a glowing agarbathi is introduced into this test tube?
Try it yourself.
- What did you observe?
- What is the reason?
Solution :
- The splinter glows into flame.
- Oxygen supports combustion, i.e. is helps burning.
Question 4:
Keep a lighted candle on the table and cover it with an inverted glass tumbler.
- Why did the candle flame get extinguished? What is your inference regarding the role of oxygen in the combustion of objects?
Solution :
- The candle burns for a few seconds and then goes off. This is because the candle needs the presence of oxygen in the air to burn. So, once the oxygen present in the glass tumbler gets used up, the flame extinguishes.
Question 5:
You are already familiar with the burning of magnesium in air.
What was the end product? Complete the equation and balance it.
—— + O2 → MgO
Solution :
The end product is magnesium oxide MgO.
The balanced chemical equation is given as
2Mg + O2 → 2MgO
Magnesium Oxygen Magnesium oxide
Question 6:
Write the equation for the formation of carbon dioxide by the burning of carbon.
Solution :
Question 7:
Are there metals which do not lose their luster in contact with air? What could be the reason? Find out.
Solution :
There are few metals such as gold and platinum which do not lose their luster even when they are exposed to air or moisture. They are called noble metals.
The reason for this is-
Noble metals are highly unreactive. In other words they do not react with any acids, bases or moisture hence, they are termed as noble metals.
Question 8:
What are the purposes for which oxygen is essential?
- For combustion of fuels
- In rocket fuels as oxidiser
- For medical purposes
- For natural degradation of materials
- ……………………………
- ……………………………
Solution :
The purposes for which oxygen is essential
- For combustion of fuels
- In rocket fuels as oxidiser
- For medical purposes
- For natural degradation of materials
- For respiration
- For welding metals
- For burning fuels: Oxidation of carbon-containing fuels. Example: Hydrocarbons such as coal, wood, charcoal.
- Acts as an anaesthetic: To render a numb area in surgical or dental procedures, anaesthesia (a mixture of oxygen and nitrous oxide) is administered to the patient.
- To be used in forming oxyacetylene torch, oxyacetylene flame or oxyhydrogen flame. This are used to produce high temperature needed for various purposes in industries.
- In the manufacture of acids such as nitric acid, sulphuric acid.
Question 9:
- Which is the major element in air?
- Which properties of nitrogen are you aware of?
Solution :
- Nitrogen is the major element present in the air.
- Properties of Nitrogen are
- Colourless and odourless gas
- Slightly soluble in water
- Chemically unreactive at ordinary temperature
- Controls combustion by diluting the activity of oxygen in the air
- An important constituent of proteins
- Essential for the growth of plants and animals Plants take in nitrogen from the soil for their growth. Animals and man get nitrogen from plants.
Page No. 132:
Question 1:
Fill up the following table after finding out the position of nitrogen in the periodic table.
Solution :
Question 2:
Animals get nitrogen through food. What about plants?
Solution :
Nitrogen is more or less inert among the gases in the atmosphere. Still, it combines with oxygen at high temperature during lightning. Nitrogen in the atmosphere gets converted to nitric oxide (NO). It mixes with the water vapour present in the atmosphere and falls down with rain. Plants take in nitrogen from the soil for their growth. Animals and man get nitrogen from plants. Nitrogen is an important constituent of proteins. It is essential for growth of plants and animals.
Question 3:
Nitrates through lightning
During lightning, nitrogen in the atmosphere is converted to nitric oxide (NO).
- What could be the reason for that?
- Complete the equation and balance it.
………….. + ………….. → NO
Solution :
When lightning occurs, high temperature is produced in the atmosphere. As a result, atmospheric nitrogen and oxygen combine to form nitric oxide.
The balanced chemical equation is given as,
N2 + O2 → 2NO
Question 4:
What are the organic wastes generally supplied to plants for their growth?
- …………………………….
- …………………………….
- …………………………….
- …………………………….
Solution :
The organic wastes generally supplied to plants for their growth are
- Vermiwash
- Vermi compost
- Bone meal
- Green manure
- Cow dung
- Excreta of organism
- Fish manure
- Ash
Question 5:
What is the importance of organic fertilizers in agriculture?
Solution :
- The chemical composition of the soil is not adversely affected.
- It is ecofriendly, so, they do not produce any harmful effect on the environment.
- Use of biofertilizers is better to humans and all other living things.
- It does not destroy the small organisms present in the soil and inturn it stimulates their number.
Question 6:
What are the limitations of organic fertilizers?
- ……………………………………………..
- ……………………………………………..
- ………………………………………………
- How can this be overcome?
Solution :
- he limitations of organic fertilizers are i. More quantity is needed iii. Does not supplement the lacking elements adequately
- ii. Does not always give immediate result
- This can be overcome by using fertilizer only in the required quantity.
Page No. 133:
Question 1:
Take some ammonium chloride in a test tube, add lime [Ca(OH)2] and heat it. Record the observations in table.
Solution :
Page No. 134:
Question 1:
Hydrogen
Take dilute hydrochloric acid in a wash bottle and put some zinc granules in it. Close the bottle and dip the free end of the tube in soap solution in a beaker.
Bring a lighted matchstick close to the bubbles that are formed.
- What do you observe?
How are bubbles formed here?
- Which is the gas that burns with a ‘pop’ sound?
- What about collecting the gas that was formed in this experiment in a balloon?
Solution :
- The gas present in soap bubble catches fire and burns with a ‘pop’ sound.
- When zinc reacts with dilute hydrochloric acid, bubbles of hydrogen gas are formed.Zn + 2HCl → ZnCl2 + H2↑
- Hydrogen gas burns with a ‘pop’ sound.
- Hydrogen gas is collected by the downward displacement of water through the delivery tube.
Question 2:
- What are the preliminary arrangements to be done for the preparation of hydrogen gas?
(Refer to the figure given below)
- What are the materials required for this experiment?
Tie the inflated balloon with a thread, detach it from the jar and leave it free.
- What happens?
- What conclusion can be reached with regard to the density of hydrogen?
Solution :
The preliminary arrangements to be done for the preparation of hydrogen gas :
Materials required:
Bottle, cork, balloon, zinc granules, dilute hydrochloric acid
Procedure:
- Take a bottle with narrow neck. Close it with a one hole stopper carrying a tube.
- Tie a balloon to the open end of the tube.
- Remove the stopper. Put a few pieces of zinc in the bottle. Pour dilute hydrochloric acid into the bottle.
- The acid should be enough to cover the zinc pieces. Close the bottle and hold the stopper firmly.
Observation:
- When zinc reacts with dilute hydrochloric acid, bubbles of hydrogen gas are formed.
- This gas then moves upward and fills the balloon.
- Just in a few minutes you will find the balloon getting inflated.
- When the inflated balloon is tied with a thread, the balloon goes up.
Conclusion:
- This happens because hydrogen is lighter than air.
Question 3:
List the compounds of hydrogen you know.
- NH3
- HCl
- ………
- ………
- ……….
Solution :
- NH3
- HCl
- H2O
- H2SO4
- H2O2
- HNO3
- NaHCO3
- H2S
- NaH
Question 4:
Locate hydrogen in the periodic table.
Solution :
The element hydrogen is located in the first group and first period of the periodic table.
Page No. 135:
Question 1:
- What is the atomic number of hydrogen?
- Mass number?
Solution :
- he atomic number of hydrogen is 1.
- The mass number of hydrogen is also 1.
Question 2:
What are the features of hydrogen that differentiate it from other atoms?
Size: ………………………
Weight: ………………………
Atomic structure: ………………………
Solution :
Size: Less
Weight: Less
Atomic structure:
Question 3:
Write the chemical formula of hydrogen.
Solution :
The chemical formula of hydrogen is H2.
Question 4:
There are hydrogen isotopes with and without neutrons. Write the names and symbols of these.
Solution :
Question 5:
You know that hydrogen is a combustible gas. Can it be used as a fuel?
Solution :
Yes, hydrogen gas can be used as a fuel.
Question 6:
Figure shown below is a graph of the heat energy produced by the combustion of one gram each of different fuels.
- Will the burning of hydrogen cause atmospheric pollution?
- Find out the equation for hydrogen burning in air
………… + ………… → ………… - Discuss and record the advantages of using hydrogen as a fuel on the basis of the following.
- Availability of hydrogen
- Available energy
- Least possibility of pollution
- Despite all these advantages, why is hydrogen not used as a common fuel?
- What are the technical difficulties in handling this fuel? Think it over in relation to hydrogen’s combustibility and find out the answer.
- And if this limitation is overcome?
Solution :
- No. The burning of hydrogen does not cause any atmospheric pollution.
- Equation for hydrogen burning in air is given by
- 2H2 + O2 → 2H2O
- The advantages of using hydrogen as a fuel are
- It is used as a fuel in the form of coal gas, water gas (i.e. mixture of carbon monoxide and hydrogen) and liquid hydrogen.
- It is plenty available in nature with a high calorific value and is produced from water.
- Burning of hydrogen does not cause atmospheric pollution.
- Despite all these advantages, hydrogen is not used as a common fuel because it is too expensive and extremely explosive and hence, is dangerous to handle.
- The explosive nature of its reaction with oxygen makes it difficult to contain. It is difficult to store and transport hydrogen.
- In order to overcome the limitation, the cheap method to produce H2 by splitting water should be brought in place.
Page No. 136:
Question 1:
The availability of fossil fuels such as petrol, diesel and kerosene is fast diminishing. In these circumstances, can hydrogen be considered as the fuel of the future?
Solution :
Yes, hydrogen can be considered as a fuel of the future.
Question 2:
Chlorine
What are the main sources of drinking water?
- Well
- …………
- …………
Solution :
The main sources of drinking water are
- Well
- River
- Pond
Question 3:
Haven’t you noticed the peculiar smell of tap water?
Solution :
The peculiar smell of tap water is due to the chlorine added to water as a part of its purification process. It is the oxidizing action of chlorine which makes water free of germs.
Chlorine does not occur in nature in the free state; it is found as chlorides.
Question 4:
Add more examples you know to the list of chlorine compounds:
- KCl
- AlCl3
- MgCl2
- CaCl2
- …………
- …………
- …………
Solution :
- KCl
- AlCl3
- MgCl2
- CaCl2
- NaCl
- CCl4
- HCl
- HClO3
- CaOCl2
Question 5:
What guess can you make, about the chemical reactivity of chlorine based on the fact that chlorine is found in nature only as its compounds?
Solution :
The reactivity of chlorine is high.
Question 6:
Use the periodic table to collect more details about chlorine and fill up the table below.
Atomic number | |
Atomic mass | |
Electronic configuration | |
Valency |
Solution :
Atomic number | 17 |
Atomic mass | 35.5 |
Electronic configuration | 2, 8, 7 |
Valency | 1 |
Question 7:
What is the reason for the high chemical reactivity of chlorine? Arrive at a conclusion by considering its electronic configuration and valency.
Solution :
- The electronic configuration of chlorine is 2, 8, 7.
- Valency of chlorine is 1. All halogens have a tendency to accept one electron to complete its octet and achieve the stable noble gas configuration. Hence, they are very reactive elements.
- Each chlorine atom needs one more electron to achieve stable configuration.
- But it is difficult for the chlorine atom to lose its valence electron to another chlorine atom. In this case, the chlorine atom shares one of the electrons from its outermost shell with another chlorine atom.
- Then each atom gets the concession of another electron in addition to the electrons present in it. So, in this way both of them attain stability. Due to these reasons chlorine has high chemical reactivity.
- The bond energy of Cl ‒ Cl bond in chlorine molecule is comparatively near to the energy of the photon in visible light. Hence, in the presence of sunlight, Cl2 decomposes easily and changes into independent atoms. This is the reason why Cl2 shows high reactivity in the presence of sunlight.
Question 8:
Preparation of Chlorine
The figure shows the arrangement for preparing chlorine in the laboratory. Analyse the figure.
16 HCl + 2 KMnO4→ 2 KCl+2 MnCl2 + 8 H2O + 5 Cl2
- What are the reactants used?
- What are the products?
- Chlorine is collected by the upward displacement of air in the jar. From this what can you deduce regarding the density of chlorine?
- Why is chlorine gas passed through concentrated sulphuric acid? Find out by examining the products.
- Examine whether the equation is balanced.
- The colour of the gas that was produced.
- Smell (Don’t inhale)
Solution :
- The reactants used are potassium permanganate, hydrochloric acid.
- The products formed are KCl, MnCl2, H2O, Cl2.
- Chlorine gas has higher density as compared to air.
- The chlorine gas is passed through the concentrated sulphuric acid to remove the water vapour formed along with the chlorine gas.
- Yes. The given equation is balanced.
- The gas which is produced is greenish yellow in colour.
- It has pungent and suffocating odour.
Page No. 137:
Question 1:
Bleaching Activity of Chlorine
Let us do an experiment using chlorine. Take petals of colourful flowers, green leaves and coloured pieces of clothes and wet them in water. Put them in a gas jar. Prepare chlorine and pass it through the jar.
Solution :
Observation
After some time the coloured matter dipped in water starts losing its colour and eventually becomes colourless. Chlorine is a strong bleaching agent. It bleaches the coloured matter and makes it colourless. Here, bleaching action takes place through oxidation.
Question 2:
- Which is the substance used for purifying drinking water in ponds and wells?
- Take a pinch of bleaching powder and smell it. Are you able to recognize the main component of bleaching powder from its smell? What is it?
Solution :
- Bleaching powder is used for purifying drinking water in ponds and wells.
- Yes. We can recognize the main component of bleaching powder from its smell. The main component of bleaching powder is chlorine.
- Bleaching powder is made by passing chlorine through dry slaked lime. It is used as a source of chlorine for common purposes.Ca(OH)2 + Cl2 → CaOCl2 + H2O
Page No. 138:
Question 1:
- If so, will the absorption of ultraviolet rays in the stratosphere increase or decrease?
- What will be its after effect?
Solution :
- The absorption of ultraviolet rays in the stratosphere will decrease.
- The harmful ultraviolet rays that reach the earth can cause dreadful diseases such as skin cancer, cataract and some other diseases in human beings. These rays can cause severe damage to the soft tissues of plants and animals. The UV rays will completely destroy the phytoplankton which would disrupt the food chain. This will lead to the destruction of ecosystem and the equilibrium of nature will get disturbed and gradually natural calamities will occur.
Question 2:
What is the role of the modern way of life in the depletion of the ozone layer?
Solution :
Role of the modern way of life in the depletion of the ozone layer
- Fuel used in planesBurning of fuels in planes emits large quantity of nitric oxide and other gases in the atmosphere. Nitric oxide reacts with ozone and forms nitrogen dioxide and nitrogen trioxide. This causes depletion of ozone.
NO(g) + O3(g) → NO2(g) + O2(g)
(Nitrogen trioxide)
NO2(g) + O3(g) → NO3(g) + O2(g)
(Nitrogen dioxide) - Excessive use of chlorofluorocarbon
Chlorofluorocarbon is released by refrigerators and air conditioning systems.
It causes reduction in ozone layer which protects us from harmful ultraviolet rays (UV radiations) of the Sun.
The chlorofluorocarbons are decomposed by the ultraviolet rays to form highly reactive chlorine which is produced in the atomic form.
Question 3:
From which appliances and substances used in our day-to-day life will CFC ultimately reach the atmosphere?
Solution :
The possibility of CFC reaching the atmosphere is from refrigerators, air conditioners, cosmetics, pesticides, industrial processes and medicinal equipments.