Samacheer Kalvi 8th Science Solutions Chapter 10 Pdf
Tamilnadu Board Samacheer Kalvi 8th Science Solutions Chapter 10: Tamilnadu State Board Solution Class 8 Science Chapter 10 – Changes Around Us.
Samacheer Kalvi 8th Science Solutions Chapter 10: Overview
|
Board |
Samacheer Kalvi |
| Class |
8 |
|
Subject |
Science |
| Chapter |
10 |
|
Chapter Name |
Changes Around Us |
Samacheer Kalvi 8th Science Solutions Chapter 10 Pdf
(I) Choose the best answer .
(1) Burning of paper is a chemical change.
a) physical
b) chemical
c) physical and chemical
d) neutral
(2) Burning of matchstick is an example for chemical reaction caused by contact in physical states.
a ) contact in physical states
b) electricity
c) light
d) catalyst
(3) Iron undergoes rusting .
a ) Tin
b) Sodium
c) Copper
d) Iron
(4) The pigment responsible for browning of apples is melanin.
a ) hydrated iron (II ) oxide
b) melanin
c) starch
d) ozone
(5) Brine is a concentrated solution of sodiumchloride.
a) sodium sulphate
b) sodium chloride
c) calcium chloride
d) sodium bromide
(6) Limestone contains calcium carbonate mainly.
a) calcium chloride
b) calcium carbonate
c) calcium nitrate
d) calcium sulphate
(7) Which of the following factor induces electrolysis?
a) Heat
b) Light
c) Electricity
d) Catalysis
(8) In Haber’s process of producing ammonia iron is used as a catalyst .
a) nitrogen
b) hydrogen
c) iron
d) nickel
(9) Dissolved gases like sulphur dioxide and nitrogen oxides in rain water causes acid rain.
a ) acid rain
b) base rain
c) heavy rain
d) neutral rain
(10) Carbon dioxide,Methane,Chlorofluorocarbonsis/are responsible for global warming.
a ) Carbon dioxide
b) Methane
c) Chlorofluorocarbons
d) Carbon dioxide , Methane , Chlorofluorocarbons
(II) Fill in the blanks.
1 ) Photosynthesis is a chemical reaction that takes place in the presence of sunlight.
2) Iron objects undergo rusting when exposed to water and oxygen.
3) Ammonia is the basic material to manufacture urea.
4) Electrolysis of brine solution gives chlorine and hydrogen gases.
5) Catalyst is a chemical substance which alters the speed of a chemical reaction.
6) Polyphenol oxidase or tyrosinaseis the enzyme responsible for browning of vegetables and fruits.
(III) Say true or false. If false, correct the statement.
1 ) A chemical reaction is a temporary reaction.
This statement is false.
Explanation : A chemical reaction is not a temporary reaction but rather ,it is a permanent reaction.
2 ) Decomposition of lead nitrate is an example for a chemical reaction caused by light.
This statement is false.
Explanation :
Decomposition of lead nitrate does not depict an example for chemical reaction that is caused by light but instead, it manifests an example for a chemical reaction that is caused by heat.
3) Formation of slaked lime from quicklime is an endothermic reaction.
This statement is false.
Explanation :
Slaked lime which is formed from quicklime is not an endothermic reaction but instead, it is an exothermic reaction.
4) CFC is a pollutant .
This statement is true.
5) Light energy may come out due to chemical reactions.
This statement is true.
(IV) Match the following .
a)
| Rusting | Photosynthesis |
| Electrolysis | Haber’s process |
| Thermolysis | Iron |
| Food | Brine |
| Catalysis | Decomposition of limestone |
b.)
| Spoilage | Decomposition |
| Ozone | Biocatalyst |
| Tarnishing | Oxygen |
| Yeast | Chemical reaction |
| Calcium oxide | Food |
Answer
a.)
| Rusting | Iron |
| Electrolysis | Brine |
| Thermolysis | Decomposition of limestone |
| Food | Photosynthesis |
| Catalysis | Haber’s process |
b.)
| Spoilage | Food |
| Ozone | Oxygen |
| Tarnishing | Chemical reaction |
| Yeast | Biocatalyst |
| Calcium oxide | Decomposition |
(V) Answer briefly .
1 ) Define a chemical reaction.
A chemical change represents a permanent and irreversible change that leads to the production of a new substance. Chemical changes are also known as chemical reactions because one or more substances goes through a process of reaction for the purpose of forming one or more new substances or products.
2) Mention the various conditions required for a chemical reaction to occur.
Chemical changes does not takes place at all situations . There are requirement of certain specific conditions, for a chemical change to occur . Contact in physical states, Solution of reactants , Electricity, Heat , Light and Catalyst are the various conditions which facilitates the occurrence of chemical change .
3) Define catalysis.
Catalyst refers to those chemical substances, that are used for the purpose of speeding up chemical reaction and the process is known as catalysis.
4) What happens when an iron nail is placed in copper sulphate solution?
When an iron nail is placed in the solution of copper sulphate ,then there is a formation of ferrous sulphate because iron has displaced copper. Therefore ,there is conversion of the blue colour of copper sulphate into green colour due to the creation of ferrous sulphate.
5) What is pollution?
Our environment has provided us with everything that is essential for our survival. As for instance, food ,water, air and materials for constructing shelter. Nowadays, our environment is severely affected by the increasing number of automobiles and negative impact of industrial processes. As a result of which, the physical ,chemical and biological properties of the environment has undergone an undesirable change. This is known as pollution. Pollutants refers to those substances that are responsible for bringing about such changes. Air pollution ,water pollution and land pollution are mainly the three types of pollution.
6) What is tarnishing? Give an example.
The lustrous appearance of the shiny metal surfaces and articles fades away because of the occurrence of chemical reaction on the surface. As for instance ,when exposed to atmospheric air, silver articles turns blackish in colour.
7 ) What happens to the brine during electrolysis?
During electrolysis, the brine tends to form chlorine and hydrogen gases together with sodium hydroxide. So, in order to produce chlorine industrially, this is an essential reaction.
8) On heating, calcium carbonate gives calcium oxide and oxygen. Is it an exothermic reaction or an endothermic reaction?
Calcium carbonate produces calcium oxide and oxygen, the moment it is heated. So, it an endothermic reaction. Endothermic reaction refers to those chemical reaction, where there is an involvement of absorption of heat.
(9) What is the role of a catalyst in a chemical reaction?
Catalyst refers to those chemical substances, that are used by the industries for the purpose of speeding up chemical reaction. As for instance, while manufacturing ammonia, metallic iron is used as a catalyst using Haber’s process. Therefore, catalytic reactions refers to those reactions ,whose speed is affected by the catalyst.
10 ) Why photosynthesis is a chemical reaction?
Photosynthesis refers to a process in which, the plants uses light energy from the sun in order to prepare starch from carbon dioxide and water.The sunlight performs an essential function in inducing the chemical reaction that occurs between carbon dioxide and water and which ultimately leads to the formation of starch. Therefore, the photochemical reactions refers to those chemical reactions that are induced by light.
(VI) Answer in detail .
1 ) Explain the environmental effects of chemical reaction?
Environmental effects
a ) Pollution
Our environment has provided us with everything that is essential for our survival. As for instance, food ,water, air and materials for constructing shelter. Nowadays, our environment is severely affected by the increasing number of automobiles and negative impact of industrial process. As a result of which, the physical ,chemical and biological properties of the environment has undergone an undesirable change. This is known as pollution. Pollutants refers to those substances that are responsible for bringing about such changes. Air pollution ,water pollution and land pollution are mainly the three types of pollution. Increased human activities can lead to the production of numerous chemical substances, which brings about a harmful impact on both the living and non living things.
b) Rusting
When there is combination of iron with oxygen in the air ,then it leads to the formation of corrosionon the iron materials and this process is known as rusting. Rust can bring about a negative affect on iron and its alloys. Iron materials becomes weaker with time period because rusting replaces the strong iron with brittle and flaky powder.
c) Tarnishing of metal articles
The lustrous appearance of the shiny metal surfaces and articles fades away because of the occurrence of chemical reaction on the surface. As for instance ,when exposed to atmospheric air, silver articles turns blackish in colour. In a similar manner, brass vessels which are comprised of copper becomes greenish in colour when exposed to air for quite a long period of time. This happens because, a chemical reaction takes place between copper and moist air which leads to the formation of copper carbonate and copper hydroxide.
2) Explain how food items are spoiled by a chemical reaction?
a ) Spoilage of food and vegetables
The occurrence of any kind of changes that makes the food unsuitable for consumption is known as food spoilage. The enzymes plays an important role in accelerating the chemical reactions, which in turn degrades the quality of foods by developing poor taste, stinky odour and deficiency of nutrients.
- A bad odour comes from the rotten eggs because of the creation of hydrogen sulphide gas. This is one of the perfect example of food spoilage by chemical reaction.
b) Rancidity of fishes and meat.
Both fish and meat that consists high levels of polyunsaturated fatty acids goes through the process of oxidation. When exposed to air or light, it causes bad smell and this process is known as rancidity.
- c) Apples and fruits turns brown when cut.
When there is an occurrence of chemical reaction with oxygen in the air, then some of the fruits and apples becomes brownish in colour. Browning refers to such chemical reactions. Polyphenol oxidase ortyrosinase is an enzyme that are contained in the cells of apples ,fruits and other vegetables. When it comes into contact with oxygen, then there is a generation of biochemical reaction which enables the phenolic compounds, that are present in plants to turn into a brown pigment which is called melanin.
3) Explain any three conditions that is required for a chemical reaction to take place . Give example.
Chemical changes does not takes place at all situations . There are requirement of certain specific conditions, for a chemical change to occur . Contact in physical states, Solution of reactants , Electricity, Heat , Light and Catalyst are the various conditions which facilitates the occurrence of chemical change .
1 ) Solution of reactants
Due to chemical reaction, there is a transformation in the colour of the milk and the decoction, the moment milk is mixed with coffee decoction. There is an occurrence of a chemical reaction between the mixture of two substances in solution form, in order to create new substances. As for example, when a small quantity of solid silver nitrate and sodium chloride are taken in a test tube, we cannot notice any kind of changes because the reactants in solid state does not depict any reaction. Now, when same reactants are dissolved in water in separate test tubes and mixed well, then a reaction will occur between silver nitrate solutionand sodium chloride solution for the purpose of forming a white precipitate of silver chloride and sodium nitrate solution. So, the above reaction clearly depicts that, there are certain chemical reactions that occurs only in the solution form and not in the solid state.
2) Electricity
Electricity performs an essential function in our daily life. We use electricity for several purposes , such as cooking, lighting , grinding and watching television. But it is also important to know that, apart from fulfilling these purposes, electricity is also used for executing chemical reactions. Most of the chemical reactions that occurs with the aid of electricity are very essential for industrial purposes. There is liberation of hydrogen and oxygen gases , the moment electricity is passed through water which consists small quantity of sulphuric acid. During electrolysis, the brine tends to form chlorine and hydrogen gases together with sodium hydroxide. So, in order to produce chlorine industrially, this is an essential reaction. So, we can infer that there are some chemical reactions that occurs only with the help of electricity. Therefore, such reactions are termed as electrochemical reactions or electrolysis.
3) Light
As sunlight is essential for us, in an equal manner it is also important for the plants. Photosynthesis refers to a process in which, the plants uses light energy from the sun in order to prepare starch from carbon dioxide and water. The sunlight performs an essential function in inducing the chemical reaction that occurs between carbon dioxide and water and which ultimately leads to the formation of starch. Therefore, the photochemical reactions refers to those chemical reactions that are induced by light.
(VII) Higher orderthinking questions .
1 ) Explain the role of yeast in making cakes and buns in a bakery ?
As we know that, yeast is a biocatalysts, which means it contributes in speeding up the chemical reactions. When there is breakdown of fermentable sugars in the dough , then there is generation of carbon dioxide by the yeast which ultimately helps in rising the cake evenly.
2 ) Burning of fossil fuels is responsible for global warming . Justify the statement.
The moment fossil fuels are burned, a large quantity of carbon dioxide are released into the atmosphere. We all know that, carbon dioxide acts as a greenhouse gas which contributes in the rise of global warming.
3) Discuss how acid rain occurs due to emission of smoke from vehicles and industries.
Vehicles and industries releases certain pollutants such as sulphur dioxide and nitrogen oxide in the air and the presence of these pollutants makes the rain acidic in nature. So, when these pollutants like sulphur dioxide and nitrogen dioxide reacts with water molecules in the atmosphere, then it leads to the occurrence of acid rain.
4) Is rusting good for iron materials? Explain.
Rusting is not at all good for iron materials but instead it brings about a negative affect on iron materials. Rust falls under the category of iron oxide. When there is combination of iron with oxygen in the air ,then it leads to the formation of corrosion on the iron materials and this process is known as rusting. Rust can bring about a negative affect on iron and its alloys. Iron materials becomes weaker with time period because rusting replaces the strong iron with brittle and flaky powder.
5) Do all the fruits and vegetables undergo browning? Explain.
No, all the fruits and vegetables does not go through browning . When there is an occurrence of chemical reaction with oxygen in the air, then some of the fruits and apples becomes brownish in colour. Browning refers to such chemical reactions. Polyphenol oxidase or tyrosinase is an enzyme that are contained in the cells of apples ,fruits and other vegetables. When it comes into contact with oxygen, there is a generation of biochemical reaction which enables the phenolic compounds, that are present in plants to turn into a brown pigment which is called melanin.
6) Classify the following day to day activities based on chemical reactions by physical contact, solutions of reactants, heat ,light, electricity and catalyst.
a) Burning of crackers during festivals.
b) Fading of coloured clothes on drying under sunlight.
c) Cooking of eggs
d) Charging of batteries
| a ) Burning of crackers during festivals | Heat |
| b) fading of coloured clothes on drying under sunlight | Light |
| c) Cooking of eggs | Heat |
| d) Charging of batteries | Electricity |
(VIII) Value Based Questions .
1 ) Kumar is going to build a house. To purchase the iron rods required for construction, he visited and iron and steel shop nearby. The seller showed him some iron rods which are fresh and good. He also showed him little older iron rods which are brownish in appearance. The price of fresh rods is more than the older ones. The seller also gave some offer to older ones. Kumar’s friend Ramesh advised him not to buy the cheaper rods .
a ) Is Ramesh right in his suggestion?
The suggestion that Ramesh gave was absolutely right. So, he is right in his suggestion.
b) Could you explain the reason for his suggestion?
The older rods have become rusted, for that reason they have turned brownish in colour. Rusting brings about a negative affect on the iron rods and it also makes them weaker. So, it is clear that, rusting deteriorates the quality of iron rods and thus , causes the iron rod to corrode . Owing this reason, the older rods will be quite dangerous for the purpose of construction. Therefore, it is always advisable to buy new iron rods instead of the old ones.
c) What are the values shown by Ramesh?
Responsibility, friendship ,awareness and care are for instance ,some of the values that are shown by Ramesh.
- As Ramesh was a friend of Kumar, so he never wanted his friend to face any kind of problematic situation. This point clearly depicts the value of friendship and care.
- Ramesh was also aware about the negative impact of rusting on the iron materials. So, he prevented his friend from buying the older iron rods . This point clearly portrays, the values of awareness and responsibility.
2) Palanikumar is a Lawyer. He lives in a luxurious flat. Due to high rent, he wants to shift his residence to a place where he has a chemical industry nearby. There the rent is very cheap and the area is less polluted also. His son Rajasekar , studying VIII, does not like this and likes to go to some other place.
a) Is Rajasekar right in his attitude?
Rajasekar is absolutely right in his attitude.
b) Why did he refused to go there?
Rajasekar was aware of the fact that, as there was a chemical industry nearby, so a large quantity of harmful pollutants would be released from this industry ,which would ultimately result in air pollution. So, the effects of air pollution will pose a harmful impact on their health . For this reason, herefused to shift there .
c) What are the values shown by Rajasekar?
Care, affection and environmental awareness are for instance, some of the values that are shown by Rajasekar.
- Rajasekar knew that the impact of air pollution could bring about a detrimental effect on the health of their family members, so he refused to go there. This point clearly portrays the value of care and affection.
- Rajasekar was aware about the harmful effects of air pollution, due to this reason he did not like to go there. This point clearly manifests the value of environmental awareness.
