Samacheer Kalvi Class 8 Science Unit 10 Changes Around Us Solutions
Welcome to NCTB Solutions. Here with this post we are going to help 8th class students by providing Solutions for Samacheer Kalvi Class 8 Science Unit 10 Changes Around Us. Here students can easily find all the solved solution for Changes Around Us Exercise questions. Also here our Expert Science Teacher’s solved all the questions with easily understandable language with proper guidance so that all the students can understand easily. Here on this post students will get Unit 10 Changes Around Us exercise solutions. Here all the solutions are based on Tamil Nadu State Board latest syllabus.
Unit 10 Changes Around Us Exercise Questions Solutions :
(I) Choose the best answer :
(1) Burning of paper is a __ change
(a) Physical
(b) Chemical physical and chemical
(c) Chemical
(d) Neutral
Answer :
Correct Option → (c)
Burning of paper is a Chemical change.
(2) Burning of matchstick is an example for chemical reaction caused by ____
(a) Contact in physical states
(b) Electricity
(c) Light
(d) Catalyst
Answer :
Correct Option → (c)
Burning of matchstick is an example for chemical reaction caused by Light.
(3) __ undergoes rusting.
(a) Tin
(b) Sodium
(c) Copper
(d) Iron
Answer :
Correct Option → (d)
Iron undergoes rusting.
(4) The pigment responsible for browning of apples is ___
(a) Hydrated iron 2 oxide
(b) Melanin
(c) Starch
(d) Ozone
Answer :
Correct Option → (b)
The pigment responsible for browning of apples is Melanin.
(5) Brine is a concentrated solution of ____
(a) Sodium sulphate
(b) Sodium chloride
(c) Calcium chloride
(d) Sodium bromide
Answer :
Correct Option → (b)
Brine is a concentrated solution of Sodium chloride.
(6) Limestone contains ___ mainly
(a) Calcium chloride
(b) Calcium carbonate
(c) Calcium nitrate
(d) Calcium sulphate
Answer :
Correct Option → (b)
Limestone contains Calcium carbonate mainly.
(7) Which of the following factor induces electrolysis ___
(a) Heat
(b) Light
(c) Electricity
(d) Catalysis
Answer :
Correct Option → (c)
From the above Electricity induces electrolysis.
(8) In haber’s process of producing ammonia ___ is used as a catalyst
(a) Nitrogen
(b) Hydrogen
(c) Iron
(d) Nickel
Answer :
Correct Option → (c)
In haber’s process of producing ammonia Iron is used as a catalyst.
(9) Dissolved gases like sulphur dioxide and nitrogen oxides in rain water causes ___
(a) Acid rain
(b) Base rain
(c) Heavy rain
(d) Neutral rain
Answer :
Correct Option → (a)
Dissolved gases like sulphur dioxide and nitrogen oxides in rain water causes Acid rain.
(10) ____ is/are responsible for global warming
(a) Carbon dioxide
(b) Methane
(c) Chlorofluorocarbons
(d) Carbon dioxide, methane, chlorofluorocarbon
Answer :
Correct Option → (a)
Carbon dioxide are responsible for global warming.
(II) Fill in the blanks
(1) Photosynthesis is a chemical reaction that takes place in the presence of ___
(2) Iron objects undergo rusting when exposed to ___ and ___
(3) ___ is the basic material to manufacture urea.
(4) Electrolysis of brine solution gives ___ gases.
(5) ___ is a chemical substance which alters the speed of a chemical reaction.
(6) ___ is the enzyme responsible for browning of vegetables and fruits.
Answer :
(1) → Sunlight
(2) → Water and oxygen
(3) → Ammonia
(4) → Hydrogen gas
(5) → Catalyst
(6) → Polyphenol oxidase.
(III) Say true or false. If false, correct the statement
(1) A chemical reaction is a temporary reaction.
(2) Decomposition of lead nitrate is an example for a chemical reaction caused by light.
(3) Formation of slaked lime from quicklime is an endothermic reaction.
(4) CFC is a pollutant.
(5) Light energy may come out due to chemical reactions.
Answer :
(1) → False.
Because a chemical reaction is permanent reaction.
(2) → True
(3) → False
(4) → True
(5) → False
Because Chemical energy come from out due to chemical reaction.
(V) Answer briefly
(1) Define a chemical reaction.
Answer :
A chemical reaction is defined as a one or more substances (reactant 0) undergoes a reaction to form one or more new substances (products) is called chemical reaction or chemical changes.
(2) Mention the various conditions required for a chemical reaction to occur.
Answer :
There are some condition which is required for chemical changes: –
(a) Contact in physical state
(b) Solution of reactants
(c) Electricity
(d) Heat
(e) Light
(f) Catalyst
(3) Define catalysis.
Answer :
The chemical substance which is used for speed up to chemical reaction are known as catalysis.
(4) What happens when an iron nail is placed in copper sulphate solution?
Answer :
If we place an iron nail in copper sulphate solution, iron will displace copper from its salt solution by a displacement reaction. This happens because iron is more reactive metal than copper. The blue colour of copper sulphate solution will fade and the solution will turn into green. This is because of the formation of iron sulphate. Iron sulphate and copper metal is the product of this reaction.
Word equation of the reaction :
Copper sulphate (CuSO4) + Iron (Fe) → Iron sulphate (FeSO4) + Copper (Cu)
(5) What is pollution?
Answer :
Pollution is the contamination of natural factors like air, water and land by damage causing pollutants.
(7) What happens to the brine during electrolysis?
Answer :
During electrolysis of brine sodium hydroxide is also produced.
(8) On heating, calcium carbonate gives calcium oxide and oxygen. Is it an exothermic reaction or an endothermic reaction?
Answer :
On heating calcium carbonate gives calcium oxide and oxygen then it is an endothermic reaction.
(9) What is the role of a catalyst in a chemical reaction?
Answer :
Catalysis do not take part in the reaction but they speed up the reaction, increases the speed of chemical reaction.
(10) Why photosynthesis is a chemical reaction?
Answer :
Photosynthesis is the process in which light energy forms the sun is used by plants to prepare starch from water and CO2. In this process chemical reaction induced by light therefore photosynthesis is known as chemical reaction.
(VI) Answer in detail
(1) Explain the environmental effects of chemical reactions?
Answer :
(a) Pollution : The unwanted change in physical , chemical and biological properties of the environment is known as pollution and the substance which causes this changes are known as pollutants,. There are three types of pollution are seen.
(1) Air pollution : Due to air pollution there are some effects like acid rain, global warming , respiratory problems like asthma etc
(2) Water pollution : Due to water pollution there are some effects like decrease in the quality of water, skin diseases caused by water pollution.
(3) Land pollution : effects of land pollution is spoilage of land ,cancer, respiratory diseases etc.
Different types of chemical substances are also effects on environment.
(b) Rusting : When the iron metal in contact with water and oxygen it undergoes a chemical reaction is called rusting.
(c) Trashing of metal articles : Shiny metals surfaces and other articles lose their shining appearance due to chemical reaction on surface is known as tarnishing of metal articles. For example – silver metals articles become black when exposed to air for long time.
This are different effects of chemical reactions on environment.
(2) Explain how food items are spoiled by chemical reactions?
Answer :
Food items are spoiled by chemical reactions like as follows :-
(a) the chemical reaction catalysed by the enzymes result in the degradation of food quality in the form of development of bad taste and odour, deterioration and lose nutrients is the spoiling of food due to chemical reactions for example – rotten eggs develop a bad smell due to formation of hydrogen sulphide gas.
(b) rancidity of fishes and meat as we know fishes and meat containing high levels of poly unsaturated fatty acids undergo oxidation it causes bad odour when exposed to air or light this is called rancidity it also spoil the food items. These are the some food items which are spoiled by chemical reactions.
(3) Explain any three conditions that is required for a chemical reaction to take place. Give example.
Answer :
There are six condition which is required for chemical reaction like contact in physical states, solution of reactants, electricity, heat, light, catalyst etc. Now we can see any three chemical reaction conditions –
(A) Heat : It is important condition for chemical reaction, when enough heat is given then conversion of row food material takes place into form cooked. In this type two forms of reaction take place endothermic and exothermic reaction. The chemical reaction can be achieved by the supply of heat only is known as thermo chemical reactions .
(B) Light : The chemical reaction which is induced by light are known as photo chemical reactions . photosynthesis in plants are the examples of light include chemical reaction.
(C) Catalyst : Catalyst are the substance which do not take part in the chemical reaction but increases the speed of the chemical reactions. The reactions which include catalyst are called catalytic reactions. This type of reactions are used mainly in industrial area. For example – Haber’s process.
(VII) Higher order thinking questions :
(1) Explain the role of yeast in making cakes and buns in a bakery?
Answer :
Yeast is used as fermenting material in the process of cake and burns in bakery because for the production of bakery products fermentation is necessary therefore yeast is important or useful for making bakery products.
(2) Burning of fossil fuels is responsible for global warming. Justify the statement.
Answer :
Yes, burning of fossil fuels is responsible for global warming because when fossil fuels are burn they release or large amount of carbon dioxide which is responsible for global warming.
(4) Is rusting good for iron materials? Explain.
Answer :
Rusting damaged material specially iron materials, after rusting the iron is not useful it becomes useless and it is impossible to get the original iron back, in rusting iron permanently rust therefore rusting is not good for iron materials.
(5) Do all the fruits and vegetables undergo browning? Explain.
Answer :
There are some fruits and vegetables when they contact with oxygen in air forms browning because enzyme called polyphenol oxidase or tyrosinase is present in them. For example – apple, potato etc. Therefore the undergoes browning not all fruits and vegetables undergoes browning.
Next Chapter Solution :
👉 Air
