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GSEB Solutions for ધોરણ ૧૦ English

GSEB std 10 science solution for Gujarati check Subject Chapters Wise::

The addition of oxygen to a substance is called …………. whereas removal of oxygen is called …………. .

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જવાબ : oxidation, reduction


The addition of hydrogen to a substance is called …………. whereas removal of hydrogen is called …………. .

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જવાબ : reduction, oxidation


Precipitation reactions produce insoluble …………. .

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જવાબ : salts


Reactions in which energy is given out are known as …………. .

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જવાબ : exothermic reactions


Reaction in which an element displaces another element from its compound is called …………. .

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જવાબ : displacement reaction


Two antioxidants which are usually added to fat and oil containing foods to prevent rancidity, are …………., …………. .

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જવાબ : BHA & BHT


…………. is the process in which metals are eaten up gradually by the action of air, moisture or a chemical on their surface.

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જવાબ : Corrosion


2 FeSO4 → Fe2O3 + SO2 + ………….

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જવાબ : SO3


Na2SO4 + BaCl2 → …………. + 2NaCl

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જવાબ : BaSO4


Complete the missing components/variables given as x and y in the following reactions:
(a) Pb (NO3)2 (aq) + 2KI (aq) → Pbl2 (x) + 2KNO3 (y)
(b) Cu (s) + 2AgNO3 (aq) → Cu (NO3)2 (aq) + x (s)

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જવાબ : (a) x → (s); y → (aq);
(b) x → 2Ag


………….. is burnt in air to form magnesium oxide.

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જવાબ : Magnesium


Respiration is an ………….. reaction.

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જવાબ : exothermic


Zinc and lead are more reactive elements than …………..

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જવાબ : copper


Any reaction that produces a ………….. is called a precipitation reaction.

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જવાબ : Precipitate


Oxidation is the gain of ………….. or loss of …………..

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જવાબ : oxygen, hydrogen


………….. are added to foods containing fats and oil.

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જવાબ : Antioxidants


In rusting of iron, reddish brown coating formed on iron is …………..

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જવાબ : Fe2O3


………….. can be retarded by storing foods away from light.

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જવાબ : Rancidity


The oxidation and reduction reaction are also called ………….. Reactions.

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જવાબ : redox


Magnesium is able to displace copper from copper sulphate solution because magnesium is ………….. reactive than copper.

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જવાબ : more


Why doesn't a wall immediately acquire a white color when a coating of calcium hydroxide is applied on it?

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જવાબ : Slaked lime as such is not very white. When applied on the wall, CO2 gas present in air reacts with calcium hydroxide to form calcium carbonate. It is quite white and therefore, imparts white look to the wall.
Ca(OH)2 + CO2(g) ———> CaCO3(s) + H2O(l).


What is rust?

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જવાબ : It is a brown mass referred to as hydrated oxide. Its formula is Fe2O3.xH2O.


Identify the foremost reactive and least reactive metal: Al, K, Ca, Au.

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જવાબ : Most reactive metal: K (potassium); Least reactive metal: Au (gold).


Which of the subsequent may be a combination reaction and which may be a displacement?
(a) Cl2 + 2KI ——–> 2KCl + I2
(b) 2K + Cl2 ——–> 2KCl.

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જવાબ : (a) It is a displacement reaction,
(b) It is a combination reaction.


What is the difference between the subsequent two reactions?
(a) Mg + 2HCl ——–> MgCl2 + H2
(b) NaOH + HCl ——–> NaCl + H2O

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જવાબ : (a) It is a single displacement reaction,
(b) it's a double displacement also called neutralization.


Identify the compound which is oxidized within the following reaction-
H2S + Br2 ———–> 2HBr + S.

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જવાબ : H2S is oxidized to S because H2S has lost hydrogen.


Suggest two ways to see the rancidity of food articles.

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જવાબ : (a) Keep the articles in airtight containers,
(b) Keep the articles in refrigerator.


Name two metals which do not get corroded.

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જવાબ : Gold (Au) and platinum (Pt) don't get corroded.


Identify the substance oxidized and reduced within the reaction:
CuO(s) + Zn(s) ———-> ZnO(s) + Cu(s).

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જવાબ : Zinc is oxidized to flowers of zinc and oxide is reduced to copper.


How will you recognize whether a sample of cheese has become rancid or not ?

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જવાબ : If the cheese starts giving foul smell, it means it's become rancid.


Why are eatables preferably packed in aluminum foil?

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જવાબ : Aluminum foils do not corrode in atmosphere albeit kept for an extended time. Actually, a protective coating of alumina (Al2O3) is made on the surface of the metal. It stops any longer reaction of the metal with air (oxygen) and water. The eatables do not get spoiled.


What happens chemically when quick lime is added to water?

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જવાબ : Calcium hydroxide (or slaked lime) is made amid a hissing sound. So much heat is evolved during the reaction that the reaction mixture starts boiling.


Give an example of exothermic reaction.

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જવાબ : CH4(g) + 2CO2(g) ———-> CO2(g) + 2H2O(g) + heat, (evolved)


Give an example of endothermic reaction.

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જવાબ : N2(g) + O2(g) ———> 2NO(g) – heat, (absorbed).


Name the gas which will be used for the storage of fresh sample of chips for an extended time.

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જવાબ : The gas is nitrogen (N2). It checks rancidity of food articles.


Name the type of reaction
N2(g) + 3H2(g) ———-> 2NH3(g)

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જવાબ : It is an example of combination reaction.


Give an example of a double displacement (only reaction with complete balanced equation).

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જવાબ : HCl(aq) + NaOH(g) ——–> NaCl(aq) + H2O(l)


Why decomposition reactions are called the other of combination reactions ? Write equations for these reactions.

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જવાબ : A decomposition could also be defined because the reaction during which one substance decomposes or splits into two or more substances under suitable conditions.
For example,
It may be concluded that a particular substance is made or synthesized together reaction and it breaks or splits in decomposition . Therefore, the two reactions oppose each other.


In the reaction MnO2 + 4HCl —————> MnCl2 + 2H2O + Cl2; identify which one is reduced and which one is oxidized ?

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જવાબ : In this reaction HCl is oxidized to Cl2 and MnO2 is reduced to MnCl2.


Take a little amount of quicklime or quick lime during a beaker and slowly add water to the present. Is there any change in temperature?

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જવાબ : Yes, the temperature increases since the method of dissolution of quicklime (CaO) in water is very exothermic in nature.


Name two salts that are utilized in black and white photography.

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જવાબ : Both silver chloride and silver bromide are used in black and white photography.


State the chemical process that takes place when lime stone is heated?

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જવાબ : Calcium carbonate decomposes on heating to offer quicklime and CO2.
CaCO3(s) heat , CaO(s) + CO2(g)


Identify the substance oxidized and substance reduced within the following reactions
(i) ZnO(s) + C(s) ———> Zn(s) + CO(g)
(ii) 2Na(s) + O2(g) ———> 2Na2O(s)
(iii) CuO(s) + H 2(g) ———> Cu(s) + H2O(l).

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જવાબ : (i) C is oxidized to CO and ZnO is reduced to Zn.
(ii) Na is oxidized to Na2O and O2 is reduced.
(iii) H2 is oxidized to H2O and CuO is reduced to Cu.


Which types of reactions are represented by the following equations ?
(a) CaO + CO2 ——-> CaCO3
(b) Mg + CuSO4 ——–> MgSO4 + Cu
(c) CH4 + 2O2 ———–> CO2 + 2H2O
(d) NH4NO2 ———-> N2 + 2H2O.

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જવાબ : (a) Combination reaction
(b) Displacement reaction
(c) Combustion reaction
(d) Decomposition reaction


Aluminum is a reactive metal but is still used for packing food articles. Why ?

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જવાબ : From the position of the aluminum (Al) metal in the activity series, it seems to be quite reactive. However, it is not so reactive. Actually, when the metal is kept in air or oxygen for some time, it is converted into its oxide called aluminum oxide (Al2O3). This gets deposited as the surface of the metal as a thin coating. It is rather passive which means that it is not reactive. Therefore, the metal is used for packing food articles which do not get spoiled under the foil.


Give one example each of :
(i) Thermal decomposition reaction
(ii) Electrolytic decomposition reaction
(iii) Photo decomposition reaction. (CBSE 2014)

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જવાબ : Previous Year Question Papers for CBSE Class 10 Science Chapter 1 Chemical Reactions and Equations 3


What are neutralization reactions? Why are they so named? Give one example.

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જવાબ : A neutralization reaction is a chemical reaction between an acid and base dissolved in water. For example,
KOH(aq) + HNO3(aq) ———-> KNO3(aq) + H2O (aq)
It is called neutralization as both KN03 (salt) and H20 that are formed as the products, are of neutral nature.


(a) Why is combustion reaction an oxidation reaction ?
(b) How will you test whether the gas evolved in a reaction is hydrogen ?
(c) Why does not silver evolve hydrogen on reacting with dilute sulphuric acid ?

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જવાબ : (a) Combustion reaction is an oxidation reaction because it is always carried in the presence of air or oxygen. For example,
CH4(s) + 2O2(g) ——–> CO2(g) + 2H2O (l)
(b) Bring a burning match stick close to the mouth of the tube from which hydrogen gas escapes. The gas will immediately catch fire and this will be accompanied by pop sound.
(c) Silver is a less reactive metal in the sense that it occupies a place below hydrogen in the reactivity series. Therefore it does not evolve hydrogen gas on reacting with either dilute sulphuric acid or dilute hydrochloric acid.


What is an oxidation reaction? Identify in the following reactions.
(i) The substance oxidized
(ii) the substance reduced.

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જવાબ : ZnO + C ———> Zn + CO
Oxidation involves the addition of oxygen or the removal of hydrogen in a chemical reaction. In the given reaction, carbon is oxidized to carbon monoxide while zinc oxide is reduced to zinc.


(a) Define a balanced chemical equation. Why should an equation be balanced?
(b) Write the balanced chemical equation for the following reaction:
(i) Phosphorus burns in presence of chlorine to form phosphorus penta chloride.
(ii) Burning of natural gas.
(iii) The process of respiration.

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જવાબ : (a) Balanced chemical equation has an equal number of atoms of different elements in the reactants and products. According to law of conservation of mass, matter can neither be created nor be destroyed in a chemical reaction.
(b)(i) P4 (s) + 10Cl2 (g) ———> 4PCl5 (S)
(i)CH4 (g) + 2O2 (g) ———> CO2 (g) + 2H2O(l) + heat energy
(iii) C6H12O6 (s) + 6O2 (g) + 6H2O ———> 6CO2 (aq) + 12H2O (l) + energy


(a) Explain two ways by which food industries prevent rancidity.
(b) Discuss the importance of decomposition reaction in metal industry with three points.

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જવાબ : (a) (i) Rancidity can be prevented by adding antioxidants to food containing
fat and oil, e.g. butylated hydroxy anisole is added to butter as antioxidant.
(ii) It can be prevented by packaging fat and oil containing foods in nitrogen gas.
(b) (i) Molten NaCl is electrolytically decomposed to form sodium metal.
(ii) Aluminum metal is obtained by electric decomposition of bauxite ore mixed with cryolite.
(iii) Carbonate ores are thermally decomposed to give metal oxide which on reduction give metal.


A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.
(a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
(b) Name the black substance formed and give its chemical formula

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જવાબ : (a) Silver articles turn black when kept in the air for a few days because H2S gas present in the air attacks silver forming a coating of black silver sulphide. The phenomenon is called corrosion.

(b) Black substance formed is silver sulphide (Ag2S)
2Ag (s) + H2S (g) → Ag2S (s) + H(g).


The gases hydrogen and chlorine do not react with each other even if kept together for a long time. However, in the presence of sunlight, they readily combine. What actually happens?
 

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જવાબ : In chemical reactions, energy is needed to break the bonds present in the reacting molecules so that they may combine to form the products. In this reaction, sunlight is the source of energy in the form of photons. The energy made available by sunlight helps in breaking the bonds and this leads to chemical reaction between hydrogen and chlorine.


What is corrosion? State conditions necessary for rusting of iron. How is rusting harmful? 

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જવાબ : Corrosion.

The process of eating away of the metal surface by the action of atmospheric reagents like water, oxygen and acids changing the metal into its compound is called corrosion.

Rusting of iron. When iron objects are exposed to atmosphere, they are attacked by air and moisture (water) of the atmosphere and a brown and orange colored layer is formed on the surface. It is called rust which is mainly hydrated iron (III) oxide Fe2O3. xH2O.

Harmful effect of rusting. Hydrated iron (III) oxide is a brittle substance and falls off from the surface of iron and thus the object is damaged. Holes, cavities and roughness of surfaces are the result of rusting of an iron object.

Conditions necessary for rusting:

  • Open surface of the metal
  • Presence of air (oxygen)
  • Presence of moisture (water).


During the reaction of some metals with dilute hydrochloric acid, following observations were made,
(a) Silver metal does not show any change.
(b) The temperature of the reaction mixture rises when aluminium (Al) is added.
(c) The reaction of sodium metal is found to be highly explosive.
(d) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
Explain these observations giving suitable reasons.   

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જવાબ : (a) No change takes place because silver metal does not react with hydrochloric acid in normal situations.
(b) The reaction between hydrochloric acid and aluminium is exothermic, thus the temperature of the reaction mixture rises when aluminium is added.
(c) Since, sodium is a highly reactive metal, thus it reacts with hydrochloric acid vigorously and produces a large amount of heat. Thus, the reaction is exothermic.
(d) Bubbles of hydrogen gas are formed when lead react with dilute hydrochloric acid.
Pb + 2HCl → PbCl2 + H2


What happens when aqueous solutions of sodium sulphate and barium chloride are mixed? What type of reaction is it?

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જવાબ : On mixing the solutions of sodium sulphate and barium chloride, a white precipitate of barium sulphate is obtained.
 
It is a double displacement reaction.


What do you understand by precipitation reaction? Explain with suitable examples.

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જવાબ : The reaction in which two compounds in their aqueous state react to form an insoluble compound. When two reactants react and product formed remains insoluble and settles as a solid it is substance (precipitate) is called a precipitation reaction.

For example,
(i) When aqueous solution of sodium sulphate is mixed with an aqueous solution or barium chloride, barium sulphate is obtained as a white precipitate.
Na2SO(aq) + BaCl(aq) → BaSO(s) + 2NaCl (ag)

(ii) When aqueous solution of sodium chloride is mixed with an aqueous solution of silver nitrate, silver chloride is obtained as a white precipitate.


You are given the following materials
(i) Marble chips (ii) Zinc granules
Identify the type of reaction when marble chips and zinc granules are added separately to acid taken in two test tubes.

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જવાબ : (i) Marble chips react with dilute hydrochloric acid to form calcium chloride and carbon dioxide. It is a double displacement reaction.
CaCO3 + 2HCl → CaCl2 + H2O + CO2

(ii) Zinc granules react with dilute hydrochloric acid to give hydrogen gas. It is a displacement reaction.
Zn (s) + 2HCl → ZnCl(aq) + H(g)


Describe an activity to demonstrate the change that takes place when white silver chloride is kept in sunlight. State the type of chemical reaction which takes place.

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જવાબ : Aim: To demonstrate the change that takes place when white silver chloride is kept in sunlight.
Materials Required: AgNO3(aq), NaCl(aq), test tubes.

 
Procedure:
1. Take 5 ml of silver nitrate solution in a test tube.
2. Prepare sodium chloride solution in another test tube.
3. Add sodium chloride solution into test tube containing silver nitrate solution.
4. Observe the color of silver chloride formed chloride to grey silver metal Dry it with the help of filter papers and place it on the watch glass.
5. Place the watch glass under sunlight for some time.
6. Observe the color of the silver chloride after some time. Observation: White silver chloride turns grey in sunlight because silver metal is formed.


Explanation: Silver chloride is photosensitive. It decomposes in presence of sunlight to form silver metal and chlorine gas.
Conclusion: Decomposition of silver chloride in presence of sunlight is photochemical decomposition reaction.


(a) A solution of substance ‘X’ is used for white washing. What is the substance ‘X’? State the chemical reaction of ‘X’ with water.
(b) Why does the color of copper sulphate solution change when an iron nail is dipped in it?

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જવાબ : (a) ‘X’ is calcium oxide (CaO).
CaO(s) + H2O(l) —–> Ca(OH)2(aq) + heat
(a) It is because iron displaces copper from CuS04 to form FeS04 which is pale green.
Fe(s) + CUS04 (aq)—–> FeS04(aq) + Cu(s)
Blue                       Pale green


Using a suitable chemical equation, justify that some chemical reactions are determined by:
(i) change in color, (ii) change in temperature.

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જવાબ :


What is redox reaction? Identify the substance oxidized and the substance reduced in the following reactions.
(i)2PbO + C —–> 2Pb + CO2
(ii)MnO2 + 4HCl —–> MnCl2 + 2H20 + Cl2

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જવાબ : Those reactions in which oxidation and reduction takes place simultaneously are called redox reactions.
(i) PbO is getting reduced and C is getting oxidized.
(ii) MnOs is getting reduced and HCl is getting oxidized.


Write balanced chemical equation for the reactions that take place during respiration. Identify the type of combination reaction that takes place during this process and justify the name. Give one more example of this type of reaction.

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જવાબ : CgH1206 + 6O2 —————> 6CO2 + 6H20 + heat
It is an exothermic combination reaction because heat is evolved.
CH4(g) + 2O2(g) ————–>CO2 (g) + 2H20
Combustion of methane is another example of exothermic combination reaction.


What is rancidity? Mention any two ways by which rancidity can be prevented.

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જવાબ : The process in which taste and smell of food gets spoiled is called rancidity. It happens due to oxidation.
Prevention from rancidity:
(i) Antioxidants are added to fatty acids to prevent oxidation, e.g., chips are packed in presence of nitrogen gas which prevents spoilage by oxidation.
(ii)Food should be kept in airtight container in refrigerator.


The following diagram displays a chemical reaction. Observe carefully and answer the following questions
 
(a) Identify the type of chemical reaction that will take place and define it. How will the color of the salt change?
(b)Write the chemical equation of the reaction that takes place.
(c) Mention one commercial use of this salt.

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જવાબ : (a) Photochemical decomposition reaction: Those reactions in which a compound breaks down into simple substances in presence of light are called photochemical decomposition reaction. The color of salt will change from white to grey.
 
(c) Silver chloride is used in photography.


What is the color of ferrous sulphate crystals? How does this color change after heating?

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જવાબ : The color of ferrous sulphate is pale green. The color changes to reddish brown on heating due to formation of iron (III) oxide.
Give an example each for thermal decomposition and photochemical decomposition reactions. Write relevant balanced chemical equations also.
Thermal decomposition reaction:


Describe an activity to observe what happens when quick lime is added to water taken in a beaker. State two important observations and name the type of reaction taking place.

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જવાબ : Aim: To observe what happens when quicklime is added to water taken in a beaker.
Materials Required: - Quicklime (calcium oxide), water, beaker.


What is meant by skeletal type chemical equation? What does it represent? Using the equation for electrolytic decomposition of water, differentiate between a skeletal chemical equation and a balanced chemical equation.

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જવાબ : The equations in which gaseous are written in atomic form instead of molecular form and equation is not balanced, are called skeletal type equation. They represent gaseous elements formed in atomic state and equation is not balanced


(a) Write one example for each of decomposing reaction carried out with help of
(i) Electricity (ii) Heat (iii) Light
(b) Which of the following statements is correct and why copper can displace silver from silver nitrate and silver can displace copper from copper sulphate solution.

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જવાબ :


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