CBSE Solutions for Class 10 English

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 oxidised to carbon monoxide while zinc oxide is reduced to zinc.

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.

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

જવાબ : A neutralisation 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 neutralisation as both KN03 (salt) and H20 that are formed as the products, are of neutral nature.

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

જવાબ :

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

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

જવાબ : From the position of the aluminium (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 sometime, 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.

જવાબ : (i) Solution becomes milky due to the formation of calcium carbonate

(ii) Milkiness disappears because calcium carbonate changes to calcium hydrogen carbonate which is colourless in nature.

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

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

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

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

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

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

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

જવાબ : oxidation, reduction

જવાબ : Magnesium

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

જવાબ : BaSO4

જવાબ : SO3

જવાબ : Corrosion

જવાબ : BHA & BHT

જવાબ : displacement reaction

જવાબ : exothermic reactions

જવાબ : salts

જવાબ : reduction, oxidation

જવાબ : more

જવાબ : redox

જવાબ : Rancidity

જવાબ : Fe₂O₃

જવાબ : Antioxidants

જવાબ : Answer: oxygen, hydrogen

જવાબ : Precipitate

જવાબ : copper

જવાબ : exothermic

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).

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

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

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 synthesised together reaction and it breaks or splits in decomposition . Therefore, the two reactions oppose each other.

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

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

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

જવાબ : Aluminium foils donot 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.

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. The chemical equation for the reaction is :

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

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

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

જવાબ : It is an example of combination reaction.

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.

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.

જવાબ : Corrosion.

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

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

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.

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.

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

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 colour 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 sometime.
6. Observe the colour of the silver chloride after sometime. 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.

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

જવાબ :

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

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.

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.

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 colour of salt will change from white to grey.

(c) Silver chloride is used in photography.

જવાબ : The colour of ferrous sulphate is pale green. The colour 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:

Photochemical decomposition reaction:

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

Procedure:
1. Take 5 g of calcium oxide in a beaker.
2. Add water to it slowly.
3. Touch the beaker.
4. Note down the observations.
Observation: Calcium oxide reacts with water
vigorously to form calcium hydroxide with the evolution of heat.
Chemical Reaction:

Conclusion: The reaction between CaO (Calcium oxide) and H₂O is a combination reaction. It is an exothermic process because heat is evolved.

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

જવાબ :

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) Aluminium 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.

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

જવાબ :

1. Displacement
2.  Rancidity
3.  Neutralisation
4. Precipitation

જવાબ :

જવાબ :

(a) → (q)
(b) → (r)
(c) → (p)
(d) → (s)

જવાબ :

જવાબ :