CBSE Class 10 Science Chemical Reactions and Equations Assignment Set A

Question. When ferrous sulphate is heated strongly it undergoes decomposition to form ferric oxide as a main product accompanied by a change in color from: 
(a) Blue to green.
(b) Green to blue.
(c) Green to brown.
(d) Green to yellow.

Answer : C

Question. In the equation, NaOH + HNO3 -> NaNO3 + H2O nitric acid is acting as 
(a) An oxidizing agent
(b) An acid
(c) A nitrating agent
(d) A dehydrating agent

Answer : B

Question. Select the oxidising agent for the following reaction: 
H2S + I2 > 2HI + S
(a) I2
(b) H2S
(C) HI
(d) S

Answer : A

Question. The Following Reaction Is An Example Of : 4NH3(G) + 5O2(G) → 4NO(G) + 6H2O(G) 
(a) Displacement reaction and Neutralisation reaction
(b) Combination reaction and Redox reaction
(c) Displacement reaction and Redox reaction
(d) Neutralisation reaction and Redox reaction

Answer : C

Question. A substance which oxidized itself and reduces other is known as 
(a) Oxidizing agent
(b) Reducing agent
(c) Both of these
(d) None of these

Answer : B

Question. Consider reaction: Al(s) + O₂ (g) → Al₂O₃. Moles of Al(s) needed to balance equation are 
(a) 1
(b) 2
(c) 3
(d) 4

Answer : D

Question. It is necessary to balance a chemical equation in order to satisfy the law of: 
(a) Conservation of motion
(b) Conservation of momentum
(c) Conservation of energy
(d) Conservation of mass

Answer : D

Question. Which of the following does show an oxidation reaction? 
(a) Gain of oxygen
(b) Loss of oxygen
(c) Gain of hydrogen
(d) None of the above

Answer : A

Question. MnO₂ + 4HCl → 2 + 2H₂O + Cl₂ Identify the substance oxidized in the above equation. 
(a) MnCl2
(b) HCl
(c) H2O
(d) MnO2

Answer : D

Question. When crystals of lead nitrate are heated strongly in a dry test tube 
(a) crystals immediately melt
(b) a brown residue is left
(c) white fumes appear in the tube
(d) a yellow residue is left

Answer : B

Question. Which of the following is Not True with respect to the neutralisation reaction? 
(a) Salt is formed.
(b) Reaction occurs between an acid and a base.
(c) Reactive element displaces less reactive element.
(d) Reactants are in gaseous state.

Answer : D

Question. An element X on exposure to moist air turns reddish-brown and a new compound Y is formed. The substances X and Y are 
(a) X = Fe, Y = Fe₂O₃
(b) X = Ag, Y = Ag₂S
(c) X = Cu, Y = CuO
(d) X = Al, Y = Al₂O₃

Answer : A

Question. If magnesium is gently heated, it forms 
(a) Magnesium oxide
(b) Magnesium sulfide
(c) Magnesium nitrite
(d) Magnesium carbonate

Answer : A

Question. What chemicals are used in fireworks? 
(a) Copper chloride
(b) Calcium chloride
(c) Barium chloride
(d) All of above

Answer : D

Question. In a chemical reaction between sulphuric acid and barium chloride solution the white precipitates formed are of: 
(a) Hydrochloric acid
(b) Barium sulphate
(c) Chlorine
(d) Sulphur

Answer : B

Question. Color of Solid magnesium is 
(a) Dark grey
(b) Silver grey
(c) Black
(d) Whitish silver

Answer : B

Question. Consider equation: Cu⁺² (aq) + 2OH⁻(aq) → Cu(OH)₂ (s). precipitate of Copper Hydroxide (Cu(OH)₂) will be of 
(a) Green color
(b) Blue color
(c) Brown color
(d) White color

Answer : B

Question. Consider The Following Statements, Choose The Incorrect One(S): 
(a) The chemical equation is balance to satisfy the law of conservation of mass in chemical reaction.
(b) We should never change the formula of an element or compound to balance and equation.
(c) Those reaction in which heat is evolved are known as exothermic reactions.
(d) When Methane (CH4) burns in oxygen of air it forms carbon monoxide and water vapour.

Answer : D

Question. Which of the following reactions can also be termed as thermal decomposition reaction? 
(a) Combination Reaction
(b) Decomposition Reaction
(c) Displacement reaction
(d) Double displacement reaction

Answer : B

Question. What is the name of the process where fatty foods become rancid? 
(a) Corrosion
(b) Oxidation
(c) Reduction
(d) Hydrogenation

Answer : B

Question : State one basic difference between a physical change and a chemical change.
Answer :  In a physical change, no new substance is forme(d) In a chemical change, a new substance is forme(d)

Question :  Why eatables are preferably packed in aluminum foils?
Answer: Aluminum foils do not corrode in atmosphere even if kept for a long time. Actually, a protective coating of aluminum oxide (Al₂O₃) is formed on the surface of the metal. It stops any further reaction of the metal with air (oxygen) and water. The eatables do not get spoile(d)

Question : What happens when ZnCO₃ is heated in the absence of air? Give the relevant equation.
Answer :  ZnO(s) and CO₂(g)CO₂(g) are forme(d) Chemical Equation:
                 ZnCO₃ → ZnO + CO₂

Question : What happens when an iron nail is put inside the copper sulfate solution? Write a reaction with observation.
Answer :  Iron nail turns brown, blue color of CuSO4 changes to colorless. (or light green)
                  Fe(s)+CuSO4(aq)→FeSO4(aq)-+Cu(s)

Question :  You are given the following materials:
(i) Iron nails
(ii) Copper sulphate solution
(iii) Barium chloride solution
(iv) Copper powder
(v) Ferrous sulphate crystals
(vi) Quick lime.
Identify the type of chemical reaction taking place when :
(a) Barium chloride solution is mixed with copper sulphate solution and a white precipitate is observe(d)
(b) On heating, copper powder in air in a china dish, the surface of copper powder becomes black.
(c) On heating green ferrous sulphate crystals, reddish brown solid is left and a gas having smell of burning sulphur is notice(d)
(d) Iron nails when left dipped in blue copper sulphate solution become brownish in colour and blue colour of copper sulphate solution fades away.
(e) Quick lime reacts vigorously with water releasing a large amount of heat.

Question : Define a combination reaction. Give one example of a combination reaction which is also exothermi(c)
Answer :  A combination reaction is said to have occurred when two or more than two substances combine to form a single substance.

Question : Which of the following is a displacement reaction?

Answer: B

Question : Why do we store silver chloride in dark colored bottles? Explain in brief.
Answer :  Silver chloride on exposure to sunlight may decompose as per the following reaction
                     2AgCL → 2Ag + Cl₂
Therefore it is stored in dark colored bottles.

Question : (i) Account for the following :
(a) White silver chloride turns grey in sunlight.
(b) Brown coloured copper powder on heating in air turns into black coloured substance.
(ii) What do you mean by
(a) Displacement reaction
(b) Reduction reaction
(c) Combination reaction?
Write balanced chemical equation in support for all
Answer:
(i) (a) White coloured silver chloride undergoes decomposition in the presence of sunlight and forms silver (grey in colour) and chlorine.

(b) Brown coloured copper powder on heating in air gets oxidised to copper oxide which is black in colour.

(ii) For the different types of reactions,
(a) In a displacement reaction, one element takes the place of another in a compound dissolved in a solution. For example,
Fe(s) + CuSO₄ (aq) ———> FeSO₄ (aq) + Cu(s)
(b) Combination reaction may be defined as the reaction in which two or more substances combine under suitable conditions to form a new substance. For example,

(c) A decomposition reaction may be defined as the reaction in which a single substance decomposes or splits into two or more substances under suitable conditions.
For example,

It may be concluded that a certain substance is formed or synthesised in combination reaction and it breaks or splits in decomposition reaction. Therefore, the two reactions oppose each other.