CBSE Class 10 Chemistry Chemical Reactions And Equation Worksheet Set F

Question. In which of the following, the identity of initial substance remains unchanged ?
(a) Curdling of milk
(b) Formation of crystals by process of crystallisation
(c) Fermentation of grapes
(d) Digestion of food 
Answer : B

Question. To balance Al(OH)₃ + HNO₃ → Al(NO₃)₃ + H₂O number of HNO₃ molecules required will be :
(a) 2
(b) 4
(c) 3
(d) 8
Answer : C

Question. The reaction between calcium oxide and water is :
(a) Combination reaction
(b) Decomposition reaction
(c) Displacement reaction
(d) Double-decomposition reaction
Answer : A

Question. The colour of ferrous sulphate crystals is :
(a) Deep green
(b) Light green
(c) Bluish green
(d) None of the above
Answer : B

Question. What is the chemical name for slaked lime ?
(a) Sodium hydroxide
(b) Calcium oxide
(c) Calcium hydroxide
(d) Sodium chloride
Answer : C

Question. Heating of ferrous sulphate is a type of :
(a) Decomposition reaction
(b) Combination reaction
(c) Displacement reaction
(d) All of the above
Answer : A

Question. Which metal is displaced when lead is put in the solution of copper chloride ?
(a) Lead
(b) Copper
(c) Chlorine
(d) All of the above
Answer : B

Question. On the basis of evolution or absorption of heat,chemical reactions can be divided in how many types ?
(a) Two
(b) Three
(c) Four
(d) One
Answer : A

Question. Which of the following metal is protected by a layer of its oxide ?
(a) Copper
(b) Iron
(c) Aluminium
(d) Sodium
Answer : C

Question. The oxidation reaction which produces heat and light is called :
(a) Endothermic
(b) Photochemical
(c) Exothermic
(d) Combustion
Answer : D

Match the following
Column I                                                               Column II
(a) BaCl_2(aq) + ZnSO_4(aq) → H₂CO_3(aq)               (i) Displacement
(b) 2AgCl_(s) → FeSO_4(aq) + Cu_(s)                        (ii) Combination
(c) CuSO_4(aq) + Fe_(s) → BaSO₄↓ + ZnCl_2(aq)      (iii) Decomposition
(d) H2_O(l) + CO_2(g) → 2Ag_(s) + Cl_2(g)                   (iv) Double displacement
Answer : (a) (iv), (b) (iii), (c) (i), (d) (ii).

Question. Fill in the blanks
(a) The conversion of ferrous sulphate to ferric sulphate is .................. reaction.
(b) Boiling of water to give water vapour is a .................. change.
(c) The slow process of decay or destruction of a metal due to effect of air, moisture and acids on its own is known as .................. .
Answer : (a) Oxidation, (b) Physical, (c) Corrosion.

 

Very Short Answers Type Questions

Question. What is a chemical reaction ?
Answer : A process in which a new substance is formed and original substance lose its identity is called a chemical change.

Question. Identify the type of reaction :
Zn + CuSO₄ → ZnSO₄ + Cu
Answer : Displacement reaction.

Question. Which substance is used in white washing ?
Answer : Calcium hydroxide (slaked lime) is used in white washing.

Question. A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.
Answer : Calcium oxide
CaO(s) + H₂O(l) → Ca(OH)2(aq)

Question. Why should an equation be balanced ?
Answer : An equation should be balanced because according to the law of conservation of mass, mass can neither be created nor be destroyed. Therefore, the number of atoms on both the sides of equation must be equal.

Question. Why is hydrogen included in activity series of metals ?
Answer : Hydrogen is included in activity series of metals because like metals, hydrogen can also lose electrons to form positive ions.

Question. Why is a copper vessel covered with a green coating in rainy season ?
Answer : Copper vessel is covered with a green coating in rainy season due to the attack of oxygen, carbon dioxide and water vapours of the air on copper forming green coloured basic copper carbonate.

Question. Name the most reactive metal and least reactive metal of the activity series of metals.
Answer : Most reactive metal is potassium and least reactive metal is gold.

Question. What is the reason behind various metals such as iron get wasted every year in our country ?
Answer : Due to corrosion various metals such as iron get wasted every year in our country.

Question. What happens when a dilute solution of ferrous sulphate was gradually added to a beaker containing acidified permanganate solution ? Explain the reason.
Answer : The light purple colour of the solution fades and finally disappears. The colour of the solution disappears because of dilution. No reaction is involved in this.

Question. When the powder of common metal is heated in open china dish, its colour turns black. However, when hydrogen is passed over the hot black substance so formed, it regains its original colour. Based on the above information answer the following questions :
(a) What type of chemical reaction takes place in each of the two given steps ?
(b) Name the metal initially taken in the powder form.
Answer :
(a) In the first step, oxidation takes place and in the second step, redox reaction takes place.
(b) The metal initially taken in powder form was copper.

 

Short Answers Type Questions

Question. Mention with reason the colour changes observed when :
(a) silver chloride is exposed to sunlight.
(b) copper powder is strongly heated in the presence of oxygen.
(c) a piece of zinc is dropped in copper sulphate solution. 
Answer :
(a) When silver chloride (white) is exposed to sunlight, it undergoes photochemical decomposition forming black metallic coloured silver and greenish yellow gas chlorine. Thus, the change in colour is observed due to the oxidation of silver chloride in the presence of sunlight.
(b) Heated copper metal reacts with oxygen to form the black copper oxide. Thus, the change in colour is observed when copper powder is strongly heated.
2Cu (s) + O₂ (g) → 2CuO (s)
(c) On adding zinc to CuSO₄ solution, zinc displaces copper from copper sulphate and forms zinc sulphate solution. This is indicated by colour change from blue to colourless. CuSO₄ solution has a blue colour while ZnSO₄ solution is
colourless.
Zn(s) + CuSO₄ (aq) → Cu(s) + ZnSO₄ (aq)

Question. 2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for sometime. What will be your observation in this case ? Write the chemical reaction involved in the form of a balanced chemical equation. Identify the type of chemical reaction. 
Answer : 2AgCl      Sun light→    2Ag + Cl₂
Initially the colour of silver chloride is white but when it is kept in sunlight it breaks down to give silver and chlorine. Hence, the colour changes to grey. It is an example of photo-chemical decomposition.

Question. Identify the type of reactions taking place in each of the following cases and write the balanced chemical equation for the reactions.
(a) Zinc reacts with silver nitrate to produce zinc nitrate and silver.
(b) Potassium iodide reacts with lead nitrate to produce potassium nitrate and lead iodide.
Answer :
(a) The given reaction is a displacement reaction.
Zn(s) + 2 AgNO₃(aq) → Zn(NO₃)₂ (aq) + 2Ag(s)
(b) It is a double displacement reaction.
2KI(aq) + Pb(NO₃)₂(aq) → 2 KNO₃(aq) + PbI₂(s)

Question. What does one mean by exothermic and endothermic reactions ? Give examples. 
Answer : Chemical reactions that release energy in the form of heat, light or sound are called exothermic reactions. Combination reactions are exothermic. Example : Sodium oxide dissolves in water to form sodium hydroxide and releases large amount of energy.
Na₂O + H₂O → 2NaOH + Energy
Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.
Example : Combination of nitrogen and oxygen to form nitric oxide.
N₂ + O₂ + Heat → 2NO

Question. What do you mean by a precipitation reaction ? Explain by giving examples.
Answer : A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.
For example :
Na₂CO₃(s)      +   CaCl₂(s)          →    CaCO₃(s)        +     2NaCl (aq)
Sodium Calcium   Calcium Sodium    carbonate chloride   Carbonate chloride
In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction.

Question. Identify the oxidising agent (oxidant) in the following reactions :
(a) Pb₃O₄ + 8HCl → 3PbCl₂ + Cl₂ + 4H₂O
(b) 2Mg + O₂ → 2MgO
(c) CuSO₄ + Zn → Cu + ZnSO₄
(d) V₂O₅ + 5Ca → 2V + 5CaO
(e) 3Fe + 4H₂O → Fe₃O₄ + 4H₂
(f) CuO + H₂ → Cu + H₂O
Answer :
(a) Pb₃O₄    (b) O₂
(c) CuSO₄   (d) V₂O₅
(e) H₂O       (f) CuO

Question. Why should a magnesium ribbon be cleaned before burning in air ? 
Answer : Magnesium is a very reactive metal, it reacts with oxygen to form a layer of magnesium oxide on its surface when stored. This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen. Hence, this layer is removed by cleaning magnesium ribbon by sand paper so that the underlying metal can be exposed into air.

Question. 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.
Answer :
(a) Metals such as silver when attacked by substances around it such as moisture, acids, gases etc., are said to corrode and this phenomenon is called corrosion.
(b) The black substance is formed because silver (Ag) reacts with H₂S present in air. It forms thin black coating of silver sulphide (Ag₂S).

Question. Oil and fat containing food items are flushed with nitrogen. Why ? 
OR
Explain why, food products containing fats and oils (like potato chips) are packaged in nitrogen.
Answer :
Oil and fat containing food items are flushed with nitrogen because it is an inert gas and does not easily react with these substances. On the other hand, oxygen reacts with food substances and makes them rancid. Thus, bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack. When oxygen is not present inside the pack, rancidity of oil and fat containing food items is avoided.

Question. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773 K to form ammonia gas.
(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H2SO4 .
(d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.
Answer :
(a) N₂(g) + 3H₂ → 2NH₃(g)
Combination Reaction
(b) NaOH(aq) + CH₃COOH(aq) → CH₃COONa(aq) + H₂O(l)
Double displacement reaction or neutralisation reaction.
(c) C₂H₅OH(l) + CH₃COOH(l) → CH₃COOC₂H₅(l) + H₂O(l)
Double displacement reaction or Esterificaton reaction.
(d) C₂H₄(g) + 3O₂(g) → 2CO₂(g) + 2H₂O(g) + Heat + Light
Redox reaction or combustion reaction.

Question. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case :
(a) Thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat.
Answer :
(a) Fe₂O₃(s) + 2Al(s) → Al₂O₃(s) + 2Fe(l) + Heat
Displacement reaction or redox reaction
(b) 3Mg(s) + N₂(g) → Mg₃N₂(s)
Combination reaction
(c) 2KI(aq) + Cl₂(g) → 2KCl(aq) + I₂(s)
Displacement reaction
(d) C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l) + Heat
Redox reaction or combustion reaction

Question. In the reaction :
MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂
(a) Name the compound (i) oxidised, (ii) reduced.
(b) Define oxidation and reduction on its basis.
Answer :
(a) (i) HCl is oxidised in the reaction.
(ii) MnO₂ is reduced in the reaction.
(b) Oxidation is the gain of oxygen or loss of hydrogen whereas reduction is the gain of hydrogen or loss of oxygen.

 

Long Answers Type Questions

Question. Write balanced chemical equations to explain what happens, when
(i) Mercuric oxide is heated.
(ii) Mixture of cuprous oxide and cuprous sulphide is heated.
(iii) Aluminium is reacted with manganese dioxide.
(iv) Ferric oxide is reduced with aluminium.
(v) Zinc carbonate undergoes calcination.
Answer :
(i) Cinnabar (HgS) is an ore of mercury.
When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating.
2HgO(s)   Heat→   2Hg(l) + O₂(g)
(ii) When a mixture of copper oxide and copper sulphide is heated metallic copper is formed along with the evo lution of the sulphur dioxide gas. The reaction equation is as follows:
2Cu₂O + Cu₂S → 6Cu + SO₂
(iii) When aluminium powder is reacted with manganese dioxide, Manganese and aluminium oxide are formed with the evolution of heat and the following reaction takes place :
3MnO₂(s) + 4Al(s) → 3Mn(l) + 2Al₂O₃(s) + Heat
(iv) When ferric oxide is reduced with aluminium a displacement reaction takes place and this reaction is highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state. In fact, the reaction of iron (III) oxide (Fe₂O₃) with aluminium is used to join railway tracks or cracked machine parts. This reaction is known as the thermite reaction.
Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + Heat
(v) The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination. The chemical reaction that takes place during calcination of zinc ores can be shown as follows :
ZnCO₃(s) Heat→ZnO(s) + CO₂(g)

Question. (a) State the various characteristics of chemical reactions.
(b) State one characteristic each of the chemical reaction which takes place when :
(i) Dilute hydrochloric acid is added to sodium carbonate.
(ii) Lemon juice is added gradually to potassium permanganate solution.
(iii) Dilute sulphuric acid is added to barium chloride solution.
(iv) Quick lime is treated with water.
(v) Wax is burned in the form of a candle.
Answer :
(a) The various characteristics of chemical reactions are :
(i) Evolution of a gas
(ii) Formation of a precipitate
(iii) Change in colour
(iv) Change in temperature
(v) Change in state.
(b) (i) Evolution of carbon dioxide gas.
(ii) Change in colour from purple to colourless.
(iii) Formation of white precipitate of barium sulphate.
(iv) Change in temperature.
(v) Change in state from solid to liquid and gas.

Question. Give the characteristic tests for the following gases :
(a) CO₂, (b) SO₂, (c) O₂, (d) H₂.
Answer :
The characteristic test for
(a) Carbon dioxide (CO₂) : This gas turns lime water milky when passed through it due to the formation of insoluble calcium carbonate.
Ca(OH)₂    +   CO₂ →          CaCO₃      +    H₂O
Lime water   Carbon dioxid   Calcium carbonate
(b) Sulphur dioxide (SO₂) : This gas when passed through acidic potassium permanganate solution (purple in colour) turns it colourless because SO₂ is a strong reducing agent.
2KMnO₄ + 2H₂O + 5SO₂ → K₂SO₄ + 2MnSO₄  + 2H₂SO₄
                                                  Manganese sulphate
(c) Oxygen : The evolution of oxygen (O₂) gas during a reaction can be confirmed by bringing a burning candle near the mouth of the test tube containing the reaction mixture. The intensity of the flame increases because oxygen supports burning.
(d) Hydrogen (H₂) : This gas burns with a pop sound when a burning candle is brought near it.
2Cu(NO3)2 (s) → 2CuO (s) + O₂(g) + 4NO₂(g)
(Colourless)      (Colourless)    Oxygen

 

Assertion and Reasoning Based Questions
Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If assertion is false but reason is true.

Question. Assertion : Chemical equations should be balanced.
Reason : As per the law of conservation of mass, mass can neither be created nor be destroyed.
Answer A

Question. Assertion : Hydrogen peroxide is kept in coloured bottles.
Reason : Hydrogen peroxide is a moderately reactive metal that can react with light or heat slowly to produce water.
Answer : C

Question. Assertion : Silver bromide is kept in the coloured bottles.
Reason : Silver bromide decomposes in presence of light.
Answer : A

Question. Assertion : Colour of copper sulphate solution changes when an iron nail is kept immersed in it.
Reason : The decomposition reaction takes place between iron and copper leading to the formation of iron sulphate.
Answer : C

Question. Assertion : Hydrogen is not included in the activity series of metals.
Reason : It is because it can lose electrons to form positive ions.
Answer : D

 

Creating Based Questions

1. 5 ml of sulphuric acid was put into a small conical flask during some experiment in a laboratory. A small balloon has been fixed on the glass pipe inserted through the middle of the stopper cork. A student working in the lab adds some zinc granules to the conical flask by mistake and observes the balloon is blown up. Also, the conical flask became hot in the process.

Question. What may be the reason behind blowing up of balloon ?
Answer : The zinc granules undergo a chemical reaction with sulphuric acid to give hydrogen gas as a product.
This evolved hydrogen gas fills the balloon and balloon gets blown up.

Question. What may be the chemical representation of the above observation ?
Answer : As this is a chemical reaction, this can be
represented by the following chemical equation :
Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

Question. Write a balanced chemical equation with state symbols for the following reactions :
(a) Glucose molecule (C₆H₁₂O₆) reacts with oxygen molecule to give carbon dioxide gas and gaseous water.
(b) Iron dust reacts with gaseous water to give iron oxide (Fe₃O₄) precipitate and hydrogen gas.
Answer :
(a) C₆H₁₂O₆(s) + 6O₂(g) → 6CO₂(g) + 6H₂O
(b) 3Fe(s) + 4H₂O (g) → Fe₃O₄(s) + 4H₂(g)

Question. Annie was happy to see her small house getting cleaned and whitewashed. She observed that the workers dissolved some pale white powdery material called quick lime into water (a vigorous reaction takes place while mixing) left it for some time and applied the white suspension obtained to the walls. At first the wall looked pale white and watery but in 2-3 days the walls became shiny bright white in colour. How can you describe what she observed through chemical equations ?
Answer : Quick lime is chemically known as calcium oxide. It reacts vigorously with water to produce slaked lime (calcium hydroxide), releasing a large amount of heat.
CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat
Quick lime                Slaked lime
The slaked lime after application to wall reacts slowly with carbon dioxide present in atmosphere, to give a thin layer of calcium carbonate on the walls after 2-3 days giving the walls a shiny bright white colour.
Ca(OH)₂(aq) + CO₂(g) → CaCO₃ + H₂O(l)
Slaked lime                   Calcium carbonate

Question. Give reason and name the type of chemical reaction taking place in each case :
(a) Dissolution of ammonium chloride in water leads to cooling of the glass apparatus used for dissolutions.
(b) Silver chloride powder which is white in colour, turns grey when kept in sunlight.
(c) Blue colour of copper sulphate solution fades when an iron nail is dipped inside the solution.
Answer :
(a) Dissolution of ammonium chloride in water is an endothermic reaction where heat is absorbed from surroundings hence making the surrounding cooler than before :
NH₄Cl(s) + H₂O(l)      →     NH₄OH(aq)    +    HCl(aq)
Ammonium                        Ammonium          Hydrochloric
chloride                             hydroxide            Acid
(b) Silver chloride undergoes decomposition reaction in sunlight to give silver metal and chlorine :
2AgCl(s)     →     2Ag(s)     +   Cl₂(g)
Silver chloride    Silver metal
(White)               (Grey)
(c) Iron displaces copper from its solution, hence the colour of copper sulphate solution becomes less blue or fades. This is an example of displacement reaction :
Fe(s) + CuSO₄(aq)    →    FeSO₄(aq) + Cu(s)
Copper sulphate              Ferrous sulphate
(Blue)

Question. Which species out of (1) and (2) is getting oxidised and which one is getting reduced in the below given reactions and why :
(a) CuO + H₂ → Cu + H₂O
     (1)     (2)
(b) MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂
     (1)        (2)
What is the general name for these types of reactions ?
Answer :
(a) Here cuprous oxide (1) is getting reduced (to give copper metal) as it is losing oxygen and hydrogen
(2) is getting oxidised as it is combining with oxygen to give water.
(b) Here manganese dioxide (1) is getting reduced (to MnCl₂) as it is losing oxygen and hydrochloric acid
(2) is getting oxidised to water.
MnO₂      +      4HCl    →   MnCl₂ + 2H₂O + Cl₂
Manganese   Hydrochloric
dioxide         acid
Generally, these type of reactions are known as redox reaction.

 

 

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