CBSE Class 10 Science Chemical Reactions and Equations VBQs Set 03

PRACTICE QUESTIONS

Question. Identify the type of reaction
\( Fe(s) + CuSO_4(aq) \longrightarrow FeSO_4(aq) + Cu(s) \)
(i) Displacement reaction
(ii) Redox reaction
(iii) Combination reaction
(iv) Double displacement reaction
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)
Answer: (a) (i) and (ii)

Question. \( CH_4 + 2O_2 \longrightarrow CO_2 + 2H_2O \)
The above reaction is
(a) oxidation
(b) decomposition reaction
(c) endothermic reaction
(d) double displacement reaction
Answer: (a) oxidation

Question. Which of the following observations help(s) us to determine that a chemical change has taken place?
(a) Change in temperature
(b) Change in colour
(c) Evolution of gas
(d) All of the options
Answer: (d) All of the options

Question. On placing a copper coin in a test tube containing green ferrous sulphate solution, it will be observed that the ferrous sulphate solution
(a) turns blue, and grey substance is deposited on copper coin.
(b) colourless and a grey substance is deposited on the copper coin.
(c) turns colourless and a reddish brown substance is deposited on the copper coin.
(d) remains green with no change in the copper coin.
Answer: (d) remains green with no change in the copper coin.

Question. Which of the following represents a balanced chemical equation?
(a) \( Fe(s) + 4H_2O(g) \longrightarrow Fe_3O_4(s) + 4H_2(g) \)
(b) \( 3Fe(s) + 4H_2O(g) \longrightarrow Fe_3O_4(s) + 4H_2(g) \)
(c) \( 3Fe(s) + H_2O(g) \longrightarrow Fe_3O_4(s) + H_2(g) \)
(d) \( 3Fe(s) + 4H_2O(g) \longrightarrow Fe_3O_4(s) + H_2(g) \)
Answer: (b) \( 3Fe(s) + 4H_2O(g) \longrightarrow Fe_3O_4(s) + 4H_2(g) \)

Question. The chemical reaction between copper and oxygen can be regarded as
(a) displacement reaction
(b) decomposition reaction
(c) combination reaction
(d) double displacement reaction
Answer: (c) combination reaction

Question. Why is it important to balance a skeletal chemical equation?
(a) To verify law of conservation of energy.
(b) To verify law of constant proportion.
(c) To verify law of conservation of mass.
(d) To verify law of conservation by momentum.
Answer: (c) To verify law of conservation of mass.

Question. Lime stone \( \xrightarrow{Step 1 \text{ Heated}} X + CO_2 \);
\( X + H_2O \xrightarrow{Step 2} \text{Slaked lime} \)
The Step 1 and Step 2 respectively are
(a) endothermic, exothermic
(b) both endothermic
(c) both exothermic
(d) exothermic, endothermic
Answer: (a) endothermic, exothermic

Question. Give two example of double displacement reaction.
Answer: (i) \( Na_2SO_4(aq) + BaCl_2(aq) \longrightarrow BaSO_4(s) + 2NaCl(aq) \)
(ii) \( AgNO_3(aq) + NaCl(aq) \longrightarrow AgCl(s) + NaNO_3(aq) \)

Question. Consider the following chemical reaction
X + Barium chloride \(\longrightarrow\) Y + Sodium chloride (White ppt.)
(a) Identify ‘X’ and ‘Y’.
(b) The type of reaction.
Answer: (a) 'X' is Sodium sulphate (\( Na_2SO_4 \)) and 'Y' is Barium sulphate (\( BaSO_4 \)).
(b) It is a double displacement reaction (Precipitation reaction).

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: Observation: White silver chloride turns grey in sunlight.
Chemical Equation: \( 2AgCl(s) \xrightarrow{Sunlight} 2Ag(s) + Cl_2(g) \)
Type of reaction: Photochemical decomposition reaction.

Question. 2 g of lead nitrate powder is taken in a boiling tube. The boiling tube is heated over a flame. Now answer the following:
(a) State the colour of the fumes evolved and the residue left.
(b) Name the type of chemical reaction that has taken place stating its balanced chemical equation.
Answer: (a) Brown fumes are evolved (Nitrogen dioxide) and yellowish brown residue is left (Lead oxide).
(b) It is a thermal decomposition reaction.
Balanced equation: \( 2Pb(NO_3)_2(s) \xrightarrow{Heat} 2PbO(s) + 4NO_2(g) + O_2(g) \)

Question. Balance the following chemical equations:
(a) \( C_6H_{12}O_6 + O_2 \longrightarrow CO_2 + H_2O \)
(b) \( CH_4 + O_2 \longrightarrow CO_2 + H_2O \)
(c) \( KClO_3 \longrightarrow KCl + O_2 \)
(d) \( CO + H_2 \longrightarrow CH_3OH \)
(e) \( CuSO_4 + NaOH \longrightarrow Cu(OH)_2 + Na_2SO_4 \)
(f) \( Fe + H_2O \longrightarrow Fe_3O_4 + H_2 \)
Answer: (a) \( C_6H_{12}O_6 + 6O_2 \longrightarrow 6CO_2 + 6H_2O \)
(b) \( CH_4 + 2O_2 \longrightarrow CO_2 + 2H_2O \)
(c) \( 2KClO_3 \longrightarrow 2KCl + 3O_2 \)
(d) \( CO + 2H_2 \longrightarrow CH_3OH \)
(e) \( CuSO_4 + 2NaOH \longrightarrow Cu(OH)_2 + Na_2SO_4 \)
(f) \( 3Fe + 4H_2O \longrightarrow Fe_3O_4 + 4H_2 \)

Question. Write the balanced equation for the following equations for the following reactions.
(a) Hydrogen combines with nitrogen to form ammonia.
(b) Magnesium burns in oxygen to form magnesium oxide.
(c) Barium chloride solution is added to copper sulphate solution to form barium sulphate along with copper chloride solution.
Answer: (a) \( 3H_2(g) + N_2(g) \longrightarrow 2NH_3(g) \)
(b) \( 2Mg(s) + O_2(g) \longrightarrow 2MgO(s) \)
(c) \( BaCl_2(aq) + CuSO_4(aq) \longrightarrow BaSO_4(s) + CuCl_2(aq) \)

Question. (a) What happens when
(i) a piece of magnesium metal is placed in copper sulphate solution?
(ii) a piece of copper metal is placed in iron sulphate solution?
(b) Giving an example list two information which make a chemical equation more useful (informative).
Answer: (a) (i) Magnesium being more reactive than copper displaces copper from copper sulphate solution. The blue colour of the solution fades.
\( Mg(s) + CuSO_4(aq) \longrightarrow MgSO_4(aq) + Cu(s) \)
(ii) No reaction occurs as copper is less reactive than iron.
(b) (i) Indicating physical states of reactants and products (s, l, g, aq).
(ii) Indicating the conditions under which the reaction takes place (heat, pressure, catalyst).

Question. Give an example, each for thermal decomposition and photochemical decomposition reactions. Write balanced equation for the same.
Answer: Thermal Decomposition: \( CaCO_3(s) \xrightarrow{Heat} CaO(s) + CO_2(g) \)
Photochemical Decomposition: \( 2AgBr(s) \xrightarrow{Sunlight} 2Ag(s) + Br_2(g) \)

Redox Reactions, Corrosion and Rancidity

Question. A student notices that new hammer made of iron is shiny while an old one kept in the tool box has a reddish brown deposit over it. What does the change in colour of hammer indicate?
(a) Effect of moisture on metals
(b) Iron hammer turns brown after sometime.
(c) Effects of kept in a box for longer duration.
(d) Iron changes colour when kept with other tools.
Answer: (a) Effect of moisture on metals

Question. A student notices her jewellary turned dull and had grey black film over it after wearing for a few months. What results in the change in its colour?
(a) Dust deposit over the jewellary which changes its colour.
(b) The jewellary comes in contact with air, moisture, acids and corrodes.
(c) The polish over the jewellary was removed after wearing for few months.
(d) Silver breaks due to wear and tear and turns its colour change due to rusting.
Answer: (b) The jewellary comes in contact with air, moisture, acids and corrodes.

Question. A student notices that bread kept out has a green coating over it after few days. What explains the reason for the student’s observation?
(a) The oils of bread oxidises and cause rancidity.
(b) Bread comes in contact with atmospheric moisture and corrodes.
(c) The oils in the bread reduces and causes change in colour of bread.
(d) Comes in contact with the atmospheric nitrogen and layer deposit over it.
Answer: (b) Bread comes in contact with atmospheric moisture and corrodes.

Question. A student learns that food companies fill bags of chips with nitrogen gas. What is the purpose of packing it with \( N_2 \) gas?
(a) It prevents rancidity of chips.
(b) It keeps mosquitos away from chips.
(c) It keeps the chips dry if pack falls in water.
(d) Prevents chips from spilling out when pack is opened.
Answer: (a) It prevents rancidity of chips.

Question. Which of the following statements about the reaction given below are correct?
\( MnO_2 + 4HCl \longrightarrow MnCl_2 + 2H_2O + Cl_2 \)
(i) HCl is oxidised to \( Cl_2 \)
(ii) \( MnO_2 \) is reduced to \( MnCl_2 \)
(iii) \( MnCl_2 \) acts as an oxidising agent
(iv) HCl acts as an oxidising agent
(a) (ii), (iii) and (iv)
(b) (i), (ii) and (iii)
(c) (i) and (ii) only
(d) (iii) and (iv) only
Answer: (c) (i) and (ii) only

Question. In the reaction \( Hg_2Cl_2 + Cl_2 \longrightarrow 2HgCl_2 \). The reducing agent is
(a) \( Hg_2Cl_2 \)
(b) \( Cl_2 \)
(c) \( HgCl_2 \)
(d) Both \( Cl_2 \) and \( HgCl_2 \)
Answer: (a) \( Hg_2Cl_2 \)

Question. Oxidation involves
(i) gain of electron
(ii) loss of electron
(iii) addition of oxygen or electronegative element
(iv) removal of hydrogen or electropositive element
(a) (i), (ii), (iii)
(b) (ii), (iii), (iv)
(c) (i), (iii), (iv)
(d) (i), (ii), (iv)
Answer: (b) (ii), (iii), (iv)

Question. \( MnO_2 (s) + 4HCl(conc.) \longrightarrow MnCl_2(aq) + H_2O (l) + Cl_2(g) \). The oxidising agent is
(a) \( MnO_2 \)
(b) HCl
(c) \( MnCl_2 \)
(d) \( Ag + Zn(NO_3)_3 \)
Answer: (a) \( MnO_2 \)

Question. In the reaction of iron with copper sulphate solution:
\( CuSO_4 + Fe \longrightarrow Cu + FeSO_4 \)
Which option in the given table correctly represents the substance oxidised and the reducing agent?
(a) Substance Oxidized: Fe, Reducing Agent: Fe
(b) Substance Oxidized: Fe, Reducing Agent: \( FeSO_4 \)
(c) Substance Oxidized: Cu, Reducing Agent: Fe
(d) Substance Oxidized: \( CuSO_4 \), Reducing Agent: Fe
Answer: (a) Substance Oxidized: Fe, Reducing Agent: Fe

Question. Chemically the rust is
(a) Ferric sulphate
(b) Ferric oxide
(c) Hydrated ferrous oxide
(d) Hydrated ferric oxide
Answer: (d) Hydrated ferric oxide

Very Short Answer Type Questions

Question. (a) Potato chips manufacturers fill the packet of chips with nitrogen gas. Why?
(b) Why do gold and platinum not corrode in moist air?
Answer: (a) To provide an inert atmosphere to prevent chips from getting oxidised. \( N_2 \) does not allow chips to get spoiled by oxidation.
(b) They are least reactive and do not react with substances present in moist air.

Question. A reddish brown coloured metal, used in electrical wires, when powdered and heated strongly in an open china dish, its colour turns black. When hydrogen gas is passed over this black substance, it regains its original colour. Based on the above information answer the following questions.
(a) Name the metal and the black coloured substance formed.
(b) Write balanced chemical equations for both the reactions.
Answer: (a) Reddish brown metal is copper. When it is heated in china dish in presence of oxygen, black coloured copper oxide is formed.
(b) \( 2Cu(s) + O_2(g) \longrightarrow 2CuO(s) \)
When hydrogen gas is passed over heated copper oxide, reddish brown copper metal is formed e.g.
\( CuO(s) + H_2(g) \xrightarrow{heat} Cu(s) + H_2O(l) \)

Short Answer Type Questions

Question. Tina finds a paper covered with a white substance in a chemistry lab. She keeps the paper near the window of the lab and comes back to pick it up after five hours to take it home. She noticed that the white substance had turned grey.
(a) What could be the most likely substance on the paper that Tina found?
(b) The substance changed from white to grey. Write the chemical equation for this reaction.
(c) State ONE application of this property of the substance seen in daily life.
Answer: (a) Silver chloride (AgCl)/silver bromide (AgBr) is photosensitive which turn grey when exposed to sunlight.
(b) \( 2AgCl \longrightarrow 2Ag(s) + Cl_2(g) \) (Silver chloride (White) \implies Grey + Cl2(yellowish green)) or \( 2AgBr(s) \longrightarrow 2Ag(s) + Br_2(g) \) (Light yellow \implies Grey).
(c) In black and white photography. Photographic and X-ray films are coated with AgBr.

PRACTICE QUESTIONS

Question. Silver turns black if kept in air dur to formation of
(a) \( Ag_2S \)
(b) \( Ag_2O \)
(c) \( Ag_2SO_4 \)
(d) \( Ag_2CO_3 \)
Answer: (a) \( Ag_2S \)

Question. Copper turns green when exposed to air due to formation of
(a) CuO
(b) \( CuCO_3.Cu(OH)_2 \)
(c) \( Cu_2O \)
(d) \( CuSO_4 \)
Answer: (b) \( CuCO_3.Cu(OH)_2 \)

Question. What are redox reactions? Give one example.
Answer: Reactions in which both oxidation and reduction occur simultaneously are called redox reactions.
Example: \( CuO + H_2 \longrightarrow Cu + H_2O \)

Question. Why are metals good reducing agents where as non metals good oxidising agents?
Answer: Metals have a tendency to lose electrons (oxidation), thus they act as reducing agents. Non-metals have a tendency to gain electrons (reduction), thus they act as oxidising agents.

Question. (a) Define oxidation
(b) Identify oxidising as well as reducing agent in the following reaction:
(i) \( 3MnO_2 + 2Al \longrightarrow 3Mn + Al_2O_3 \)
(ii) \( Pb_3O_4 + 8HCl \longrightarrow 3PbCl_2 + Cl_2 + 4H_2O \)
Answer: (a) Oxidation is the addition of oxygen or removal of hydrogen from a substance. It also means loss of electrons.
(b) (i) Oxidising agent: \( MnO_2 \), Reducing agent: Al.
(ii) Oxidising agent: \( Pb_3O_4 \), Reducing agent: HCl.

INTEGRATED (MIXED) QUESTIONS

Question. (a) In the reaction represented by the equation.
\( CuO + H_2 \longrightarrow Cu + H_2O \)
(i) Name the oxidising agent.
(ii) Name the reducing agent.
(iii) Name the substance oxidised.
(iv) Name the substance reduced.
(b) What type of chemical reactions are represented by the following equations?
(i) X + YZ \(\longrightarrow\) XZ + Y (ii) X + Y \(\longrightarrow\) Z
Answer: (a) (i) \( CuO \)
(ii) \( H_2 \)
(iii) \( H_2 \)
(iv) \( CuO \)
(b) (i) Displacement reaction (ii) Combination reaction

Question. (a) Identify the type of reaction from the following equations:
(i) \( CH_4 + 2O_2 \longrightarrow CO_2 + 2H_2O \)
(ii) \( Pb(NO_3)_2 + 2KI \longrightarrow PbI_2 + 2KNO_3 \)
(iii) \( CaO + H_2O \longrightarrow Ca(OH)_2 \)
(iv) \( CuSO_4 + Zn \longrightarrow ZnSO_4 + Cu \)
(v) \( 2KNO_3(s) \longrightarrow 2KNO_2(s) + O_2(g) \)
(vi) \( Zn(s) + 2AgNO_3(aq) \longrightarrow Zn(NO_3)_2 + 2Ag(s) \)
(b) Name the reducing agent in the following reaction:
\( 3MnO_2 + 4Al \longrightarrow 3Mn + 2Al_2O_3 \)
State which is more reactive, Mn or Al and why?
Answer: (a) (i) Combustion/Oxidation (ii) Double displacement/Precipitation (iii) Combination (iv) Displacement (v) Decomposition (vi) Displacement.
(b) Reducing agent: Al. Al is more reactive than Mn because it displaces Mn from its oxide.

Question. (a) Explain how rancidity can be retarded by storing foods away from light?
(b) Give reason for the following: Digestion of food in the body is an example of decomposition reaction.
(c) Write the balanced chemical equation for the following reaction:
(i) phosphorus burns in presence of chlorine to form phosphorus pentachloride.
(ii) burning of natural gas.
(iii) the process of respiration.
Answer: (a) Light accelerates the oxidation of fats and oils. Storing away from light slows down this process.
(b) During digestion, complex food molecules like carbohydrates, proteins, and fats are broken down into simpler substances like glucose, amino acids, and fatty acids.
(c) (i) \( P_4 + 10Cl_2 \longrightarrow 4PCl_5 \)
(ii) \( CH_4 + 2O_2 \longrightarrow CO_2 + 2H_2O + \text{Heat} \)
(iii) \( C_6H_{12}O_6 + 6O_2 \longrightarrow 6CO_2 + 6H_2O + \text{Energy} \)

Question. (a) Explain two ways by which food industries prevent rancidity.
(b) Discuss the importance of decomposition reaction in metal industry with three points.
Answer: (a) (i) Adding antioxidants (ii) Flushing bags with nitrogen gas.
(b) (i) Extraction of metals from oxides (Electrolytic decomposition). (ii) Refining of metals. (iii) Decomposition of carbonates/sulphides to oxides for easier reduction.

Question. State one characteristic each of the chemical reaction which takes place when:
(a) \( Zn + H_2SO_4 \longrightarrow ZnSO_4 + H_2 \)
(b) \( Ca(OH)_2 + CO_2 \longrightarrow CaCO_3 + H_2O \)
(c) \( 2Pb(NO_3)_2 \longrightarrow 2PbO + 4NO_2 + O_2 \)
(d) \( CH_4 + 2O_2 \longrightarrow CO_2 + 2H_2O \)
(e) \( 2H_2 + O_2 \longrightarrow 2H_2O \)
Answer: (a) Evolution of gas (\( H_2 \)). (b) Formation of white precipitate (\( CaCO_3 \)). (c) Change in colour (yellowish brown residue) and evolution of brown gas (\( NO_2 \)). (d) Evolution of heat (Exothermic). (e) Change in state (gas to liquid).

Question. Identify the type of chemical reaction taking place in each of the following:
(a) Barium chloride solution is mixed with copper sulphate solution and a white precipitate is observed.
(b) On heating copper powder in air in a china dish, the surface of copper powder turns black.
(c) On heating green coloured ferrous sulphate crystals, reddish brown solid is left and smell of a gas having odour of burning sulphur is experienced.
(d) Iron nails when left dipped in blue copper sulphate solution become brownish in colour and the blue colour of copper sulphate fades away.
(e) Quick lime reacts vigorously with water releasing a large amount of heat.
Answer: (a) Double displacement reaction (Precipitation). (b) Combination/Oxidation reaction. (c) Thermal decomposition reaction. (d) Displacement reaction. (e) Combination/Exothermic reaction.