NCERT Exemplar Class 10 Science Chapter 1 Chemical Reactions And Equation
Short Answer Type Questions
1.Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
Solution
(a) Thermit 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.
Ans.
2. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction.
Solution
It is a double displacement reaction. It is also a precipitation reaction as AgCl is a white precipitate.
3.Write the balanced chemical equations for the following reactions.
(a)Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogen-carbonate.
(b)Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.
(c)Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (Cu2I2), liberates iodine gas and also forms potassium sulphate.
Solution
4.Why do fireflies glow at night?
Solution. It is because protein present in fireflies undergoes oxidation in presence of air and an enzyme. This chemical reaction involves emission of visible light. Therefore, fireflies glow at night.
5.Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?
Solution - Grapes when attached to plants are living and therefore they have their immune system due to which they cannot get fermented. When microbes attack plucked grapes in absence of air, they undergo fermentation to form alcohol. This is a chemical process.
6.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.
(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.
Solution -
(a) It is because silver is less reactive than hydrogen. It cannot displace hydrogen from dilute acid.
(b) It is because the reaction is exothermic.
(c) It is because sodium is highly reactive and forms hydrogen gas in the presence of moisture (H2O) which catches fire as the reaction is highly exothermic and H2 is highly inflammable.
(d) It is due to formation of hydrogen gas. The reaction becomes slow after some time as PbCl2(s) covers Pb metal.
7.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.
Solution -
The substance ‘X’ is calcium oxide (CaO), element is calcium. Calcium oxide is used in cement industry. Calcium is present in bones in form of calcium phosphate.
Calcium oxide dissolves in water forming alkali which turns red litmus blue. CaO(s)+
8.Why do we store silver chloride in dark coloured bottles?
Solution -
It is because silver chloride decomposes to silver and chlorine gas in presence of sunlight.
9.A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.
Solution -
(а)Write the chemical formulae of X and Y.
(b)Write a balanced chemical equation, when X is dissolved in water.
Ans.
10.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.
Solution -
a) Silver reacts with H2S gas present in atmosphere to form a black compound Ag2S (silver sulphide) on its surface. This phenomenon is called corrosion.
(b) Ag2S(silver sulphide) is a black coloured solid.
11.Write the balanced chemical equation for the following equations for the following reaction 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 presence of cone. H2SO4.
(d)Ethene is burnt in presence of oxygen to form carbon dioxide, water and releases heat and light.
Solution -
12.Complete the missing components/variables given as x and y in the following reactions :
Solution -
13.Which among the following changes are exothermic or endothermic in nature?
Solution -
(a)Decomposition of ferrous sulphate
(b)Dilution of sulphuric acid
(c)Dissolution of sodium hydroxide in water
(d)Dissolution of ammonium chloride in water
Ans. (a) It is endothermic reaction.
(b)It is exothermic process.
(c)It is exothermic process.
(d)It is endothermic process.
14. Identify the reducing agent in the following reactions :
Solution -
a)HN3 is reducing agent.
(b)F2 is reducing agent.
(c)CO (Carbon monoxide) is reducing agent.
(d)H2 is reducing agent.
15.Identify the oxidising agent (oxidant) in the following reactions :
Solution -
a)Pb3O4 (Red lead). It is also called Sindur used by married ladies. It is an oxidant (oxidising agent).
(b)O2 is oxidising agent.
(c)CuSO4 is oxidising agent.
(d)V2O5 is oxidising agent.
(e)H2O is oxidising agent.
(f)CuO is oxidising agent.
16.Ferrous sulphate decomposes with the evolution of gas having a characteristic order of burning sulphur. Write the chemical reaction involved and identify the type of reaction.
Solution -
It is decomposition reaction.
17.Which among the following are physical or chemical changes
(a)Evaporation of petrol.
(b)Burning of liquefied petroleum gas (LPG).
(c)Heating of an iron rod to red hot.
(d)Curdling of milk.
(e)Sublimation of solid ammonium chloride
Solution -
(a)Physical change
(b)Chemical change
(c)Physical change
(d)Chemical change
(e)Physical change
18.Write a balanced chemical equation for each of the following reactions and also classify them.
(a)Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
(b)A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.
(c)Iron (III) oxide on heating with carbon monoxide reacts to form solid iron and liberates carbon dioxide gas.
(d)Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water.
Solution -
19.Balance the following chemical equations arid identify the type of chemical reaction:
Solution -
20.Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why?
Solution -
Zinc is more reactive than hydrogen whereas copper is less reactive than hydrogen. Therefore, Zn displaces hydrogen from dil.HCl whereas copper does not
21.On heating blue coloured powder of copper (II) nitrate in boiling tube, copper oxide (black), oxygen gas and a brown gas ‘X’ is formed.
(a)Write a balanced chemical equation of the reaction.
(b)Identify the brown gas ‘X’ evolved.
(c)Identify the type of reaction.
(d)What could be the pH range of aqueous solution of the gas ‘X’?
Solution -
(b) The brown gas ‘X,’ is nitrogen dioxide (NO2).
(c) The reaction is a thermal decomposition reaction.
(d) The gas ‘X’ is acidic in nature because it is a non-metallic oxide. Its aqueous solution has pH less than 7.
22.Give the characteristic tests for the following gases.
(a) CO2 (b) SO2 (c) O2(d) H2
Solution -
a)Pass the gas through limewater. Limewater turns milky which confirms the presence of CO2.
Limewater Carbon dioxide Calcium carbonate Water
(b) Pass the gas through acidified potassium dichromate solution (orange in colour). The solution will become green in colour due to formation ofCr2(SO4)3. It is a redox reaction. Acidified K2Cr2O7 is oxidising agent whereas SO_{ 2 } is reducing agent.
Alternative:
Pass the gas through acidified potassium permanganate solution (pink/purple in r colour). It will become colourless because SO2 reduces KMnO4 toMn2+ion which is colourless. It is a redox reaction. AcidifiedKMnO4is an oxidising agent.
(c) Bring a candle near oxygen gas. The intensity of candle flame is increased, it shows the presence of oxygen gas which is a supporter of combustion.
(d) Bring a burning matchstick near hydrogen gas. The gas will burn explosively ‘ with a pop sound. It confirms the presence of hydrogen.
23.What happens when a piece of
(a)zinc metal is added to copper sulphate solution?
(b)aluminium metal is added to dilute hydrochloric acid?
(c)silver metal is added to copper sulphate solution? Also, write the balanced chemical equation if the reaction occurs.
Solution -
(a)The solution will become colourless due to formation of zinc sulphate and reddish brown
(b)aluminium chloride solution will be formed.
(c) No reaction will take place because silver is less reactive than copper, it cannot displace copper from copper sulphate.
24.What happens when zinc granules are treated with dilute solutions of H2SO4, HCl, HNO3, NaCl and NaOH? Also write the chemical equations if reaction, occurs.
Solution -
25.On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, white precipitate is obtained.
(a)Write a balanced chemical equation of the reaction involved.
(b)What other name can be given to this precipitation reaction?
(c)On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why?
Solution -
(b)It is also called double displacement reaction.
It is because barium sulphite reacts with HC1 to form barium chloride which is soluble in water and liberates SO2(g).
26.You are provided with two containers made up of (A) copper and (B) aluminium. You are also provided with solutions of (a) dilute HCl (b) dilute HNO3(c) ZnCl2 and (d) H20. In which of the above containers these solutions can be kept?
Solution -
.A. When solutions are kept in copper container-
(a)Dilute HC1: No reaction takes place as copper is less reactive than hydrogen. Therefore, dil. HC1 can be kept in copper container.
(b)Dilute HNOs: Copper will react with dil. HNOs as it is an oxidising agent and will form copper nitrate and nitrogen monoxide gas.
Therefore, HNO3(dil.) cannot be kept in copper container.
(c) ZnCl2: No reaction takes place because copper is less reactive than Zn, therefore ZnCl2 can be kept in copper container.
(d)H2O : NO reaction takes place because copper is less reactive than hydrogen. Therefore, water can be kept in copper container.
Thus, dil. HCl, ZnCl2 and H2O can be kept in copper container whereas dil. HNO3 cannot be kept in it.
B.When solutions are kept in aluminium container-
(a)Dilute HCl: Aluminium reacts with dil. HCl to form aluminium chloride . and hydrogen gas is formed.
2Al(s)+6Hcl(dil.)⟶2AlCl3(aq.)+3H2(g)
So, dil. HCl cannot be kept in aluminium container.
(b)Dilute HNO3: Aluminium gets oxidised by HNO3 to form a layer of aluminium oxide which does not react further therefore dil. HNO3can be kept in aluminium container.
(c) ZnCl2: It reacts with ‘AT to form aluminium chloride and zinc metal will get deposited.
3ZnCl2+2Al⟶2AlCl3+3Zn
Therefore, Zinc chloride cannot be stored in aluminium container.
(d)H2O2 : It can he stored in aluminium container because aluminium does not react with cold as well as hot water.
A1 reacts with steam to form aluminium oxide and hydrogen
2Al(s)+3H2O(g)⟶Al2O3(s)+3H2(g)
Thus.dil. HNO3 and H2O can be kept in aluminium container whereas dil. HCl and ZnCl2 solution cannot be stored in it.
Access Answers of NCERT exemplar for Class 10 Science Chapter 1 – Chemical Reactions and Equations
Multiple Choice Questions
1. Which of the following is not a physical change?
(a) Boiling of water to give water vapour
(b) Melting of ice to give water
(c) Dissolution of salt in water
(d) Combustion of Liquefied Petroleum Gas (LPG)
Solution
Answer is (d) Combustion of Liquefied Petroleum Gas (LPG)
Explanation:
Combustion is always a chemical change because a new compound is formed after burning and it is irreversible.
2. The following reaction is an example of a:
4NH3 (g) + 5O2 (g) → 4NO(g) + 6H2O(g)
(i) displacement reaction
(ii) combination reaction
(iii) redox reaction
(iv) neutralisation reaction
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (iii) and (iv)
Soln: (c) (i) and (iii)
Explanation:
The reaction provided is a mixture of displacement and redox reaction. Oxygen displaces hydrogen in the ammonia, making it a displacement reaction. Nitrogen gets oxidized and oxygen is reduced, resulting in a redox reaction.
3. Which of the following statements about the given reaction are correct?
3Fe(s) + 4H2O(g) → Fe3O4 (s) + 4H2 (g)
- Iron metal is getting oxidised
- Water is getting reduced
- Water is acting as a reducing agent
- Water is acting as an oxidising agent
- (a) (i), (ii) and (iii)
- (b) (iii) and (iv)
- (c) (i), (ii) and (iv)
- (d) (ii) and (iv)
Soln: (c) (i), (ii) and (iv)
Here, oxygen combines with water to get oxidized. Oxygen is removed from water hence, it is getting reduced. Water is providing oxygen and it acts as an oxidizing agent.
4. Which of the following are exothermic processes?
- (i) The reaction of water with quick lime
- (ii) Dilution of an acid
- (iii) Evaporation of water
- (iv) Sublimation of camphor (crystals)
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)
Soln: (a) (i) and (ii)
Explanation:
The exothermic processes release an enormous amount of heat – Hence, heat energy is released when water reacts with quick lime and acid reacts with water.
5. Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas, in the case of beaker C, the temperature of the solution falls. Which one of the following statement(s) is(are) correct?
(i) In beakers A and B, the exothermic process has occurred.
(ii) In beakers A and B, the endothermic process has occurred.
(iii) In beaker C exothermic process has occurred.
(iv) In beaker C endothermic process has occurred.
(a) (i) only
(b) (ii) only
(c) (i) and (iv)
(d) (ii) and (iii)
Solution
Answer is (c) (i) and (iv)
Explanation:
Exothermic processes will increase the temperature whereas endothermic processes will decrease the temperature.
6. A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?
(a) KMnO4 is an oxidising agent, it oxidises FeSO4
(b) FeSO4 acts as an oxidising agent and oxidises KMnO4
(c) The colour disappears due to dilution; no reaction is involved
(d) KMnO4 is an unstable compound and decomposes in the presence of FeSO4 to a colourless compound.
Solution - (a) KMnO4 is an oxidising agent, it oxidises FeSO4
Explanation:
In this reaction, potassium permanganate (KMnO4) is an oxidizing agent.
The solution is coloured purple because of the KMnO4 and it eventually disappears when all the KMnO4 in the solution is utilized.
7. Which among the following is(are) double displacement reaction(s)?
(i) Pb + CuCl2 → PbCl2 + Cu
(ii) Na2 SO4 + BaCl2 → BaSO4 + 2NaCl
(iii) C + O2 → CO2
(iv) CH4 + 2O2 → CO2 + 2H2O
(a) (i) and (iv)
(b) (ii) only
(c) (i) and (ii)
(d) (iii) and (iv)
Solution
The answer is (b) (ii) only
Explanation:
Here, Sodium and Barium are displaced from each other’s salts, hence it is a double displacement reaction.
8. Which among the following statement(s) is (are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to
(i) the formation of silver by decomposition of silver chloride
(ii) sublimation of silver chloride
(iii) decomposition of chlorine gas from silver chloride
(iv) oxidation of silver chloride
(a) (i) only
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (iv) only
Soln:
Answer is (a) (i) only
9. Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by the liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?
(i) It is an endothermic reaction
(ii) It is an exothermic reaction
(iii) The pH of the resulting solution will be more than seven
(iv) The pH of the resulting solution will be less than seven
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)
Soln:
The answer is (b) (ii) and (iii)
Explanation:
When solid calcium oxide reacts vigorously with water, it forms calcium hydroxide which is accompanied by the generation of heat. This event proves the reaction is exothermic. pH of the solution will be more than 7 because oxides and hydroxides of metals are alkaline.
10. Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?
(i) Displacement reaction
(ii) Precipitation reaction
(iii) Combination reaction
(iv) Double displacement reaction
(a) (i) only
(b) (ii) only
(c) (iv) only
(d) (ii) and (iv)
Soln:
Answer is (d) (ii) and (iv)
Explanation:
Ammonium and barium are getting displaced from their respective salts. Hence this is a double displacement reaction. It is also called a precipitation reaction due to the formation of white precipitate of barium sulphate.
11. Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is
(a) 1:1
(b) 2:1
(c) 4:1
(d) 1:2
Soln:
Answer is (b) 2:1
Explanation:
1 Mole of water has 2 moles of Hydrogen and 1 mole of water. Hence mole ration between hydrogen and oxygen is 2:1.
12. Which of the following is(are) an endothermic process(es)?
(i) Dilution of sulphuric acid
(ii) Sublimation of dry ice
(iii) Condensation of water vapours
(iv) Evaporation of water
(a) (i) and (iii)
(b) (ii) only (c)
(iii) only
(d) (ii) and (iv)
Soln:
Answer is (d) (ii) and (iv)
Explanation:
Change of solid to gas or liquid to gas absorbs heat hence sublimation of dry ice and evaporation is an endothermic reaction.
13. In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?
(a) Lead sulphate (insoluble)
(b) Lead acetate
(c) Ammonium nitrate
(d) Potassium sulphate
Soln:
The answer is (b) Lead acetate
Explanation:
To get lead iodide we need a compound containing lead hence Ammonium nitrate and Potassium sulphate are ruled out. Lead sulphate is insoluble hence it cannot be used so the answer is (b) Lead acetate
14. Which of the following gases can be used for storage of fresh sample of an oil for a long time?
(a) Carbon dioxide or oxygen
(b) Nitrogen or oxygen
(c) Carbon dioxide or helium
(d) Helium or nitrogen
Soln:
The answer is (d) Helium or nitrogen
Explanation:
Oxygen cannot be used as it is an oxidizing agent. Helium can be used as it is an inert gas. Nitrogen is less reactive and it is cheaper than Helium. In most cases, nitrogen is used in packet to prevent rancidity.
16. Which one of the following processes involve chemical reactions?
(a) Storing of oxygen gas under pressure in a gas cylinder
(b) Liquefaction of air
(c) Keeping petrol in a china dish in the open
(d) Heating copper wire in presence of air at high temperature
Soln:
The answer is (d) Heating copper wire in the presence of air at high temperature
Explanation :
In first three options given here, there is no involvement of chemical reaction. When copper is heated in the presence of air at high-temperature copper undergoes oxidation reaction to give out copper oxide.
Short Answer Questions
19. 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 773K 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 H2 SO4.
20. 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.
Soln:
(a) Thermit reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
FE2O3 + 2Al → Al2O3(s)+ 2Fe (l)
This is a Single displacement reaction
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
3 Mg(s)+ N2 → Mg3N2
The reaction is a Combination reaction
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
Cl2(g)+2KI (aq) → 2KCl(Aq) +I2(s)
This is a Single displacement reaction
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat.
C2H5OH+ 3O2 → 2CO2+ 3H2O+ heat
This is a Combustion reaction
21. Complete the missing components/variables given as x and y in the following reactions
(a) Pb(NO3 ) 2 (aq) + 2KI(aq) → PbI2 (x) + 2KNO3 (y)
(b) Cu(s) + 2Ag NO3 (aq) → Cu(NO3 ) 2 (aq) + x(s)
(c) Zn(s) + H2 SO4 (aq) → ZnSO4 (x) + H2 (y)
(d) CaCO3 (s) →x CaO(s) + CO2 (g)
Soln:
(a) Pb(NO3 ) 2 (aq) + 2KI(aq) → PbI2 (s) + 2KNO3 (aq)
(b) Cu(s) + 2Ag NO3 (aq) → Cu(NO3 ) 2 (aq) + 2Ag(s)
(c) Zn(s) + H2 SO4 (aq) → ZnSO4 (aq) + H2 (g)
(d) CaCO3 (s) →heat→ CaO(s) + CO2 (g)
x(s), y (aq)
x is 2Ag
x-(aq) y(g)
x is heat
22. Which among the following changes are exothermic or endothermic in nature?
(a) Decomposition of ferrous sulphate
(b) Dilution of sulphuric acid
(c) Dissolution of sodium hydroxide in water
(d) Dissolution of ammonium chloride in water
Soln:
Exothermic reactions
(b) Dilution of sulphuric acid
(c) Dissolution of sodium hydroxide in water
Endothermic reaction
a) Decomposition of ferrous sulphate
(d) Dissolution of ammonium chloride in water
23. Identify the reducing agent in the following reactions
(a) 4NH3 + 5O2 → 4NO + 6H2O
(b) H2O + F2 → HF + HOF
(c) Fe2O3 + 3CO → 2Fe + 3CO2
(d) 2H2 + O2 → 2H2O
Soln:
NH3-Ammonia
H2O – Water
CO-Carbon momnoxide
H2- Hydrogen
24. 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
Soln:
Pb3O4
O2
CuSO4
V2O5
H2O
CuO
25. Write the balanced chemical equations for the following reactions
(a) Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogencarbonate.
(b) Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.
(c) Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (Cu2 I2 ), liberates iodine gas and also forms potassium sulphate.
Soln:
(a) Na2CO3 + HCl → NaCl + NaHCO3
(b) NaHCO3 + HCl → NaCl + H2O + CO2
(c) 2CuSO4+4Kl →2K2SO4+CU2I2+I2
26. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of chemical reaction?
Soln:
KCl(aq) + AgNO3(aq) → AgCl(s) + KNO3(aq)
This is double displacement and precipitation reaction.
27. Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.
Soln
2FeSO4=Fe2O3+SO2+SO3
This is a decomposition reaction.
28. Why do fireflies glow at night?
Soln:
Fireflies produce a chemical reaction inside their bodies which allows them to glow at night. Oxygen combines with calcium, ATP and luciferin in the presence of an enzyme called luciferase. This results in bioluminescence.
29. Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?
Soln:
Grapes on the plant do not ferment because of the defence mechanism of plants. When grapes are plucked from the plant, grapes react with yeast to carry out fermentation. Here, sugar changes to alcohol and it is a chemical change.
30. Which among the following are physical or chemical changes?
(a) Evaporation of petrol
(b) Burning of Liquefied Petroleum Gas (LPG)
(c) Heating of an iron rod to red hot.
(d) Curdling of milk
(e) Sublimation of solid ammonium chloride
Soln:
Physical changes
Evaporation of petrol
Heating of an iron rod to red hot.
Sublimation of solid ammonium chloride
Chemical changes
Burning of Liquefied Petroleum Gas (LPG)
(d) Curdling of milk
31. During the reaction of some metals with dilute hydrochloric acid, the 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
Some bubbles of gas are seen when lead (Pb) is reacted with the acid.
Explain these observations giving suitable reasons.
Soln:
There will not be any reaction between silver and dilute HCL as silver lies in low reactive series of metals.
Because it is an exothermic reaction temperature increases
Sodium is highly reactive metals it reacts with atmospheric oxygen to form exothermic reaction which results in temperature increase.
When lead reacts with acid it produces Hydrogen gas which is responsible for the formation of bubbles.
32. 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.
Soln:
Compound X is Calcium oxide. CaO is extensively used in the cement industry. On treatment with water, CaO produces Ca(OH)2 which is alkaline in nature and turns red litmus to blue colour.
Ca +H2O→ Ca(OH)2
33. Write a balanced chemical equation for each of the following reactions and also classify them.
(a) Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
(b) A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.
(c) Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
(d) Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water.
Soln:
(a) Pb(CH3COO)2 + 2HCI – PbCl2 + CH3COOH
This is a Double Displacement reaction.
(b) 2Na + 2C2H5OH + 2C2H5ONa+ H2
This is a Displacement reaction.
(c) Fe2O3 + 3CO + 2Fe + 3CO2
This is a redox reaction.
(d) 2 H2S+O2 → 2 s + 2 H2O
This is a replacement reaction.
34. Why do we store silver chloride in dark coloured bottles?
Soln:
Silver chloride decomposes into silver and chlorine gas when exposed to sunlight. Hence Silver chloride is stored in dark colored bottles.
35. Balance the following chemical equations and identify the type of chemical reaction.
(a) Mg(s) + Cl2 (g) → MgCl2 (s)
(b) HgO(s) → Heat Hg(l) + O2 (g)
(c) Na(s) + S(s) → Fuse Na2S(s)
(d) TiCl4 (l) + Mg(s) → Ti(s) + MgCl2 (s)
(e) CaO(s) + SiO2 (s) → CaSiO3 (s)
(f) H2O2 (l) → U V H2O(l) + O2 (g)
Soln:
(a) Mg(s) + Cl2(g) → MgCl2(s)
This type of reaction is called a combination reaction or a synthesis reaction.
(b) 2HgOis) — (Heat) → 2 Hg(I) + O2(g)
This is an example of thermal decomposition reaction.
(c) 2Na(s) + S(s) — (Fuse) → Na2S(s)
This is an example of a Combination reaction.
(d) TiCI4 (1) + Mg(s) → Ti(s) + 2MgCl2 (s)
This reaction falls under the category of Displacement reactions
(e) Cao(s) + SIO2(s) + CaSIO3(s)
This is a synthesis reaction.
(f) 2H2O2 (I) — UV → 2H2O(I) + O2 (g)
This is a decomposition reaction.
36. A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.
(a) Write the chemical formulae of X and Y.
(b) Write a balanced chemical equation, when X is dissolved in water.
Soln:
2Mg + O₂ →2MgO
Compound X→ MgO [ Magnesium Oxide ]
Compound Y →Mg₃N₂ [ Magnesium Nitride ]
If Magnesium Oxide is dissolved in water, the product is Magnesium Hydroxide
MgO + H₂O → Mg(OH)₂
37. Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why?
Soln:
Zinc is more reactive than copper as Zinc is placed above Hydrogen and Copper is placed below hydrogen in the activity series of metals. Because of this Zinc reacts with HCl whereas Copper will not react.
38. 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.
Soln:
Silver reacts with H2S present in the atmosphere to form a black colour compound Silver Sulphide. This phenomenon is called corrosion.
The black colour compound formed is Silver Sulphide
2Ag+ H2S →Ag2S+H2
Long Answer Questions
39. On heating blue coloured powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed
(a) Write a balanced chemical equation of the reaction.
(b) Identity the brown gas X evolved.
(c) Identify the type of reaction.
(d) What could be the pH range of aqueous solution of the gas X?
Soln:
(a)
Class 10 Chapter 1 Science Chemical Reactions and Equations
(b) The brown gas X is nitrogen dioxide, NO2.
(c) The reaction involved is Thermal decomposition.
(d) pH< 7 because NO2 dissolves in water to form acidic solution (pH range below 7).
40. Give the characteristic tests for the following gases
(a) CO2
(b) SO2
(c) O2
(d) H2
Soln:
Pass CO2 into limewater which will turn water into milky. This is the confirmation test for the presence of Carbon-di-oxide.
The smell is the characteristic feature of SO2, which smells like a rotten egg.
Test for oxygen involves burning of match stick near oxygen makes it burn even more brightly.
When Burning matchstick is brought near H2 gas, the flame burns with the pop sound. This is the test to confirm Hydrogen gas.
41. What happens when a piece of
(a) zinc metal is added to copper sulphate solution?
(b) aluminium metal is added to dilute hydrochloric acid?
(c) silver metal is added to copper sulphate solution?
Also, write the balanced chemical equation if the reaction occurs
Soln:
a) When Zinc is added to copper sulphate solution Zinc displaces copper to form Zinc sulphate.
Zn(s)+ CuSo4(aq)→ ZnSo4(aq)+ Cu(s)
b)Aluminium metals react with dilute HCl to for Aluminum Chloride and Hydrogen gas is evolved in the reaction.
2Al (s)+ 6HCl(aq)→ 2AlCl3(aq)+ 3 H2
c)When silver metal is added to Copper Sulphate solution there will not be any reaction as silver is non-reactive metal.
42. What happens when zinc granules are treated with a dilute solution of H2SO4, HCl, HNO3, NaCl and NaOH, also write the chemical equations if a reaction occurs.
Soln:
When Zinc granules react with dil H2SO4 displacement reaction takes place leading to the formation of ZnSo4 liberating H2 gas
Zn( s)+ H2SO4(aq)→ ZnSo4 (aq)+H2 (g)
When Zinc granules react with dil HCl displacement reaction takes place leading to the formation of ZnCl2 liberating H2 gas
Zn( s)+ H2Cl(aq) →ZnCl2 (aq)+H2 (g)
When Zinc granules react with dil HNO3 it leads to the formation of Zinc nitrate evolving H2O and nitrous oxide
4Zn(s)+10 HNO3(aq) 4Zn(NO3)2(aq) +5H2O(i)+N2O (g)
When Zinc granules react with NaCl there will not be any reaction
When Zinc granules react with NaOH solution
Zn(s)+ NaOH(aq)→ Na2ZnO2 (aq)+H2 (g)
43. On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, a white precipitate is obtained.
(a) Write a balanced chemical equation of the reaction involved
(b) What other names can be given to this precipitation reaction?
(c) On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why?
Soln:
a)On adding a drop of Barium Chloride solution to an aqueous solution of sodium sulphite, barium sulphite is obtained which is white colour precipitate.
BaCl2 + Na2SO3——>BaSO3 + 2NaCl
b) In this case, the precipitation reaction is a double displacement.
c) When we add dilute HCl to this reaction mixture Barium chloride, Sulphur dioxide and water are formed. Barium chloride is a soluble substance which will make the white precipitate disappear.
BaSO3 + HCl→ BaCl3 + SO2 + H2O.
44. You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO3, ZnCl2 and H2O. In which of the above containers these solutions can be kept?
These solutions can be kept in a copper container because copper is a noble metal which will not react with HCl or even HNO3. If we keep the solution in an aluminium container, aluminium reacts with acids to form Zinc chloride.
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Study Notes