Notes And Questions For NCERT Class 10 Science Chemical Reactions and Equations

Chapter Notes Notes for Class 10

Students should refer to the below Chemical Reactions and Equations Class 10 notes prepared as per the latest curriculum issued by CBSE and NCERT. These notes and questions are really useful as they have been developed based on the most scoring topics and expected questions in upcoming examinations for Class 10. Chemical Reactions and Equations is an important topic in Science Class 10 which if understood properly can help students to get very good marks in class tests and exams.

Chemical Reactions and Equations Class 10 Notes and Questions PDF Download

Read the notes below which will help you to understand all important and difficult topics in this chapter. There are some topics in Chemical Reactions and Equations chapter which you should understand carefully as many questions can come from those parts. Our team of teachers have designed the revision notes so that its helpful for students to revise entire course prior to the class tests.

♦ Chemical Reaction : –Whenever a chemical change occurs we can say that a chemical reaction has taken place
eg – Food gets digested in our body, Rusting of iron.
♦ Chemical Equation :–Achemical reaction can be expressed symbolically by using chemical equation eg magnesium is burnt into air to form magnesium oxide can be represented as Mg + O2 →MgO
– We can observe or recognise a chemical reaction by observing change in state, colour, by evolution of gas or by change in temperature.
♦ Physical state of the reactant and products are mentioned to make chemical reaction more informative. eg we use (g) for gas, (l) for liquid, (s) for solid and (aq) for aqueous.
♦ Balancing Equation :– We balance the chemical equation so that no. of atoms of each element involved in the reaction remain same at the reactant and product side.
eg Fe + H2O → Fe2O3 + H2 can be written as
3 Fe(s) + 4H2O(g) → Fe2O3(s) +4H2(g)

♦ Combination Reaction :– The reaction in which two or more substances combine to form a new single substance

eg CaO(s)   +    H2O(l)  →   Ca(OH)2 (aq)
    Calcium        Water             Calciumhydroxide
      oxide     (slaked lime)
Quick lime
– Ca(OH)2 slaked lime is used for white washing walls. It reacts will CO2 to form CaCO3 and gives a shiny finish to the walls.
Ca(OH)2(aq)  + CO2(g) → CaCO3(s)+ H2O (l)
Calcium                          Calcium
hydroxide                      Carbonate

– Burning of Coal
C(s) + O2(g) → CO2(g) + heat + light

– Formation of water
2H2(g) + O2(g) → 2H2O(l)

♦ Exothermic Reactions :– Reaction in which heat is released along with the formation of products.
eg. CH4(g) + 2O2(g) →CO2(g) + 2H2O(g)
– Respiration is also exothermic reaction.
– De composition of vegetable matter into compost.

♦ De compositon Reactions :– The reaction in which a single substance decomposes to give two or more substances. De composition reactions can be of three types
Thermal Decompositon :–When a decompositon reaction is carried out by heating

Notes And Questions For NCERT Class 10 Science Chemical Reactions and Equations

– Silver bromide behaves similarly

– The above two reactions are used in black and white photography.

– Endothermic Reactions – The reactions which require energy in the form of heat, light or electricty are called Endothermic Reactions.
2Ba(OH)2 + NH4Cl    →   2BaCl2 + NH4OH
– Displacement Reaction : The chemical Reaction in which an element displaces another element from its solution
Fe(s) + CuSO4(aq) →      FeSO     +   Cu(s)
          Copper (aq)
          Sulphate                Iron Sulphate

Notes And Questions For NCERT Class 10 Science Chemical Reactions and Equations

Question: A person suffered a head injury, due to which he faces breathing problem. No problem was detected with his respiratory system. What could be the cause of this problem?
Ans. As the problem is caused due to head injury, it could be related to “Pons” a part of Hind brain responsible for regulation of respiration.

– The nail becomes brownish in colour and the blue colour of Copper Sulphate solution fade.
– Other examples Zn(s) + CuSO4   →   ZnSO4 + Cu(s)
                                        (aq)              (aq)
                                   Copper               Zinc 
                                   Sulphate          Sulphate

Pb(s) + CuCl2 → PbCl2 + Cu(s)
            (aq)             (aq)
          Copper          Lead
         Chloride        Chloride

Zinc and lead are more reactive elements than copper. They displace copper from its compounds.

– Double Displacement Reaction : The reaction in which two different atoms or group of atoms are mutually exchanged
eg. Na2 SO4 + BaCl2 → BaSO4(s) + 2NaCl
                (aq)      (aq)                         (aq)
      Sodium     Barium    Barium      Sodium
      Sulphate  Chloride   Sulphate    Chloride

A white substance is formed due to above reaction. The insoluble substance is called precipitate.
Precipitation Reaction –Any reaction that produces a precipitate is called a precipitation reaction.
eg. Pb(NO3)2   +  2KI     →    PbI2 ↓   + 2KNO3
             (aq)          (aq)       (aq)
    Lead Nitrate    Potassium   Lead       Potassium
                             Iodide    Iodide         Nitrate

Notes And Questions For NCERT Class 10 Science Chemical Reactions and Equations

– Oxidation : Oxidation is the gain of oxygen or loss of hydrogen
eg. 2Cu + O2 ¾¾He¾at¾→ 2CuO
When Copper is heated a black colour appears. If this CuO is reacted with hydrogen gas then again Cu becomes brown as reverse reaction takes place
CuO + H2 ¾¾He¾at¾→ Cu + H2O
– Reduction : Reduction is the loss of oxygen or gain of hydrogen.
– Redox Reaction : The reaction in which one reactant gets oxidised while other gets reduced

– Corrosion : When a metal is attacked by substances around it such as moisture, acids etc.
eg. Reddish brown coating on iron.
(ii) Black coating on Silver.
– Rancidity : When fats and oils are oxidised they become rancid and their smell and taste change.
– Antioxidants are added to foods containing fats and oil.

Important Questions chemical reactions and equations Class 10 Science

Question: A man becomes unconscious due to head injury. A pin is pricked on his foot, he withdraws his foot. Why? Explain.
Ans. It is reflex action. Stimulus is perceived by receptor (skin). Sensory nerve sends the sensation from receptor to the spinal cord. Then spinal cord sends the message through motor nerves to the effectors. Effectors i.e. muscles help in withdrawing his foot.

Question: In a family of normal sized members, there are two exceptions, one member is dwarf and one is tall like “Khali”. What could be the cause of it?
Ans. In case of dwarfs, there is a deficiency of growth hormone from Pituitary gland and in case of giants excess of growth hormone is produced during childhood.

Question: Why do you blink your eyes as bright light is focused on you?
Ans. We blink in order to protect the eye from bright light which otherwise would damage the retina.

More class 10 science life process notes below

Question: There is a potted plant in your drawing room, after few days you note that plant has bent to one side. What could be the reason? How has this movement been co coordinated?
Ans. The plant has bent to one side due to phototropic movement of the stem. This movement is due to unequal growth of the stem on both sides. This growth is initiated by the hormone auxin.

Question: A leaf shaped gland is present above the intestine. The secretion of this gland regulates the metabolism of sugar in blood. Name the secretion and gland.
Ans The name of the gland is pancreas. The secretion is Insulin from special cells in it.

Question. (A) Mention any four information given by a chemical equation.
(B) State the law of conservation of mass as applicable in a chemical reaction.
Answer : (A) A balanced chemical equation tells:
(1) number of atoms and molecules of reactants and products involved.
(2) chemical formula of reactants and products involved.
(3) catalyst involved in the reaction if any.
(4) physical state of reactants and products involved.

Question. Translate the following statements into chemical equations and balance them (if needed):
(A) Lead nitrate undergoes thermal decomposition to form lead monoxide, nitrogen dioxide and oxygen gas.
(B) Quicklime combines with carbon dioxide to form calcium carbonate.
(C) Aluminium metal granule is added in sulphuric acid to form aluminium sulphate and hydrogen gas.  

Answer :   

Question. 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 
Answer : (A) The decomposition of ferrous sulphate absorbs heat during reaction. Therefore, it is an example of endothermic reaction.
(B) When we dissolve sulphuric acid in water, a large amount of heat is liberated, so it is an exothermic reaction.
(C) When we dissolve sodium hydroxide in water, a large amount of heat is liberated, so it is an exothermic reaction.
(D) The mixing of ammonium chloride in water absorbs heat from the reaction mixture. Therefore, it is an example of endothermic reaction.

Question. No chemical reaction takes place when granules of a solid A are mixed with the powder of another solid B. However when the mixture is heated, a reaction takes place between its components. One of the products, C, is a metal and settles down in its molten state, while the other product, D, floats over it. It was observed that the reaction is highly exothermic.
(1) Based on the given information, make an assumption about A and B and write a chemical equation for the chemical reaction indicating the conditions of the reaction, physical state of reactions and products and thermal status of reaction.
(2) Mention any two types of reaction under which the above chemical reaction can be classified.

Answer : Here, A is solid manganese granules while B is aluminium powder. When they are mixed together, no reaction takes place. However, on heating, thermite reaction takes place. Here, the aluminium takes the oxygen from the manganese dioxide to form molten metallic manganese. It also results in the formation of aluminium oxide which floats over manganese metal. The chemical reaction is as follows: 

Since this chemical reaction releases a lot of heat (exothermic reaction), it results in oxidation of aluminium and reduction of manganese. Hence, it is also a redox reaction.

Question. 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 
Answer : (A) The decomposition of ferrous sulphate absorbs heat during reaction. Therefore, it is an example of endothermic reaction. (B) When we dissolve sulphuric acid in water, a large amount of heat is liberated, so it is an exothermic reaction. (C) When we dissolve sodium hydroxide in water, a large amount of heat is liberated, so it is an exothermic reaction. (D) The mixing of ammonium chloride in water absorbs heat from the reaction mixture. Therefore, it is an example of endothermic reaction.

Question. In the electrolysis of water:
(A) Name the gases liberated at anode and cathode.
(B) Why is it that the volume of gas collected on one electrode is two times that on the other electrode?
(C) What would happen if dil. H2SO4 is not added to water?
Answer : (A) Gas liberated at anode – Oxygen Gas liberated at Cathode–Hydrogen
(B) On electrolysis water decomposes into hydrogen and oxygen:
2H2O(l)  Electric→
Current 2H2(g) + O2(g)
Water decomposes to hydrogen and oxygen in the ratio of 2 : 1 by volume. The double volume collected is hydrogen.
(C) If dilutes sulphuric acid is not added to water, electrolysis will not take place as water is not a good conductor, if distilled water is used. Otherwise otherwise also conductivity will be very low if tap water is used. Sulphuric acid is added to water to make it a good conductor.

Question. A solution of potassium chloride when mixed with silver nitrate solution forms an insoluble white substance. Write the chemical reaction involved and also mention the type of the chemical reaction.
Answer : When a solution of potassium chloride is mixed with silver nitrate solution, we get a precipitate of silver chloride. Chlorides are usually soluble but one important exception to this rule is silver chloride. The chemical reaction is: KCl + AgNO3 → KNO3(aq) + AgCl(s) This type of chemical reaction is called a double displacement reaction.

Question. Grapes hanging from 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?
Answer : When the grapes are attached to the plants, they are still considered as living. They have their immune system intact and thus oxygen reaches in the cell leading to aerobic respiration taking place and no fermentation is possible under aerobic conditions. After plucking grapes from plants, fermen-tation of sugar is carried out in the presence of yeast, which changes sugar to ethanol and carbon dioxide. This process occurs in the absence of oxygen, i.e., in anaerobic conditions. Here, fermentation is a chemical change as it results in the formation of new substances: alcohol and carbon dioxide.

Question. 1 g of copper powder was taken in a China dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equations of reactions, the name and the color of the products formed in each case.
Answer : When 1 g of copper powder was heated in a China dish, a black coating is formed on the surface of copper of copper
(ii) oxide or cupric oxide. 

The name of product is copper (ii) oxide and it is black in colour. When hydrogen gas is passed over copper (ii) oxide, CuO reduced to copper.

The product formed is Cu and its colour is reddish brown.

Question. Why do we store silver chloride in dark coloured bottles?
Answer : We store silver chloride in dark coloured bottles to prevent the breakdown of the salt into its elements (photo decomposition). When silver chloride is exposed to light, it breaks down into elemental silver and chlorine gas. 

In order to prevent the decomposition of silver chloride to silver, we store them in dark coloured bottles which block the light.

Question. (A) Write two observations when lead nitrate is heated in a test tube.
(B) Name the type of reaction.
(C) Write a balanced chemical equation to represent the above reaction.
Answer : (A) It turns yellow due to formation of lead oxide and Reddish brown fumes evolve.
(B) Thermal decomposition reaction.   
(C) 2Pb(NO3)2 Heat→ 2PbO + 4NO2 + O2

Question. A chemical compound ‘X‘ is used in the soap and glass industry. It is prepared from brine.
(A) Write the chemical name, common name and chemical formula of ‘X‘.
(B) Write the equation involved in its preparation.
(C) What happens when it is treated with water containing Ca or Mg salts?
Answer : (A) Chemical name of compound ‘X‘–Sodium carbonate common name of compound
‘X‘—washing soda
Chemical formula of compound
‘X‘ = Na2CO3. 10H2O
(B) Na2CO3 + 10H2O → Na2CO3.10H2O

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) The metal surface of silver articles reacts with atmospheric sulphur compounds like hydrogen sulphide and forms black layer of sulphides. This phenomenon is called as corrosion or tarnishing of silver.
(B) The black substance that is formed by the reaction of hydrogen sulphide and atmospheric oxygen is silver sulphide (Ag2S).

4Ag + O2 + 2H2S → 2Ag2S + 2H2O

Question. P, Q and R are 3 elements which undergo chemical reactions according to the following equations:
(i) P2O3 + 2Q → Q2O3 + 2P
(ii) 3RSO4 + 2Q → Q2(SO4)3 + 3R
(iii) 3RO + 2P → P2O3 + 3R
Answer the following:
(A) Which element is most reactive?
(B) Which element is least reactive?
(C) State the type of reaction listed above.

Answer : Element Q displaces P and R from their compounds in reaction ‘a’ and reaction ‘b’respectively.
So element Q is more reactive than P and R.
Also element P displaces element R in reaction ‘c’. So we can say that
(A) Q is the most reactive element
(B) R is the least reactive element.
(C) The above reactions are displacement reactions.

Question. Lead nitrate solution is added to a test tube containing potassium iodide solution.
(A) Write the name and colour of the compound precipitated.
(B) Write the balanced chemical equation for the reaction involved.
(C) Name the type of this reaction justifying your answer.
Answer : (A) When lead nitrate solution is added to a test tube containing Potassium iodide solution, a yellow precipitate of lead iodide is produced along with potassium nitrate solution.
(B) Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3 Lead iodide (yellow ppt.) Lead Potassium iodide nitrate
(C) The reaction is double displacement. In this double displacement reaction, two compounds, lead nitrate solution and potassium iodide solution react to form two new compounds, lead iodide and potassium nitrate. An exchange of ions takes place in this reaction. For example, the lead ions (Pb2+) of lead nitrate react with iodide (I–) of potassium iodide to form a new compound lead iodide (Pb2+I– or PbI2). Similarly, the potassium ions (K+) of Potassium iodide react with the nitrate ions (NO3–) of lead nitrate to form new compound, potassium nitrate (K+NO3– or KNO3). Lead iodide (PbI2) is formed as an insoluble yellow precipitate so it is also called precipitation reaction.

Long Answer Type Questions

Question. 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) 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?

Answer : 

(B) X is nitrogen dioxide gas (NO2) that has evolved as brown, choking fumes.
(C) A thermal decomposition reaction.
(D) Nitrogen dioxide dissolves in water to form an acidic solution because it is an oxide of non-metal. Therefore, the pH level of this solution is less than 7.

Question. (A) Arrange the following metals in the increasing order of their reactivities:
Copper, Zinc, Aluminium and Iron
List two observations you would record in your notebook

minutes after adding iron filings to copper sulphate solution. 
Answer : (A) Metals arranged in increasing order of reactivity: Cu<Fe< Zn<Al
(B) When iron filings are added to copper sulphate solution we will observe:
(1) Colour of the solution changes from blue to green.
(2) Deposition of brown colour on iron filings.

(B) X is nitrogen dioxide gas (NO2) that has evolved as brown, choking fumes.
(C) A thermal decomposition reaction.
(D) Nitrogen dioxide dissolves in water to form an acidic solution because it is an oxide of non-metal. Therefore, the pH level of this solution is less than 7.

Question. What happens when zinc granules are treated with dilute solution of H2SO4, HCl, HNO3, NaCl and NaOH. Also write their chemical equations, if reaction occurs.
Answer : Dilute H2SO4: Zn reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas. 

Dilute HCl: Zn reacts with HCl and form zinc chloride with the evolution of hydrogen gas. 

Dilute HNO3: Reaction with dilute HNO3 is different as compared to other acids because nitric acid is an oxidizing agent and it oxidizes H2 gas, evolved to H2O.
4Zn(s) + 10HNO3(aq) → 4Zn(NO3)2(aq) + 5H2O(l) + N2O(g)

Zinc reacts with cold and dilute nitric acid and forms zinc nitrate, water and nitric oxide. NaCI solution: No reaction will take place as sodium is more reactive than Zn.
Zn(s) + NaCl(aq) → No reaction

NaOH solution: Zinc reacts with NaOH solution and forms sodium zincate and hydrogen gas.
Zn(s) + 2NaOH(aq) → Na2ZnO2(aq) + H2(g)
Sodium zincate

Question. (A) Design an activity to demonstrate the decomposition reaction of lead nitrate.
(B) Draw labelled diagram of the experimental set-up. List two main observations.
(C) Write balanced chemical equation for the reaction stating the physical state of the reactant and the products.
Answer : (A) Take a small amount of lead nitrate powder in a boiling tube. Hold the boiling tube with a pair of tongs and heat it over the flame first gently and then strongly.
(B) Labeled diagram of the experimental setup:    

(1) We observe emission of brown fumes of a gas which is nitrogen dioxide.
(2) The white colour of lead nitrate changes to yellow colour as lead oxide is formed.
(3) Balanced equation: 2Pb(NO3)2(s) → 2PbO(s) + 4NO2(g) + O2(g)

Question.(A) Hydrous ferrous sulphate crystals are heated in a boiling tube for a few seconds. Water droplets are seen in the inner sides of test tube and the colour of the crystals changes. On continuous heating, a colourless gas X with the smell of burning sulphur is evolved and a residue Y is obtained.
(i) What is the colour of the crystals before and after mild heating?
(ii) Identify gas X and the residue Y formed.
(iii) Write a balanced chemical equation for the above reaction.
(B) Write balanced chemical equations for the following reactions:
(i) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(ii) Sodium metal reacts with water to give sodium hydroxide and hydrogen gas. 
Answer : (A) (i) The ferrous sulphate crystals are hydrated crystals (green color). When heated in a boiling tube, the hydrated ferrous crystals turn anhydrous and change their colour to white. (ii) When heated more strongly, the anhydrous crystals decompose and result in the formation of ferric oxide as residue. The gases obtained are sulphur dioxide and sulphur trioxide.
(iii) The chemical reaction is:   

Question. Answer the following:
(A) Define oxidizing agent.
(B) Translate the following statements into chemical equations and balance them.
(i) Hydrogen gas combines with nitrogen to form ammonia.
(ii) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(iii) Potassium metal reacts with water to give potassium hydroxide and Hydrogen gas.

Answer : (A) Oxidizing agent: It is a substance which loses oxygen or gains hydrogen.
For example in the given reaction:
CuO + H2 → Cu + H2O
CuO has given oxygen, hence it is oxidizing agent.
(B) (i) Hydrogen gas combines with nitrogen to form ammonia.
H2 + N2 → NH3
Balanced:
3H2(g) + N2(g) → 2NH3(g)
(ii) Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
H2S + O2 → H2O + SO2
Balanced:
2H2S(g) + 3O2(g) → 2H2O(l) +
2SO2(g)
(iii) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
K + H2O → KOH + H2
Balanced:
2K(s) + 2H2O(l) →2KOH(s) + H2(g)

Question. 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 containers can these solutions be kept?
Answer : (A) Reactions of Copper with:
(1) Dilute HCI: Copper exhibits no reaction with HCl, so it can be stored in the copper container.
(2) Dilute HNO3: Nitric acid acts as a strong oxidizing agent and reacts with copper vessel. With dilute nitric acid, copper metal forms copper nitrate with nitric oxide and water, so dilute nitric acid cannot be stored in the copper container.
Cu(s) + 8HNO3(dil) → 3Cu(NO3)2(aq) + 2NO(g) + 4H2O(l)
(3) ZnCl2: Since Cu metal is less reactive than Zn, it cannot displace Zn from its compounds and there will be no reaction. Hence, zinc chloride can be stored in the copper container.
(4) H2O: There is no reaction between water and copper metal at room temperature, so water can be stored in a copper container.

(B) Reactions of Aluminium with: 
(1) Dilute HCI: Al reacts with dilute HCI and forms aluminium chloride with hydrogen gas evolved, so it cannot be stored in the aluminium container.
2Al + 6HCl → 2AlCl3 + 3H2
(2) Dilute HNO3: Nitric acid is an oxidizing agent and in its presence, aluminium metal gets oxidized to form a layer of Al2O3, and forms a protective layer of oxide, so it will not react further. Hence,dilute nitric acid can be stored in the aluminium container.
(3) ZnCl2: Aluminium, being more reactive than zinc, can displace zinc ion from the solution. It readily reacts with zinc chloride and forms aluminium chloride with zinc metal.
2Al + 3ZnCl2 → 2AlCl3 + 3Zn
Hence, it cannot be stored in the aluminium container.
(4) H2O: At room temperature, there will be no reaction between aluminium metal and hot or cold water, so it can be stored in the aluminium container.
Aluminium is attacked by steam to form aluminium oxide and hydrogen.
2Al(s) + 3H2O(g) → Al2Cl3(s) + 3H2(g)

Question. Identify the type of reaction 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) When zinc reacts with silver nitrate solution, it forms zinc nitrate and silver.
Zn (s) + 2AgNO3 (aq) → Zn(NO3)2 (aq) + 2Ag(s)
This is a displacement reaction which occurs because zinc is more reactive than silver due to which zinc displaces silver from silver nitrate solution to give to zinc nitrate and silver.
(B) When potassium iodide is added to lead nitrate solution, a yellow precipitate of lead iodide is formed alongwith potassium nitrate solution.
Pb(NO3)2 (aq) + 2KI (aq) → PbI2 (s) + 2KNO3 (aq)
This is a double displacement reaction in which two compounds react by an exchange of ions to form two new compounds. This is also called precipitation reaction as an insoluble solid (precipitate) is formed.

Question. (A) Classify the following reactions into different types:
(i) AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
(ii) CaO(s) + H2O(l) → Ca(OH)2(aq)
(iii) 2KClO3(s) → 2KCl(aq) + 3O2(g)
(iv) Zn + CuSO4 → ZnSO4 + Cu
(B) Translate the following statement into a balanced chemical equation:
‘‘Barium chloride reacts with aluminium sulphate to give aluminium chloride and barium sulphate.’’
Answer : (A) Type of reactions are:
(i) Double Displacement reaction.
(ii) Combination reaction
(iii) Decomposition reaction
(iv) Displacement reaction
(B) The balanced chemical equation for the reaction between barium chloride and aluminium sulphate to give aluminium chloride and barium sulphate.
3BaCl2(aq) + Al2(SO4)3(aq) → 3BaSO4(s) + 2AlCl3(aq)

Question. (A) Write the balanced chemical equations for the following reactions:
(i) Zinc + Silver nitrate → Zinc nitrate + Silver
(ii) Aluminium + Copper chloride → Aluminium chloride + Copper
(B) Why is respiration considered an exothermic reaction? Explain.
(C) Why should magensium ribbon be cleared before burning in air?

Answer : (A) Balanced chemical equations for the following reactions:
(i) Zinc + Silver nitrate → Zinc nitrate + Silver
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag

(ii) Aluminium + Copper chloride →
    Aluminium chloride + Copper
2Al + 3CuCl2 → 2AlCl3 + 3Cu
(B) Respiration is considered as an exothermic reaction because in respiration oxidation of glucose takes place which produces large amount of energy.
This is shown in following chemical equation:
C6H12O6 + 6O2 → 6CO2 + 6H2O
                                        + Energy
(C) Magnesium is a reactive metal. When kept exposed in air for a long time, a layer of MgO (magnesium oxide) is formed on the surface of metal. The oxide layer does not burn when flame is brought in contact with metal.

Question. (A) What is a double displacement reaction?
Explain with an example.
(B) A small amount of quick lime is added to water in a beaker.
(i) Name and define the type of reaction that has taken place.
(ii) Write balanced chemical equation for the above reaction and the chemical name of the product formed.
(iii) List two main observations of this reaction. 
Answer : (A) Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions.
Example: When we mix sodium sulphate solution and barium chloride solution, a white precipitate of barium sulphate is formed by the reaction of SO4
2– and Ba2+.
The other product formed is sodium chloride which remains in the solution..
The equation for the reaction taking place is:
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)

(B) (i) Type of chemical reaction taking place when water is added to quick lime or calcium oxide is combination reaction. Combination reactions are those reactions in which two or more reactants combine to form a single product.
(ii) Equation of the reaction taking place is:
CaO(s) + H2O (l) → Ca(OH)2 (aq) + Heat Product formed is calcium hydroxide or slaked lime.
(iii) Two observations are:
(1) The reaction of quicklime with water is very vigorous.
(2) It is an exothermic reaction as a large amount of heat is produced.

Question. Give characteristic tests for the following gases:
(A) CO2
(B) SO2
(C) O2
(D) H2 
Answer : (A) CO2 gas: When CO2 gas is passed through lime water, it forms insoluble calcium carbonate which turns the solution milky.
This is called as lime water test.
Ca(OH)2(aq) + CO2 → CaCO3(s) + H2O
Lime water Carbon Calcium Water (Colourless) dioxide carbonate (White) The solution becomes clear in the excess of CO2 because of the formation of soluble calcium bicarbonate.

(B) SO2 gas: Due to its acidic nature, sulphur dioxide gas turns moist litmus paper from blue to red. Sulphur dioxide gas when passed through acidic dichromate solution (orange in colour) turns it to green because sulphur dioxide is a strong reducing agent.

K2Cr2O7 + 3SO2 + H2SO4 → Cr2(SO4)3 + K2SO4 + H2O
Potassium                          Chromium
dichromate                         sulphate

Sulphur dioxide (SO2) 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

(C) O2 gas: 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. Oxygen gas burns brightly with a wooden splinter, which proves the combustible nature of oxygen gas.

C + O2 → CO2 + Heat + Light

(D) H2 gas: Hydrogen (H2) gas burns with a pop sound when a burning candle is brought near it.

Question. What is observed after about 1 hour of adding the strips of copper and aluminium separately to ferrous sulphate solution filled in two beakers? Name the reaction if any change in colour is noticed. Also, write chemical equation for the reaction.
Answer : When strip of copper is added to ferrous sulphate solution taken in a beaker, no change is observed. On adding a strip of aluminium to ferrous sulphate solution taken in another beaker, we observe that the greenish colour of ferrous sulphate solution starts fading and it becomes colourless after about an hour. Reaction taking place is Displacement reaction. Equation of the reaction taking place is:

2Al + 3FeSO4 → 3Fe + Al2(SO4)3

Question. A student wants to study a decomposition reaction by taking ferrous sulphate crystals.
Write two precautions he must observe while performing the experiment. 
Answer : Precautions to be observed for studying decomposition reaction:
(1) Use only hard boiling test tube.
(2) Hold the test tube in an inclined position away from your body and do not point the mouth of the boiling tube at your neighbours or yourself.
(3) Use a pair of tongs for holding the boiling tube while heating and don’t touch the boiling tube with your bare hands.

(4) Do not inhale the gases emitted directly, it should be inhaled by wafting gently towards your nose. (Any 2 of 4 can be written to get full marks)

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 : When 2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for sometime, we will observe that silver chloride turns grey. This is because of the decomposition of silver chloride into silver and chlorine by sunlight. The balanced chemical reaction involved is:

Question. 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? 
Answer : (A) Balanced chemical equation:
Na2SO3(aq) + BaCl2(aq) → BaSO3(s)  + 2NaCl(aq)

(B) This reaction is also known as double displacement reaction. 
(C) BaSO3 is a salt of a weak acid (H2SO3).
Therefore, a dilute acid such as HCl decomposes barium sulphite to produce sulphur dioxide gas, which has the smell of burning sulphur.
BaSO3(s) + 2HCl(aq) → BaCl2 + H2O + SO2(g)
White ppt.
BaCl2 is soluble in water; hence, white precipitate disappears.

Question. When potassium iodide solution is added to a solution of lead (II) nitrate in a test tube, a precipitate is formed.
(A) What is the colour of this precipitate? Name the compound precipitated.
(B) Write the balanced chemical equation for this reaction.
(C) List two types of reactions in which this reaction can be placed.
Answer : (A) Colour of precipitate when potassium iodide solution is added to a solution of lead (II) nitrate is yellow and compound precipitated is lead iodide.
(B) Balanced chemical equation for the reaction taking place is
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3
                                                        (aq)
(C) This is a Double displacement reaction and also a precipitation reaction.

Question. A student mixes sodium sulphate powder in barium chloride powder. What change would the student observe on mixing the two powders? Justify your answer and explain how he can obtain the desired change.
Answer : No reaction takes place when sodium sulphate and barium chloride powders are mixed as no ions are formed in their solid state. He can get the desired change by taking aqueous solutions of both the reactants as ionic compounds dissociate into ions only in presence of water and then exchange of ions takes place. The equation for the chemical reaction taking place is:

BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl
                                                               (aq)

Question. While Abhi was about to burn magnesium ribbon in the chemistry laboratory, the teacher asked him to clean the ribbon with a sandpaper before burning it. What could be the reason for the above instruction by the teacher? After burning the magnesium ribbon, Abhi obtained a white coloured residue. Name this residue. What type of chemical reaction has occurred? Write a balanced chemical equation to explain the reaction.
Answer : When magnesium is kept in the open, the oxygen from the atmosphere reacts with it. This results in the formation of a protective oxide layer on top of magnesium to form magnesium oxide. When the magnesium ribbon is rubbed using sandpaper, the layer of oxide is removed, resulting in exposing the magnesium underneath. When magnesium ribbon is burnt in air, it results in the formation of magnesium oxide. This is a white coloured substance that is obtained as residue (combination reaction).

2Mg + O2 → 2MgO

Question. (A) In the following reaction:
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
Identify the oxidant and reductant.

(B) Give reasons:
(i) Antioxidants are added to foods containing fats and oils. 
(ii) White silver chloride turns grey in sunlight.

Answer : (A) (1) MnO2 is an oxidant/oxidizing agent; as MnO2 undergoes reduction.
(2) HCl is a reductant/ reducing agent.
HCl is getting oxidized.

(B) (i) To prevent rancidity of fats and oils.
(ii) Silver chloride undergoes decomposition when exposed to sunlight to form silver and chlorine. Silver is grey in colour.

2AgCl  Sunlight→ 2Ag(s) + Cl2
                             grey  (any one)

Question. What would you observe on adding zinc granules to freshly prepared ferrous sulphate solution? Give reason for your answer.
Answer : The green colour of the solution changes to queyish – white On there is a displacement who realtion occurrami Zine being more reactive than ison displaced it from to al solution.

Question. A pale green solution of ferrous sulphate was taken in four separate test tubes marked I, II, III and IV. Pieces of Cu, Zn and Al were dropped in test tubes II, III and IV respectively.
In which case(s)
(A) the colour of ferrous sulphate solution will match with the colour in test tube (I)? Give reason.
(B) the colour of ferrous sulphate solution will fade and black mass will be deposited on the surface of the metal?
Answer : (A) In test tube (II) as copper is less reactive
than iron, so cannot displace Fe from its salt solution.
(B) In test tubes (III) & (IV) both, because they both, i.e. Zn and Al are more reactive than Fe and will displace Fe from FeSO4.

Question. Write a balanced equation for the following chemical reactions:
(A) Hydrogen + Chloride → Hydrogen chloride
(B) Zinc + Silver nitrate → Zinc nitrate + Silver

Answer : (A) Hydrogen + Chloride → Hydrogen chloride
H2 + Cl2 → 2HCl
(B) Zinc + Silver nitrate → Zinc nitrate + Silver
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag

Question. Write down the balanced chemical equation for the following:
(A) Silver chloride is decomposed in presence of sunlight to give silver and chlorine gas.
(B) Calcium oxide reacts with water to give lime water.
(C) Sodium hydroxide reacts with hydrochloric acid to give sodium chloride and water.
(D) Dilute hydrochloric acid is added to copper oxide to give green coloured copper chloride and water.
(E) Solution of barium chloride and sodium sulphate in water reacts to give insoluble barium sulphate and solution of sodium chloride.

Answer : (A) Silver chloride is decomposed in presence of sunlight to give silver and chlorine gas.
2AgCl(s) → 2Ag(s) + Cl2(g)
(B) Calcium oxide reacts with water to give lime water. 
CaO(s) + H2O(l) → Ca(OH)2
(C) Sodium hydroxide reacts with hydrochloric acid to give sodium chloride and water.
NaOH(s) + HCl(aq) → NaCl(aq) + H2O(l)
(D) Dil. hydrochloric acid is added to copper oxide to give green coloured copper chloride and water.
CuO + 2HCl(dil.) → CuCl2 + H2O
(E) Solution of barium chloride and sodium sulphate in water reacts to give insoluble barium sulphate and solution of sodium chloride.
BaCl2(aq) + Na2SO4 → BaSO4 + 2NaCl(aq)

chemical reactions and equations class 10 notes