Chemical Reactions and Equations: Important Questions and Explanation

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Multiple Choice Type Questions [1 Mark]

Question: Why is the magnesium ribbon rubbed with sandpaper before being burnt in the air?

(a) For removing the moisture from the surface of the ribbon.

(b) For removing the magnesium carbonate layer from the surface of the ribbon

(c) For making the surface of the ribbon shinier

(d) For removing the layer of magnesium oxide from the surface of the ribbon

Ans: (d) For removing the layer of magnesium oxide from the surface of the ribbon.

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Question: The reaction H₂+Cl₂ → 2HCl represents:

(a) Reduction

(b) Oxidation

(c) Decomposition

(d) Combination

Ans: (d) Combination

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Question: Name the gas that is helpful in the storage of fat and oil-containing foods for a longer period: 

(a) Carbon dioxide

(b) Oxygen

(c) Nitrogen

(d) Neon

Ans: (c) Nitrogen

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Question: The substance which can oxidize itself and reduce others is:

(a) Oxidising and Reducing Agent

(b) Oxidising agent

(c) Reducing agent

(d) None of these

Ans: (c) Reducing agent

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Question: Heat evolves in which type of reaction?

(a) During Displacement Reaction

(b) During Endothermic Reaction

(c) During Exothermic Reaction

(d) During Combination Reaction

Ans: (c) During Exothermic Reaction

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Question: Copper displaces which metal from its salt solution:

(a) AgNO₃

(b) FeSO₄

(c) ZnSO₄

(d) NiSO₄

Ans: (a) AgNO₃

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Question: Chemical equations satisfies the law of:

(a) Conservation of motion

(b) Conservation of momentum

(c) Conservation of energy

(d) Conservation of mass

Ans: (d) Conservation of mass

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Question: What’s the ratio in which hydrogen and oxygen are available in water by volume?

(a) 1:2

(b) 1:1

(c) 2:1

(d) 1:8

Ans: (c) 2:1

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Question: Name the chemical reaction that takes place when electricity is passed through water.

(a) Displacement

(b) Combination

(c) Decomposition

(d) Double displacement

Ans: (c) Decomposition

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Question: Pb + CuCl₂ → PbCl₂ + Cu

The above reaction is an example of:

(a) Combination reaction

(b) Double displacement reaction

(c) Decomposition reaction

(d) Displacement reaction

Ans: (d) Displacement reaction

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Very Short Answer Type Questions [1 Mark]

Question: State the reason for the combustion of Liquefied Petroleum Gas (LPG) being a chemical change. 

Ans: Combustion of Liquefied Petroleum Gas (LPG) is a Chemical Change because it is an irreversible reaction which means the substances formed cannot be turned back into LPG. The new products Carbon Dioxide and Water Vapour are formed and a lot of heat is also produced during the reaction. 

Question: Identify the mistake and balance the following equation.

Mg + O →MgO 

Ans: Here, Oxygen should be in molecular form (O₂) as oxygen exists as bimolecular gas 

2Mg + O₂ → 2MgO

Question: Potassium chlorate (KCIO₃), after heated, results in oxygen and potassium chloride. State the balanced equation for this reaction. 

Ans: 2KClO₃(s) → 2KCl(s) + 3O₂(g)

2 molecules of Potassium chlorate (KClO₃) on heating form 2 molecules of potassium chloride and 3 molecules of oxygen.

Question: After heating copper(II) nitrate, blue colored powder in a boiling tube, copper oxide (black), oxygen gas, and a brown gas 'X' is formed. Can you Identify the brown gas 'X'?

Ans: The equation of the reaction after balancing it is-

2Cu(NO₃)₂(S) → 2CuO(S) + 4NO₂(g) + O₂(g)

So, The "X" is nitrogen dioxide(brown).

Question : Write the chemical equation for : an aq. solution of ferrous sulphate reacting with an aq. solution of sodium hydroxide to form a ppt. of ferrous hydroxide and sodium sulphate remaining in solution.

Also, Balance the equation. 

Ans: FeSO₄(aq) + 2NaOH(aq) → Fe(OH)₂(s) + Na₂SO₄(aq)

Question: Balance this chemical reaction: 

Pb(NO₃)₂ → PbO + NO₂ + O₂

Ans: 2Pb(NO₃)₂ → 2PBO + 4NO₂ + O₂

Question: Give an example of a combination exothermic reaction.

Ans: When quicklime(CaO) reacts with water, slaked lime [Ca(OH)₂] is formed. A heavy amount of heat is released during the reaction. So, this reaction is exothermic.

CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat

Question: State the reason: 

Copper powder that is heated becomes black when air is passed on it.

Ans: When air is passed on brown colored copper powder, it turns into black color due to the formation of black Copper Oxide. 

2Cu(s) + O₂(g) → 2CuO(s)

Question: Can you identify the differences between these two types of reactions? 

AgNO₃ + HCl → AgCl + HNO₃ 

Mg + 2HCl → MgCl₂ + H₂ 

Ans: The first one is Double Displacement Reaction whereas the second one is displacement reaction. 

Question: State the reason behind keeping hydrogen peroxide in colored bottles.

Ans: Hydrogen peroxide is a very reactive chemical that can react with Light or heat to produce Water. It is highly unstable and slowly decomposes when kept in the presence of Light. So, to prevent this Hydrogen Peroxide is kept in colored bottles. 

Question: Observe these reactions: 

(i) Fe + CuSO₄ → FeSO₄ + Cu 

(ii) Cu + FeSO₄ → CuSO₄ + Fe 

Question: Which reactions can take place and why? 

Ans: The first reaction will take place because Fe (iron) is more reactive than Cu (copper), so it can displace Cu from its compound (CuSO₄). On the other hand, copper (Cu) cannot displace iron (Fe), so the second reaction will not take place.

Question: Suggest one example of a reaction that is a double displacement reaction and also a precipitation reaction.

Ans: AgNO₃(aq)+NaCl(aq)→AgCl(s)↓(ppt.)+NaNO₃(aq)

Question: Digestion of food in our body is which type of reaction? 

Ans: Decomposition reaction takes place during the digestion of food in our body. 

Question: At the moment when the products are highly soluble or highly ionised, Can a double displacement reaction take place? 

Ans: No, Double displacement reaction cannot take place in this situation as it takes place only when there’s a formation of a slightly soluble salt after the reaction.

Question: Name the oxidising and reducing agent in this reaction: 2H₂S + SO₂ → 2H₂O + 3S ↓ 

Ans: SO₂ is the Oxidising Agent and 2H₂S is the Reducing Agent.

Dowload :  Class 10^th Science Sample paper 2021

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Short Answer Type Questions [3 Marks] 

Question: Write the chemical equations for these and also balance them: 

1. A Precipitate of lead sulphate and nitric acid is produced when Lead Nitrate and Sulphuric Acid react. 
2. Magnesium being burnt in the availability of nitrogen and forming magnesium nitride. 
3. To produce aluminium chloride and hydrogen gas, an Aluminium metal strip is added to hydrochloric acid.

Ans:

1. Pb(NO₃)₂(aq) + H₂SO₄(aq) → PbSO₄ (s) + 2HNO₃ (aq)
2. 3Mg(s) + N₂(g) → Mg₃N₂(s)
3. 2Al(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂(g)

Question: State an example of thermal decomposition and photochemical decomposition reactions. Also, Write balanced equations for them.

Ans: Calcium carbonate decomposing to produce calcium oxide and carbon dioxide is an example of a Thermal Decomposition reaction. 

CaCO₃(s) → CaO(s) + CO₂(g)

When the silver chloride (AgCl) is kept in sunlight, it decomposes into silver and chlorine. It is a Photochemical Decomposition reaction. 

2AgCl(s) → 2Ag(s) + Cl₂(g)

Question: Write the balanced chemical equations and also identify the type of reaction in the Following :

(i) Nitrogen gas reacts with hydrogen in the presence of a catalyst at 773 K temperature to form ammonia gas. 

(ii) Sodium hydroxide solution is reacted with acetic acid to produce sodium acetate and water. 

(iii) Ethene being burnt in the availability of oxygen to form carbon dioxide, water and releases heat and light. 

Ans: (i) N₂ + 3H₂ + Catalyst/773 K → 2NH₃. 

It is a Combination Reaction. 

(ii) NaOH + CH₃COOH → CH₃COONa + H₂O 

 It is a Double Displacement Reaction. 

(iii) C₂H₄ + 3O₂ → 2CO₂ + 2H₂O + Heat + Light. 

It is a Redox reaction. 

Question: Name the type of chemical reaction taking place in the following equation:

(i) CaO + H₂O → Ca(OH)₂ 

(ii) 3BaCl₂ + Al₂(SO₄)₃ → 2AICl₃ + 3BaSO₄ 

(iii) 2FeSO₄ → Fe₂O₃+ SO₂ + SO₃

Ans: (i) Combination reaction.

(ii) Double displacement reaction.

(iii) Decomposition reaction.

Question: Pen down the chemical equations and then balance the equations for: 

(i) Phosphorus Pentoxide being produced when Phosphorus is burnt in oxygen.

(ii) Aluminium metal replacing iron from ferric oxide, Fe₂O₃, producing aluminium oxide and iron. 

(iii) To produce carbon dioxide and sulphur dioxide, Carbon disulphide is burnt in the air. 

Ans: (i) P₄ + 5O₂ → 2P₂O₅

(ii) 2Al + Fe₂O₃ → Al₂O₃+ 2Fe

(iii) CS₂ + 3O₂ → CO₂ + 2SO₂

Question: Identify the oxidant in the following reactions. 

(i) Pb₃O₄ + 8HCL → 3PbCl₂ + Cl₂ + 4H₂O 

(ii) 2Mg + O₂ → 2MgO 

(iii) CuSO₄ + Zn → Cu + ZnSO₄

(iv) V₂O₅ + 5Ca → 2V + 5CaO 

(v) 3Fe + 4H₂O → Fe₃O₄ + 4H₂ 

(vi) CuO + H₂ → Cu + H₂O 

Ans: (i) Pb₃O₄ gets reduced to PbCl₂ and oxidises HCl to Cl₂

(ii) O₂ is an Oxidant as it Oxidises Mg to MgO.

(iii) CuSO₄ is an Oxidant as it oxidises Zn to ZnSO₄.

(iv) V₂O₅ is an Oxidant as it oxidises Ca to CaO

(v) H₂O is an Oxidant. Iron Metal is Oxidised. 

(vi) CuO is an Oxidant. CuO is reduced to Cu while H₂ gets oxidised to H₂O.

Question: Identify the type of reaction in these examples: 

(i) Na₂SO₄(ag) + BaCl₂(aq) → BaSO₄(s) + NaCl(ag) 

(ii) Fe(s) + CuSO₄(aq) →FeSO₄(aq) + Cu(s) 

(iii) 2H₂(g) + O₂(g) →2H₂O(l) 

Ans: (i) Double Displacement Reaction

(ii) Displacement Reaction

(iii) Combination Reaction

Question: These observations were made when some metals were treated with dilute hydrochloric acid : 

(i) Silver Metal does not show any Change. 

(ii) The temperature of the reaction mixture increases when aluminium is being added. 

(iii) The reaction of sodium metal is seen to be highly explosive. 

(iv) Some bubbles of gas are noticed when lead (Pb) is reacted with the acid.

Explain these observations stating suitable reasons. 

Ans: (i) This happens because silver lies below hydrogen in the reactivity series and cannot displace hydrogen when reacted with acid.

(ii) The reaction of Aluminium with dilute HCl is exothermic, i.e. heat is evolved in the reaction. So, the temperature of the reaction mixture increases.

(iii) Sodium is a highly reactive metal. It reacts explosively with hydrochloric acid to form sodium chloride and hydrogen with the evolution of heat too. H2 Gas produced catches fire immediately. 

(iv) Lead lies just above the hydrogen in the activity series of metals. So, it is a little more reactive and displaces hydrogen from acid very slowly and to a small extent. Therefore, only bubbles of H₂ are seen to evolve.

Pb(s) + 2HCl(Aq) → PbCl₂ + H₂(g)

Question: A White Compound X is produced accompanied by emission of light when A magnesium ribbon is burnt in oxygen. If we keep the burning ribbon in an atmosphere of nitrogen, it keeps on Burning and forms a compound Y. 

(i) Pen down the chemical formula of X and Y. 

(ii) Also show the balanced chemical equation when X is dissolved in water. 

Ans: (i) Magnesium ribbon burns in oxygen(O₂) to form magnesium oxide (MgO). 

2Mg + O₂ → 2MgO

Therefore X is MgO.

Burning magnesium ribbon reacts with nitrogen(N₂) to form magnesium nitride(Mg₃N₂).

3Mg + N₂ → Mg₃N₂

Therefore, Y is Mg₃N₂

(ii) If X is dissolved in water, it produces magnesium hydroxide.

MgO(s) + H₂O(l) → Mg(OH)₂(Aq.)

Question: (i) What do you notice in a test tube when a potassium iodide solution is added to a lead nitrate solution?

(ii) What type of reaction is this? 

(iii) Also write a balanced chemical equation.

Ans: (i) A precipitate of lead iodide (PbI₂) Is formed that is Yellow.

(ii) Precipitation Reaction/Double displacement reaction.

(iii) Pb(NO₃)₂(aq.) + 2KI(aq.) → PbI₂(s) + 2KNO₃(aq.)

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Long Answer Type Questions [5 Marks] 

Question: Observe the below Equation and then answer the questions

CuO + H₂ → Cu + H₂O

(i) Which Substance is getting oxidised. 

(ii) Which Substance is getting reduced. 

(ii) Which is the oxidising agent. 

(iv) Which is the reducing agent. 

(v) What type of reaction is this? 

Ans: (i) The substance getting oxidised is H₂. 

(ii) The substance getting reduced is CuO. 

(iii) CuO is the oxidising agent. 

(iv) H₂ is the reducing agent. 

(v)This is a redox reaction as oxidation and reduction is taking place.

Question:.You have: 

(a) Quick lime

(b) Cu powder

(c) Bacl₂

(d) CuSO₄ solution

(e) Ferrous sulphate crystal

(f) Iron Nails

Write at least 5 reactions that can take place from these substances

Ans: (i) Fe + CuSO₄→FeSO₄ +Cu

(ii) CuSO₄ + BaCl₂→BaSO₄ + CuCl₂

(iii) CaO+ FeSO₄ → CaSO₄ + Fe₂O₃

(iv) BaCl₂+CaO→BaO+CaCl₂

(v) BaCl₂+FeSO₄→BaSO₄+FeCl₂

Question: Give the Characteristic tests for the following gases: (i) H₂ (ii) SO₂ (iii) O₂ (iv) CO₂

Ans: (i) H₂ gas produces a pop sound when a burning candle is brought near it.

(ii) When SO₂ gas is passed through acidic potassium permanganate solution (purple), SO₂ being a Strong Reducing Agent Changes it to colorless. 

2KMnO₄+ 2H₂O+ 5SO₂ → K₂SO₄+ 2MnSO₄+ 2H₂SO₄

(iii) When we bring a burning candle near the test tube that contains the reaction mixture. The intensity of the flame rises as oxygen(O₂) supports burning.

(iv) When CO₂ gas is passed through lime water, it turns milky because insoluble calcium carbonate is formed.

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Question: Show through an experiment that hydrogen and oxygen are released when electric current is passed through water. 

Ans: 

(i) Take a plastic vessel and make two holes at the bottom. Set rubber stoppers and Insert carbon electrodes. Also, make a Connection to these electrodes with a 6-12 volt battery and a switch. 

(ii) Fill the vessel with water and immerse the electrodes. Also, add some drops of dilute sulphuric acid.

(iii) Take two graduated test tubes and fill them with water. Then put them in an inverted Position over the two carbon electrodes. 

(v) Switch on the current. 

(vi)Wait for some time and you will notice the bubbles at both electrodes. These bubbles displace water in the graduated tubes. 

(vii) Remove the test tubes when they are filled with gases. 

(viii) Test these gases by bringing a burning candle to the mouth of test tubes. When the candle is brought close to the mouth of one test tube, the intensity of flame rises and when it is brought close to the mouth of another test tube, the gas burns with a pop. Oxygen is the only common gas that increases the intensity of the flame and hydrogen gas burns with a pop.

Question: ‘Iron is more reactive than copper’. Justify the statement with the help of an experiment. 

Ans: A more reactive metal displaces the less reactive metal. With the help of the Reactivity Series of Metals, We can say that Iron is More reactive than Copper and Can displace Copper Sulphate from its Salts. 

(i) Take a solution of Copper Sulphate in a Test Tube.

(ii) Dip an iron nail in that Solution.

(iv)Notice the Reaction after some time.

You’ll notice that the reaction has occurred in iron nail and copper sulphate solution. The Initial Blue Color of the Solution turns to light green. Iron takes the sulphate away from copper. A brown coating can be seen on the iron nail. The color change is due to the formation of Iron Sulphate Solution which is light green. 

Copper sulphate + Iron → Iron sulphate + Copper

Now, We can say that more reactive metal i.e. iron has displaced less reactive metal i.e, Copper, from Copper Sulphate Solution. 

Question: Explain these terms with at least one example each.

1. Corrosion
2. Rancidity

Ans: Corrosion: It is the natural process in which metals are slowly transformed into undesirable substances by the action of water, air moisture, or chemicals. Rusting of iron is an example of corrosion where iron is eaten up by the action of air and moisture and a reddish-brown coating of iron oxide is formed.

2Fe+3H₂O→Fe₂O₃+3H₂

Rancidity: This is the process in which the substance containing oils and fats that are exposed to air gets oxidised and becomes rancid due to which their smell, taste, and color change. Change in smell and taste of butter due to exposure to air for a long time is an example of Rancidity. 

Question: Pen down the Chemical equation when zinc granules are treated with a dilute solution of HNO₃, H₂SO₄, NaCl, HCl, and NaOH?

Ans: The reaction of Zn granules with

(i) Dilute HNO₃ 

4Zn(s) + 10HNO₃(aq) → 4Zn(NO₃)₂(aq) + 5O₂(l) + N₂O(g)

(ii) Dilute H₂SO₄

Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g) 

(iii) NaCl solution

Zn(s) + NaCl(aq) → No reaction.

(iv) Dilute HCl 

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g) 

(v) NaOH solution  

Zn(s) + 2NaOH(Aq.) → Na₂ZnO₂(Aq.) + H₂(g)

Question: (i) Crystals of copper sulphate are being heated for a small time in a beaker. 

(a) What’s the color of copper sulphate crystals before and after they have been heated? 

(b) Name the source of liquid droplets observed on the inner upper side of the test tube while heating? 

(ii) A metal 'X' is dipped in an Aq. solution of aluminium sulphate and no reaction is seen whereas when it is dipped in an aq. solution of ferrous sulphate, the pale green solution changes to colorless. Can You Identify the metal 'X' with reason? 

Ans: (i) (a) The copper sulphate crystals Color before heating is blue and changes to white after heating. 

(b) The liquid droplets are the water droplets. The source of these liquid droplets is the water of crystallisation of hydrated copper sulphate crystals (CuSO₄.5H₂O). 

(ii) When metal ‘X' is dropped in an aqueous solution of aluminium sulphate, no reaction is noticed which signifies it is less reactive than aluminium. But when it is dropped in iron sulphate solution, the initial pale green solution turns colorless, so 'X' is more reactive than iron and thus displaces it from its solution. 

So, 'X' must be zinc. 

Zn(s) + FeSO₄(aq) → ZnSO₄(aq) + Fe(s)

Question: (a) Justify combustion reaction being an oxidation reaction.

(b) State the reason behind silver not evolving hydrogen on reacting with dilute sulphuric acid?

(c) State the method to test that the hydrogen gas is evolved in a reaction. 

Ans: (a) Yes, combustion is an example of an oxidation reaction because when combustion takes place, oxygen is added up to the thing which is burning, this burning can only occur in the presence of Oxygen. 

(b) Silver is less reactive than hydrogen and so placed below hydrogen in the reactivity series. Less reactive Metals than hydrogen cannot displace hydrogen from acids. So, Silver does not displace H₂ in dilute sulphuric acid solution. When silver metal is added to dilute sulphuric acid, no reaction takes place.

(c) Pop test is a common test used to check the evolution of hydrogen gas in any Reaction. When a candle is brought near the hydrogen gas, it produces a pop sound. Moreover, it Produces a pungent and irritating smell when evolved.

Question: Define neutralisation reactions. State the reason behind being named so and Give one example of this reaction. 

Ans: The reaction between an acid and bases is called a neutralization reaction.

The reaction produces salt and water. It is named so because the Acid and Base neutralize each other to form Water and Salt. The H+ ion and H- ions react to form H₂O. 

Acid + Base → Salt + Water

Example: Formation of Sodium Chloride (Common Salt):

HCl + NaOH → NaCl + H₂O

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