Question 1

Question 1Which of the statements about the reaction below are incorrect?2PbO (s) + C (s) ⟶ 2Pb (s) + CO2 (g)(a) Lead is getting reduced.(b) Carbon dioxide is getting oxidised.(c) Carbon is getting oxidised.(d) Lead oxide is getting reduced(a) and (b)(a) and (c)(a), (b) and (c)all

Accepted Answer

(a) and (b)Reason — Carbon is getting oxidised to carbon dioxide due to gain of oxygen and lead oxide is getting reduced to lead as oxygen is lost.

Question 2

Question 2Fe2O3 + 2Al ⟶ Al2O3 + 2FeThe above reaction is an example of acombination reaction.double displacement reaction.decomposition reaction.displacement reaction.

Accepted Answer

displacement reactionReason —The above reaction is an example of a displacement reaction because Fe in Fe2O3 has been displaced by Al and the reaction is of type : YZ + X ⟶ XZ + Y

Question 3

Question 3What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.Hydrogen gas and iron chloride are produced.Chlorine gas and iron hydroxide are produced.No reaction takes place.Iron salt and water are produced.

Accepted Answer

Hydrogen gas and iron chloride are produced.Reason — When dilute hydrochloric acid is added to iron fillings hydrogen gas and iron chloride are produced.Fe(s) + 2HCl(aq) ⟶ FeCl2(aq) + H2 ↑

Question 4

Question 4What is a balanced chemical equation? Why should chemical equations be balanced?

Accepted Answer

A balanced equation is one in which the number of atoms of each element of the reactant is equal to the number of atoms of each element of the products.An equation must be balanced in order to comply with the "Law of Conservation of Mass", which states that mass is neither created nor destroyed in the course of a chemical reaction. An unbalanced equation would imply that atoms have been created or destroyed.

Question 5

Question 5Translate the following statements into chemical equations and then balance them.(a) Hydrogen gas combines with nitrogen to form ammonia.(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Accepted Answer

(i) 3H2 (g) + N2 (g) ⟶ 2NH3 (g)(ii) 2H2S (g) + 3O2 (g) ⟶ 2H2O (l) + 2SO2 (g)(iii) 3BaCl2 (aq) + Al2(SO4)3 (aq) ⟶ 2AlCl3 (aq) + 3BaSO4 (s)(iv) 2K (s) + 2H2O (l) ⟶ 2KOH (s) + H2 (g)

Question 6

Question 6Balance the following chemical equations.(a) HNO3 + Ca(OH)2 ⟶ Ca(NO3)2 + H2O(b) NaOH + H2SO4 ⟶ Na2SO4 + H2O(c) NaCl + AgNO3 (aq) ⟶ AgCl + NaNO3(d) BaCl2 + H2SO4 ⟶ BaSO4 + HCl

Accepted Answer

(a) 2HNO3 + Ca(OH)2 ⟶ Ca(NO3)2 + 2H2O(b) 2NaOH + H2SO4 ⟶ Na2SO4 + 2H2O(c) NaCl + AgNO3 ⟶ AgCl + NaNO3(d) BaCl2 + H2SO4 ⟶ BaSO4 + 2HCl

Question 7

Question 7Write the balanced chemical equations for the following reactions.(a) Calcium hydroxide + Carbon dioxide ⟶ Calcium carbonate + Water(b) Zinc + Silver nitrate ⟶ Zinc nitrate + Silver(c) Aluminium + Copper chloride ⟶ Aluminium chloride + Copper(d) Barium chloride + Potassium sulphate ⟶ Barium sulphate + Potassium chloride

Accepted Answer

(a) Ca(OH)2 (aq) + CO2 (g) ⟶ CaCO3 (s) + H2O (l)(b) Zn (s) + 2AgNO3 (aq) ⟶ Zn(NO3)2 (aq) + 2Ag (s)(c) 2Al (s) + 3CuCl2 (aq) ⟶ 2AlCl3 (aq) + 3Cu (s)(d) BaCl2 (aq) + K2SO4 (aq) ⟶ BaSO4 (s) + 2KCl (aq)

Question 8

Question 8Write the balanced chemical equation for the following and identify the type of reaction in each case.(a) Potassium bromide (aq) + Barium iodide (aq) ⟶ Potassium iodide (aq) + Barium bromide (s)(b) Zinc carbonate (s) ⟶ Zinc oxide (s) + Carbon dioxide (g)(c) Hydrogen (g) + Chlorine(g) ⟶ Hydrogen chloride (g)(d) Magnesium (s) + Hydrochloric acid (aq) ⟶ Magnesium chloride (aq) + Hydrogen(g)

Accepted Answer

(a) 2KBr (aq) + BaI2 (aq) ⟶ 2KI (aq) + BaBr2 (s)Type — Double displacement reaction(b) ZnCO3 (s) ⟶ ZnO (s) + CO2 (g)Type — Decomposition reaction(c) H2 (g) + Cl2 (g) ⟶ 2HCl (g)Type — Combination reaction(d) Mg (s) + 2HCl (aq) ⟶ MgCl2 (aq) + H2 (g)Type — Displacement reaction

Question 9

Question 9What does one mean by exothermic and endothermic reactions? Give examples?

Accepted Answer

Exothermic reactions — Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.For example, burning of natural gas gives out large amount of heat:CH4 (g) + 2O2 (g) ⟶ CO2 (g) + 2H2O (g) + HeatEndothermic reactions — Reactions in which energy is absorbed are known as endothermic reactions.For example, when carbon is heated with sulphur at high temperature, liquid carbon disulphide is formed:C + 2S →Heat\xrightarrow{	ext{Heat}}Heat​ CS2

Question 10

Question 10Why is respiration considered an exothermic reaction? Explain?

Accepted Answer

During digestion, food is broken down into simpler substances such as carbohydrates. These carbohydrates are broken down to form glucose. Glucose combines with oxygen in the cells and provides energy. The special name of this reaction is respiration.As energy is released in this process, it is an exothermic process.C6H12O6[Glucose] (aq)+6O2 (aq)⟶6CO2 (aq)+6H2O (l)+energy\underset{	ext{[Glucose]}}{	ext{C}_6	ext{H}_{12}	ext{O}_6}	ext{ (aq)} + 6	ext{O}_2	ext{ (aq)} \longrightarrow 6	ext{CO}_2	ext{ (aq)} + 6	ext{H}_2	ext{O}	ext{ (l)} + 	ext{energy}[Glucose]C6​H12​O6​​ (aq)+6O2​ (aq)⟶6CO2​ (aq)+6H2​O (l)+energy

Question 11

Question 11Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions?

Accepted Answer

In a decomposition reaction, a single reactant breaks down to give simpler products.CaCO3 →Δ\xrightarrow{\Delta}Δ​ CaO + CO2In a combination reaction, a single product is formed from two or more reactants.CaO + H2O ⟶ Ca(OH)2Hence, we can say that the decomposition reaction is opposite of combination reaction.

Question 12

Question 12Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

Accepted Answer

CaCO3 (s) →Heat\xrightarrow{	ext{Heat}}Heat​ CaO (s) + CO2 (g)2AgCl (s) →sunlight\xrightarrow{	ext{sunlight}}sunlight​ 2Ag (s) + Cl2 (g)2H2O (l) →electricity\xrightarrow{	ext{electricity}}electricity​ 2H2 (g) + O2 (g)

Question 13

Question 13What is the difference between displacement and double displacement reactions? Write equations for these reactions?

Accepted Answer

Displacement reactionDouble displacement reactionsIn a displacement reaction, an element displaces another element from its compound.In double displacement reaction, atoms or groups of atoms (ions) are exchanged.Example:Zn + CuSO4 ⟶ ZnSO4 + CuExample:NaOH + HCl ⟶ NaCl + H2O

Question 14

Question 14In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved?

Accepted Answer

Cu (s) + 2AgNO3 (aq) ⟶ Cu(NO3)2 (aq) + 2Ag (s)

Question 15

Question 15What do you mean by a precipitation reaction? Explain by giving examples.

Accepted Answer

A chemical reaction in which two compounds in their aqueous state react to form an insoluble substance (precipitate) as one of the products is called a precipitation reaction.Some examples of precipitation reactions are:Take a solution of silver nitrate in a test tube and add dil. hydrochloric acid. A curdy white ppt. of AgCl is formed.AgNO3 (aq) + HCl (l) ⟶ AgCl (s) ↓ + HNO3 (g)When sodium sulphate reacts with barium chloride, a white ppt. of barium sulphate appears.Na2SO4 (aq) + BaCl2 (aq) ⟶ BaSO4 (s) ↓ + 2NaCl (aq)

Question 16

Question 16Explain the following in terms of gain or loss of oxygen with two examples each.(a) Oxidation(b) Reduction

Accepted Answer

(a) Oxidation is gain of oxygen by a substance.For example,Copper is oxidised to Copper oxide:2Cu + O2 →Heat\xrightarrow{	ext{Heat}}Heat​ 2CuOCarbon is oxidised to Carbon dioxideC + O2 ⟶ CO2(b) Reduction is loss of oxygen from a substance.For example,Copper (II) oxide is reduced to CopperCuO + H2 →Heat\xrightarrow{	ext{Heat}}Heat​ Cu + H2OZinc (II) oxide is reduced to Zinc.ZnO + C ⟶ Zn + CO

Question 17

Question 17A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black coloured compound formed.

Accepted Answer

Element 'X ' is copper. On heating in air it forms Copper (II) oxide, which is black in colour.2Cu (s) + O2 (g) →Heat\xrightarrow{	ext{Heat}}Heat​ 2CuO (s)

Question 18

Question 18Why do we apply paint on iron articles?

Accepted Answer

Paint is applied on iron articles primarily to protect them from corrosion and rust formation by creating a barrier between the iron surface and moisture and oxygen in the air.

Question 19

Question 19Oil and fat containing food items are flushed with nitrogen. Why?

Accepted Answer

Oil and fat containing food items are flushed with nitrogen to extend their shelf life by displacing oxygen, which can lead to oxidative rancidity and spoilage. Nitrogen helps create an oxygen-free environment that maintains the quality and freshness of the food items.

Question 20

Question 20Explain the following terms with one example each.(a) Corrosion(b) Rancidity

Accepted Answer

(a) Corrosion — When a metal is attacked by substances around it such as moisture, acids, etc, it is said to corrode and this process is called corrosion.For example, iron articles are shiny when new, but get coated with a reddish brown powder when left for some time due to rusting.(b) Rancidity — When taste and smell of food items containing fat and oil change due to oxidation, then this condition is called rancidity.For example, when butter is left exposed to air for a long time, it becomes rancid, making it unsuitable for consumption and cooking.

Chemical Reactions and Equations

Exercises

Intext Questions 1

Intext Questions 2

Intext Questions 3