IX Model Test Questions Chemistry Test # 11 for Chapter # 7 (Electrochemistry)

 

Short Answer-questions

Q1.  Define oxidation, reduction reactions with examples.

Q2.   Define oxidizing agent and reducing agent with examples.

Q3.   Write down 5 differences between oxidation and reduction.

Q4.   Write down 3 examples of each of oxidizing and reducing agent.

Q5.  Identify the oxidizing and reducing agents from the following.

(i) Al (RA)          (ii) Na (RA)        (iii) H₂S (RA)     (iv) H₂SO₄ (OA)                (v) KMnO₄ (OA) (vi) Zn (RA)

Q6. Identify the oxidizing and reducing agents for the following reaction.

H₂ (RA)+ Cl₂ (OA)  → 2HCl

Q7. Describe the construction of electrochemical cell. Write names of two types of electrochemical cells.

Q8. Differentiate between electrolytes and non-electrolytes with examples.

Q9.  Differentiate between strong electrolytes and weak electrolytes with examples.

Q10.  Identify strong and weak electrolytes from the following:

HCl (S), KI (S), NaOH (S), H₂S (W), CH₃COOH (W), NH₄OH (W), NaCl (S), C₂H₅OH (W)

Q11. Why ionic compounds conduct electricity in molten or in aqueous solutions only?

Q12.  What is electrolytic cell? Explain with diagram. Describe the construction and working of electrolytic cell

Q13.      Sketch electrolytic cell for electrolysis of molten potassium chloride and identify cathode and anode, oxidation, reduction reaction, movement of electron

Q14. Define electrochemistry, electrochemical reactions, electrochemical cell, electrolyte, non-electrolyte, salt bridge, cell, Galvanic cell, electrolytic cell, battery, electrode, cathode, anode, oxidation, reduction, redox reactions, electrochemical equivalent, and chemical equivalent.

Q15. What is electroplating? On which principle this process works? Give its merits.

Q16.  What is corrosion of metal and rusting? How it can be prevented? or Name the methods which are used to protect metal form corrosion. How cathodic protection prevent metal from corrosion?

Q17. Write down 4 applications of electrolytic cells or electrolysis.

Q18. Describe the process of nickel plating and tin plating.

Q19. Write down the composition of following alloys:

Brass (Cu-Zn,[4:1]), Bronze (Cu-Sn-Zn),   [9:1], Bell metal (Cu-Sn), Monel (Ni-Cu-Fe), Amalgam (Hg-Ag-Cu-Zn), Pewter (Sn-Cu-Pb-Sb-Bi), White gold (Au-Pb-Ag-Cu (18 karat), Duralumin (Al-Cu-Mg-Ni)

Long Answer-questions

Q1   State and explain Faraday’s Laws of electrolysis.

Q2    Describe the construction and working of Daniel cell and lead battery.

Q3    Describe the dry cell with diagram

Q4    What is battery? How lead storage battery works?

Q5   Explain the process of electrolysis in electrolytic cell

Q6    What is alloy? Explain its classification with examples

Q7          What is electroplating? How steel object can be electroplated with zinc and silver?

Q8          Examine the following chemical equations and identify

(i) oxidation      (ii) reduction            (iii) Oxidizing agent       (iv) reducing agent

a)  Zn (RA)  +  Cl₂ (OA)        → ZnCl₂                 (Zn is oxidized and Cl₂ is reduced)

b)  H₂S (RA) +  Br₂ (OA)      → 2HBr + S         (H₂S is oxidized and Br₂ is reduced)

c)   2Ca (RA) +  O₂ (OA)       → CaO                (Ca is oxidized and O₂ is reduced)

d)  2Li (RA) +  S (OA)           → Li₂S                 (Li is oxidized and S is reduced)

Q9          Identify the alloy

Short Answer-questions

Q1.  Define oxidation, reduction reactions with examples.

Answer

Oxidation

(i)  Oxidation as addition of oxygen or removal of hydrogen from a substance

Oxidation may involve introduction of oxygen or removal of Hydrogen from a chemical substance.    

C     +   O →         CO₂                          (Oxidation of carbon by burning of coal through addition of O)

2C₈H₁₈     +   25O₂ →  16CO₂ + 18 H₂O (Oxidation of octane by its combustion)

N₂H₄ +   O₂ →        N₂ + 2H₂O   (Oxidation of Hydrazine by removal of H)

(ii)  Oxidation as loss of electron and increase in oxidation number

The electrochemical reaction in which atom molecule or ion loses electron and its oxidation number increases is called oxidation reaction.

Cu → Cu²⁺  + 2e^– (Oxidation of copper by loss of electrons increasing its oxidation no from 0 to 2+)

Reduction

(i) Reduction as addition of hydrogen or removal oxygen from a substance

reduction may involve addition of Hydrogen or removal of oxygen from a chemical substance.

CuO  +     C    → Cu      + CO        (Reduction of cooper oxide by removal of O)

Fe₂O₃ +     2Al   → Al₂O₃ + 2Fe + heat   (Reduction of ferric oxide by removal of O)

CH₂=CH₂ +     H₂   → CH₃-CH₃         (Reduction of ethene by addition of H)

(ii)   Reduction as gain of electron and decrease in oxidation number

The electrochemical reaction in which atoms, molecule or ion accepts electron and its oxidation number decreases is called reduction reaction.

    S  + 2e^– → S^2–           (reduction of sulphur by the gain of electrons)

Q2. Define oxidizing agent and reducing agent with examples.

Answer

Oxidizing and Reducing Agents

Oxidizing agents are substances that accept electrons. Oxidation occurs due to oxidizing agent

Reducing agents are substances which lose electrons. Reducing agent is responsible for reduction.

Examples of Oxidizing agent

All non-metals e.g. F₂, Cl₂, Br₂, I₂, O₂, O₃

All oxyacids e.g. H₂SO₄, HNO₃,

All oxysalts  e.g.  KMnO₄, K₂Cr₂O₇

Examples of Reducing agent

All metals   e.g. Alkali metals (Li, Na, K etc.), Mg, Al, Zn

All binary acid e.g. HCl, H₂S etc.

Ionic hydrides e.g. NaH, KH, etc.

Example

Zinc undergoes oxidation by losing electrons and it act as reducing agent while chlorine undergoes reduction by accepting electrons and act as oxidizing agent.

Q3. Write down 5 differences between oxidation and reduction.

Answer

Q4. Write down 3 examples of each of oxidizing and reducing agent.

Answer

 Examples of Oxidizing agent

All non-metals        e.g.     F₂, Cl₂, Br₂, I₂, O₂, O₃

All oxyacids             e.g.     H₂SO₄, HNO₃,

All oxysalts              e.g.     KMnO₄, K₂Cr₂O₇

Examples of Reducing agent

All metals                  e.g.   Alkali metals (Li, Na, K etc.), Mg, Al, Zn

All binary acid        e.g.   HCl, H₂S etc.

Ionic hydrides        e.g.   NaH, KH, etc.

Q5. Identify the oxidizing and reducing agents from the following.1.  Al (RA)         2. Na (RA)         3. H₂S (RA)       4. H₂SO₄ (OA)  5. KMnO₄ (OA)                6. Zn (RA)

Answer

Al …………….  Reducing agent (all metals are RA)

Na ……………. Reducing agent (all metals are RA)

H₂S …………... Reducing agent (Binary acids are RA)

H₂SO₄ ………. Oxidizing agent  (All oxyacids are oxidizing agent)

KMnO₄……… Oxidizing agent (All oxysalts are oxidizing agent)

Zn ……………. Reducing agent (all metals are RA)

Q6. Identify the oxidizing and reducing agents for the following reaction.

H₂ (RA)+ Cl₂ (OA) → 2HCl

Answer

Q7          Describe the construction of electrochemical cell. Write names of two types of electrochemical cells.

Answer

Definition

The electrochemical reactions are carried out in electrochemical cells. The device or cell which is used to convert chemical energy into electrical energy or vice versa using redox reaction is called electrochemical cell. (These cells use spontaneous chemical reactions to generate an electric current through oxidation-reduction (redox) reactions or use an electric current to drive a non-spontaneous redox reaction).

Construction/Structure

1.            It consists of a vessel or pot containing two electrodes at which redox reaction occurs.

2.            The electrode at which oxidation takes place is called Anode.

3.            The electrode at which reduction occurs is called Cathode.

4.            The reactions occurs at each electrode is called half-cell reaction.

5.            The overall cell reaction is the combination of two half-cell reactions.

6.            Each electrode is in contact with battery or voltmeter and electrolyte is present in cell.

types of electrochemical cells

There are two types of electrochemical cells namely

1.            Galvanic cell

2.            Electrolytic cell

Q8.         Differentiate between electrolytes and non-electrolytes with examples.

Difference between Electrolytes and Non-electrolytes

	Electrolytes	Non-Electrolytes
1	The compounds, which ionize or dissociate into negative and positive ions in aqueous solution, conduct electric current are called Electrolytes.	The compounds which do not ionize in aqueous solution, do not conduct electric current are called Non-Electrolytes.
2	Electrolytes are conductors.	non-electrolytes are insulators.
3	They are polar compounds.	They nonpolar compounds
4	They have ionic bond.	They have covalent bonds.
5	They dissociate into ions.	They do not dissociate into ions.
6	All acids, bases and salts are electrolytes. e.g. HCl, NaOH, NaCl etc.	Most of organic compounds are non-electrolytes e.g. sugar, glucose, urea, chloroform, glycerine, etc.

Q9.         Differentiate between strong electrolytes and weak electrolytes with examples.

Difference between Strong and Weak Electrolytes

	Strong Electrolytes	Weak Electrolytes
1	The electrolytes which are highly dissociated (their %age dissociation is high) conduct large amount of current are called strong Electrolytes.	The electrolytes which are poorly dissociated (their %age dissociation is low) conduct electricity slightly are called weak Electrolytes.
2	Strong electrolytes ionize to a large extent in dilute aqueous solutions & therefore conduct electric current to large extent.	Weak electrolytes ionize to a small extent in aqueous solution and therefore conduct electric current poorly.
	Examples (a)          Strong Acids; HCl, H2SO4 (b)          Strong Bases; NaOH, KOH (c)          All Salts; NaCl, NaNO3	Examples (a)          Weak acids; Acetic acid, benzoic acid (b)         Weak bases; NH4OH

Q10. Identify strong and weak electrolytes from the following: HCl (S), KI (S), NaOH (S), H₂S (W), CH₃COOH (W), NH₄OH (W), NaCl (S), C₂H₅OH (W)

Answer

Strong Electrolytes …………….. HCl, KI, NaOH, NaCl

Weak Electrolytes………………. H₂S, CH₃COOH, NH₄OH, C₂H₅OH

Q11.      Why ionic compounds conduct electricity in molten or in aqueous solutions only?

Answer

Conduction of electricity is achieved by the movement of charged particles. Substances can conduct electricity if there is a way for charge to flow through that substance. For a substance to conduct electricity, it needs to contain some sort of charge carrier such as an electron or an ion - that is free to move within the substance.

Ionic compounds do not conduct electricity in solid form as their ions are held in fixed positions due to strong electrostatic forces and cannot move. This means there is no possible movement of charge, so a solid ionic compound cannot conduct electricity.

Ionic compounds when molten (liquid) or in aqueous solution (dissolved in water), their constituent ions are free to move within the compound (throughout the solution /molten solid) from place to place and carry charge through it, i.e. conduct electricity.

Q12. What is electrolytic cell? Explain with diagram. Describe the construction and working of electrolytic cell

Answer

Electrolytic cell

Electrolysis is carried out in a specialized apparatus called Electrolytic Cell. The type of cell which uses electricity for a non-spontaneous redox reaction to occur is called electrolytic cell.

Construction and working of an electrolytic cell

An electrolytic cell consists of electrolyte in a vessel, electrodes and a battery.

The figure shows that electrons from battery enter through cathode at which positive ions are reduced by accepting electrons. At anode negative ions loses electrons and undergoes oxidation. It means at cathode reduction occurs and oxidation takes place at anode.

Ionization.…………….     M X   →    M⁺  + X^– (Splitting of electrolyte into its ions)

Cathode reaction…..     M⁺  +     e^–  →  M   (Reduction; gain of electron)

Anode Reaction…….     X^–    →    X   +   e^– (Oxidation; loss of electron)

Q13. Sketch electrolytic cell for electrolysis of molten potassium chloride and identify cathode and anode, oxidation, reduction reaction, movement of electron

Answer

Q14. Define electrochemistry, electrochemical reactions, electrochemical cell, electrolyte, non-electrolyte, salt bridge, cell, Galvanic cell, electrolytic cell, battery, electrode, cathode, anode, oxidation, reduction, redox reactions, electrochemical equivalent, and chemical equivalent.

Answer

Electrochemistry

electrochemistry is the branch chemistry which deals with electrochemical reactions, electrolyte and electrochemical cells. Electrochemistry is the study of the relationship between electricity and chemical

electrochemical reactions

The chemical reactions in which chemical energy changes into electrical energy or Vice Versa are called electrochemical reactions.

electrochemical cells

The electrochemical reactions are carried out in electrochemical cells. The device or cell which is used to convert chemical energy into electrical energy or vice versa using redox reaction is called electrochemical cell.

Electrolytic Cells

An electrolytic cell is a type of electrochemical cell in which an external voltage (electric current) drives a non-spontaneous redox reaction. It is a device, which is used to convert electrical energy into chemical energy.

Galvanic or Voltaic Cells

Galvanic or Voltaic Cells is a type of electrochemical cell in which a spontaneous redox reaction generates an electric current. In other words, it is an electrochemical cell, which converts chemical

Electrolytes

An electrolyte consists of free moving ions and conduct electricity. Acids, bases and salts in molten or in aqueous solution form are electrolytes. The chemical compounds that conduct electric current in molten state or through their aqueous solutions with chemical change (decomposition) are called Electrolytes.

Strong Electrolytes

The electrolytes, which are highly dissociated due to their high % age dissociation conduct large amount of current, are called strong electrolytes. Strong electrolytes ionize to a large extent in dilute aqueous solutions & therefore conduct electric current to large extent.

Weak Electrolytes

The electrolytes, which are poorly dissociated due to their low % age dissociation conduct electricity slightly, are called weak electrolytes. Weak electrolytes ionize to a small extent in aqueous solution and therefore conduct electric current poorly.

Non-electrolytes

The substances which are unable to conduct electricity in molten state or in aqueous solution form are called non electrolytes. The chemical compounds that do not conduct an electric current in molten state or in aqueous solutions are called Non-electrolytes.

Electrolysis

the process of the movement of cation and anion of an electrolyte in fused state or in its aqueous solution and their conversion into neutral species (atoms or molecules) at their respective electrodes under the influence of an applied electric filed is called electrolysis. Electrolysis is the process in which electrical energy is used to bring about a non-spontaneous redox reactions.

Electroplating

The process of deposition of metal at the surface of other metal through electrolysis is called electroplating.

Faraday’s First Law of Electrolysis

The amount of any substance (element) deposited or liberated at an electrode during electrolysis is directly proportional to quantity of electricity passed through the electrolyte.

Faraday’s Second Law of Electrolysis

The amount of different substances deposited or liberated due to passage of same quantity of current through different electrolytes are proportional to their chemical equivalent masses.

Chemical Equivalent

The mass of a substance (element) deposited or liberated on electrodes during electrolysis on passing one faraday (96500 C) of electric charge through an electrolyte is known as Equivalent Mass (weight) or Gram Equivalent Mass or Chemical Equivalent or Gram Chemical Equivalent denoted by e (or C.E). The chemical equivalent of an element is numerically equal to its gram atomic mass divided by its valency.

Battery

A battery consists of group of galvanic cells connected in a series. We use lot of electrical devices having batteries as a source of electricity.

Electrochemical equivalent (Z)

The electrochemical equivalent (Z) is the weight of the substance collected at the electrodes when one coulomb of electric charge is passed through the electrolyte (or 1 ampere electric current for 1 second).

Q15. What is electroplating? On which principle this process works? Give its merits.

Answer

Definition of Electroplating

The process of deposition of metal at the surface of other metal through electrolysis is called electroplating.

(Electroplating is the process of deposition of a thin layer of corrosion-resistant, more attractive and costly metal (usually Ag, Au, Cr, Ni, Cu, Sn etc.) over an inferior or baser metals (usually iron, steel etc.) through the process of electrolysis in an electrolytic cell). 

Basis of Electroplating

1 Electroplating is based on the process of electrolysis.

2. The cheaper or baser metal (such as iron, steel etc.) to be electroplated is made cathode

3.  The metal whose fine layer is to be coated (plating metal) is made anode.

Applications or Objectives (or uses) of Electroplating

1.    Corrosion Protection           

2.    Durability and Decoration                 

3.    Low Cost Articles   

4.    Repair

Q16. What is corrosion of metal and rusting? How it can be prevented? or Name the methods which are used to protect metal form corrosion. How cathodic protection prevent metal from corrosion?

Answer

Definition of Corrosion

Metals react with oxygen in presence of moisture and can form harmful metal oxide. These metal oxide layers are porous and expose metal for further reaction with oxygen to form harmful metal oxide. It is called Corrosion of metal.

Rusting of Iron

Corrosion of iron is called rusting which an electrochemical process. Iron undergoes redox reaction in presence of air or water to form iron (III) oxide (Fe₂O₃.nH₂O) called rusting of iron. Rusted surface of iron provide no protection to underlying iron and eventually convert whole iron into reddish brown rust. Rusting occurs at different places of metal surface. A metal surface area of less moisture acts as anode and oxidizes iron in this region. Metal surface with high moisture contents acts as a cathode and reduces atmospheric oxygen to OH^– ions The Fe²⁺ ions further reacts with oxygen to form rust, iron(III) oxide (Fe₂O₃.nH₂O).

            Fe_(s)         → Fe²⁺_(aq)  + 2e^–     ………… (Oxidation)

         O₂ + 2H₂O + 4e^–→ 4OH^–_(aq)     ………… (Reduction)

Prevention from corrosion

All metals can be prevented from corrosion by following methods.

1.            Alloying

Formation of alloy prevents metal from corrosion by reducing its ability of oxidation.

Example: Iron (Fe) can be changed into stainless steel by mixing with chromium (Cr) and Nickel (Ni). Thus iron (Fe) is prevented from corrosion.

2.            Metallic Coating (Electroplating)

All metals can be protected from corrosion by coating its surface with other metal like tin (Sn) or zinc (Zn). The coating of metal at the surface of other metal by electrolytic process is called electroplating. Metals like iron can be electroplated with chromium (Cr), Nickel (Ni) and silver (Ag).

3.            Cathodic Protection

It is applied to protect underground pipes tanks, oil rigs etc. from corrosion by making these materials as cathode. The active metal like magnesium (Mg) or aluminum (Al) is used as Anode and connected with iron (Fe). These active metals itself oxidizes and prevent other metal from corrosion.

4.            Coating with paint

A metal is commonly coated with paint to protect it from corrosion. Paint prevents the reaction of metal with oxygen, moisture and other harmful chemical agents.

Q17. Write down 4 applications of electrolytic cells or electrolysis.

Answer

Applications of Electrolytic cells/ Electrolysis

Important uses of electrolytic cell are given below.

1. It is used for extraction of metals from their ores

(i)  It is used to extract sodium metal from molten sodium chloride using the down's cell.

  (ii). It is used to extract aluminum metal using Hall-Heroult Cell.

2. It is used for refining of impure metals like in electro refining of copper.

3.  It is used for electroplating of metals.

4. It is used to manufacture caustic soda (NaOH) from aqueous sodium chloride by Nelson's cell. It is also used to obtain chlorine gas.

Q18. Describe the process of zinc plating and tin plating.

Answer

Zinc Plating/Galvanizing

Definition

The process of depositing (or coating) thin layer of metallic zinc on cheap or baser metals (usually iron, steel etc.) by the process of electroplating (i.e. electrolysis) in an electrolytic cell is called galvanizing or zinc plating. The process in which zinc is electrolytically coated at the surface of other base metal is called galvanizing.

Method of Galvanizing

The process is carried out in an electrolytic cell. Cathode is made up of the steel object (or metallic object), which is to be coated (galvanized). Anode is made up of the rod of pure zinc metal. Both electrodes are immersed in solution of Potassium zinc cyanide, K₂Zn(CN)₄ as electrolyte to produce zinc (Zn²⁺) ions. The two electrodes are joined with a battery.

During electrolysis, Zn deposits at cathode and Zinc (Zn) anode is then changed into zinc ion (Zn²⁺).

Electrolytic Reactions

Ionization;……………..   K₂Zn(CN)_4(aq) → 2K⁺_(aq) +Zn²⁺_(aq)  +  CN^–                         

Anode Reaction;……..  Zn_(s) (Anode)→ Zn²⁺_(aq)   +   2e^– ………….. (Oxidation)

Cathode Reaction;……. Zn²⁺_(aq)   +   2e^–→ Zn_(s)(cathode)………… (Reduction)

Overall Redox Reaction;…   Zn_(s) (Anode) → Zn_(s)   (cathode) 

Tin Plating

Definition

The process of depositing (or coating) thin layer of metallic tin on cheap or baser metals (usually iron, steel etc.) by the process of electroplating (i.e. electrolysis) in an electrolytic cell is called Nickel Plating.

Method of Tin plating

The process is carried out in an electrolytic cell. Cathode is made up of the steel spoon (or metallic object), which is to be coated (tin plated). Anode is made up of the rod of pure tin. Both electrodes are immersed in solution of acidified tin suphate (SnSO₄) as electrolyte. The two electrodes are joined with a battery.

Working and Electrolytic Reactions

When current passes through electrolyte, tin ions (Sn²⁺) deposit at cathode as tin (Sn) metal. Tin (Sn) anode is then changes into tin ion (Sn²⁺).

Electrolytic Reactions

Ionization;………………. SnSO_4(aq)           → Sn²⁺_(aq)    +   SO₄^2– …………        

Anode Reaction;………  Sn _(s) (Anode) → Sn²⁺_(aq)    +   2e^– ………… (Oxidation)

Cathode Reaction;…… Sn²⁺_(aq)   +   2e^– → Sn_(s)(cathode) ………… (Reduction)

Overall Redox Reaction;….. Sn_(s) (Anode)  → Sn_(s)   (cathode)    

Q19. Write down the composition of following alloys: Brass (Cu-Zn,[4:1]), Bronze (Cu-Sn-Zn) [9:1], Bell metal (Cu-Sn), Monel (Ni-Cu-Fe), Amalgam (Hg-Ag-Cu-Zn), Pewter (Sn-Cu-Pb-Sb-Bi), White gold (Au-Pb-Ag-Cu (18 karat), Duralumin (Al-Cu-Mg-Ni)

Answer

XI Chemistry Important Objectives and MCQs for 2023

 XI MCQs Chapter 1 ………… Stoichiometry

1.   If the volume occupied by oxygen gas (O₂) at STP is 44.8dm³, the number molecules of O₂ in the vessels are:

(a) 3.01 x 10²³                    

(b) 6.02 x 10²³                                    

(c) 12.04 x 10²³                  

(d) 24.08 x 10²³

Explanation; (Answer, c)

22.4 dm³ (1 mole) of any gas at STP contains 6.02 x 10²³ molecules. Hence 44.8 dm³ (2 mole) of any gas at STP would contain twice of 6.02 x 10²³ molecules i.e. 12.04 x 10²³ molecules.

No. of molecules = V_g/V_m x N_A = 44.8/22.4 x 6.02 x 10²³ = 12.04 x 10²³ or 1.204 x 10²⁴ molecules.

2.  The number of carbon atoms in 1 mole of sugar (C₁₂H₂₂O₁₁) are approximately:

(a) 6 x 10²³                          

(b) 24 x 10²³                                       

(c) 60 x 10²³                                        

(d) 72 x 10²³

Explanation; (Answer, d)

1 mole of sugar (C₁₂H₂₂O₁₁) = 12 moles of carbon atoms

12 moles of carbon atoms = n x N_A = 12 x 6.02 x 10²³ = 72 x 10²³ or 7.2 x 10²⁴ carbon atoms.

3. In the reaction 2Na + 2H₂0 → 2NaOH + H₂, if 23g of Na reacts with excess of water, the volume of hydrogen gas (H₂) liberated at STP should be

(a) 11.2dm³                        

(b) 22.4dm³                                        

(c) 33.6dm³                                         

(d) 44.8dm³

Explanation; (Answer, a)

From stoichiometric ratio in the given equation:

46g (2 mole) Na liberates 22.4 dm³ of hydrogen gas at STP

23g (1 mole) Na liberates 22.4/46 x 23 dm³ of hydrogen gas at STP = 11.2 dm³ of hydrogen gas

4.  Which of the following sample of substances contains the same number of atoms as that of 20g calcium:

(a) 16g S                              

(b) 20g C                                              

(c) 19 g K                                             

(d) 24g Mg

Explanation; (Answer, a)

Species containing same number of moles will have same number of particles (atoms, molecules or formula units). 20 g Ca and 16 g S constitute same number of moles (0.5 moles), hence they have same number of atoms.

No. of moles in 20 g Ca = mass/molar mass = 20/40 = 0.5 mol

No. of moles in 16 g S = mass/molar mass = 16/32 = 0.5 mol

5.  The minimum number of moles are present in:

(a) 1 dm³ methane gas at STP                                       

(b) 5 dm³ of helium gas at STP

(c) 10 dm³ of hydrogen gas at STP                               

(d) 22.4 dm³ of chlorine gas at STP

Explanation; (Answer, a)

For gases at STP, minimum number of moles are present in that gas which has least volume. Here 1 dm³ methane gas at STP has least number of moles as it has least volume.

6.  Number of atoms in 60g carbon are:

(a) 3.01x 10²³                     

(b) 3.01 x 10²⁴                    

(c) 6.02 x 10²³                                    

(d) 6.02 x 10²⁴

Explanation; (Answer, b)

No. of atoms = (Mass/molar mass) x N_A = 60/12 x 6.02 x 10²³ = 3.01 x 10²⁴

7. Maximum number of molecules present in the following sample of gas:

(a) 100g O₂                         

(b) 100g CH₄                      

(c) 100g CO₂                                       

(d) 100g Cl₂

Explanation; (Answer, b)

The species containing greatest moles will have greatest number of molecules.

For species having same mass, the specie having least molar mass would have greatest number of moles. Here CH₄ has least molar mass of 16, so its 100 g would contain maximum number of moles and also maximum number of molecules.

8.   Which of the following statement is incorrect?

(a) The mass of 1 mole Cl₂ gas is 35.                            

(b) One mole of H₂ gas contains 6.02 x 10²³ molecules of H₂

(c) Number of atoms in 23g Na and 24 g Mg are equal           

(d) One moles of O₂ at S.T.P occupy 22.4 dm³ volume

Explanation; (Answer, a)

The statement a is incorrect as the mass of 1 mole of Cl2 is 71 g (not 35).

9. For Avogadro's number, this statement is incorrect?

(a) It is the no. of particles in one mole of any substance      

(b) Its numerical value is 6.02x 10²³

(c) Its value change if temperature increases                                           

(d) Its value change if number of moles increases.

Explanation; (Answer, c)

Avogadro’s number is independent of temperature and pressure. Its value only depends upon the number of moles and volume of gas at STP.

10. Generally actual yield is:

(a) Greater than theoretical yield

(b) Less than theoretical yield

(c) Equal to the theoretical yield  

(d) Some times greater & some times less than theoretical yield

Explanation; (Answer, c)

Generally actual yield is Less than theoretical yield mainly due to side reactions and mechanical loss of product.

XI MCQs Chapter 2 …… Atomic Structure

1. Bohr's theory is not applicable to which of the following

(a) H                                     

(b) H⁺                                                    

(c) He¹⁺                                

(d) Li²⁺

Explanation; (Answer, b)

One of the limitations of Bohr's atomic model is that it does not explain the spectra of multi-electron atoms. Bohr's theory is applicable to hydrogen like atoms or hydrogenic ions (single electron system). 

All the given species like H, He⁺ and Li²⁺ are isoelectronic and have only one electron. Their electronic configurations are same and so their spectra is explained by Bohr's atomic model. But H⁺ has no electron at all and hence cannot form spectrum.

2. Nitrogen has the electronic configuration 1s² 2s² 2px¹ 2py¹ 2pz¹ and  1s² 2s² 2px² 2py¹.This is determined by

(a) Aufbau principle         

(b) Pauli’s rule                                  

(c) Hund's rule                   

(d) n+l rule

Explanation; (Answer, c)

The filling of electrons in degenerate orbitals like p, d and f is governed by Hund’s rule of maximum electron multiplicity accordingly electrons in degenerate orbitals tend to remain singly with same spin until all of the degenerate orbitals become half filled then pairing of electrons are allowed in them.

3. Quantum number values for 3s orbital are

(a) n=0, l=1                         

(b) n=1, l=0                                         

(c) n=3, l=1                         

(d) n=3, l=0  

Explanation; (Answer, d)

In the notation 3s (nl), 3 stands for n while s represent l.

For 3s orbital, n =3 and l=0.

4.  The radius of first orbit of hydrogen atom is .....

(a)529Å                               

(b) 52.9 Å                                            

(c) 5.29 Å                             

(d) 0.529 Å

Explanation; (Answer, d)

Where a_o is known as Bohr’s constant or Bohr radius and it the radius of first orbital of hydrogen atom. and its value is 0.529 x 10⁻¹⁰ m or 0.529 x 10⁻⁸ cm or 0.529 Å or 0.0529nm or 52.9 pm. This is the radius of the first orbit of H. This equation is used for the determination of n^th orbit of hydrogen atom and hydrogen like ions like He⁺, Li²⁺ etc.

5. Line spectrum is used as a tool for the identification of ....

(a) Colors                            

(b) Electrons                                      

(c) Elements                                       

(d) Molecules

Explanation; (Answer, c)

samples of same element always produces same characteristic line spectrum. Each element emit of light of specific wavelength therefore the number of lines and the distance between them depends upon the nature of element, so line spectra is used as “Finger Print” for the identification of elements. For example, line spectrum of sodium contains two yellow coloured lines separated by a definite distance.

6. The shape of orbital for which l = 0 is

(a) Spherical                       

(b) Dumbbell                                      

(c) Double dumbbell                        

(d) Complicated

Explanation; (Answer, a)

Its values show shape of orbitals. It has values l = 0 to (n – 1). e.g.

l = 0, used for s-orbital, spherical in shape

l = 1, used for p-orbital, dumb-bell in shape

l = 2, used for d-orbital, double dumb-bell in shape

l = 3, used for f-orbital, complicated shape

7. When 4d orbital is filled, the next electron enter into

(a) 5s                                    

(b) 5p                                                   

(c) 5d                                                    

(d) 6s

Explanation; (Answer, b)

According to n+ l rule, electrons are filled in various orbitals in the increasing order of (n+l) value. Those orbitals which have lower value of (n+l) value filled first. In case, if two orbitals which have same (n+l) value, then orbital having lower ‘n’ value will be filled first.

The n+l value of 4d orbital is 4+2 =6. The next orbital to be filled must have n+l value either equal to 6 or greater than 6. The n+l value of 5d orbital is 5+2 =7, for 5s it is 5+0=5, for 5p it is 5+1=6 and for 6s it is 6+0=6. Since 5p and 6s orbitals have same n + l value, hence the electron first go to that orbital which has least n value i.e. 5p.

8.  Which of the following is not an iso electronic pair?

(a) Na⁺ and Ne                   

(b) Na⁺ and F⁻                                    

(c) Na and Ca                                      

(d) Na⁺ and Mg²⁺

Explanation; (Answer, b)

The species having same number of total electrons and hence have same electronic configuration are called isoelectronic pair. Na⁺ and F⁻ are isoelectronic pair as both of them contains 10 electrons.

9. Balmer series appears in the hydrogen spectrum if electron jumps from any appropriate higher energy orbit to

(a) Second orbit                

(b) Third orbit                                   

(c) Fourth orbit                                

(d) Fifth orbit

Explanation; (Answer, a)

Balmer noted first that the Hydrogen spectrum consisted of some well defined discrete lines in the visible region (i.e. having l between 4000 to 7000Å) of spectrum. This series is obtained by the transition of electrons from any higher orbit (n₂ = 3, 4, 5, 6, 7 …. µ) to 2^nd orbit (n₁ = 2).

10.   In 1935 A.D. James Chadwick was awarded Nobel Prize because ...

(a) He discovered proton                                               

(b) He discovered neutron

(c) He determined the radius of hydrogen atom     

(d) He gave the rules for electronic configuration

Explanation; (Answer, b)

James Chadwick won the 1935 Nobel Prize in Physics for the discovery of the neutron.

XI MCQs Chapter 3 … Chemical Bonding

1.  If the bond angle is AB₂  type molecule is 104.5^o, it geometry should be;

(a) Linear                              

(b) Pyramidal                                     

(c) Bent                                                

(d) Planar Trigonal    

Explanation; (Answer, c)

The bond angle of 104.5^o is the characteristic of AB₂ type of molecules with bent or V-shaped or angular geometry.

2.             The highest bond energy in the following is:

(a) Cl–Cl                               

(b) H–F                                                 

(c) H–O                                                 

(d) H–N

Explanation; (Answer, b)

Bond energy is directly proportional to the bond polarity or partial ionic character which in turn is proportional to the difference in electronegativity of the bonded atoms. Greater the ΔEN, greater is the bond energy. H – F bond has the greatest ΔEN (1.9) and hence it has the highest bond energy (in fact highest among all diatomic molecules containing single bond; 570 kJmol⁻¹).

The second highest bond energy is for H – O bond with second highest ΔEN (1.4). The next highest bond energy is for H – N bond with third highest ΔEN (0.9). Cl–Cl being non-polar has the least bond energy.

3.The molecule which has zero dipole moment is:

(a) NH₃                                   

(b) HCl                                                  

(c) H₂O                                               

(d) CCl₄

Explanation; (Answer, d)

Symmetrical molecules with linear, trigonal or tetrahedral geometry show zero dipole moment. CCl₄ has symmetrical tetrahedral structure in which all four bond moments for C – Cl bonds being directed in opposite directions are cancel out giving net zero dipole moment.

4. The molecule which has maximum bond angle

(a) CS₂                                                     

(b) H₂O                                                 

(c) NH₃                                                  

(d) BF₃

Explanation; (Answer, a)

Linear molecules like CS₂, CO₂, BeCl₂, C₂H₂, HgCl₂, ZnCl₂ etc. with AB₂ formula has the largest bond angle of 180^o.

5. The shape and hybridization of BCl₃ molecule is:

(a) Tetrahedral and sp³     

(b) Linear and sp                              

(c) Planar trigonal and sp²                   

(d) Angular and sp³

Explanation; (Answer, c)

Being AB₃ molecule with no non-bonding orbital, BCl₃ has sp² hybridization with planar trigonal shape.

6.   Amongst the following molecules which one has trigonal pyramidal shape?

(a) SO₂                                                    

(b) CO₂                                                                           

(c) NH₃                                                  

(d) C₂H₄

Explanation; (Answer, c)

The ÄB₃ molecules like NH₃, PH₃, PCl₃, NCl₃ etc. with one lone pair and 3 bond pairs has trigonal pyramidal shape

7.             A simple covalent molecule possesses two bond pairs and two lone pairs around the central atom, its shape should be:

(a) Linear                             

(b) Planar trigonal                            

(c) Angular                                          

(d) Tetrahedral

Explanation; (Answer, c)

The presence of two bond pairs and two lone pairs around the central atom gives rise to angular shape to the molecules. Such molecules have :ÄB₂ type general formula.

8.   The correct relation between Debye and coulomb meter is:

(a) 1D = 3.33x10⁻³⁰Cm     

(b) 1D = 1.6x10⁻¹⁹Cm                       

(c) 1D = 1.88x10⁻¹²Cm                     

(d) 1D = 1.23x10⁻⁸Cm

Explanation; (Answer, a)

The SI unit of dipole moment C-M and cgs unit debye is inter related as

1D = 3.33x10⁻³⁰Cm     

9.             The bond order of N₂  molecule is:

(a) 0                                       

(b) 1                                                      

(c) 2                                                      

(d) 3

Explanation; (Answer, d)

The bond order of N₂  molecule is 3 showing that it has triple bond between two nitrogen atoms.

10. The number of sigma and pi bonds in C₂H₄ molecules are respectively:

(a) 3 and 1                           

(b) 2 and 2                                           

(c) 5 and 1                                           

(d) 4 and 2

Explanation; (Answer, c)

There are total 5 sigma and one pi bond in in C₂H₄ molecule.

XI MCQs Chapter 4 State of Matter, Gas

1. According to Graham’s Law of diffusion, the ratio of diffusion of H₂ and O₂ are respectively:

(a) 1:2                                   

(b) 2:1                                                   

(c) 1:4                                                   

(d) 4:1

Explanation; (Answer, d)

r₁/r₂= √M₂/√M₂ ⇒ r₁/r₂= √32/√2 ⇒ r₁/r₂= √16 ⇒ r₁/r₂= 4:1

2.   Collection of gas over water is an example of:

(a) Graham’s law               

(b) Dalton’s law                                 

(c) Avogadro’s law                          

(d) Gay-Lussac law  

Explanation; (Answer, b)

Collection of gas over water is an example of Dalton’s law. The pressure of dry gas is calculated by using Dalton’s law.

P_{dry gas} = P_{moist gas} – P_{water vapours}

3.            The molar volume of oxygen gas is maximum at:

(a) 0°C and 1 atm              

(b) 0°C and 2 atm                              

(c ) 25°C and 1 atm                           

(d) 25°C and 2 atm   

Explanation; (Answer, c)

The molar volume of a gas varies directly with temperature and varies inversely with pressure. The molar volume of a gas is maximum at highest temperature and least pressure. In option c and d, temperature is highest hence deciding factor will be pressure which is least in option c.

4. The volume of gas would be theoretically zero at:

(a) 0°C                                   

(b) 0 K                                                   

(c) 273 K                                              

(d) 273°C

Explanation; (Answer, b)

The volume of gas would be theoretically zero at 0 K (-273°C).

5.  If the Kelvin temperature of ideal gas is increase to double and pressure is reduced to one half, the volume of gas will:

(a) Remains same             

(b) Double                                           

(c) Reduced to half                            

(d) Four times

Explanation; (Answer, d)

PV=nRT ⇒ PV = T (R and n = constant) ⇒ V = T/P ⇒ V = 2/ ½ = 2 x 2 = 4

Thus, doubling the Kelvin temperature and halving the pressure quadruples the volume.

6. The molar volume of oxygen gas is 22.4 dm³ at:

(a) 0°C and 1 atm              

(b) 25°C and 0.5 atm                          

(c) 0 K and 1 atm                               

(d) 25 K and 0.5 atm 

Explanation; (Answer, a)

The molar volume of a gas is 22.4 dm³ at STP i.e. at 0C and 1 atm.

7. Under similar condition CH₄ gas diffuses........ times faster than SO₂ gas:

(a) 1.5 times                      

(b) 2 times                                               

(c) 4 times                                           

(d) 16 times

Explanation; (Answer, b)

r₁/r₂= √M₂/√M₂ ⇒ r₁/r₂= √64/√16 ⇒ r₁/r₂= √4 ⇒ r₁/r₂= 2

8. Which one of the following statement is incorrect about the gas molecules?

(a) They have large spaces                                              

(b) They possess kinetic energy

(c) Their collision is elastic                                              

(d) Their molar mass depends upon temperature

Explanation; (Answer, d)

The molar mass of gas is independent of temperature.

9. The diffusion rate of C₃H₈ and CO₂ are same because:

(a) Both are poly atomic gases                                       

(b) Both are denser than air

(c) Both have same molar mass                                     

(d) Both contains carbon atoms

Explanation; (Answer, c)

The rate of diffusion depends upon molar masses of gases. The gases with same molar masses would have same rate of diffusion. The given gases ethane (C₃H₈) and CO₂ have same molar mass of 44 gmol⁻¹.

10. Real gas reaches the ideal behavior at:

(a) Low temperature and low pressure                      

(b) High temperature and high pressure

(c) Low temperature and high pressure                     

(d) High temperature and low pressure     

Explanation; (Answer, d)

High temperature and low pressure make the ideal.

XI MCQs Chapter 7 -Chemical Equilibrium

1.  In the equilibrium system of PCl_5(g) ⇌ PCl_3(g)+ Cl_2(g), the correct relationship between K_c and K_p is:

(a) K_p> K_c                             

(b) K_p< K_c                                            

(c) K_p = K_c                            

(d) K_p/K_c=1

Explanation; (Answer, a)

2.  In the reaction A_(g)+ B_(g) ⇌2C_(g), the equilibrium constants K_p=K_c because:

(a) ∆n > 1                             

(b) ∆n < 1                                            

(c) ∆n = 1                             

(d) ∆n = 0

Explanation; (Answer, d)

3.  What happens to the value of K_c when a catalyst is added to a chemical system at equilibrium?

(a) It decreases                   

(b) it increases                                   

(c) It becomes zero           

(d) it remains unchanged

Explanation; (Answer, d)

4.  The correct K_sp expression of a sparingly soluble salt Li₂C₂O₄ among the following is

(a) K_sp=[Li⁺][C₂O₄²⁻]        

(b) K_sp=[Li⁺]²[C₂O₄²⁻]                       

(c) K_sp=[2Li⁺][ C₂O₄²⁻]      

(d) K_sp=[2Li⁺]²[C₂O₄²⁻]²

Explanation; (Answer, b)

5.  If the equilibrium expression of a reversible reaction is

                 K_c = [C]²/[A][B]

The balanced equilibrium equation should be:

(a) C ⇌ A+B                         

(b) A+B ⇌ C        

(c) 2C ⇌ A+ B     

(d) A+B ⇌ 2C

Explanation; (Answer, d)

6.  The term active mass use in law of mass action means:

 (a) No. of mole                   

(b) No. of molecules                         

(c) mole per dm³                               

(d) gram per dm³

Explanation; (Answer, c)

7. The equilibrium of N_2(g) +O_2(g) ⇌ 2NO_(g) (∆H = +ve) is affected by change in:

(a) Temperature only                                                      

(b) Pressure only

(c) Both temperature & pressure                                  

(d) Neither temperature nor pressure

Explanation; (Answer, a)

8.    The equilibrium of which of the following reaction would not be affected by an increase in pressure:

(a) PCl_5(g) ⇌ PCl_3(g)+ Cl_2(g)                                                

(b) 2NO_(g)  + Cl_2(g) ⇌ 2NOCl_(g)                 

(c) N_2(g) + O_2(g) ⇌ 2NO_(g)                                                   

(d) 2SO_2(g) + O_2(g) ⇌ 2SO_3(g)

Explanation; (Answer, b)

9.  NaCl when added to an aqueous silver chloride solution:

(a) Decreases the solubility of AgCI             

(b) Increases the solubility of AgCl              

(c) Forms a clear solution                               

(d) Does not effect

Explanation; (Answer, a)

10.  Some reactions are nearly to completion in the forward direction and identified by their:

(a) Very high value of K_c 

(b) Very low value of K_c 

(c) Very high value of ∆H                

(d) Very low value of ∆H

Explanation; (Answer, a)