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– → S2– (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;………………. SnSO4(aq) → Sn2+(aq) + SO42– …………
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
No comments:
Post a Comment