Electrolysis note for students

  IONIC THEORY

Ionic theory as proposed by Arrhenius states that when an ionic compound is dissolved in water or melted, some or all its particles dissociate (break up) into free moving charged particles called ions. This dissociation into ions is called ionization.

These free ions move randomly in all directions inside the solution. as seen in fig. A

But the ions lose their freedom as soon as an electric current is passed through the solution and they become orderly, surrounding themselves around the opposite pole or electrode as they begin to pull electrons from the electrodes or lose electrons to the electrodes and come out of the solution.

 Electrolysis is defined as the chemical decomposition of a compound by the passage of electricity through the solution of the compound or its molten form.

Terms commonly used in Electrolysis 

i. ELECTROLYTE: An electrolyte is a compound which allows the passage of electricity through its solution or its molten state and is decomposed in the process. 

Examples of electrolytes include dilute Acids and Alkalis and all electrovalent compounds like NaCl.

 Electrolytes are grouped in two

 1. Strong Electrolytes: These are compounds which ionize completely in solutions.

They usually have large amounts of ions in solution and hence are good conductors. Examples are all sodium and potassium salts, minerals acids, and caustic alkalis.

      NaCl_(aq) →Na⁺_(aq)  +  Cl-_(aq)

Weak Electrolytes: These are compounds that ionize partially in solution

 There is slight dissociation of the ions in dilute solutions, and so they contain less ions in solution. Examples include organic acids, aqueous ammonia, etc.

   CH₃COOH_(aq) →CH₃COO-_(aq) + H⁺(_(aq)

 Non-Electrolytes: These are compounds which do not conduct electricity at all, whether molten or in solution 

 Non-electrolytes are mostly covalent compounds and only exist as molecules. Examples include vegetable oils, organic solvents like alcohols, benzene sugar solution 

  Conductor and Non-conductor

  Conductors:  These are metals which allow the passage of electricity through them.

 Examples include all metals in general Silver is the best conductor followed by copper and ionic solutions

 Non-conductor (Insulators): These are substances that do not conduct or allow electricity to pass through them.  Examples include wood, paper, air, rubber, plastic.

  Electrodes: these are wires rods or plates through which an electric current enters or leaves the electrolytes

2.  Anodes:  This is the positive electrode through which electrons leave electrolytes. It is  the electrode where oxidation occurs

 3. Cathode: This is the negative electrode through which electrons enter the electrolyte. It is also the electrode where reduction takes place

 4.  Cations: - these are positively charged ions. They migrate to the cathode (negative electrode) during electrolysis.

5.  Anions: these are negatively charged ions. They migrate to the anode (positive electrode) during electrolysis.

5. Electrolytic Cell: This is a vessel or container containing two electrons connected to a battery and an electrolyte. It is used for Electrolysis.

When electrolysis is carried out on the solution of an ionic compound. There are usually two cations and two anions which  migrate to the cathode and anode respectively but only one of each ion is  preferentially discharged at the electrodes.

The following factors determine which ion gets discharged at each electrode.

1. Position of ions in the electrochemical series.

The ions at the bottom of the series for the positive ions are preferentially discharged to the ions at the top of the series, for example for a solution of sodium chloride containing Na⁺ and Cl^-, H⁺ and OH^- hydrogen is below sodium in the series and so will be preferentially discharged. For non-metals the less electronegative element is preferentially discharged to the more electronegative. So OH^- is preferentially discharged to Cl^-

2. Concentration of ion in the electrolyte. For a concentrated solution of a salt, the more concentrated ion is preferentially discharged to the less concentrated ion. but concentration does not matter where there is a large gap between the two ions in the series.

3. Nature of the electrodes: - Electrodes that have affinity for certain ions will cause those ions to be preferentially discharged during electrolysis. But both Platinum and Carbon are two electrodes that are considered as neutral or passive electrodes since they have no affinity for any element. 

 Examples of Electrolysis

1. Electrolysis of Acidified Water (water containing drops of H₂SO₄)

                
The Hoffman Voltameter is used; both the anode and cathode are platinum foil. 

The ions present in the electrolyte are:

          Cations          Anions

H₂SO₄ → 2H⁺_(g)    +       SO₄^2-            

H₂O →       H⁺_(aq)    +   OH^-_(aq)

At the Cathode: H⁺ ion migrate to the cathode and take up electrons to form neutral hydrogen atoms.

H+_(aq)  + e-→ H(g)

The hydrogen atoms then combine to form hydrogen gas molecule

H_(g) + H_(g)→ H_2(g) 

 Overall equation

2H⁺_(aq)  +  2e^- →H_2(g)

 At the anode: Both SO₄^2- and OH^- ions migrate to the anode where OH^- ions being lower in the electrochemical series is preferentially discharged and lose its electrons to the anode to become a neutral - OH group.

OH^-_(aq) → OH  + e

The neutral –OH group combines in pairs to form one molecule of water and one atom of oxygen.

OH  +  OH → H₂O_(l)  +  O_(g)

The oxygen atoms then combine with another free oxygen atom to form an oxygen gas molecule.

O_(g) + O_(g)→O_2(g)        

Overall equation

 4OH^-_(aq)→2H₂O_(l)  +  O_2(g) +  4e^-

 Note: At the end of the electrolysis the solution becomes more concentrated or more acidic as the components of water (H₂ and O)

H+(aq)  + e–→ H_(g)

The hydrogen atoms then combine in pairs to form diatomic hydrogen gas molecule 

H_(g) + H_(g)→H_2(g).

Overall equation

2H⁺_(aq)  +  2e^-→ H_2(g)

Thus, hydrogen gas is obtained at the cathode.

At the anode: both Cl- and OH^- ions migrate to the anode where Cl^- ions are preferentially discharged. This is because it is  higher in concentration than OH^- ion and the two ions are close to each other in the series.  

      Cl^-_(aq)→Cl_(g)  +  e^- 

 The chlorine atoms combine to give the molecules. 

       Cl_(g)  +  Cl_(g)→Cl₂

Overall equation

2Cl^-_(aq)→ Cl_2(g)  +   2e^-

Chlorine gas is obtained at the anode.

 

3.Electrolysis Of Copper (II) Tetraoxosulphate (VI) Solution Using Different  Anode: 

1. With carbon or platinum electrodes.

               Cations            Anions

CuSO₄  →    Cu²⁺_(g)    +    SO₄^2-_(aq)   

H₂O      →     H⁺_(aq)    +     OH^-_(aq)

At the Cathode: Cu²⁺ and H⁺ ion migrate to the cathode where Cu²⁺ being lower than and less electropositive than H⁺ is preferentially discharged  as metallic copper on the cathode.

 Cu²⁺_(aq)  + 2e^-→ Cu_(s)

 

At the anode: SO₄^2- and OH^- ions migrate to the anode where OH^- ions lose their electrons to become a neutral  - OH group.

OH^-_(aq) → OH  + e^-

OH  +  OH → H₂O_(l)  +  O_(g)

O_(g) + O_(g)→O_2(g)        

 Overall equation

4OH^-_(aq) →2H₂O_(l) + O_2(g) + 4e-

Electrolysis of CuSO₄ using different electrodes

1. Using Pt. or C- electrodes: - Pt. and C-electrodes as we know are inert or passive electrodes and do not determine the product of the electrolysis

Uses Of Electrolysis 

1. Extraction of metals like Na, K, Mg, Ca and Al.

2. Purification of metals copper, 

3. Electroplating

4. Preparation of some elements like Cl₂ as sodium hydroxide, hydrogen and chlorine from electrolysis of brine using cathode.

 

OBJECTIVE QUESTIONS

1. Electrolysis is the process of

(a) producing electricity from chemicals
(b) using electricity to cause chemical change
(c) breaking compounds by heating
(d) mixing acids and bases

2. The substance that is decomposed during electrolysis is called the
(a) electrode
(b) electrolyte
(c) conductor
(d) catalyst

3. Which of the following is NOT an electrolyte?
(a) Molten sodium chloride
(b) Dilute sulphuric acid
(c) Distilled water
(d) Sodium hydroxide solution

4. In electrolysis, oxidation occurs at the
(a) cathode
(b) anode
(c) electrolyte
(d) battery

5. Reduction takes place at the
(a) anode
(b) cathode
(c) electrolyte
(d) circuit

6. The positive electrode in an electrolytic cell is the
(a) cathode
(b) anode
(c) electrolyte
(d) salt bridge

7. Which particle moves to the cathode during electrolysis?
(a) Anion
(b) Cation
(c) Electron
(d) Neutron

8. During the electrolysis of molten sodium chloride, the product at the cathode is
(a) chlorine gas
(b) sodium metal
(c) hydrogen gas
(d) oxygen gas

9. During electrolysis of acidified water, the gas collected at the anode is
(a) hydrogen
(b) oxygen
(c) chlorine
(d) nitrogen

10. Which of the following statements is correct?
(a) Oxidation occurs at the cathode
(b) Reduction occurs at the anode
(c) Anions move to the anode
(d) Cations move to the anode

11. A substance that allows electric current to pass through it by movement of ions is called a
(a) conductor
(b) semiconductor
(c) electrolyte
(d) insulator

12. The electrodes used in electrolysis may be
(a) active or inert
(b) solid or liquid
(c) metals only
(d) non-metals only

13. Which of the following is an example of an inert electrode?
(a) Zinc
(b) Copper
(c) Platinum
(d) Iron

14. The process of coating an object with a thin layer of metal using electricity is called
(a) electrolysis
(b) electroplating
(c) electrolysis reaction
(d) electrorefining

15. In the electrolysis of copper(II) sulphate using copper electrodes, the anode
(a) dissolves
(b) gains mass
(c) remains unchanged
(d) produces hydrogen

16. Which law of electrolysis states that the mass of a substance deposited is proportional to the quantity of electricity passed?
(a) Ohm’s law
(b) Faraday’s first law
(c) Boyle’s law
(d) Charles’ law

17. The electrolyte in a dry cell is usually
(a) sodium chloride
(b) potassium hydroxide
(c) ammonium chloride paste
(d) sulphuric acid

18. In electrolysis, electrons flow through the
(a) electrolyte
(b) external circuit
(c) electrode
(d) salt solution

19. Which of the following products is obtained at the cathode during electrolysis of dilute sulphuric acid?
(a) Oxygen
(b) Hydrogen
(c) Chlorine
(d) Sulphur

20. The main purpose of electrorefining is to
(a) produce alloys
(b) extract metals from ores
(c) purify metals
(d) coat metals

ALKENES at a glance

 ALKENES

Alkenes are a homologous series of unsaturated hydrocarbons with a general molecular formular C_nH_2n.

They are named by replacing the ending "ane" of the corresponding alkane with "ene" for each member of the series.

NOTE: because alkenes contain double bonds between carbon to carbon i.e C=C n=1 does not exist.

When n=	General Molecular Formulae CnH2	Name
2.	C2H2x2= C2H4	Ethene
3.	C3H2x3 = C3H6	Propene
4.	C4H2x4 = C4H8	Butene
5.	C5H2x5 = C5H10	Pentene
6.	C6H2x6 = C6H12	Hexene
7.	C7H2x7 = C7H14	Heptene
8.	C8H2x8 = C8H16	Octene
9.	C9H2x9 = C9H18	Nonem
10.	C10H2x10 = C10H20	Decene

 

NOMENCLATURE OF ALKENES

When naming the alkenes, care must be taken because unlike the alkanes which have only single bonds, the alkenes contain double bonds, and so the naming of the substituents is based on the position of the double bond. For example, the molecule CH₃CH=CHCH₃ is named but-2-ene.

Although the double bond joins carbon atoms 2 and 3, the number 2 is used because it gives the lowest number to the double bond.

other examples include 

(i)  CH₃-CH₂-CH₂-CH=CH₂           

        Pent-1-ene or Pentene

(ii) CH₃CH₂CH=CHCH

        Pent-2-ene

                     

                    CH₃
                     |
(iii)       CH₃C=CHCH₃                    

         2-methylbut-2-ene

                          CH₃

                           |

(iv)       CH₃-C=C-CH₃
                       |   

                       CH₃  

       2,3-dimethylbut-2-ene

                    CH₃         
                          |   
           CH₃CH₂C=CCH₂CH₃                                      
                               |

                              CH₃

         3,4-dimethylhex-3-ene

             CH₃            CH₃

                |                   |

(vi)   CH₃C-CH=CH-C-CH₃
                 |                  |      
                CH₃            CH₃

    2,2,5,5-tetramethylhex-3-ene

MOLECULAR STRUCTURES OF ALKENES

	ALKENES molecular formula /name	STRUCTURAL FORMULAR	Condensed  FORMULAR
2.	C2H4 Ethene	H             H            ∖         ∕              C=C          ∕         ∖       H           H	H2C=CH2
3.	C3H6 Propene	H    H     H            |      |         ∕  H — C — C=C            |       |        ∖           H     H       H	CH3CH=CH2
4.	C4H8 Butene	H H H   H         |   |   |      ∕    H-C-C-C=C         |   |   |       ∖         H H H      H	CH3CH2CH=CH2
5.	C5H10 Pentene	H H H  H        H        |   |   |    |       ∕   H-C-C-C-C=C        |   |   |   |       ∖       H H H H        H	CH3(CH2)2CH=CH2
6.	C6H12 Hexene	H H H H  H     H        |   |   |   |    |       ∕   H-C-C-C-C-C=C         |   |   |   |   |     ∖        H H H H H      H	CH3(CH2)3CH=CH2
7.	C7H14 Heptene	H H H H H H       H       |   |    |   |   |   |       ∕  H-C-C-C-C-C-C=C       |    |   |   |   |   |       ∖      H H H H H H        H	CH3(CH2)4CH=CH2
8.	C8H16 Octene	H H H H H H  H     H        |   |    |   |   |   |   |      ∕  H-C-C-C-C-C-C-C=C        |  |    |   |   |   |   |      ∖       H H H H H H H      H	CH3(CH2)5CH=CH2
9.	C9H18 Nonene	H H H H H H H  H     H       |   |   |    |   |   |    |   |      ∕                          H-C-C-C-C-C-C-C-C=C       |   |   |   |    |   |   |   |     ∖        H H H H H H H H   H	CH3(CH2)6CH=CH2
10.	C10H20 Decene	H H H H H H H H  H     H      |  |    |    |    |  |    |   |   |     ∕ H-C-C-C-C-C-C-C-C-C=C      |   |   |    |   |   |  |   |    |     ∖           H H H H H H H H H      H	CH3(CH2)7CH=CH2

LABORATORY PREPARATION OF ETHENE

Ethene is prepared in the laboratory by dehydration of alkanols such as ethanol (C₂H₅OH) by concentrated H₂SO_4.

DIAG.

                                                     Laboratory preparation of Ethene

equation for the reaction

step i:      C₂H₅OH + H₂SO₄ → C₂H₅HSO₄ + H₂O.

  step ii.   C₂H₅HSO₄ →C₂H₄ + H₂SO₄

When ethylhydrogentetraoxosulphate (VI) is heated, it releases ethene which is collected over water.

 

NOTE: The wash bottle containing sodium hydroxide is to remove Sulphur (iv)oxide.

PHYSICAL PROPERTIES OF ETHENE (ALKENES)

1. It is colourless and odourless gas

2. It is neutral litmus paper

3. It is almost insoluble in water

4. It is less dense than air.

Chemical Properties Of Ethene

Alkenes such as ethene undergoes addition reaction 

1. Reaction of ethene with hydrogen in the presence of nickel as a catalyst

                                  Ni    
          H₂C=CH₂ + H₂ →   CH₃CH₃         
              ethene                   ethane

This reaction is important in the conversion of oil into margarine by the process known as HYDROGENATION.

2. Reaction of ethene with chlorine to produce 1,2-dichloroethane.

 CH₂=CH₂ + Cl₂ → ClCH₂-CH₂Cl

3. Reaction of ethene with bromine to produce 1,2-dibromoethane

 CH₂=CH₂ + Br₂ → CH₂Br-CH₂Br

4. Reaction of ethene with oxygen or combustion reaction of ethene (alkenes) to produce carbon(iv)oxide and water

  CH₂=CH₂ + 3O₂ →2CO₂ + 2H₂O

5. Reaction of ethene with hydrogen halide (Hydrogen chloride) (HCl) to produce ethylchloride.

 CH₂=CH₂ + HCl → CH₃CH₂Cl  

6. Reaction of ethene with water in the presence of dilute H₂SO₄ to produce ethanol

   CH₂=CH₂ + H₂O →CH₃CH₂OH

7. Reaction of ethene with neutral KMnO₄ to produce 1,2-ethan-diol (glycol)

 CH₂=CH₂ + KMnO₄ → CH₂—CH₂
                                            |          |
                                           OH     OH    

                                     ethan-1,2-diol

 KMnO4 is decolorized in the above reaction, and this reaction distinguishes alkenes from alkanes which do not decolorize KMnO₄

Uses Of Ethene

1. In the production of polythene which is used for making nylon or polythene bags and wrappers

2. In the manufacturing of margarine by the process of hydrogenation.

 Other examples of alkenes are as follows

(i)      CH₃CH₂C = CCH₃                                           (ii)     CH₃C = CHCH₃
                                 |       |                                                                   |
                           CH₃ CH₃                                                            CH₃
            

             2,3-dimethylpent-2-ene                                  3-methylbut-2-ene

                       CH₃                                                                                                CH₃ 
                        |                                                                                                      |    
(iii)       CH₂= C — CH—CH₂CH₂CH=CH₂        (iv)        CH₃CH₂CHCH=CHCH=C=CH₂ 
                                |                                                                            |
                                CH₂CH₃                                                              CH₂CH₃  
         

              2-methyl, 3-ethylhept-1,6-diene                                6-ethyl, 3-methyloct-1,2,4-triene

                                                                                    Cl
                                                                                     |
(v)       CH₃CH=CHCH₃                        (vi)      CH₃-C-CH=CH₂ 
                            |                                                         |
                           Cl                                                      Cl
            3-chlorobut-2-ene                               3,3-dichlorobut-1-ene

(vii)     CH₃CH₂C=CH=CHCH₃              (viii)     CH₃C=CHC=CH₃  
                           |            |                                              |           |
                          Cl         Br                                           Cl        Cl
            2-bromo, 4-chlorohex-2,3-diene        2,4-dichloropent-1,3-diene

                           

                                 Cl                                                                   Cl
                                  |                                                                       |
(ix)      CH₂=C=CH-C=C-CH₃                         (x)     CH₃CHCH=C-CH₃  
                                       |                                                    |             |
                                      Br                                                 Cl         Cl

                5-bromo,3-chlorohex-1,2,4-triene                 4,2,2-trichloropent-2-ene

              

          H H H            H                                                        CH₂CH₃
               |    |  |            ∕                                                          ∕
(xi)  H-C-C-C-C=C                              (xii)   CH₃CH = C
             |    |   |   |      ∖                                                        ∖                                     
            H H   | H        H                                                       CH₂CH₂Cl
                      |                                                                     5-chloro -3-ethylpent-2-ene
                 H-C-H                                              
                      |
                     H                                                                       
       3-methylpent-1-ene

                       

                                    CH₃
(xiii)                          ∕
            H₂C = C = C
                                 ∖
                                   H
            But-1,2-diene 

OBJECTIVE QUESTIONS

1. Hydrogenation of butene yields 

a. Butyne 

b. butane

c. pentene

d. butanol

2. Geometric (cis- trans) isomerism is exhibited by

a. C₂H₂Cl₂

b. C₂H₆Cl

c. C₄H₁₀

d. C₅H₁₂

3. which of the following is the general formula for the alkenes

a. CnH2n-2

b. CnH2n

c. CnH2n+2

d. CnH2n+1

4. Alkenes underg the reactions

THEORY QUESTIONS

1. Use the reaction scheme below to answer the following questions 

(i).  

Carbon II oxide at a glance

 CARBON (II) OXIDE

LABORATORY PREPARATION

1.  Carbon (II) oxide is prepared by the dehydration of methanoic (formic) acid or ethanedioic (oxalic) acid, using concentrated tetraoxosulphate (VI) acid.

HCOOH_(l)   ^{Conc. H2SO4}   CO_(g)   +   H₂O

Methanoic acid

Note: Pure CO is obtained by passing the gaseous mixture is passed through concentrated NaOH to remove CO₂.

The major air pollutants that can result from smoky vehicles are Carbon (ii) oxide and Carbon particles.

 2.  Carbon (II) oxide can also be prepared by passing Carbon (IV) oxide through red-hot carbon.

  The gaseous mixture is passed through concentrated NaOH to remove excess Carbon (IV) oxide.

CO_2(g) + C_(s) →2CO_(g)

Pure Carbon (II) oxide is collected over water.

Caution: The preparation of CO must be done in a fume cupboard as the gas is poisonous.

Exposure to even as low as 0.05% for a short while may cause death, by suffocation.

 

Physical Properties Of CO

(1) It is a colourless, tasteless and odourless gas.

(2) It is insoluble in water, but dissolves in a solution of ammoniacal copper (I) chloride.

(3) It has the same density as air 

(4) It is neutral to litmus

Chemical Properties Of CO

(1) It is a strong reducing agent: reducing most metal oxides to the metsl

     Fe₂O_3(s) + 3CO_(g) → 2Fe_(s) + 3CO_2(g)

     CuO_(s) + CO_(g) → Cu_(s) + CO_2(g)

2.  Combination reaction

(a). With oxygen: CO burns in air with a faint pale blue flame to form CO₂ .

    2CO_(g) + O_2(g) →2CO_2(g)

3.  CO combined with Chlorine gas when expose to ultra-violet light or passed over a catalyst of activated charcoal at 150⁰C to form carbonyl chloride.

CO_(g) + Cl_2(g) →COCl_2(g)

This product, COCl₂, is also known as Phosgene and was employed as a poisonous gas in the First World War. It is now use in the manufacture of dyestuff.

 It is considered a poisonous gas because it combines irreversibly with the  haemoglobin in the red blood cells to form carboxy-haemoglobin thereby preventing the red corpuscle from carry oxygen.

 

Test for Carbon (II) oxide

 Inserteda lighted splinter into a test tube containing into the unknown gas if it burns with a pale blue flame and the gas produced turns lime water milky.

 

Uses of Carbon (ii) oxide

(1) CO is used in the extraction of metals from their ores.

(2) It is an important constituent of gaseous fuels like producer gas and water gas.

(3) CO gas is used in the manufacture of methyl alcohol, synthetic petrol, carbonyl chloride, oxalate and formate.

 

 

 Objective Questions

1. Gas prepared by the reaction between methanoic acid and concentrated tetraoxosulphate (vi) acid is (a) SO₂         

 (b) CO             

 (c) CO₂          

 (d) H₂S.

2.  Gas which dissolves in ammoniacal copper (i) chloride but insoluble in water is

(a) NH₃

 (b) CO

 (c) N₂O 

(d) CO₂.

3. It is dangerous to stay in a badly ventilated room which has a charcoal fire because of the presence of

 (a) carbon (II) oxide

 (b) carbon (iv) oxide

 (c) hydrogen sulphide 

(d) producer gas.

 

THEORY

1(a) Why is important for the laboratory preparation of carbon (II) oxide to be done in a fume chamber?

2.  Why it is not advisable to stay in a closed garage for a long time when racing a car engine.

Carbon IV oxide at a glance

 CARBON (IV) OXIDE: - About 0.03% of atmospheric air is Carbon (IV) oxide by volume while dissolved air contains about 0.50% by volume. This percentages are usually maintained by processes which use up and releases CO2 into the atmosphere, such processes include burning of fossil fuels and organic materials, respiration, deforestation and Photosynthesis 

 

Laboratory preparation

Carbon (IV) oxide is prepared in the laboratory by the action of dilute hydrochloric acid on CaCO₃ which can be in the form of   marble chips or limestone. 

Reaction between CaCO₃ and HCl can be carried out in a Kipp’s apparatus.

     CaCO_3(s)  + 2HCl_(aq) →CaCl_2(aq) + H₂O_(l)

Note: The dry gas is obtained by passing the gas through potassium hydrogen trioxocarbonate (IV) solution to remove any acid fumes and then through fused Calcium chloride in a U-tube to dry the gas. The dry gas is then collected by downward delivery because it is heavier than air.

INDUSTRIAL PREPARATION

CO₂ is obtained industrially as a byproduct in fermentation processes and when limestone is heated to make quicklime.

 

PHYSICAL PROPERTIES

(1) CO₂ is a colourless.

(2) It is an odourless gas with a sharp refreshing taste.

(3) It is about 1.5 times denser than air.

(4) It is soluble in water.

(5). CO₂ dissolves in water to yield trioxocarbonate (IV) acid.

(6) It readily liquefies and solidifies at -78⁰C on cooling to form a white solid known as dry ice.

 

CHEMICAL PROPERTIES

1). It turns damp blue litmus paper pink because

1. Reaction with water: Carbon (IV) oxide dissolves in water to form trioxocarbonate (IV) acid (Soda water). It is a weak dibasic acid ( i.e it ionizes slightly)

(a)  CO_2(g) + H₂O_(l)→H₂CO_3(aq)

On heating rioxocarbonate (IV) acid it decomposes to form H₂O_(l) and CO_2(g).

 

2. Reaction with alkalis: It reacts to form  trioxocarbonate (IV)

CO_2(g) + 2NaOH_(aq)→Na₂CO_3(aq)+ H₂O_(l)

Limited

Excess CO₂ reacts with alkalis to produce Hydrogen trioxocarbonate (iv) salt.

      CO_2(g) + NaOH_(aq)→NaHCO_3(aq)

     Excess.

3.  Reaction with burning Na, K or Mg:  when passed over burning Na, K andd Mg CO₂ is reduced to carbon.

      CO_2(g) + 2Mg_(s)  →C_(s) + 2MgO_(s)

Note: CO₂ does not support combustion.

 

4.  Reaction with red hot carbon: CO₂ is reduced to CO when passed over red-hot coke.

          CO_2(g) + C_(s) →2CO_(g)

The reaction is important in the blast furnace and in the manufacture of gaseous fuels.

 

Test for CO₂: Bubble the unknown gas through a solution of lime water (Calcium hydroxide) if the lime water turns milky due to the formation of insoluble calcium trioxocarbonate (IV) then the unknown gas is CO₂

Ca(OH)_2(aq) + CO_2(g) →CaCO_3(s) + H₂O_(l).

If the CO_2(g) is bubbled in excess, the milkiness will disappear and turn to a clear solution. This is due to the formation of soluble calcium hydrogen trioxocarbonate (IV).

   CaCO_3(s)+ H₂O_(l) + CO_2(g) →Ca(HCO₃)_(aq)

Finally, if the clear solution is heated, the milkiness reappears due to the decomposition of soluble Ca(HCO₃)₂ to form insoluble CaCO₃

Ca(HCO₃)_2(aq) →CaCO_3(s) +  H₂O_(l) + CO_2(g)

 

Uses of carbon (iv) oxide

1.  It is used as fire extinguishers since it does not support combustion.

2.  It is used in making carbonated (aerated) drinks their refreshing taste.

3.  It is used in the manufacture of Na₂CO₃ (washing soda) by the Solvay process.

4.  It is used as a leavening agent in the baking of bread. Yeast and baking powder produces CO₂ which make the dough of bread to rise.

5.  It is used in the manufacture of fertilizer (such as urea and (NH₄)₂SO₄.

6.  Solid CO₂ (i.e dry ice) is used as a refrigerant for perishable goods e.g ice cream. (It sublimes on warming and provides a lower temperature).

7.  Gaseous CO₂ is used to preserve fruits.

8.  CO₂ is also used as a coolant in nuclear reactors.

Objective Questions 

1. Kipp’s apparatus is important in the laboratory because it 

(a) allows intermittent supply of gases. 

(b) is used for preparing poisonous gases.

 (c) is used to prepare light gas

. (d) is used to prepare sensitive gas

2.  Where else is CO₂ found in free state apart from the atmosphere?

(a) In carbonated drinks.

 (b) Dissolved form in water. 

(c) In corals. 

(d) In limestone region

Theory Questions 

1) State the property of CO₂ that makes it to be used in

 (i) carbonated drinks (ii) fire extinguishers

(b). State what is observed when 

(i) excess CO₂ is bubbled through lime water. (ii) the solution in b(i) above is heated.

 

 

CARBON AND ITS ALLOTROPES school notes

   Carbon is found in group IV period II in the periodic table.  It has an electronic configuration of 1s22s22p2.

OCCURRENCE

 It exists naturally as a free element in both crystalline and non-crystalline forms (allotropes).  0v 

ALLOTROPES OF CARBON

Allotropy is the phenomenon whereby an element can exist in two or more different forms but in the same physical state. 

The different forms of the element are known as allotropes. Hence

Allotropes are different forms of an element but in the same physical state

  Allotropes have the same chemical properties but different physical properties.

Carbon exists in several allotropic forms:

(1). Crystalline Allotropes e.g Diamond, Graphite and Fullerene

(2). Non-crystalline Allotropes/Amorphous allotropes  e.g coal, charcoal, coke, lampblack and carbon black (soot)

 

Crystalline Allotropes of carbon

1. Diamond: Diamond is the purest form of carbon.  It is a giant molecule in which the carbon atoms are tetrahedrally bonded (i.e, the carbon atoms in diamond uses all four valence electrons for bonding), closely packed and held together by strong covalent bonds giving diamond an octahedral shape

 

 

Basic tetrahedral arrangement of C-atoms in Diamond Crystals

 

PROPERTIES OF DIAMOND

(1)   Diamond is the hardest substance know

(2)   It has a high melting and boiling point because of strong covalent bond.

(3)   It has a high density

(4)    It is resistant to chemical attack 

(5)    It does not conductor electricity because there are no free valence electrons in the crystal

(6)   It is transparent and has high refractive index (ability to scatter light.)

 

USES

(1) It is used industrially for making drilling machines

(2) It is used to sharpen very hard tools.

(3) It is used for cutting glass and metals.

(4) It is also used as pivot supports in precision instruments and as dies for drawing wires

(5) It is used as jewelry

Artificial diamond is made by subjecting graphite to a very high temperature and pressure for several hours in the presence of nickel or rhodium catalyst.

 

GRAPHITE:  

-Graphite is a dark and opaque allotrope.  

-The carbon atoms in graphite use only 3 out of the 4 valence electrons for bonding (hence graphite contain free mobile electrons) forming flat hexagonal layers.

- Each hexagonal layer is arranged one above the other held by week van der wall forces to form a crystal lattice, 

-These week forces of attraction cause each layer to easily slide over the other which make graphite to also flakes easily

 

 

PROPERTIES OF GRAPHITE

(1)    Graphite is soft and slippery because of weak forces holding its layers. Each layer can slide over one another. Hence, graphite acts as a lubricant.

(2)     It is less dense than diamond

(3)     It is not affected by chemical attack (due to its open structures in layers).

(4).    It is a good conductor of electricity (because of the presence of free delocalized electrons (mobile electron) in the crystal lattice.)

(5)     It has high melting and boiling point.

 

USES

(1) It is usually used on bicycle chains and for the bearings of some motor cars.

(2) It is used as a dry lubricant.

(3) It is used as electrodes in electroplating and in dry cells.

(4) It is used to line crucibles for making high-grade steel and other alloys (since it can withstand high temperature).

(6) It is used in making lead pencils i.e. combining it with clay makes lead in pencils.

(7) It is used as a black pigment in paints.

(8) It is used as a neutron moderator in atomic piles.

 

INDUSTRIAL PREPARATION OF GRAPHITE

Graphite is produced industrially by heating coke in an electric furnace to a very high temperature for about 20 to 30 hours in the absence of air and under sand. This process is called the Acheson process. .

 

 

 

DIFFERENCES IN PROPERTIES BETWEEN GRAPHITE AND DIAMOND

Graphite	Diamond
1. It has a density of 2.3gcm-3	1. It has a density of 3.5gcm-3
2. It is a black, opaque solid	2. It is a colourless, transparent solid
3. It is very soft, marks paper	3. It is the hardest known substance.
4. It is a good conductor of electricity	4. It is a non-conductor of electricity
5. Attacked by potassium trioxochlorate (v) and trioxonitrate (v) acid together.	5. Not attacked by these reagents.

Note: Diamond is transparent to x-rays while glass is almost opaque.

 

Fullerenes 

Fullerenes are a type of carbon molecule, consisting of 60 carbon atoms (C60) arranged in a unique spherical structure. They're also known as buckyballs.

*Properties and applications*

1. *Unique structure*: Fullerenes have a hollow, cage-like structure, making them suitable for applications like drug delivery and nanoencapsulation.

2. *Electronic properties*: Fullerenes exhibit interesting electronic properties, making them potential candidates for use in materials science and electronics.

3. *Superconductivity*: Some fullerene derivatives have shown superconducting properties.

*Potential uses*

1. *Medicine*: Fullerenes are being explored for potential medical applications, such as drug delivery, imaging, and therapy.

2. *Materials science*: They're being researched for use in creating new materials with unique properties.

3. *Energy storage*: Fullerenes might have applications in energy storage and conversion.

Would you like to know more about fullerenes or their potential applications?

AMORPHOUS CARBON

These non-crystalline structures which are not considered to be true allotropes include:

 

CHARCOAL: This is made by burning wood, bones, or sugar in a limited supply of  air. Charcoal is used to remove colour from substances. Wood charcoal is used in absorbing poisonous gases while animal charcoal is used in absorbing colours.

 

CARBON BLACK AND LAMP BLACK: Lamp black is obtained by burning vegetable  oil lamp  that it leaves a deposit of soot  while carbon black is obtained from burning coal gas, natural gas or petroleum. Carbon black and lamp black are used as an additive to rubber tyres. They are also used in making printer’s ink, carbon paper, black shoe polish, type writing.

COAL

Coal is an impure form of carbon. Coal is a complex mixture of compounds composed mainly of carbon, hydrogen and oxygen with small amounts of nitrogen, sulphur and phosphorus as impurities.

Carbonization of coal.

Coal was formed by the gradual decomposition of plant vegetation under pressure and in the absence of air under sand. A time  known as the carboniferous Era. Carbon (iv) oxide, methane, and steam were liberated, leaving behind a material that contained a very high percentage of carbon.

During this process of carbonization, the vegetable material was converted in stages into several stages of coal namely

 

Types of Coal

There are 4 different types of coal namely:

(1) Peat-like coal: It contains about 60% of carbon by mass.

(2) Lignite coal (brown coal): It contains about 67% of carbon by mass.

(3) Anthracite coal (or hard coal): It is tough and hard. It contains about 94% of carbon by mass. Impurities present may include nitrogen, sulphur and phosphorus. Anthracite is the last stage of coal.

(4) Bituminous (soft) coal: These are use every day at home. It contains about 88% by mass of carbon.

 

Destructive Distillation of Coal

This is when coal is heated to a very high temperature in the absence ofair.

Yielding the following products

Coal            Coal gas   + Coal tar   Ammoniacal liquor  + Coke

 

Uses of coke

(i) Coke is mainly used as a fuel.

(ii) It is a very important industrial reducing agent and is used in the extraction of metals, especially iron, from their ores.

(iii) It is also used in the production of gaseous fuels, like water gas and producer gas.

(iv) It is used for the manufacture of graphite, calcium carbide, silicon carbide and carbon (iv) sulphide.

2. 

(a) Ammoniacal liquor: is a solution of NH₃ in water. It is used to make Fertilizers

(b) Coal tar :- it is used for road construction and also to produce other chemicals like toluene, phenol, benzene, naphthalene and anthracene which are used in the synthesis of important commercial product like dyes, paints, insecticides, drugs, plastics and explosives

Distillates of Coal	Uses
1.Ammoniacal liquor	To produce (NH4)2SO4 for fertilizer.
2.Coal tar	To produce useful chemicals such as disinfectants and perfumes
3.Coal gas	Used as industrial fuel.

 

Uses of coal

1.  Coal is used mainly as fuel to generate power for steam engines, factories and electrical plants.

2.  It is also used

 

FUEL GASES/GASIFICATION OF COKE

There are 3 types of fuel gases.

1.     Producer gas: Producer gas is a mixture of nitrogen and carbon (ii) oxide. It is prepared by passing a stream of air through red hot coke.

2C_(s)h   +  O_2(g)   +  N_2(g)           2CO_(g)     +     N_2(g)   +    Heat

Producer gas

2. Water gas: Water gas is a mixture of hydrogen and carbon (ii) oxide gas. It is prepared by passing steam over white hot coke.

H₂O_(g)    +        C_(s)                     CO_(g)      +       H_2(g)

Steam         white hot coke               Water gas

2.      Hydrogen gas:-water gas is then mixed with excess steam, and the mixture passed over iron (iii) oxide catalyst at 450⁰C.The carbon (ii) oxide decomposes the steam and the product are hydrogen and carbon (iv) oxide.

CO_(g)   +   H_2(g)      +    H₂O_(g)            CO_2(g)   +    2H_2(g)

 

Caustic soda or water is used to absorbed carbon (iv) oxide from the mixture. Ammoniacal copper (i) chloride can be used to remove unreacted carbon (ii) oxide. The final product is hydrogen.

 

Differences between Producer Gas and Water Gas

(1) Producer gas has a lower heating ability than water gas. ( because water gas consists of equal volumes of hydrogen  and carbon (ii) oxide both of which are combustible whereas producer gas consists of 33% combustible CO and 67% non-combustible N₂.

Water gas is an important industrial fuel and is used in the manufacture of hydrogen and other organic compounds e.g. methanol and butanol.

3.  Synthetic gas: It is a mixture of hydrogen and carbon (ii) oxide gas. It is prepared by mixing steam with methane (obtained as natural gas) and passing them over Nickel catalyst at about 800⁰C.

CH_4(g)     +      H₂O_(g)             CO_(g)   +   3H_2(g)

Synthetic gas is not a major source of air pollution because sulphur is removed in the gasification process/it does not contain sulphur or sulphur compounds.

 

CHEMICAL PROPERTIES OF CARBON

(1) Combustion:

(a) All forms of carbon burn in excess oxygen to produce carbon (iv) oxide gas.

C_(s)       +     O_2(g)          CO_2(g)          ( Complete combustion)

(b) All forms of carbon also burn in a limited supply of air to produce carbon (ii) oxide.

C_(s)      +     O_2(g)           CO_(g)               ( Incomplete combustion)

(2) Combination reaction: Carbon combines directly with certain elements such as Sulphur, Hydrogen, Calcium and Aluminium at very high temperatures.

C_(s)    +    2S_(s)                     CS_2(l)

Carbon (iv) sulphide

C_(s)   +    2H_2(g)                   CH_4(g)

Methane

2C_(s)   +     Ca_(s)                  CaC_2(s)

Calcium carbide

3C_(s)   +     4Al_(s)                   Al₄C_3(s)

Aluminium carbide.

(3) As a reducing agent: Carbon is a strong reducing agent. It reduces the oxides of the less active metals to the metals, while carbon is itself oxidized to either carbon (iv) oxide or carbon (ii) oxide, depending on the reaction conditions.

Fe₂O_3(s) + 3C_(s) →2Fe_(s) + 3CO_(g)

2CuO_(s) + C_(s) → 2Cu_(s) + CO_2(g)

 

(4) Reaction with strong oxidizing agents: When carbon is heated with conc. HNO₃ or conc. H₂SO₄, it is oxidized to Carbon (iv) oxide.

C_(s) + 4HNO_3(aqp → 2H₂O_(l) + 4NO_2(g) + CO_2(g)

C_(s) + 2H₂SO_4(aq) → 2H₂O_(l)+2SO_2(g)+ CO_2(g)