ALKANOIC ACID at a glance

 

ALKANOIC ACIDS

The alkanoic acids are a homologous series of organic compounds containing a carbonyl (-CO) group attached to the hydroxyl group (-OH).   They have the general molecular formula of C_nH_2n+1COOH and a functional group of R– COOH.

They are named by replacing the ending ‘e’ of the corresponding parent alkane with – oic acid. 

In the IUPAC method we take into consideration the functional group

    O
    ||
(–C–OH) and the positions of other substituents on the carbon chain.  The lowest number is given to the C- atom carrying the functional group.  

NAMING OF ALKANOIC ACIDS

The formular of the first 10 members of the series shown in the table below. Members. By applying the general molecular formular (C_nH_2n+1COOH) we have

When n=	General Molecular Formulae  CnH2n+1COOH	Name
0.	C0H2x0+1COOH =     HCOOH	Methanoic acid
1.	C1H2x1+1COOH   = CH3COOH	Ethanoic acid
2.	C2H2x2+1COOH    = C2H5COOH	Propanoic acid
3.	C3H2x3+1COOH    = C3H7COOH	Butanoic acid
4.	C4H2x4+1COOH     = C4H9COOH	Pentanoic acid
5.	C5H2x5+1COOH     = C5H11COOH	Hexanoic acid
6.	C6H2x6+1COOH     = C6H13COOH	Heptanoic acid
7.	C7H2x7+1COOH     = C7H15COOH	Octanoic acid
8.	C8H2x8+1COOH     =   C8H17COOH	Nonanoic acid
9.	C9H2x9+1COOH     =   C9H19COOH	Decanoic acid
10.	C10H2x10+1COOH  =  C10H21COOH	Undacanoic acid

 MOLECULAR STRUCTURES OF ALKANOIC ACIDS

N	ALKANOIC ACID	STRUCTURAL FORMULAR	MOLECULAR FORMULAR
1.	HCOOH Methanoic acid	O           ||          C -OH           |           H	HCOOH
2.	CH3COOH Ethanol	H   O         |   ||    H-C-C-OH         |           H	CH3COOH
3.	C2H5COOH Propanoic acid	H H  O       |   |   ||  H-C-C-C-OH       |   |          H H	CH3CH2COOH
4.	C3H7COOH Butanoic acid	H H H O         |   |   |   ||   H-C-C-C-C-OH         |   |   |           H H H	CH3(CH2)2COOH
5.	C5H11COOH Pentanoic acid	H H H H  O        |   |    |   |   ||   H-C-C-C-C-C-OH         |   |   |   |            H H H H	CH3(CH2)3COOH
6.	C6H13COOH Hexanoic acid	H H H H H  O        |   |   |    |   |   ||   H-C-C-C-C-C-C-OH        |   |   |    |   |            H H H H H	CH3(CH2)4COOH
7.	C7H15COOH Heptanoic acid	H H H H H H  O       |   |    |   |   |   |   ||  H-C-C-C-C-C-C-C-OH        |   |   |   |   |   |           H H H H H H	CH3(CH2)5COOH
8.	C8H17COOH Octanoic acid	H H H H H H H  O        |   |   |    |   |   |   |   ||   H-C-C-C-C-C-C-C-C-OH         |   |   |   |   |   |   |            H H H H H H H	CH3(CH2)6COOH
9.	C9H19COOH Nonanoic acid	H H H H H H H H  O       |    |   |   |   |   |    |   |   ||  H-C-C-C-C-C-C-C-C-C-OH       |   |   |    |    |   |   |   |          H H H H H H H H	CH3(CH2)7COOH
10.	C10H21COOH Decanoic acid	H H H H H H H H H  O      |   |    |  |    |   |   |   |   |   || H-C-C-C-C-C-C-C-C-C-C-OH       |   |   |   |   |   |   |   |    |   |       H H H H H H H H H H	CH3(CH2)8COOH

                                                                                                    

The alkanoic acids like the alkanols are classified into groups based on the number of caboxyl group present in the molecule. Thus we have  

1. Monocarboxylic acids: These are carboxylic acid which have only one -COOH per molecule. Examples include 

ii.   H   O

        |   ||
   H-C-C-OH
        |   
       H

2. Dicarboxylic acids: alkanoic acids with two -COOH groups. Examples include 

 (i)    C₁OOH   

         |              Ethanedioic acid              C₁OOH

    

(ii)  C₂OOH   

         |                              

        C₂H₂
                                   
                                                             C₃OOH
                                                            Propane-1,3-dioic acid 
3.  Tricarboxylic acids:-  These are carboxylic acids containig three carboxylic groups per molecule           

                  C₁OOH
|
                  C₂H – CH₃
|
          CH₃-C₃ – CH₃
|       
                  C₄OOH
            2,2,3- trimethyl butan-1,3- dioic acid

In this chapter we will be concentrating on monocarboxylic acids.

-They are colourless liquid at room temperatures

-lower members behave as typical acids, but as the number of carbon atom increases their solubility in water as well as their acidic nature decreases

-they have higher boiling points than normal because of the presence of hydrogen bonding

The first two members of the series are methanoic acid HCOOH and ethanoic acid with general formula CH₃COOH.

ETHANOIC ACID :- This is the second member of the series, it is a liquid at room temperature. it has a characteristic pungent smell.

LABORATORY PREPARATION OF ETHANOIC ACID

Ethanoic acid can be prepared in the laboratory in two ways or stages by oxidation of ethanol with potassium hexaoxodichromate (iv) (K₂Cr₂O₇) acidified with tetraoxosulphate (vi) (H₂SO₄)

STAGE 1:              K₂Cr₂O₇
               C₂H₅OH   →     CH₃CHO + H₂O
                Ethanol               Ethanal

                                     

STAGE 2:                      K₂Cr₂O₇ 
                       CH₃CHO   →     CH₃COOH
                        Ethanal                  ethanoic acid

PHYSICAL PROPERTIES OF ETHANOIC ACID

1. It is a colourless liquid

2. It has a pungent and characteristic  of vinegar odour

3. It has a boiling point of 118⁰C and freezes at temperature below 17⁰C (glass-like crystals known as glacier ethanoic acids

4. It is very soluble in water

5. It is weak electrolyte.

CHEMICAL PROPERTIES OF ETHANOIC ACID

1.      i).  It turns blue litmus paper red

2.      2) As an acid it reacts with alkalis and base to form salts called ethanoates (esters) and water    

 (i).  It reacts with sodium hydroxide (NaOH) to form sodium ethanoate (CH₃COONa) and water

          CH₃COOH + NaOH →CH₃COONa + H₂O

4.      ii) And with moderately reactive metals such as magnessium to liberate hydrogen gas.

→            2CH₃COOH + Mg   ^heat (CH₃COO)₂Mg+ H₂

5.      When heated with soda lime (NaOH) it forms methane gas (CH₄) and carbon (iv) oxide

          CH₃COOH + NaOH →   CH₄ + CO₂ 

3). ESTERIFICATION: -This is the process whereby alkanoic acids reacts with alkanol to form  alkanoate (ester) and water in the [presence of an acid as catalyst) 

RCOOH + ROH →   RCOOR + H2O        

 

 CH₃COOH + CH₃CH₂OH → CH₃COOCH₂CH₃ + H₂O
                                          Ethyl ethanoate

CH₃COOH + PCl5  → CH₃COCl(l) + HCl(l) +  PCl3(l)

USES OF ETHANOIC ACID

1. As vinegar for preserving food

2. For making cellulose ethanoate

3 . For making non-inflammable safety film

4. For making textile fibres such as rayon

5. For making vinylethanoate which is used in emulsion paints,

6. It is used in making adhesives for wood, glass and paper

7. It is used  to coagulate rubber latex.

TEST FOR ALKANOIC ACIDS

1. It has a characteristic Pungent and sharp smell and turns blue litmus paper red.

2. Put some of the unknown substance into a solution sodium hydrogentrioxocarbonate (IV) (NaHCO₃).  If there is effervescence and the of a gas is colourless, odourless and tasteless then the substance is ethanoic acid.  

ALKANOLS at a glance

 

ALKANOL

Alkanols are a homologous series of organic compounds containing one or more hydroxyl groups linked to an alkyl or aryl radicals. They have the general molecular formular of C_nH_2n+1OH and a functional group of OH. The first – two members of the series are both liquids. They are methanol (CH₃OH) and ethanol (CH₃CH₂OH). Alkanols are named by replacing the "–e" in the parent alkanes by "–ol".

CLASSES OF ALKANOLS

 Alkanols are classified based on the number of hydroxyl groups in the molecule.

1.MONOHYDRIC ALKANOLS: These are alkanols that have only one hydroxyl group (OH) per molecule e.g

     CH₃OH

    Methanol 

      

  CH₃CH₂OH    ethanol

  CH₃CHCH₃    propan-2-ol

           |                                                      OH                         

                                                               CH₃CH₂CHCH₃                

                     |

                     OH

                 butan-2-ol

2.DIHYDRIC ALKANOLS: These are alkanols that contain two hydroxyl group (OH) per molecule.g

            CH₂CH₂                  
             |      | 
            OH  OH

      Ethan-1,2-diol

CH₃CHCH₂CH₂
        |            |             
       OH       OH                        
     Butan-1,3-diol

3.TRIHYDRIC ALKANOLS: Alkanols that contains three hydroxyl group (OH) per molecule are know as trihydric alkanols. e.g

         CH₂CHCH₂                     
          |       |   |
         OH  OH OH

  Propan-1,2,3-triol

 

 CH₂-CH-CH₂-CH₂
          |      |       |      
         OH  OH   OH                              

       Butan-1,2.4-triol

MONOHYDRIC ALKANOLS 

The table below shows the formular of the first 10 members of monohydric alkanol derived from the general molecular formular (C_nH_2n+1OH)

When n=	General Molecular Formulae CnH2n+1OH	Name
1	CH3OH	Methanol
2.	C2H5OH	Ethanol
3.	C3H7OH	Propanol
4.	C4H9OH	Butanol
5.	C5H11OH	Pentanol
6.	C6H13OH	Hexanol
7.	C7H15OH	Heptanol
8.	C8H17OH	Octanol
9.	C9H19OH	Nonanol
10.	C10H21OH	Decanol

 

MOLECULAR STRUCTURES OF FIRST 10 MONOHYDRIC ALKANOLS

N	ALKANOL	STRUCTURAL FORMULAR	MOLECULAR FORMULAR
1.	CH3OH Methanol	H           |      H-C -OH           |            H	CH3OH
2.	C2H5OH Ethanol	H  H         |   |    H-C-C-OH         |   |        H H	CH3CH2OH
3.	C3H7OH Propanol	H H H       |    |   |  H-C-C-C-OH       |   |    |       H H H	CH3(CH2)2OH
4.	C4H9OH Butanol	H H H H         |   |   |   |   H-C-C-C-C-OH         |   |   |   |        H H H H	CH3(CH2)3OH
5.	C5H11OH Pentanol	H H H H H        |   |    |   |   |   H-C-C-C-C-C-OH         |   |   |   |   |          H H H H H	CH3(CH2)4OH
6.	C6H13OH Hexanol	H H H H H H        |   |   |    |   |   |   H-C-C-C-C-C-C-OH        |   |   |    |   |    |        H H H H H H	CH3(CH2)5OH
7.	C7H15OH Heptanol	H H H H H H H       |   |    |   |   |   |   |  H-C-C-C-C-C-C-C-OH        |   |   |   |   |   |    |       H H H H H H H	CH3(CH2)6OH
8.	C8H17OH Octanol	H H H H H H H H        |   |   |    |   |   |   |   |   H-C-C-C-C-C-C-C-C-OH         |   |   |   |   |   |   |    |        H H H H H H H H	CH3(CH2)7OH
9.	C9H19OH Nonanol	H H H H H H H H H       |    |   |   |   |   |    |   |   |  H-C-C-C-C-C-C-C-C-C-OH       |   |   |    |    |   |   |   |    |      H H H H H H H H H	CH3(CH2)8OH
10.	C10H21OH Decanol	H H H H H H H H H H       |  |   |   |  |   |   |   |   |   |    | H-C-C-C-C-C-C-C-C-C-C-OH       |   |   |   |   |   |   |   |    |    |       H H H H H H H H H H	CH3(CH2)9OH

                  H
(i)               |
         CH₃-C-OH                                    
                  |                                               
                 CH₃                 
            Propan-2-ol

                

(ii)   CH₃CH₂C- OH
                       |    
                      CH₃       

            Butan-2-ol

           

                    CH₃                                      
(iii)               |                                           
           CH₃-C-CH₂OH        
                      CH₃                                        

           2,2-dimethylpropan-1-ol             

 

                        CH₃
(iv)                   |
                CH₃-C-CH₂CH₂CH₃
                         |                
                        OH
                    2-methylpentan-2-ol

                  CH₃                                                    
(v)              |                                                       
         CH₃-C-CH₂CHCH₂CH₃      
                   |           |                                           
                 CH₃     OH                                    
           5,5-dimethylhexan-3-ol               

                           

                       OH      
                        |
     (vi)     OH-C-OH
                       |               
                     OH                                      
           methan-1,1,1,1-tetraol

                         CH₃          OH OH                                                                    
(vii)                         |                |      |
       CH₃-CH₂CH₂-C—CH—CH-CHCH₃  
                                |       |                                                           
                               CH₃  CH₂CH₃                                                
            5,5-dimethyl, 4-ethyloctan-2,3-diol                       

                                                                  
  (viii)     CH₃CHCH₂CHCH₂CHCH₃
                        |            |           |                
                       OH       OH      OH            
                   heptan-2,4,6-triol

                 

TYPES OF ALKANOLS

Alkanols can be classified into three types depending on the number of the alkyl group or H- atom  attached to the C-atom carrying (attached to) the  functional group (-OH). We have

1. PRIMARY ALKANOLS: These are alkanols in which the hydroxyl group (OH) is directly attached to a carbon atom. i.e                H    

Examples include                            

              H                           H   H                             H    H   H     H
               |                             |     |                               |      |     |       |
       H—C—OH          H—C – C – OH            H – C – C – C – C – OH
               |                            |      |                              |      |      |      |
              H                          H    H                             H    H    H    H
        Methanol                  ethanol                             propanol

2. SECONDARY ALKANOLS: These are alkanols in which the Carbon atom carrying the hydroxyl group (OH) is itself attached to two alkyl group (or two other carbon atoms) or one hydrogen atom. 

          i.e,                      H                                  
                                      |
                              R—C—OH                                               
                                      |
                                     R    

Examples include 

                 H                                  H                                     H    
(i)              |                  (ii)             |                        (iii)          |
     CH₃—C—OH             CH₃—C – CH₂CH₃         CH₃ – C – CH₂CH₂CH₃
                 |                                     |                                        |             
                CH₃                              OH                                    OH
          Propan-2-ol                     Butan-2-ol                     Pentan-2-ol

3. TERTIARY ALKANOLS: These are alkanols in which the carbon-atom carrying the hydroxyl group (OH) is itself attached to three other alkyl group that is, no hydrogen attached to the carbon atom carrying the -OH group.         

                                                R                                                                
                                                 |
                                         R—C—OH                  
                                                 |
                                                R    

          Examples include

(i)           CH₃                               CH₃      CH₃                                    
               |                                      |             |
   CH₃—C—OH               CH₃—C – CH­₂CHCH₃                
               |                                      |                     
              CH₃                              OH                                              

•   2-methylpropan-2-ol    2,4-dimethylpentan-2-ol               

       ETHANOL: This is the second and greatly used member of the series. it has a molecular formula of C2H5OH and a structural formula of 

                        H   H  
                         |      |                           
                 H—C – C – OH            
                         |      |            
                        H    H     

LABORATORY PREPARATION OF ETHANOL

Ethanol is prepared in the laboratory by the process hydrolysis iodoethane with an alkali

CH₃CH₂I + NaOH → CH₃CH₂OH + NaI

Industrially ethanol is prepared by

(i) Hydrolysis of ethene

     STAGE 1:

            C₂H₄ + H₂SO₄ → C₂H₅HSO₄ 
                                         Ethylhydrogen tetraoxosulphate (IV)  

    STAGE: II  

                      C₂H₅HSO₄ + H₂O →C₂H₅OH

 

(ii)  Fermentation: -This is a reaction in which simple sugar such as glucose (C₆H₁₂O₆) is converted into ethanol (C₂H₅OH) and carbon (IV) oxide (CO₂) by the action of an enzyme called zymase present in the yeast.

                        C₆H₁₂O₆ → 2C₂H₅OH + CO₂
   Glucose         ethanol

PREPARATION OF ETHANOL FROM STARCHY FOODS

The starchy food (like sweet potato) is first crushed, and pressure cooked using a pressure cooker for some time. The crushed potato releases starch granules and this starch granules are treated with malt (partially germinated barley) for an hour at about 60⁰C. Malt contains the enzyme diastase. The starch contained in the potato is then converted by the enzyme diastase into maltose by hydrolysis.  

                                 Diastase     
 2(C6H10O5)n(s) + H2O(l) →    C12H22O11(aq)
                                 maltase     
 C12H10O11(aq) + H2O(l) →    2C6H12O6(aq)
                 Zymase     
 C6H12O6(aq)   →   2 C2H5OH(aq) + 2CO2(g)

reacts with 

OBJECTIVES

1. What is the major product formed when C2H5OH with

a. C2H5COOH

b.  C2H5COCH3 

c. CH3COOC2H5

d. C3H7COOH

2.

THEORY

1. What is fermentation

1a. with chemical equations only, show how ethanol can be produced from starch

 

OXIDATION NUMBER at a glance

 Oxidation number (O.N) of an element is the charge on an atom of the element whether it is by itself or bonded to another atom. It indicates the number of electrons the atom has gained or lose at that moment. That is, it is the charge an element will have if electrons were transferred to or from it. It is usually zero (0) for an element in the uncombined state. It is also referred to as the oxidation state of the element

          NOTE: - The sign or charge for O.N is written before the number (–2) but it is written after the number for an ionic charge i.e O^2–

Rules for calculating oxidation number

The following rules are applied when assigning an oxidation number or calculating the oxidation number of an element thus

1.       The O.N of oxygen is always equal to -2 except in peroxides (–1)

2.   O.N of hydrogen is always equal to plus one (+1) except again in metallic hydrides (–1).

3.        The O.N for an element in the elemental (or ground) state O.N = O (zero) e.g.

          Na = O, Cl₂ = O,  O₂ = O etc.

4.   For an for a simple ion is equal to the charge on it for example 

   Na+ = +1,   Cl^– = –1,     O^2–  =  -2

5. Oxidation number of a radical is equal to the charge on it e.g  CO₃^2- = –2,  NO₃^- =-1,  SO₄^2- =-2

3   The  O.N of a compound is equal O (because it is the sum of the e.g.

   H₂O = O, 

 i.e (O.N of H × no of H atoms) + (O.N of O) =

      (+1 x 2) + ( -2 x1) 

          2 -2 = 0

NaOH = (+1 x1) + (-2 x 1) + (1 x 1) 

                         +1 - 2+ 1

                           +2-2=0

      

Rules for specific groups in the PT.

I        For group 1A elements (comprising Li,Na,K, e.t.c) their O.N = +1

II       For group 2A elements (comprising Be, Mg, Ca e.t.c) their O.N = +2 in all compounds

III     For group 3 elements (B, Al, e.t.c) their O.N = +3 especially in their binary compounds.

IV     For group 5 = -3

V     For group 6 = -2 except Oxygen (O) in peroxides).

 VI   For group 7 = –1 respectively especially in their binary compounds 

 

Determination of the oxidation number of an element

1   Find the O.N of the underlined elements in the following

  a). ZnCl₂        b). SO₃      c). NO₃^-         d). Ca²⁺

          Solution

  To determine the O.N of the underlined elements, we must follow the general rules for calculating O.N of an element.

   a). ZnCl₂: The O.N of a compound is zero, i.e. ZnCl₂  = O. 

Since Cl is a group 7(A) element and ZnCl₂ is a binary compound then the O.N of Cl is –1, therefore, the O.N of Zn is

    (O.N of Zn) + (O.N of Cl ´ 2) = 0
                   x + (–1 ´ 2) = 0
                   x – 2 = 0
                   x = +2

 

          b)      SO₃

                    Solution

(O.N of S) + (O.N of 0 ´ 3) = 0
            x + (–2 ´ 3) = 0
             x – 6 = 0
           x = +6

      Trioxosulphate(IV) ion

   c)        NO₃^-

                   Solution

        The O.N of a radical is equal to the charge on it, hence

                    NO₃^- = –1
                   that is,
     

 (O.N of N) + (O.N of 0x3) = –1

                   x + (–2x3) = –1
                   x – 6 = –1
                   x = +6 – 1
                    = +5

   Trioxonitrate (V) ion

    d) Ca²⁺  The O.N of an ion is the charge on it, i.e., Ca²⁺ = +2  Calcium  = ion

 Uses of oxidation number

Oxidation number is used for the

1.   It is used in the IUPAC (International Union of Pure and Applied chemistry) system of naming compounds e.g. H₂SO₄: Tetraoxosulphate(VI) acid

2. It is used to know the oxidation state or number of an element in a compound 

 

OBJECTIVE QUSETION

1. The oxidation number of an element in its free (uncombined) state is
   A. +1
   B. 0
   C. –1
   D. variable

2. The oxidation number of hydrogen in most of its compounds is
   A. –1
   B. 0
   C. +1
   D. +2

3. Hydrogen has an oxidation number of –1 in
   A. HCl
   B. H₂O
   C. NaH
   D. NH₃

4. The oxidation number of oxygen in most compounds is
   A. –1
   B. –2
   C. 0
   D. +2

5. Oxygen has an oxidation number of –1 in
   A. CO₂
   B. H₂O
   C. H₂O₂
   D. Na₂O

6. The oxidation number of chlorine in NaCl is
   A. +1
   B. –1
   C. 0
   D. +7

7. The sum of oxidation numbers of all atoms in a neutral compound is always
   A. zero
   B. one
   C. two
   D. equal to the number of atoms

8. The sum of oxidation numbers of atoms in a polyatomic ion is equal to
   A. zero
   B. the charge on the ion
   C. the atomic number
   D. the mass number

9. What is the oxidation number of sulphur in H₂SO₄?
   A. +2
   B. +4
   C. +6
   D. –2

10. The oxidation number of nitrogen in NH₃ is
    A. –3
    B. –1
    C. +3
    D. +5

11. What is the oxidation number of manganese in KMnO₄?
    A. +2
    B. +4
    C. +6
    D. +7

12. The oxidation number of iron in Fe²⁺ is
    A. +1
    B. +2
    C. +3
    D. 0

13. In the compound CaCO₃, the oxidation number of carbon is
    A. +2
    B. +4
    C. –2
    D. –4

14. Which of the following elements always has an oxidation number of +1 in compounds?
    A. Calcium
    B. Sodium
    C. Magnesium
    D. Aluminium

15. The oxidation number of aluminium in Al₂O₃ is
    A. +1
    B. +2
    C. +3
    D. +6

16. What is the oxidation number of chromium in K₂Cr₂O₇?
    A. +3
    B. +4
    C. +6
    D. +7

17. An increase in oxidation number indicates
    A. reduction
    B. oxidation
    C. neutralization
    D. hydrolysis

18. A decrease in oxidation number indicates
    A. oxidation
    B. reduction
    C. combustion
    D. displacement

19. The oxidation number of chlorine in Cl₂ is
    A. –1
    B. 0
    C. +1
    D. +5

20. Which of the following statements about oxidation number is correct?
    A. It is always positive
    B. It represents the actual charge on an atom
    C. It is a theoretical charge assigned to an atom
    D. It is equal to the atomic number

     21.       Which species undergoes reduction in the reaction represented by the equation below?

  H₂S_(aq)+2FeCl_3(aq)→S_(s) + 2HCl +3FeCl₂

   (a) Fe³⁺    

   (b). H₂S            

   (c). Cl^–     

   (d)  S

22. Oxidation is a reaction which involves the following except 

   (a). Loss of electrons

   (b). Increase in oxidation number 

   (c). Gain of oxygen 

   (d). addition of hydrogen

23.  The O.N of the following underlined elements are Na₂SO₄               

          (a)  +4,  

          (b)  -2,  

          (c)  +6

          (d)  –5

  24.     Al (H₂O)₆]³⁺         

           (a) +3

           (b) –3

           (c) +6

           (d) –6

     25.     K₂Cr₂O₇             

           (a) +5

           (b) +4

           (c) –6

           (d) +6

      26.     Mn                                     

           (a) +6

           (b) +7

           (c) +5

           (d) +3

THEORY QUESTION

2. Find the oxidation numbers of the following underlined elements.

  (a) K₂Cr₂O₇             (b) KMnO₄         (c) HNO₃

  (d). S^2-                   (e). Cl^-              (f). Cr₂

2.a State two applications of oxidation numbers 

b.  What is the oxidation state of manganese in each of the following species?

 i.  MnO₂   ii MnO₄^-    iii.   MnCl₂

SODIUM at a glance

 

Sodium:  is found in group 1 period III on the periodic table. It has an atomic number of 11 and an atomic mass of 23. 

 It does not occur as a free element in nature because it is very reactive. However, it is found mainly in the combined state as sodium chloride in sea water, and as rock salt (Halite) in underground deposits. 

It is extracted from fused sodium chloride by electrolysis using the Dawn's Cell. a little amount of CaCl2 is added to lower the melting point (from about 801 to 600)

 Chemistry of the reaction

at the cathode

At the cathode: - the sodium ions migrate to the cathode where they gain an electron each to become reduced to metallic sodium

          Na⁺_(l) + e- → Na_(s)

At the anode: - the chloride ions migrate to the anode where they loss their excess charge/electrons and become reduced to atomic chlorine

                Cl^- → Cl + e^-

the chlorine atom combines with another chlorine atom and is discharged as chlorine gas

          Cl + Cl → Cl_2(g)                                                                                     

Properties of Sodium:

i.       Sodium is soft and can easily be cut with a knife.

ii.       It has a of 0.968g/cm³ 

iii.      It has a silvery-white appearance.

iv.        It has a low melting point.

v.        It has a high boiling point.

v.        Sodium is a good conductor of electricity.

Chemical Properties

i)                   Reaction with air or oxygen: - Sodium metal tarnishes on exposure to air

 4Na_(s) + O_2(g) →2Na₂O_(s)

  Na₂O_(s) + H₂O_(l) → 2NaOH (s)   

   NaOH_(aq) + CO₂ → Na₂CO₃  

 In excess air or oxygen, it burns with a golden/bright  yellow flame to yield sodium peroxide Na₂O₂,

     2 Na_(s) + O_2(g) → Na₂O_2(s)

 In limited supply of air sodium oxide (Na₂O) is formed.

       Na_(s) + O_2(g) → 2Na₂O_(s)

 Because of its reactivity sodium is stored under paraffin oil or other organic solvents like naphtha or toluene.

ii.     Reaction with water: - It reacts violently with cold water to yield sodium hydroxide and hydrogen with large amount of heat.

Na_(s) + H₂O_(l) → NaOH_(aq) + H_2(g)

iii.      Reaction with acids: - It reacts explosively to form a salt and hydrogen gas  

   Na_(s) + HCl_(aq) →NaCl_(aq) + H_2(g)

      Na_(s) H₂SO_4(aq) → Na₂SO_4(aq) + H_2(g)

 This reaction is highly dangerous and should not be carried out in the school laboratory.

Reaction with non-metals: - sodium combines directly with the following non-metals when heated to form binary compounds.  

               Na_(s) + S_(s) →Na₂S_(s)

               Na_(s) + H₂ → NaH_(s)

               Na_(s) +P_(s) → Na₃P_(s)

              Na_(s) + Cl_(g) → NaCl_(s)

Sodium does not react with carbon, boron and nitrogen

Reaction with mercury: - Sodium forms various stable mixture with mercury known as sodium amalgam of varying composition such as  NaHg, Na₂Hg, Na₃Hg etc.

Sodium amalgam reacts with water to yield hydrogen.

          Na_(s) + Hg_(l) →NaHg_(l)

v.                  Reaction with ammonia: - Sodium reacts with ammonia to form sodamide and hydrogen gas.

 Na_(s) + NH_3(g) → NaNH_2(s) + H_2(g)

 As a reducing agent: - Sodium act as a strong reducing agent. It reduces some metallic chlorides and oxides to their metals.    

 Na_(s) + BeCl_2(s) → NaCl_(s) + Be_(s)

Test for sodium ions

i).   Flame test: when sodium compounds give a bright or golden yellow flame when burnt in a non-luminous flame

Uses of Sodium:

-i). Sodium is used in the manufacture of other compounds like sodamide, sodium peroxide.

ii). Sodium alloys like  NaK(sodium-potassium alloy), are used as coolant in nuclear reactors.

iii). Sodium vapor lamps are commonly used for street lighting

iv) It is used in the manufacture of tetraethyl lead (C₂H₅)₄Pb, which is used as an antiknock agent in petrol.

v) It is used as a laboratory reagent (Lassaigne's extract).

vii). It is used for producing amalgams used as reducing agents.

viii)  Sodium used as a catalyst in the preparation of artificial rubber and also as a deoxidizer in the preparation of light alloys.

COMPOUNDS OF SODIUM

 Sodium compounds are generally white crystalline salts and are mostly soluble in water.

1.      Sodium chloride (NaCl): (table salt) it is found naturally in sea water and in underground deposits as rock salt.

Properties

- It is a white anhydrous crystalline solid

- It has a melting point of 801⁰C and a boiling point of 1420⁰C.

- The pure form is not deliquescent.

Uses

1. It is used as a food preservative.

2. It is used as an important raw material for the manufacturing of Na, NaOH, Cl₂, Na₂CO₃, NaClO₃ and other compounds.

3.  It is used for salting out soap

4. It is used in glazing earthenware

5.  It is used in regenerating water softener.

2.  Sodium hydroxide (NaOH):  It is a white crystalline solid, made into flakes or pallets

Properties

-i). It is a white crystalline solid

ii).  It is highly deliquescent 

iii) It has a melting point of 320⁰C without decomposing.

iii).  It dissolves in water to give a strong alkaline solution with the evolution of heat

Chemical properties

With acids: - NaOH produce salt and water.

2NaOH_(aq) + H₂SO_4(aq) → Na₂SO_4(aq) + 2H₂O_(l)

With acidic oxides: - It form sodium salt. E.g.

NaOH_(aq) + SO_2(g) → NaHSO_3(aq)

With ammonium salts: - When heated with an ammonium salt, ammonia gas is liberated.

NaOH_(aq) + NH₄Cl_(s)→ NaCl_(aq) + H₂O_(l) + NH_3(g)

With metals – Al and Zn are amphoteric; they combine with excess NaOH to form the  alluminate (III) and respectively with hydrogen gas. 

2Al_(s) + 2NaOH_(aq) + 6H₂O_(l) → 2NaAl(OH)_4(aq) + 3H_2(g)

                                                                        sodium aluminate (III)

Zn_(s) + 2NaOH_(aq) + 2H₂O_(l) → Na₂Zn(OH)_4(aq) + H_2(g)

                                                                        sodium zincate (II)

Therefore, Aluminium or Zinc containers should not be used to store NaOH.

As a precipitating agent: - NaOH solution is most times used to precipitate insoluble hydroxides. E.g

Zn²⁺_(aq) + 2OH^-_(aq) → Zn(OH)_2(s)

Pb²⁺_(aq) + 2OH^-_(aq) → Pb(OH)_2(s)`

Zn(OH)2, Al(HO)3, Sn(OH)2, and Pb(OH)2, are amphoteric and will react excess sodium hydroxide to form complex salts. E.g

Zn(OH)_(s) + 2NaOH_(aq) → Na₂Zn(OH)_4(aq)

With non-metals: NaOH reacts with various non-metals to form sodium salts.

Reaction with glass – High concentrations of NaOH attack glass to form sodium trioxosilicate (IV). Hence, glass stoppers are not used to cover reagent bottles containing concentrated sodium hydroxide or burette because they would become stuck. This is called etching.          

Uses of NaOH

1. it is used as a strong alkali

2. it is used as an analytical and precipitating reagent

3. it is used for absorbing CO₂

4. it is used for making soap, rayon (artificial silk), 

5. I is used for making paper 

6. it is used for making various compounds like sodium trioxochlorate (V), sodium methanoate and phosphine.

7. it is used for purification of bauxite

8. it is used petroleum refining.

9. it is used for the bleaching of cotton textiles.

3.Sodium tetraoxosulphate (IV) (Na₂SO₄₎

Properties

It occurs both in the anhydrous form called saltcake or as a decahydrate form known as Glauber’s salt which is efflìorescent.

Uses Of Na₂SO₄

i.  It is used as a purgative

ii.   In producing of sodium sulphide

Iii it is in the manufacture of wood pulp, glass, and detergents

4. Sodium bicarbonate (NaHCO₃): (baking soda): - A white it is utilized in cooking and as a leavening agent in baking.

- Sodium carbonate (Na₂CO₃): Also called soda ash

Properties

-Na₂CO₃ in form of soda ash (i.e. anhydrous Na₂CO₃) is a fine white powder, while washing soda (Na₂CO₃.10H₂O) is translucent and crystalline.

i. They both dissolve in water to form an alkaline solution by hydrolysis.

ii. Washing soda is efflorescent

iii. It does not decompose on heating

iii. t reacts with acid to liberate CO₂

Uses of Na₂CO₃

i. It is used in the industrial manufacturing of glass

ii.  It is used as a water softener

iii.  It is used in manufacturing of detergent

iv. It is used in the manufacturing NaOH, borax, waterglass, soap and paper

iv.  It is used in laboratory to standardize acids and as an analytical reagent.

vi.  it is used in glass production,

vi.                It is used as a pH regulator in various industrial processes

SOLVAY PROCESS: This is the industrial preparation of NaCO3

The raw materials are sodium chloride, ammonia gas and limestone. The reactions are as follows

1.The ammonia gas in brine (conc. sodium chloride) to give a mixture known as ammoniacal brine.     

ii. This mixture is then allowed to trickle down a Solvay tower as a stream of carbon (IV) oxide is forced up the tower. It reacts with the ammonia in the mixture to yield ammonium hydrogen trioxocarbonate (IV) (NH₄HCO₃). 

  i).  NH_3(g) + CO_2(g) +H₂O →NH₄HCO_3(aq)

The NH₄HCO₃ reacts with the sodium chloride to give sodium hydrogen trioxocarbonate (IV) (NaHCO₃). 

   ii). NH₄HCO_3(aq) + NaCl_(aq) →NaHCO_3(s) + NH₄Cl_(aq)

The sodium hydrogen trioxocarbonate (IV) is slightly insoluble in water and so precipitates out as a white sludge. 

 The NaHCO₃ is then filtered, rinsed and heated to give anhydrous sodium trioxocarbonate (IV) (soda ash), steam and carbon (IV) oxide

  

 iii). NaHCO_3(s) →Na₂CO_3(s) + H₂O_(l) + CO_2(g)

The anhydrous Na₂CO_3(s) (soda ash) is redissolved in hot water and recrystallize to give the pure hydrated compound (Na2CO₃.10H₂O) called washing soda

    iv). Na₂CO_3(s) + 10H₂O_(l) →Na₂CO₃.10H₂O_(s)

some highlights of the process

-Perforated dome-shaped baffle-plates are incorporated into the Solvay tower to slow down the flow rate of the ammoniacal brine so as to allow for proper contact between the ammoniacal brine and the carbon (IV) oxide as well as increase the surface area of reaction

-The concentrated sodium chloride also serves as a carrier for the ammonia gas.

Importance and Economics of the reaction: - 

i. All the raw materials required in the Solvay process are quite cheap and are also readily available. 

ii. Almost all the carbon (IV) oxide generated during the process from the decomposition of the NaHCO_3(s) is recycled, making the process quite economical. 

iii. The sodium chloride solution is obtained from sea water or from rock salt deposits,

iv.  the carbon (IV) is got from limestone found in rich deposits around.

     CaCO_3(s) →CaO_(s) + CO_2(g)

The calcium oxide (CaO) is then reacted with the ammonium chloride to generate ammonia gas, which is also recycled back into the, producing calcium chloride as a by-product from the process.

    CaO_(s) + NH₄Cl_(aq)→ CaCl₂ +H₂O+ NH_3(g)

 5. Sodium nitrate (NaNO₃): It is a white crystalline solid produced when sodium hydroxide reacts with trioxonitrate (V) acids.

Properties

I). it is a white crystalline solid

ii). It has a melting point of 310⁰C and decomposes on further heating.

Uses

i)  it is used primarily as a nitrogenous fertilizer

ii)  In making trioxonitrate (V) acid, potassium trioxonitrate (V) and sodium dioxoxnitrate (III).

iii). It is used in the production of explosives and glass.

Objective questions 

1.

THEORY QUESTIONS 

1. Explain with equations where appropriate the functions of the following substances in the Solvay Process (i) limestone  (ii). ammonia (iii). brine.

2. Calculate the mass of sodium trioxocarbonate (IV) produced by the complete decomposition of 16.8g of sodium hydrogen trioxocarbonate (IV). [ H=1, O=16, Na=23, S=33]