ISOTOPY at a glance

                                         ISOTOPY /ISOTOPES

Isotopy is the existence of atoms of the same element having the same atomic number but different mass number or atomic mass. 

The different atoms are called isotopes. Hence

Isotopes are atoms of a particular element with the same atomic number but different mass number.

Examples of isotopes are

i.      ³⁵₁₇Cl and ³⁷₁₇Cl

ii.      ¹⁵₈O, ¹⁶₈O, ¹⁷₈O and ¹⁸₈O

iii.    ¹₁H, ²₁H and ³₁H

Relative Abundance: - when atoms exist naturally in isotopic mixture, they do so in a particular amount, when this amount is expressed in percentage, it is known as relative abundance. 

For example, chlorine is found always in two isotopic mixtures out of 100, 75 is Cl-35 and 25 is Cl-37. so, 75 and 25 when expresses in percentage are the relative abundance of the two isotopes. 

The relative abundance of an element is the amount (expressed in %) in which a particular isotope occurs in nature

Examples of isotopes are

i.   ³⁵₁₇Cl with relative abundance of 75% and ³⁷₁₇Cl with relative abundance of 25%.

ii.    ¹⁵₈O with relative abundance of 0.17, ¹⁶₈O with relative abundance of 99.76%, ¹⁷₈O with abundance of 0.05% and ¹⁸₈O with abundance of 0.02%

 RELATIVE ATOMIC MASS: - The relative atomic mass of an element is the number of times the average mass of one atom of the element is as heavy as 8one-twelfth the mass of carbon-12.

DETERMINATION OF RELATIVE ATOMIC MASS OF AN ELEMENT GIVEN THE RELATIVE ABUNDANCE

The relative abundance of an element can be calculated from their various isotopic masses, and their relative abundance as follows: -

1.   Naturally occurring exist in two isotopic mixtures ³⁵₁₇Cl with relative abundance of 75% and ³⁷₁₇Cl with relative abundance of 25% respectively. Calculate the relative atomic mass of Cl

            SOLUTION

    75 x 35 + 25 x 37 =
   100           100   

  
     26.25 + 9.25
          = 35.5

2.   An element Q has two isotopes ⁶³₂₉Q and ⁶⁵₂₉Q with relative abundance of 70% and 30% respectively. Calculate the relative atomic mass of Q

SOLUTION

70 x 63 + 30 x 65 =
100         100
  44.2 +   19.5
      = 63.70

3. X is an element which exists as an isotopic mixture containing 90% of ³⁹₁₉Xand 10% of ⁴¹₁₉X

a. How many neutrons are present in ⁴¹₁₉X isotope

b. Calculate the mean relative atomic mass of X

Solution

a. Neutrons in ⁴¹₁₉X

                    = 41-19 = 22

b. R.A.M =

               90 x 39 + 10 x 41 =
              100           100
                

                35.10 + 4.10 

                   = 39.2

 

CALCULATIONS

1. The following are more examples of calculations of relative atomic masses of elements.

2. An element Y exist in two isotopic forms ³⁹₁₈R and ⁴⁰₁₈R in the ratio 3:2 respectively. What is the relative atomic mass of the element?

SOLUTION

First you add the ratio together, that is, 3+2 =5

R.A.M of Y
    = 3 x 39 + 2 x40 = 
       5             5

    0.6 x 39 + 0.4 x 40 =
      23.4 + 16 =
        = 39.4   

3. An element with relative atomic mass 16.2 contains two isotopes ¹⁶₈R with relative abundance 90% and ^m₈R with relative abundance 10%. What is the value of m?

SOLUTION 

   16.2 = 90 x 16 + 10 x m
             100           100
   16.2 = 0.9 x 16 + 0.1m
   16.2 = 14.4 + 0.1m
   16.2 – 14.4 = 0.1m
   1.8 = 0.1 m
   m = 1.8 = 18
          0.1
  The value of m is 18

OBJECTIVE QUESTIONS

Here are 10 WAEC & NECO–style objective (multiple-choice) questions on Isotopy, suitable for your chemistry blog and student revision:

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Objective Questions on Isotopy

1. Isotopes of an element have the same
A. mass number
B. number of neutrons
C. number of protons
D. atomic mass

2. Which of the following pairs represents isotopes?

A. ¹²₆C and ¹⁴₇N
B. ³⁵₁₇Cl and ³⁷₁₇Cl
C. ²³₁₁Na and ²⁴₁₂Mg
D. ⁴⁰₂₀Ca and ⁴⁰₁₈Ar

3. Isotopes differ in their
A. atomic numbers
B. electronic configuration
C. chemical properties
D. number of neutrons

4. The chemical properties of isotopes are similar because they have the same
A. mass numbers
B. number of neutrons
C. number of protons
D. electronic arrangement

5. Which of the following elements is commonly known to exist as isotopes?
A. Sodium
B. Carbon
C. Aluminium
D. Fluorine

6. Carbon-12 and Carbon-14 are isotopes because they have the same
A. mass number
B. atomic number
C. number of neutrons
D. atomic mass

7. The presence of isotopes explains why the relative atomic mass of an element is
A. always a whole number
B. less than its atomic number
C. not a whole number
D. equal to its mass number

8. Which property of isotopes is different?
A. Valency
B. Chemical reactivity
C. Atomic number
D. Mass number

9. Which of the following statements about isotopes is correct?
A. They have different chemical properties
B. They have the same mass number
C. They have the same atomic number
D. They have different numbers of protons

10. One use of radioactive isotopes is in
A. food seasoning
B. water purification
C. medical diagnosis
D. soap production

11.    The atomic number of an element is precisely

  (a) the number of protons in the atom

 (b)  the number of electrons in the atom 

 (c)  the number of neutrons in the atom

 (d)  the number of protons and neutrons in an atom

12.    An atom can be defined more accurately as 

(a)  the smallest indivisible particle of an element that can take part in a chemical reaction 

(b)  the smallest part of an element that can take part in a chemical reaction

 (c)  a combination of protons and neutrons

(d)   is the simplest unit of an element

13. The mass number is 

(a)  proton number +   neutron number

(b)   electron number + proton number 

(c)   neutron number + electron number

(d)   electron number + atomic number 

14. Calculate the relative atomic mass of an element having two isotopes ¹⁰⁷Ag and ¹⁰⁹Ag in the ratio 1:1

 (a) 106 

(b) 107 

(c) 108

(d)  109

15. An element X has two isotopes ^18.8X and ^15.8X in the proportion of 1:9 respectively. Find the relative atomic mass of X 

(a) 16.1 

(b) 13.6 

(c) 16.8

(d) 17.0

THEORY QUESTIONS

1. (a) Define the term isotopy.

(b) Determine the number of electrons, protons and neutrons in each of the following:

  i.³⁹₁₉K    ii. ⁶³₂₆Cu    iii. ²³₁₁Na

2. If an element R has isotopes 60% of ¹²₆Qand 40% ^x₆Q and the relative atomic mass is 12.4, find x.

3. Consider the atoms represented below: ^q_rX and ^s_rX

a. State the relationship between the two atoms.

b. What is the difference between them?

c. Give two examples of other elements which exhibit the phenomenon illustrated.

4. State the number of electrons, protons and neutrons present in the following atoms/ions

(a)  ₂₀Ca 

(b)  ₁₆S^2- 

(c)  ₁₃Al³⁺ 

(d)  ₁₅P

5 a.(i)   Define Isotopy

    

      (ii). If an element R has isotopes 60% of ¹²R₆ and 40% ^xR₆ and the relative atomic mass is      12.4, find x.

     

     b.  Element ³³₁₅Z and ³¹₁₅Z occur in the ratio 1:3 

   

    (i)  Calculate the relative atomic mass of Z

    (ii).  Give a reason why the relative stomach mass of Z is not a whole number

    c.  Determine the number of electrons, protons and neutrons in each of the following: ³⁹₁₉K and ^63.5₂₉Cu  

IUPAC NOMENCLATURE at a glance

          IUPAC NOMENCLATURE

This is a systematic method of naming organic compounds using IUPAC system. That is, the International Union of Pure and Applied Chemistry.  

The IUPAC system of naming organic compounds, the following rules are to be followed.

Every organic compound has 2 or three parts to its name, 

**the root and the suffix or 

**the prefix, the root and the suffix  

Organic Compounds without branches or that does not have any subtituents apart from the main functional group will have only two parts to their name.

While those with branches will have three parts to their names.

***The ROOT: - This is got from the longest continuous carbon chain in the molecule. We use the Greek system of numbering to indicate the root as follows

Number of C-atom	Name
one C-atom	Meth-
two C-atoms	Eth-
Three C-atoms	Prop
Four C-atoms	But-
Five C-atom	Pent -
Six    C-atoms	Hex-
Seven C-atoms	Hept-
Eight C-atoms	Oct-
Nine   C-atoms	Non-
Ten     C-atoms	Dec-

*** The SUFIX: - This is usually added after the root hydrocarbon, it indicates the family or homologous series that the organic compound belongs to. 

***PREFIX / PREFIXES: - These are usually hanging atoms or groups that are not the main functional group of the compound. They are usually named before the root hydrocarbon. Their positions are usually mentioned (using arithmetic integers like 1,2,3,...)  before their names, and where you have more than one of the same types, we use mono -, di-, tri-, tetra- to indicate the number.  

when we have more than one functional group in a compound, then one is named as the prefix and the other the sufix. In this case we will not use the name as a suffix but as a prefix. (see functional groups)

RULE 1: Select the longest continuous carbon chain in the molecule and use it as the root or the parent hydrocarbon name of this chain.

RULE 2: Every branch off the main chain should be considered as a substituent derived from a corresponding hydrocarbon or any other hanging group that is not a hydrogen 

 CH₄ -methane      CH₃ –   methyl, 

C₂H₆-ethane         CH₃CH₂- ethyl, 

C₃H₈ - propane      C₃H₇ - propyl  

All of these functions as prefix

RULE 3: Number the carbon atoms of the continuous chain from a direction that gives the Carbon atom carrying the substituent ( i.e the Carbon atom carrying anything other than a H-atom will have a lower number) a small number

RULE 4: Give each substituent a name and number

RULE 5: For identical substituents, use di, tri, tetra, penta, hexa, and so on to indicate the number of identical substituents.

RULE 6: Where you have more than one substituent that are different, name them alphabetically

RULE 7: Give the lowest possible number to the functional group.

NOTE: Halogen when they occur in organic compounds are named thus, chlorine = chloro, fluorine = fluoro, bromine = bromo, iodine = iodo.

Always show your bonds when you write or draw structures of organic compounds 

 E.g .1 write the structure of 2-methyl butane. This should be written as shown below:

                       

H  H  H  H                 ׀   ׀   ׀    ׀            H-C-C-C-C-H                 ׀   ׀    ׀    ׀                H   ׀   H  H                 H-C-H                      ׀                     H

                         

Following strictly the above rules, one can then name perfectly any organic compound with ease. For example, in naming the compound below, following the rules

 

                                                            CH₃ 
                                                             |                                                                         
                                 C¹H₃C²H₂C³H₂C⁴C⁵H₂C⁶H₃
                                                             |
                                                             CH₃ 

In the above structure, there are six carbon atoms in the longest continuous chain. Therefore, the parent or the ROOT hydrocarbon has a name Hex (RULE 1). There are 2 methyl substituents derived from another hydrocarbons (RULE 2)

Counting the position of the substituents on the continuous root chain, they both stand on the 4^th carbon atom when counting from left to right, but when counting from right to left, they appear on the 3rd carbon atom, hence the lowest position of 3rd carbon atom is considered (RULE 3)

Since the two substituents are similar, they are named dimethyl (RULE 4), hence the two substituents have a number 3 and name 3 and so can be named as 3,3-dimethyl (RULE 5). When this is combined with the parent hydrocarbon (RULE 1), the name of the compound becomes 3,3-dimethylhexane.

Other examples with their names are shown below following the stated rules.

                       CH₃                                                             CH₃
(i)                    |                                                                   |
              C1H₃-C2-C3H₂-C4H-C5H₃              

(ii)        C1H₃C2H₂C3H-C4HC5H2C6H₃      
                       |            |                                                             |
                      CH₃     CH₃                                                        CH₃                                       
            2,2,4-trimethylpentane                                 3,4-dimethylhexane

                               CH₂CH₃                                                 CH₃
                                      |                                                               |
(iii)       C1H₃C2H₂-C3-C4H₂C5H₃                   (iv)       C1H₃-C2-C3H₃
                                      |                                                               |
                               CH₂CH₃                                                 CH₃
             3,3-diethylpentane                              2,2-dimethylpropane
                                                                                   

                                                                                        CH₃      CH₃
                                                                                                            |            |
(v)        CH₃CH₂CHCH₃                         (vi)       CH₃—C−CH2-CHCH₃
                     |                                                                    |
                    CH₃                                                              CH₃    
            2-methylbutane                                  2,2,4-trimethylpentane

(vii)      CH₃CH₂CH—CHCH₃                      (viii)     CH₃CH₂CHCH₃
                              ׀                                                          ׀       ׀               
                            CH₃  CH₃                                                    CH₃

             2,3-dimethylpentane                          2-methylbutane

                   

                   CH3                                                                                 CH3 
                       |                                                                                       |
(vi)       CH3 − C −CH− CH2−CH2CH2CH3                     (x)        CH3CH2CHCH2CHCH2CH2CH3 
                       |     |                                                                                             |
                     CH3  CH2CH3                                                                               CH2CH3  

            2,2-dimethyl, 3-ethylheptane                                        5-ethyl, 3-methyloctane

•                                                                                  Cl
•                                                                                  |
• (vii)       CH3CH2CHCH3                         (xii)      CH3-C-CH2CH3 
•                           |                                                       |
•                           Cl                                                    Cl
•             2-chlorobutane                                   2,2-dichlorobutane

(viii)     CH3CH2CHCH2CHCH3              (xiv)     CH3CHCH2CHCH3  

                          |            |                                          |          |

                         Cl         Br                                         Cl        Cl

            2-bromo, 4-chlorohexane                   2,4-dichloropentane

                           Cl        Br                                            Cl

                           |           |                                              |

(ix)      CH3CH2-C-CH2-C-CH3              (xvi)     CH3CHCH2-C-CH3  

                           |          |                                          |            | 

                          Cl         Br                                       Cl         Cl

            2,2-dibromo, 4,4-dichlorohexane       2,2,4-trichloropentane

                        CH3 H     H    CH3                                                               CH3  H      H    CH3 

                        

(x)    CH3 – C –  C –   C – C – CH3                  (xviii)   CH3 – C –   C –   C – C – CH3    

                       CH2 CH2 CH2 CH2                                                  CH2  CH2 CH2 CH2

                       CH3  CH3 CH3 CH3                                                       CH2  CH3 CH3 CH2

            4,5-diethyl,3,3,6,6-tetramethyloctane                      CH3                  CH3

                                                                                    5,6-diethyl,4,4,7,7-tetramethyldecane

(xi)     CH3 – CH2 – CH – CH3

                                    CH2Cl

            1-chloro – 2-methylbutane

          

ALKANES

ALKANES 

The alkanes are a homologous series of saturated aliphatic hydrocarbons with a general molecular formula of CnH2n+2.  The are the only saturated hydrocarbons because they contain only single bonds. The are found mainly in petroleum. The carbon atoms in the alkanes exhibit sp³ hybridization. There is a gradual change in the physical properties of the members from the gaseous state (for the lighter members) to the liquid state and then the solid state for the heavier compounds.

The first ten members of the series are.

1.       methane          CH₄

2.       Ethane             C₂H₆

3.       Propane           C₃H₈

4.       Butane             C₄H₁₀

_5.         Pentane           C₅H₁₂

6.        Hexane           C₆H₁₄

7.        Heptane          C₇H₁₆

8.        Octane            C₈H₁₈

9.        Nonane           C₉H₂₀

10.     Decane            C₁₀H₂₂

Chemical properties 

The alkanes undergo only two reactions, combustion and substitution reactions

1. Combustion Reaction: - this is a general property for all hydrocarbons. The alkanes burn in air or oxygen to yield Carbon (iv) oxide and water.

    CH_4(g) + O_2(g) → CO_2(g) + H₂O_(g)

2. Substitution Reaction: - Substitution reaction is the only other reactions that the alkanes can undergo because they are saturated.

A Substitution reaction is a reaction where one element (atom) replaces one or more of the hydrogen atoms in an alkane molecule.

METHANE: - This is the first and the simplest member of the alkane family. It has a molecular formula of CH₄ and a structural formula of

 

              H
               ׀
       H − C − H
               ׀
              H

It is found naturally in swamps or swampy areas when vegetations and dead organic matter decompose. It is also one of the major components in natural gas

Laboratory Preparation 

Methane is prepared in the laboratory by the action of sodium ethanoate on soda- lime.  (soda-lime is sodium hydroxide that has been slaked with lime CaO).

Soda- lime is preferred to caustic soda because 

1. It is not Deliquescent and 

2. It does not attack glass.

                                       Laboratory Preparation of methane 

CH₃COONa(S) + NaOH(s) → Na₂CO_3(s) + CH_4(g)  

Physical properties 

i.  It is a colourless gas. 

ii. It is less dense than air.

iii. It is insoluble in water.

Chemical properties 

I. Combustion: - methane burns with a pale blue flame in air or oxygen

CH_4(g) + O_2(g) → CO_2(g) + H₂O_(l) 

2. Substitution reaction: - Methane combines with Chlorine to produce various products.

The reaction is faster in the presence of light (photochemical reaction) and it occurs in stages.

I. CH_4(g) + Cl_2(g) → CH₃Cl + HCl

                             Mono chloromethane

II. CH₃Cl + Cl_2(g) → CH₂Cl₂ + HCl

                             dichloromethane

III. CH₂Cl₂ + Cl_2(g) → CHCl₃ + HCl

                            trichloromethane

IV.  CHCl₃ + Cl_2(g) → CCl₄ + HCl

                             tetrachloromethane

Uses of Methane 

I. It is used mainly as fuel sometimes mixed with other fuels

2. It is used to make hydrogen

3. It is used to make carbon black

4. When refined it is can be used as a rocket fuel

OBJECTIVE QUESTIONS 

1. What is the IUPAC name of the compound with this structure 

         H     H    H     H
         |        |      |        |   
H— C — C — C — C — H
         |        |       |         | 
         H      |      H       H
                  | 
          H —C—H
                  | 
                 H 
a. 3-methylbutane

b. 3-methylpentane

c.2-methylbutane 

d.2-methylpropane 

2.  Which of the following compounds is the structural isomer of the compound above?

a. 2,2-dimethylpropane 

b. 2-ethylpropane

c. 1,2-methylbutane 

d. 2-methylpentane

3. the energy value of petrol can be determined by a 

a. bomb calorimeter

b. catalytic cracker

c. fractionating column

d. thermometer

4. C8H18 will undergo the following reactions except 

a.  Cracking 

b. Combustion 

c. Substitution

d. Addition

5. One of the products of pentane in excess air 

a. pentanol 

b. pentene

c. nitrogen (II) oxide 

d. carbon (IV) oxide 

6. The gas produced when a mixture of sodium propanoate and soda lime is heated is 

a. Methane.

b. Pentane

c.. Ethane

d. Butene

 

THEORY QUESTIONS 

1. Methane reacts with chlorine under certain conditions to produce tetrachloromethane 

i.). State the condition for the reaction 

ii). Name the type of reaction

iii). Give two uses of methane 

iv). Name one natural source of methane.

                                                                                           ANSWERS

                                                                                           1. C 

                                                                                           2.  A

NITROGEN AND ITS COMPOUNDS note for students

NITROGEN

Nitrogen occurs mainly as a free element in the air/ atmosphere, about 78% by volume of the atmosphere. It is also found in the combined state in many compounds such as ammonia, urea, proteins and trioxonitrates (V) salts. it does not exhibit allotropy and is a diatomic gas 

LABORATORY PREPARATION

From Air

Air is collected and first passed through caustic soda to remove CO₂ and then over heated copper turnings to remove and O₂ [ the oxygen can also be removed by passing the air through alkaline pyrogallol]. The nitrogen obtained is not pure and is denser than air because it contains about 1% by volume of rare/ noble gases.

Pure nitrogen is obtained in the laboratory by any of the following method below:

1.  Thermal decomposition of ammonium dioxonitrate (III)

a.  NaNO_2(aq) + NH₄Cl_(aq) → NH₄NO_2(aq) +NaCl_(aq)

b. NH₄NO_2(aq) →2H₂O_(l) + N_2(g)              

2.       Thermal decomposition of ammonium heptaoxodichromate (VI)

             (NH₄)₂Cr₂O_7(s) → Cr₂O_3(s) + 4H₂O_(l) + N_2(g)

3.   Oxidation of ammonia by hot Copper (II) oxide

                        2NH_3(g)+3CuO_(s) → 3Cu_(s) + 3H₂O_(g)+ N_2(g)

4.    Reduction of dinitrogen (I) oxide by red-hot copper.

            N2O_(g) + Cu_(s) → CuO_(s) + N_2(g)

INDUSTRIAL PREPARATION

Industrially, nitrogen is obtained by fractional distillation of liquid air.  (see industrial preparation of Oxygen)

PHYSICAL PROPERTIES

1.         It is colourless gas.

2.          It is an odourless.

3.          It is a  tasteless

4.         Pure nitrogen is lighter than air.

5.         Slightly soluble in water

6.         Melting point -210⁰C and   boiling point is -196⁰C

CHEMICAL PROPERTIES

1.       It reacts with very electropositive metals to form nitrides

      3Mg_(s) + N_2(g) → Mg₃N_2(s)

2.       It reacts with non – metals like hydrogen and oxygen to form ammonia and oxides respectively.

     N_2(g)+ 3H_2(g) → 3NH_3(g)

                 N_2(g) + 2O_2(g) → 2N₂O_(g)

USES

1.       It is used for manufacture of ammonia.

2.       Liquid nitrogen is used as a cooling agent.

3.       It is used as preservative in packaged foods to prevent rancidity.

The stages in which nitrogen from the atmosphere is converted into soil nitrogen and back to atmospheric nitrogen is summarized below.

1.   Oxidation of atmospheric nitrogen:

N_2(g) + O_2(g) →2NO_(g)

2NO_(g) + O_2(g)→ 2NO_2(g)

4NO_(g)+O_2(g)+2H₂O_(l)→4HNO_2(q)

 4NO_(g)+O_2(g)+2H₂O_(l)→4HNO_3(aq)

2.   Action of nitrogen-fixing bacteria: 

3. Nitrification by nitrifying bacterial.

4. Denitrification by denitrifying bacteria 

COMPOUNDS OF NITROGEN

OXIDES OF NITROGEN

1. NITROGEN (I) OXIDE, N₂O

Nitrogen (I) oxide also known as laughing gas. (it can cause uncontrollable laughter when inhale).

LABORATORY PREPARATION

It is prepared in the lab by thermal decomposition of ammonium trioxonitrate (V). Ammonium trioxonitrate (V) can  not be heated directly because the reaction is highly exothermic and may to an explosion if not controlled 

a.  KNO_3(s) + NH₄Cl_(s) → KCl_(s) + NH₄NO_3(s)

b  NH₄NO_3(s) → 2H₂O_(g) + N₂O_(g)

PHYSICAL PROPERTIES

1.    It is a colourless gas 

2.   It has faintly sickly sweet smell.

3.      It has a sweetish taste.

4.  It is fairly soluble in cold water.

6.   It is a neutral gas

CHEMICAL PROPERTIES

1.       It decomposes on strong heating to form nitrogen and oxygen.

      2N₂O_(g)→ O_2(g)+2N_2(g)

2.     It  burns in any  substance which is hot enough to decom8pop88pose it.

    Mg_(s)+ N₂O_(g)→ MgO_(s)+ N_2(g)

3. it is reduced to nitrogen when in contact with very hot iron or copper. 

 Cu_(s) + N₂O_(g)→ N_2(g)+ CuO_(s)

TEST FOR N₂O

When a glowing splinter is inserted into the jar containing the unknown gas and it  rekindles, then the gas is either oxygen or nitrogen (I) oxide. If the gas has a pleasant smell and does not produce brown fumes of nitrogen (IV) oxide when burnt in air; then the gas is nitrogen (I) oxide.

USE: Nitrogen (I) oxide is used as anesthetic for minor surgical operations.

NITROGEN (II) OXIDE, NO

LABORATORY PREPARATION

Nitrogen (II) oxide is prepared by combining copper with 50% trioxonitrate (IV) acid.

3Cu_(s) + 8HNO_3(aq)→ 3Cu(NO₃)_2(aq)+ 4H₂O_(l) + 2NO_(g)

 brown fumes of nitrogen (IV) oxide produced by some of the nitrogen (II) oxide as they react with oxygen is removed as the gas is pass through water.

PHYSICAL PROPERTIES

1. It is a colourless gas 

2. It is a poisonous gas.

3.  It is a sp⁸aringly soluble in water.

3.  It is slightly denser than air.

4.  It is neutral to litmus.

CHEMICAL PROPERTIES

1.  It combines readily with oxygen to form brown fumes of nitrogen (IV) oxide

         2NO_(g) + O_2(g) → 2NO_2(g)

2.   At high temperature, it decomposes to form equal volume of nitrogen and oxygen

         2NO_(s)→ N_2(g) + O_2(g)

3.   It is reduced to nitrogen by hot metals

 2Cu_(s)+ 2NO_(g) → 2CuO_(g) + N_2(g)

4.  It decolourizing acidified potassium tetraoxomanganate (VI) slowly ( reducing agent)

3MnO₄^-_(aq)+ 4H⁺_(aq) + NO_(g)→3Mn²⁺_(aq) 5NO₃^-

Test for NO

1. With acidified  iron (II) tetraoxosulphate (VI): A solution of acdified FeSO₄ is poured into the gas jar containing the unknown gas. If the solution turns dark brown, then the gas is NO.

NITROGEN (IV) OXIDE, NO₂

LABORATORY PREPARATION

It is prepared by thermal decomposition of lead (II) trioxonitrate (V) Pb(NO3)2. 

Pb(NO3)2 is preferred because it does not contain water of crystallization which can interfere with the preparation.

          

Dig

Pb(NO₃)_2(s) → 2PbO_(s) + O_2(g)+ 4NO_2(g)

The gaseous mixture obtained is passed through a U- tube dipped in ice, Nitrogen (IV) oxide liquefies as a green liquid (yellow if pure) in the tube while oxygen escapes out.

PHYSICAL PROPERTIES

1.  It is a reddish – brown gas.

2.  It has an irritating smell 

3. It  is a poisonous gas 

4.  It liquefies into yellow liquid at 21^oC.

5.  It is denser than air.

CHEMICAL PROPERTIES

1. It turns damp blue litmus paper red

2.  Nitrogen (IV) oxide exists mainly as dinitrogen (IV) oxide, N₂O₄ at low temperature. It decomposes on heating as follows.

N₂O_4(g) + 2O_2(g) → 2NO2_(g) + O_2(g)

•  Pale                    Reddish         
•  yellow                 brown                 

2.     It decomposes on heating to nitrogen and oxygen and so supports combustion 

  2NO_2(g) → N_2(g)+ 2O_2(g)

3.  With reducing agents it is reduced to nitrogen.

  4Cu_(s) + NO2 → 4CuO_(s) + N_2(g)

4.  With dissolved in water it forms two acids, dioxonitrate (III) and trioxonitrate (V) acids, hence, It is a mixed acid anhydride.

  H₂O_(l)+ 2NO_2(g) → HNO_2(aq)+ HNO_3(aq)

5.  It reacts with alkalis to form a mixture of dioxonitrate (III) and trioxonitrate (V) salts

  2KOH_(aq)+ 2NO_2(g) → KNO_3(aq) + KNO_2(aq) + H₂O_(l)

AMMONIA

Ammonia is a hydride of nitrogen. It is found in traces in the atmosphere from the decomposition/ decay of nitrogenous matter in the absence. Because is very soluble in water, it dissolves in rainwater and is washed down into the soil.     

LABORATORY PREPARATION OF AMMONIA

Ammonia is prepared in the laboratory by heating calcium hydroxide, Ca(OH)₂ (slaked lime) with ammonium chloride.

         

          Ca(OH)_2(s)+ 2NH₄Cl_(s)→CaCl_2(s) +2H₂O_(l)+2NH_3(g).

It is dried using calcium oxide, CaO. Because it will react with drying agents like Conc. H₂SO₄ or fused CaCl₂, since it is an alkaline gas.

            

INDUSTRIAL PREPARATION

Ammonia is manufactured by the Haber process from nitrogen and hydrogen. In this process nitrogen and hydrogen are reacted in ratio 1:3 by volume. The reaction is reversible. The conditions for optimum yield of ammonia are 

i. A temperature of 450^Oc 

ii. A pressure of about 200atm and 

iii. Finely divided iron catalyst   

N_2(g) +3H_2(g) →2NH_3(g) + heat

Physical Properties of Ammonia

i.   It is a colorless gas 

ii. It has a characteristic choking/ pungent smell.

iii. When inhaled in large quantity it is poisonous 

iv.. It is the only known alkaline gas.

v. It is about less dense than air.

CHEMICAL PROPERTIES

1. Ammonia burns readily in oxygen to yield and nitrogen and water vapour 

              4NH_3(g)+3O_2(g)→6H₂O_(g)+ 2N_2(g)

2. As a reducing agent, it reduces most metallic oxides to their metals. 

            i. 3CuO_(s) + 2NH_3(g) → 3Cu_(s) + 3H₂O_(l) + N_2(g)

             ii.   With Chlorine it yields NH4Cl

            iii. 3Cl_2(g) + 8NH_3(g) → 6NH₄Cl_(s) + N_2(g)

3.  Ammonia reacts with carbon IV oxide to form Urea and water vapour.

              2NH_3(g)+ CO_2(g) → (NH₂)₂CO_(s) + H₂O_(l)
                                                   ^urea

4. With acids it forms ammoniums salts.  

                   2NH_3(g) + H₂SO_4(g)→(NH₄)₂SO_4(s)

Test For Ammonia

Ammonia has a choking and a pungent smell. It can be confirmed using:

1. Litmus paper: It turns damp red litmus paper blue

2.  Hydrochloric acid: it forms dense white fumes with concentrated HCl(aq) on a glass rod 

Uses Of  Ammonia

1.  It is one of the raw materials in the Solvay process for the   manufacture trioxonitrate (V) acid and Sodium trioxocarbonate (IV).

2. Liquid ammonia is used as a refrigerant.

3. Aqueous ammonia is used in softening temporary hard water.

4.    Aqueous ammonia is also used in laundries as a solvent for removing grease and oil stains.

TRIOXONITRATE (V) ACID, HNO₃

Trioxonitrate (V) acid is a volatile acid. 

      LABORATORY PREPARATION

It is prepared in the laboratory by displacement of the HNO3 from any trioxonitrate salt by concentrated H₂SO₄ which is less volatile. Trioxonitrate (V) of potassium or sodium is usually used because they are cheap.

      KNO_3(s)+ H₂SO_4(aq)→ KHSO_4(aq)+HNO_3(aq)

NOTE: we use an all-glass apparatus for this preparation because the hydrogen trioxonitrate (V) acid vapour will attack cork or rubber.

INDUSTRIAL PREPARATION

It is prepared by the catalytic oxidation of ammonia:

1.    Ammonia is treated with excess air using Platinum-rhodium catalyst at 700^oC to produce

4NH_3(g)+ 5O_2(g)→ 4NO_(g)+ 6H2O the nitrogen (II) oxide formed is cooled and mixed with excess air to produce nitrogen (IV) oxide.

           2NO_(g) + O_2(g) →2NO₂(g)

2.    Nitrogen (IV) oxide formed is dissolved with excess air in hot water to yield trioxonitrate (V) acid solution of up to 50% concentration. 

              4NO_2(g)+ 2H₂O_(l)+ O_2(g) → 4HNO_3(aq)

PHYSICAL PROPERTIES

1.  Pure HNO3 acid is a colourless liquid with sharp choking smell. It fumes in air. The acid decomposes to give NO2 gas which redissolves in the acid turning it yellow after a while.

2. The density of the pure acid is 1.52 gcm^-3

3.  The pure acid boils at 86⁰C and melts at -47^oC  

4.   The pure acid dissolves in water in all proportions 

5.  The concentrated form of the acid is corrosive.

CHEMICAL PROPERTIES

1.  As an acid 

I. The dilute acid turns blue litmus red.

 ii.  it neutralizes bases and alkalis to form metallic trioxonitrate (V) and water only

NaOH_(aq)+HNO_3(aq) → NaNO_3(aq)+ H₂O_(l)

iii. it reacts with trioxocarbonate (IV) to liberate carbon (II) oxide 

 CaCO_3(s) + HNO_3(aq) → Ca(NO₃)_2(aq)+ H₂O_(l)+ CO_2(g)

3.  Unlike other acids, it rarely gives out hydrogen with metals except when very dilute solution is reacted with Ca, Mg or Mn.

4.    As an oxidizing agent, 

it oxidizes non–metal like Sulphur to form the corresponding oxides of the non – metals.

  S_(s)+ 6HNO_3(aq)→H₂SO_4(aq) + 2H₂O_(l) + 6NO_2(g)

ii.   it oxidizes least reactive metals like Cu, Pb, Hg and Ag to yield the respective trioxonitrate (V) and nitrogen (IV) oxide.  With moderate concentration it yields nitrogen (II) oxide.

Aluminum and iron are not oxidized by the acid, because of the formation of a thin coating of the oxide on the surface of the metal which is impervious to further attack on the metals. 

Hence, containers lined with aluminum and iron can be used to transport concentrated HNO_3(aq)

5.  As an oxidizing agent, it oxidizes hydrogen sulphide to sulphur

        H₂S_(g) + 2HNO_3(aq) → S_(s)+ 2H₂O_(l)+2NO_2(g)

6.  it oxidizes iron (II) salts to iron (III) salts

        6Fe²⁺_(aq) + 8H⁺_(aq) + 2NO₃^-_(aq) →   6Fe³⁺_(aq) + 4H₂O_(l) + 2NO_(g)

USES

1.  It is used as an acid, oxidizing agent and nitrating agent in the laboratory.

2. It is as rocket fuel

3. It is used in producing nylon and Terylene.

4.  It is used to produce fertilizers, dyes, drugs and explosives.

OBJECTIVE QUESTIONS 

1.  In which group of the periodic table is nitrogen found? 

(a) 2

 (b) 5 

(c) 7

(d) 6

2. The boiling point of nitrogen in ⁰C is

 (a) -183

 (b) -196

 (c) 200

 (d) 240

3.   The percentage of nitrogen in air is

 (a) 78 

(b) 75 

(c) 71

 (d) 67

4. The following are uses of nitrogen except a. as a cooling agent b. to prevent rancidity c. in the manufacture of fertilizers d. in laundry.

5. The atomicity of nitrogen is 

(a) 1

(b) 2

 (c) 3

 (d) 4

6.  Which of the following compound will leave a metal residue when heated 

a. Cu(NO₃)₂

b. AgNO₃

c. K₂CO₃

4.CaCO₃

7.  The gas given off when NH4Cl is heated with an alkali is 

a. H₂

b. Cl₂

c. N₂ 

d. NH₃

8. 

9. 

10.

11. 

12.

THEORY

 

1a(i)   State TWO physical properties and TWO chemical properties of nitrogen.

1(ii)  Mention THREE uses of nitrogen.

1(iii) Briefly describe the preparation of nitrogen from air in the laboratory. 

2a(i)   Give an equation to show the laboratory preparation of nitrogen (II) oxide.

2b. Describe a test to distinguish between nitrogen (I) oxide and oxygen gas.                    

2c(iii) Briefly describe the laboratory preparation of ammonia.

3a   State TWO physical and THREE chemical properties each of ammonia.                                       

3b.  Describe the laboratory preparation of trioxonitrate (V) acid.

3c  Write TWO equations of reactions in which trioxonitrate (V) is acting as an acid.

4a. Write an equation to show the reaction of nitrogen (IV) oxide as a mixed anhydride.

4b.  Describe the electrolysis of CuSO₄ solution using platinum electrodes.

ELEMENTS, MIXTURES and COMPOUNDS at a glance

 

ELEMENTS: - An element is a substance that cannot be split into simpler units by any ordinary chemical process. 

examples of elements include sodium, oxygen, carbon, nitrogen e.t.c.

There about 118 elements that has been discovered so far and grouped into metals and non-metals in general. we also have elements that are referred to as metalloids, these are actually nonmetals that show or exhibit some metallic properties.

Examples of metals and non-metals 

Metals                 Non-metals

Sodium              Oxygen

Potassium         Carbon

Iron                     Silicon

Gold                    Lead

Tin                      Sulphur 

Calcium              Phosphorus 

 

METALS: - These are elements that ionize by the loss of electrons.

     Na → Na⁺ + e^-

     Ca → Ca²⁺ + 2e^-

      Al → Al³⁺ + 3e^-

They form positively charged ions, that is, Cations when the loss electrons (ionize)

Physical Properties of Metals

i.  Metals are malleable, that is they can be beaten or hammered into flat sheets. 

ii. Metals are ductile, that is, they can be drawn into wires

iii. Metals are Sonorous, i.e. they produce musical notes when struck

iv. Metals conduct heat and electricity

v. Metals have metallic luster, i.e.  they shine when polished.

vi. metals have high tensile strength

Chemical Properties of Metals 

i. Ionization: - Metals ionize by the loss of their valence (outermost) electrons to form Cations

      Na_(s) → Na⁺ + e^-

      Mg_(s) → Mg²⁺ + 2e^-

      Al_(s) → Al³⁺ + 3e^-

ii. Reaction with air: - most metals especially the group I metals like sodium, potassium when exposed to air reacts with the atmospheric gases and become tarnished. Example 

     4Na_(s) +O_2(g) → 2Na₂O_(s)

     Na₂O_(s) + H₂O_(l) → 2NaOH_(aq)

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

iii. Reaction with Acids: - Most metals react with dilute acids to liberate hydrogen gas. Example

     I. Mg_(s) + H₂SO₄ → MgSO_4(aq) + H_2(g)

      ii. Ca_(s) + 2HCl_(aq) → CaCl_2(aq) + H_2(g)

Reaction with Bases: - Some metals react with Bases to form complex salts. These metals are said to be Amphoteric elements. Examples include Aluminium (Al), Tin (Sn), Zinc (Zn) and Lead (Pb).

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

Reaction with non-metals: - Most metals combine directly with nonmetals to form compounds, example metals combine with oxygen to form oxides, with sulphur to form sulphides, with nitrogen to form nitrides.

   Ca_(s) + O_2(g) → CaO_(s)

   Fe_(s) + S_(s) → FeS_(s)

    2 Mg_(s) + O_2(g) →MgO_(s)

 

NON-METALS: - These are elements that ionize by gaining electrons.

They form negatively charged ions known as Anions, when they gain electrons

Example

Physical properties of nonmetals 

i. Non-metals do not conduct heat and electricity

ii. They are hard and brittle i.e. they break easily  

iii. They have low tensile strength 

iv. They do not shine when polished

v. They are not malleable 

vi. They are not ductile 

COMPOUNDS: - A compound is a substance formed when two or more elements are chemically combined together.

examples of compounds include

 i. sodium chloride (NaCl), 

ii. calcium trioxocarbonate (IV) (CaCO₃),

Iii. Water (H₂O)

Iv. Sugar (C₆H₁₂O₆)

MIXTURES: - Mixtures are substances that contain two or constituents that can be separated by physical methods.    

                 Differences between Compounds and Mixture 

	Compounds	Mixture
i.	Can be represented by a formula	Can not be represented by a formula
ii	Is always homogenous (every part of the compound is always the same)	May be homogenous (that is, every part of the mixture is the same) or heterogenous (every part of the mixture is not the same)
iii.	Composition is always constant	Composition is not constant
iv.	Property is different from the properties of the individual elements that make up the compound	Constituents still retain their individual properties
v.	The elements are chemically combined together	The constituents are not chemically combined

 

Example of mixtures include: - 

	Mixtures	Constituents
i.	Sodium chloride solution	Sodium chloride + water
ii.	Blood	Plasma + red and white blood cells
iii.	Urine	Water + salts + Urea
iv.
v.
vi

               

In order for substances to be analyzed they have to be separated into their pure forms. The various methods for separating substances into their various pure forms are discussed in a different post.