Lesson Notes By Weeks and Term - Senior Secondary 1

Carbon and its compounds: Alkynes

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  4. Carbon and its compounds: Alkynes

Term: 3rd Term

Week: 8

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:       

Subject:      Chemistry

Topic:-       CARBON AND ITS COMPOUNDS: Alkynes

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Highlight the properties of alkynes
  2. Discuss the structure, preparation and uses of alkynes

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S ACTIVITY

STEP 1

INTRODUCTION

The teacher reviews the previous lesson on alkenes

Students pay attention

STEP 2

EXPLANATION

He highlights the properties of alkynes

 

Students pay attention and participates

STEP 3

DEMONSTRATION

He discusses the structures, preparation and uses of alkynes

Students pay attention and participate

STEP 4

NOTE TAKING

The teacher writes a summarized note on the board

The students copy the note in their books

 

NOTE

CARBON AND ITS COMPOUNDS

Alkynes

The alkynes are homologous series of hydrocarbons with a general molecular formula CnH2n-2. They are SP hybridized and Unsaturated

 

Structure of Alkynes

 

Physical properties of alkynes

  1. Ethyne (acetylene) is a colorless gas with ether-like odour when pure. Ethyne prepared from calcium carbide has garlic odour due to the presence of impurities like phosphine (PH3) and hydrogen sulphide (H2S).
  2. Ethyne is slightly soluble in water, but highly soluble in organic solvents like acetone and alcohol.
  3. It is lighter than air.
  4. It is a poisonous gas. Liquid ethyne (acetylene) is highly explosive.
  5. It has a boiling point of -840

 

Chemical properties of Ethyne

  1. Combustion: Ethyne on combustion produce carbon dioxide, water and heat.

2C2H2 + 5O2 → 4CO2 + 2H2O + Heat.

 

  1. Addition reaction:

       i. Addition of hydrogen to ethyne gives ethane after catalytic hydrogenation in presence of nickel.

       ii. Addition of halogen forms 1,1,2,2-tetrahaloethanes.

 

  1. Substitution reaction

             i. Terminal alkynes react with ammoniacal solution of copper(I) chloride at room temperature. A reddish-brown precipitate of

 

copper(I) dicarbide is formed.

C2H2(g) + 2CuCl(aq) àCu2C2(s) + 2HCl(aq)

             ii. Terminal alkynes react with ammoniacal solution of AgNO3 at room temperature. A whitish-yellow precipitate of silver dicarbide is

 

formed.

C2H2(g) + 2AgNO3(aq) àAg2C2(s) + 2HNO3(aq)

  1. Polymerization: ethyne polymerize to form the aromatic hydrocarbon, benzene, when it is passed through a hot tube containing a complex orgno-nickel catalyst.

 

USES OF ALKYNES

  1. Substances like ethanol, acetic acid, vinyl polymer and plastic like substances can be prepared from it.
  2. Ethyne is used in oxyacetylene flame used for welding of metals.
  3. On kite flying day, acetylene gas is filled in rubber balloons and the balloons are flown high in the sky.

 

EVALUATION:    1. What are alkynes?

  1. Describe the structure of alkynes
  2. Highlight two physical and chemical properties of alkynes
  3. How can alkynes be prepared?
  4. State two uses of alkynes

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively