High School “Tudor Vianu”Giurgiu CHEMISTRY LESSON PLAN

Subject: The chemical properties of acetylene 10 th Grade Type of the lesson: mixed

GENERAL COMPETENCES - To explain a couple of phenomena, processes, methods - To investigate the way chemical substances interact - To solve problems to demonstrate deductive and inductive judgements

Specific competences To describe the reactions acetylene takes part in alkyne To investigate in order to underline some caracteristics and properties To formulate rules, definitions and generalizations To learn the concept of metal acetylides To study the concept of unsaturated character determinated by the existence of the relation bond π To underline the importance of acetiylene To use specific notions

Teaching methods and procedures Heuristic conversation Questioning Experiment Cube and puzzle method

Used in theaching Microequipament used to prepare acetylene CaC2 Bromine water KMnO4 solution Reactiv Tollens Cubes Worksheets

The development of the lesson Checking the existing knowledge In order to check the existing knowledge, the teacher asks the students to solve the following reaction scheme: A : 75%C, 25%H C2H2C2H o C +H 2 O B

Tasks: Establish the formulas of the compounds A and B Write the reaction equations needed to obtain acetylene from the given reaction scheme Indicate the structure and the physical properties of acetylene

Question: Knowing the chemical structure of acetylene, indicate the common reaction types of acetylene and alkenes? Students answer: Types of reactions: - Addition reactions - Oxidation reactions - Substitution reactions

The chemical properties of acetylene A) ADDITION REACTIONS 1) Hydrogen addition - complete hydrogenation  alkane - partial hydrogenation  alkenes Pd/Pb 2+ CH ≡ CH + H 2 CH 2 =CH 2 acetylide ethene Ni CH ≡ CH + 2H 2 CH 3 -CH 3 acetylide ethan

2) Halogens Addition : Br 2, Cl 2 Br Br HC ≡ CH + Br 2 CH = CH HC ─ CH Br Br Br Br HC ≡ CH + 2Cl 2 Cl 2 HC – CHCl 2 HC ≡ CH + 2Br 2 Br 2 HC – CHBr 2 HC ≡ CH + Cl 2 2C ↓ + 2HCl 1,2 dibromoethene 1,1,2,2 tetrabromothan INERT SOLVENT 1,1,2,2 tetrachloroethan 1,1,2,2 tetrabromoethan

3) Acids Addition a) HCl addition – HgCl 2 catalyzer, 170 – 190 o C HC ≡CH + HCl H 2 C=CH-Cl (vinyl chloride) polimerization nH 2 C=CH-Cl -(-CH 2 -CH-) n - │ Cl Polyvinyl chloride used for syntetic leather, PVC carpentry.

b) HCN addition - Cu 2 Cl 2 + NH 4 Cl catalyzer b) HCN addition - Cu 2 Cl 2 + NH 4 Cl catalyzer HC ≡ CH + HCN H 2 C=CH - CN acrylonitrile polimerization nH 2 C=CH-CN -(-CH 2 -CH-) n - │ CN polyacrylonitrile Polyacrilonitrile used for syntetic fibres.

c ) CH 3 COOH addition -(CH 3 COO) 2 Zn catalyzer HC ≡ CH + CH 3 COOH H 2 C=CH- OCOCH 3 vinylacetate polimerization nH 2 C=CH-OCOCH 3 -(-CH 2 -CH-) n - │ OCOCH 3 polyvinyl acetate Polyvinylacetate used for adhesive.

4) Water Addition – Kucerov Reaction tautomery HC ≡ CH + HOH  [ H 2 C=CH-OH ]  H 3 C- CH=O Ethanal( acetaldehyde)

B) OXIDATION REACTION Occurs in the presence of KMnO 4 in a weak/ low basic or neutral medium Rules: HC ≡  -COOH - C ≡  -C=O │ HC ≡ CH + 4[O]  HOOC-COOH Oxalic acid 2KMnO 4 + H 2 O  2KOH + 2MnO 2 ↓ +3[O] brown

C. SUBSTITUTION REACTION The hydrogen atoms of acetylene and of alkyne with triple bonds located in marginal position take part in the substitution reactions. This reaction demonstrate a low acid character. Substitution reactions can be realized using alcaline metals and alkaline-earth metals or using complex combinations of transitional metals, having as a result acetylides.

150 o C HC ≡ CH + Na Na + C - ≡ CH + ½ H o C Na + C - ≡ CH + Na Na + C - ≡ C - Na + + ½ H 2 HC ≡ CH +2[ Ag(NH 3 ) 2 ]OH  AgC ≡ CAg ↓ + 4NH 3 + 2H 2 O Yellowish-white

EXPERIMENTS 1. In a 50 cc flask with a long neck insert 20cc water and add a few carbide (CaC 2 )pieces. Close quickly the flask using a stopper fitted wit a bent glass tube. It emits acetylene which will be used in the next reactions.

2. The addition of bromine to acetylene Insert ml diluted solution of bromine water in a test tube. If you bubble the acetylene that you prepared, you can notice that the bromine solution loses its colour, so it reacts with bromine

2. The oxidation of acetylene using potassium permanganate Insert some ml KMnO 4 solution and some ml Na 2 CO 3 solution in a test tube. Bubble the prepared acetylene in this mixture and you can notice the formation of a brown precipitate of manganese dioxide which deposits and the purple colour of the mixture disappears very quickly.

4. Obtaining silver acetylides Insert 10 ml Tollens reagent in a test tube and bubble a stream of acetylene. An yellowish – white precipitate of silver acetylides can be seen AgC ≡ CAg. The precipitate is filtered and dried. A small part is put on a sieve and if you luat it, small explosious occur.

HOMEWORK Create cubes and puzzles to illustrate the chemical properties of acetylene.

This project has been funded with support from the European Commission. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.