Carbon Compounds : Video Playlist

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2.9.2 - Laboratory Activity : Characteristic of Vulcanised and Unvulcanised Rubber

Laboratory Activity 2.9.2: Characteristic of Vulcanised and Unvulcanised Rubber

Aim: To make vulcanised rubber and to compare vulcanised and unvulcanised rubber.
Problem statement: What is the difference between vulcanised and unvulcanised rubber in term of elasticity?
Hypothesis: Vulcanised rubber is more elastic than unvulcanised rubber.
Variable:

	»	Fixed variable : The width and thickness of rubber strip, mass of weight
	»	Manipulated variable : Type of rubber strips
	»	Responding variable : Elasticity

Material: » Latex » Ethanoic acid » Sulphur monochloride solution in methylbenzene

Apparatus: » White tile » Knife » Glass rod » Beaker » Retort stand » Weight » Ruler

Procedure:

	►	(A) Preparation of vulcanised rubber 1. 2. 25cm3 of latex is poured into the beaker and few drops of ethanoic acid is added. 3. The mixture is stirred and quickly poured into the white tile. 4. A glass rod is used to spread out the latex to get a 1 mm thick layer of latex. 5. The latex is left to coagulate. 6. The rubber sheet formed is then cut into two strips of the same size. 7. One of the strips is dipped into the sulphur monochloride solution for 2 minutes.
	►	(B) Comparing vulcanised and unvulcanised rubber 1. 2. The unvulcanised rubber strip is hung vertically using a clip and retort stand as shown in the diagram. 3. The length of unvulcanised rubber is measured. 4. A weight of 25g is hung on the rubber strip and the length of the unvulcanised rubber strip is recorded. 5. The weight is released, and the length of the rubber strip is measured again. 6. The experiment is repeated by using the vulcanised rubber strip.

Obervation:

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Extension of rubber strip Type of rubber strip Original length (cm) Length with weight (cm) Extension (cm) Length after weight is removed (cm) Unvulcanised rubber 6 9.5 3.5 9 Vulcanised rubber 6 8 2 8

Discussion:

	►	The unvulcanised rubber strip extends more as compared to the vulcanised rubber strip.
	►	Vulcanised rubber has a greater resistance to force (weight)
	►	The vulcanised rubber strip has an ability to return to its original length after the weight is taken off. Thus, the vulcanised rubber strip is more elastic.

Conclusion:

►

Vulcanised rubber is more elastic as compared with natural rubber.

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2.9.1 - Laboratory Activity : Coagulation of Latex

Laboratory Activity 2.9.1: Coagulation of Latex

Aim: To study the coagulation process of latex.
Problem statement: What is the chemical properties of ethanol?
Hypothesis: The presence of acid causes latex to coagulate.
Variable:

	»	Fixed variable : Amount of latex and the time for coagulation
	»	Manipulated variable : Addition of acid or alkali
	»	Responding variable : Coagulation of latex

Material: » Latex » Ethanoic acid » Ammonia solution » Red and blue litmus paper

Apparatus: » Glass stirring rod » Beaker » Dropper

Procedure:

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1. 100cm3 of latex is poured into three different beakers and label them respectively A, B and C. 2. 2cm3 of ethanoic acid is dropped into the beaker A using a dropper. 3. Ammonia solution is added into beaker B until the mixture became alkaline. The alkaline solution is tested with red litmus paper. 4. Beaker C is left behind as a control experiment.

Obervation:

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Beaker Observation A – latex + ethanoic acid Latex coagulates B – latex + ammonia solution Latex does not coagulate C – control experiment Latex coagulates after 1 day

Discussion:

	►	Latex consists of groups of rubber particles dispersed in water, which can only be seen through a microscope.
	►	Each group of rubber particles is surrounded by a negative charge membranes protein.
	►	The negative particles membrane will repel other negative particles which eventually will prevent all the particles to coagulate.
	►	When acid is added to latex, the positively charged ions H+ from acid will neutralise the negative charged membrane protein of rubber particle.
	►	The neutralise rubber particles will collide to cause the membrane to break. Rubber particle is released, combine with each other and cause them to coagulate.

Conclusion:

►

Acid will coagulate latex meanwhile alkali will prevent coagulation of latex.

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2.9 Natural Rubber

Natural polymer
■ Natural polymers

	►	A polymer that exists naturally.
	►	Example of natural polymers: protein, starch and natural rubber.

■ Formation of natural polymer

	►	Proteins are natural polymers composed of long chain molecules known as polypeptides. Each molecule consists of a polypeptide amino acids monomer linked by a peptide chain.
	►	Starch is a plant storage material produced by the process of photosynthesis. When the monomers undergo condensation polymerization of glucose, starch polymers formed together with the removal of water molecules: ○ $\begin{array}{c}{\mathit{nC}}_6{H}_{12}{O}_6\\ \text{glucose}\end{array}\to \begin{array}{c}\text{~}{(C_6{H}_{10}{O}_5)}_n\text{~}\\ \text{starch}\end{array}+n{H}_{2}O$
	►	Natural rubber is a biosynthesis polymer formed in the rubber tree. The monomer of natural rubber is methylbuta-1,3-dienes or isoprene. Natural rubber polymer molecules also known as poliisoprena and is formed by the addition polymerization process. ○ $\begin{array}{c}{\mathit{CH}}_{2}C({\mathit{CH}}_3){\mathit{CHCH}}_2\\ \text{isoprene}\end{array}\to \begin{array}{c}{\mathrm{[}{\mathit{CH}}_{2}C({\mathit{CH}}_3){\mathit{CHCH}}_2\mathrm{]}}_n\\ \text{rubber polymer}\end{array}$

Properties of natural rubber
■ Properties of natural rubber

	►	Soft
	►	Elastic
	►	Does not conduct electricity.
	►	Non-heat resistant. If a natural rubber is heated to temperatures above 50°C, it will melt and sticky. When cooled, the rubber becomes hard and brittle, like plastic. Natural rubber will decompose when heated to temperatures above 200°C.
	►	Insoluble in water, dilute alkali or acid but soluble in organic solvents such as benzene, gasoline, carbon disulphide, and chlorinated hydrocarbons.
	►	The presence of the double bond in the carbon chain causing latex rubber easily oxidized by chemicals, which are strong oxidizing agents.

The uses of natural rubber
■ Original natural rubber, which is not chemically treated have limited use. Natural rubber is used as:

	►	Rubberized bitumen roads (mixture of cement, bitumen and latex rubber to the road surface paving)
	►	Elastic
	►	The insulating material like blankets and rubber foam.
	►	The material to absorb vibration such as rubber block and rubber bearings.
	►	The material to increase friction, such as footwear, sandals, rubber or door.

■ Natural rubber will be chemically treated before use.

	►	Most of the natural rubber latexes are vulcanized to modify the original properties. Vulcanized natural rubber is stronger, flexible and resistant to heat.
	►	Filler materials such as carbon powder, zinc oxide, magnesium carbonate and clay-resistant rubber is added to the original to make it more compact and powerful. This property is important in the manufacture of vehicle tires.
	►	Antioxidants is added into natural rubber to make items such as tires and rubber tubes.

Structure of the rubber particles
■ Latex

	►	Milky white fluid.
	►	A colloidal solution containing about 30% natural rubber and 70% water.

■ Structure of the rubber particle

	►	In the rubber latex, rubber molecules in small groups encompassed by the negatively charged cell membrane proteins.
	►	The protein membrane colloid particles will repel each other to prevent the rubber polymer molecules come together to become one big lump.

■ Coagulation Process of Latex

	►	Coagulation of latex can be done by adding acid to it or leaving it in the air for 1 to 2 days.
	►	This is due to the presence of acid produced by the action of bacteria in the rubber latex.
	►	Positively charged ion, H+ ions from the acid will neutralize the negative charges on the membrane of colloidal particles in natural rubber latex.
	►	Collisions between colloidal particles will break the membrane.
	►	When membranes break, polymer molecules of rubber released and combine with one another.
	►	This is known as the latex coagulation process.
	►	The latex coagulation process can be accelerated by the addition of dilute acid solutions as a supplier of H+ ions into rubber latex. Acid commonly used is methanoic acid (HCOOH) where coagulation will occur within a few minutes.
	►	The following animation shows the coagulation process of latex.

■ Preventing coagulation of latex by alkali

	►	The addition of an alkaline solution such as ammonium hydroxide (, ammonia water) solution will prevent the coagulation of rubber latex.
	►	The alkaline solution is added to neutralize the acid produced by bacteria in rubber latex.
	►	The negative charges on the membrane of colloidal particles of latex rubber can be maintained.
	►	Thus latex rubber remains as a colloidal solution.

■ This video contains information on the coagulation of rubber.

Laboratory Activity 2.9.1 : Coagulation of Latex

Vulcanisation of rubber
■ Vulcanized rubber

	►	Rubber that has been mixed and heated with sulphur.
	►	The weakness of properties such as soft, non-heat resistant in natural rubber can be overcome through a vulcanized process.
	►	Vulcanisation process can be carried out by: ○ Heat natural rubber with sulphur ○ Mix natural rubber with a solution of sulphur monochloride in methylbenzene.

■ Vulcanisation of Rubber

	►
	►	After polymerization, the natural rubber polymer chain still has a double bond which allows it to be vulcanized.
	►	In vulcanisation process, sulphur atoms diffuse into the structure of natural rubber to form cross-links between neighbour polymer chains of natural rubber.
	►	With the formation of sulphur atom cross-links, the polymer molecules become more compact.
	►	A more compact polymer chain arrangement make vulcanized rubber become less elastic and stronger.
	►	Elasticity and strength of vulcanized rubber depend on the amount of sulphur cross-links formed between rubber polymer molecules.

■ Comparison of vulcanised and unvulcanised rubber

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Differences Natural rubber Vulcanised rubber Tensile strength Low High Hardness Soft Hard Melting point / Heat resistant Lower Higher. The addition of sulphur to the rubber polymer chains has increased the relative molecular mass. Thus, the melting point of vulcanized rubber is also higher, and it is more resistant to the action of heat. Elasticity Low High Resistant to oxidation Low High. As the number of double bonds decreased due to the formation of the double bond cross-sulphur clusters, the vulcanized rubber are more resistant to oxidation.

Laboratory Activity 2.9.2: Characteristic of vulcanised and unvulcanised rubber

2.8 Fats

Oil and fats
■ Fats and oils

	►	The high-ester (large molecules) family, which occurs naturally in animal fats and plant oils.
	►	At room conditions, the fat may exist in the solid or liquid state. ○ Fat usually represent fat in the solid state. ○ Fat that exists in the liquid state was named oil.

■ Formation of fats and oils

	►	Fats are esters derived from the esterification reaction between one molecule of glycerol with three fatty acid molecules. ○ Fatty acid + Glycerol → Fats or oils
	►	The following animation shows the formation of fats and oils.
	►	The hydrocarbon chain may contain double bond(~CH=CH~) or only single bond( ~CH3-CH3~)

The importance of oils and fats for the body processes
■ The importance of oils and fats for the body processes

	►	Fat stored in the body as energy savings.
	►	Fat acts as a carrier solvent of vitamins A, D, E and K. These vitamins are only soluble in fat.
	►	The layer of fat under the skin protects the body from the cold.
	►	Fat tissue around the internal organs of the human protects organs from injury.

■ Sources of oils and fats

►

The common sources of fats are butter, ghee, cheese, meat, egg yolk, milk, nuts, etc.

■ The uses of Oils and Fats

	►	Fats are the main energy storer of the body.
	►	When hydrolysed animal fats by steam under pressure, it gives a mixture of stearic acid and palmitic that can be used to make candles.
	►	Vegetable oil can be used to make soap through the saponification process.
	►	Certain type of oil can be used to make paint, fabric, oil and linoleum.

■ This video contains information on the differences between oils and fats

■ Oils and fats differs from unsaturated fats in some aspects:

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Differences Oils Fats Sources Mainly animals Mainly plants State at room temperature Liquid Solid or semi-solid Melting point Lower Higher Number of hydrogen atom Less More Present of double covalent bond Yes (most are unsaturated compounds) No (most are saturated compounds) Example Vegetable oils Animals fats

Saturated and unsaturated fats
■ Classification of fats

	►	Saturated
	►	Unsaturated fats

■ Saturated fats

	►	Saturated fat is fat that contains saturated fatty acids. ○ Saturated fatty acid + glycerol → saturated fat
	►	Saturated fats do not have double bonds and are solids at room temperature.
	►	Example: Glyceryl tripalmitate Glyceryl tristeaate
	►	Animal fats contain high saturated fat content.
	►	The percentage of saturated fatty acids in animals fats are normally higher compared with the percentage of unsaturated fatty acids.

■ Unsaturated fats

	►	Unsaturated fat is fat containing unsaturated fatty acid. ○ Unsaturated fatty acid + glycerol → unsaturated fat
	►	Unsaturated fats have one or more double bonds and are liquids at room temperature. The presence of double bonding causes unsaturated fats have a lower melting point.
	►	Example: Glyceryl trilinoleatee Glyceryl trioleate
	►	Vegetable oils such as palm oil, soybean oil, sunflower seed and olive contains high unsaturated fat.

■ Similarity of saturated fats and unsaturated fats:

►

Both have 1 molecule of glycerol and 3 molecules of fatty acid.

■ Saturated fats differs from unsaturated fats in some aspects:

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Differences Saturated fats Unsaturated fats Sources Mainly animals Mainly plants Fatty acid Saturated Unsaturated Bonding No double bond Have double bond Hydrogen content Maximum Can be increased Cholesterol content High Low Melting point High Low

■ Conversion of unsaturated fats to saturated fats

	►	The presence of double bond in unsaturated fats allows unsaturated fats undergo addition reaction.
	►	Hydrogenation is the addition reaction with hydrogen. ○ Convert unsaturated fats to saturated fats with the addition of hydrogen to the double bond. ○ Fats in liquid state change to solid. ○ Example: Vegetable oil (unsaturated fat) is converted to a solid (saturated fat). $\text{Palm oil (unsaturated fats)}+\text{hydrogen}\begin{array}{c}\to \\ \text{hydrogenation process}\end{array}\text{margarine (saturted fat)}$ Temperature of 200°C and pressure 2 to 5 atmosphere in the presence of nickel powder catalyst

Effects of eating food with high fat content
■ Effects of Eating Food with High Fat Content

	►	Butter, ghee, etc. are saturated fats and oils are unsaturated fats.
	►	High intake of saturated fats increases blood cholesterol levels that can lead to coronary disorders and high blood pressure.
	►	Thus people who have a sedentary lifestyle such as old people should reduce the intake of saturated fats.
	►	However, people involved in heavy labour, fat intake should be more, as their energy requirement is high.

■ Cholesterol

	►	Cholesterol is a type of complex organic compounds commonly found in fat.
	►	This is because cholesterol is a fat-soluble, transported to fat and stored in fat.
	►	In fact, cholesterol can be synthesized in our body itself. Cholesterol is essential for the formation of cell membranes, bile salts, reproductive hormones and vitamins.
	►	However, scientific studies show that consumption of foods with high cholesterol can affect human health.
	►	There are two types of cholesterol, the low-density cholesterol (LDL) and high density cholesterol (HDL).
	►	Research shows that low-density cholesterol (LDL) deposited in the arteries.
	►	High density cholesterol (HDL) could be useful to our body.

■ Based on these studies, high levels of cholesterol in the blood can cause a variety of diseases.

	►	High cholesterol can lead to a disease of arteries, called arteriosclerosis.
	►	Arteriosclerosis caused by the accumulation and deposition of lipids, particularly cholesterol (a type of steroid) in combination with fatty acids and proteins, as thick layers on the surface of the wall in blood arteries.
	►	This situation, if allowed to continue can cause clogged arteries cavities and thus restricting normal blood flow.
	►	Blood clots will cause heart attacks and cause a stroke.

Industrial extraction of palm oil
■ Structure of oil palm fruit

	►
	►	Mesocarp(husk) : ○ Thick fleshy layer, orange when ripe ○ Contain a lot of oil
	►	Kernel: ○ White fleshy piece ○ Produces kernel oil
	►	Shell: ○ Hard protective layer

■ Stages in palm oil extraction from the mesocarp

	►	Sterilisation (fresh fruit bunch is heated with pressurized steam to:) ○ soften the fruits. ○ kill bacteria and other micro-organisms. ○ stop the decomposition of oil. ○ loosen the fruit from its bunches.
	►	Threshing ○ To separate fruit from its bunches.
	►	Digestion ○ The heat of the steam is used to separate mesocarp from the shell.
	►	Pressing ○ Oil is squeezed from the mesocarp with a hydraulic press.
	►	Filtration ○ To remove the foreign substances from oil.
	►	Purification ○ Palm oil is treated with phosphoric acid. ○ Steam passes through the oil to separate acid. ○ Pure palm oil is obtained.

■ Stages in palm oil extraction from the mesocarp

	►	Extraction ○ The fruits obtained from the crushing process are boiled at high pressures and cooked to remove the kernel from its shell. ○ The shell is broken, and the kernel is separate from the shell. ○ The kernel is dried at a high temperature and squeezed to obtain its oil.
	►	Purification ○ Oil from kernel is purified.

■ This video shows how sterilisation and threshing process in palm oil extraction.

The use of palm oil in food production
■ There are many uses of palm oil and palm kernel oil:

►

Cooking oil Margarine Candle Lotion Condensed milk Soap

■ Palm oil has many advantages as compared to other vegetables oils.

	►	Palm oil is a nutritious oil because it supplies fatty acids as well as important fat-soluble micronutrients like Carotenoids (including pro-vitamin A), vitamins D, E and K. ○ Beta-carotene/Vitamins A: an effective antioxidant that helps strengthen the body's immune system and reduces the risk of cancer, heart disease and cataract. Lack of Vitamin A can lead to blindness and a variety of serious medical conditions. ○ Vitamin E is a powerful anti-oxidant, capable of reducing the harmful types of oxygen molecules in the body. This means they may help to protect from certain chronic diseases, while delaying the body's ageing process. ○ Fatty acids are the raw materials for building the membranes of every cell in your body, including your bones, nerves and brain! The micronutrients keep body cells healthy and functioning properly.
	►	Palm oil is cholesterol free.
	►	The extraction cost of palm oil is lower compare to most of the vegetable oil.

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2.7.1 - Laboratory Activity : Preparation of Ester in Laboratory

Laboratory Activity 2.7.1: Preparation of Ester in Laboratory

Aim: To prepare ester in laboratory

Material: » Ethanol, C2H5OH » Ethanoic acid, CH3COOH » Concentrated sulphuric acid » Porcelain pieces » Water

Apparatus: » Liebig condenser » Beaker » Tripod stand » Wire gauze » Round-bottomed flask » Retort with stand » Bunsen burner

Procedure:

	►	(A) Preparation of ethyl ethanoate 1. 2. 20cm3 of ethanol and 10cm3 of ethanoic acid is added into a round-bottomed flask. 3. 2cm3 of concentrated sulphuric acid is added to the mixture. 4. A few small pieces of porcelain are added to the flask. 5. The mixture is heated under reflux for about 30 minutes.
	►	(B) Distillation of ethyl ethanoate 1. 2. Distillation process at a temperature range of 77°C – 80°C is used to obtain ethyl ethanoate from the mixture of product.
	►	(C) Purifying the distillate of ethyl ethanoate 1. Removal of ethanoic and sulphuric acid ○ The distillate is poured into a separating column. ○ Sodium carbonate is added slow into the distillate until no more effervescence occurs. ○ The bottom layer (water) is removed and the process is repeated until all the acids are removed. 2. Separation of ethyl ethanoate and ethanol ○ Distilled water is added. The mixture is then shaken strongly and allowed to rest. ○ Two layers of liquid will form after few minutes. ○ The bottom layer is then drained out, and the upper layer is poured into a conical flask. 3. Removal of water ○ Some anhydrous calcium chloride is used to dry ethyl ethanoate and the mixture is then filtered. ○ A colourless liquid with a fragrant smell is produced.

Obervation:

►

The following animation shows the arrangement of apparatus and the observation of the experiment.

Analysis: 

	►	(A) Preparation of ethyl ethanoate ○ Ethanoic acid and ethanol reacts to from ethyl ethanoate. $\begin{array}{c}{C}_2{H}_5\mathit{OH}\\ \text{ethanol}\end{array}+\begin{array}{c}{\mathit{CH}}_3\mathit{COOH}\\ \text{ethanoic acid}\end{array}\begin{array}{c}\mathrm{\rightleftharpoons }\\ \text{concentrated sulphuric acid}\end{array}\begin{array}{c}{\mathit{CH}}_3{\mathit{COOC}}_2{H}_5\\ \text{ethyl ethanoate}\end{array}+H_{2}O$ ○ The mixture needs to be heated under reflux to avoid loss of volatile substances. ○ Water bath is used to ensure evenly heating of the solution.
	►	(B) Distillation of ethyl ethanoate ○ The distillate contains impurities such as ethanol and ethanoic acid.
	►	(C) Purifying the distillate of ethyl ethanoate ○ The sodium carbonate solution is used to neutralise the ethanoic acid and sulphuric acid so that the acid impurities can be removed. ○ When water is added, two layers of liquid are formed.

Conclusion:

►

Pure ester (ethyl ethanoate) can be prepared with the reaction between a carboxylic acid and an alcohol.

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2.7 Ester

General formula of ester
■ Ester

	►	Ester can be represented by the general formula: ○ R – COO-R' (R and R' are alkyl groups such as methyl, ethyl, propyl and butyl) ○ CnH2n+1COOCmH2m+1 with n = 0,1,2,3, .... and m = 1, 2, 3, .......
	►	The functional group of esters is -COO-. Structure of this function is as follows:

■ Several members in the ester homologous series

►

Ester Molecular formula Structural formula Methyl methanoate HCOOCH3 Methyl ethanoate CH3COOH3 Ethyl propanoate C2H5COOC2H5 Propyl butanoate C3H7COOC3H7

■ Nomenclature of the ester

	►	Esters are compounds derived from alcohol and carboxylic group. Therefore the name of ester will have part of alcohol and carboxylic group name.
	►	The prefix of the ester is an alkyl group name found in alcohol.
	►	The second part of the ester name is derived from carboxylic acids, replacing the ending “-oic” with “-oate”. ○ Alkyl group(Originate from alcohol) + Second part(Originate from carboxylic acid)

■ This video contains information on the feneral formula of ester.

✍ Worked-example 2.7(a) Name the structural formulae of the following esters. Solution: Alkyl group originate from alcohol: propyl Part originate from carboxylic acid: ethanoate Name of ester: Propyl ethanoate Solution: Alkyl group originate from alcohol: methyl Part originate from carboxylic acid: propanoate Name of ester: methyl propanoate

✍ Worked-example 2.7(b) Based on the molecular formula of the given esters, draw their structural formulae. Butyl propanoate Ethyl butanoate Solution: (a) Butyl propanoate $\begin{array}{c}\text{butyl}\\ \downarrow \\ C_4{H}_9\end{array}+\begin{array}{c}\text{propanoate}\\ \downarrow \\ C_2{H}_5{\mathit{COO}}^{\text{-}}\end{array}$ Structural formula : C2H5COOC4H9 (b) Ethyl butanoate $\begin{array}{c}\text{ethyl}\\ \downarrow \\ C_2{H}_5\end{array}+\begin{array}{c}\text{butanoate}\\ \downarrow \\ C_3{H}_7{\mathit{COO}}^{\text{-}}\end{array}$ Structural formula : C3H7COOC2H5

Preparation of ester in laboratory
■ Preparation of ester in laboratory

	►	Ester can be prepared through the reaction of carboxylic acid and alcohol with concentrated sulphuric acid as a catalyst. ○ $\text{Alcohol}+\text{carboxylic acid}\begin{array}{c}\mathrm{\rightleftharpoons }\\ \text{concentrated sulphuric acid}\end{array}\text{Ester}+\text{water}$
	►	Function of sulphuric acid: ○ to absorb the water that is produced during reaction. ○ act as a catalyst to increase the rate of reaction.
	►	Heating under reflux is used to avoid loss of volatile substances.
	►	All members of the ester homologous series are prepared using the same method (Esterification reaction).

Laboratory Activity 2.7.1 : Preparation of Ester in Laboratory

Preparation of esters
■ Properties of esters

	►	Colourless liquids with pleasant, fruity aromas
	►	Volatile substance with the a boiling point
	►	Less dense than water
	►	Insoluble in water but soluble in organic solvents

Source of ester
■ Natural esters

	►	Aromas from fruits like apples, pears, and strawberries are esters.
	►	Fats and oils: an ester of fatty acid and glycerol.
	►	Pheromones (animal sex hormone) are natural esters.
	►	Essential oil like lavender are esters.

Uses of ester
■ Uses of esters

►

As food additive To make perfumes and cosmetics As fragrances To make medicines To make clothes, tyres and plastic bottles

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