Chemistry IGCSE Textbook

NES/Chemistry/IGCSE Chemical Properties of Carboxylic Acids Types of reactions: 1. Esterification 1. Esterification Type Of Reaction Esterification General Equation carboxylic acid + alcohol  ester + water Conditions concentrated sulfuric acid Example 28 heat under reflux CH3COOH + C2H5OH  CH3COOC2H5 + H2O Concentrated sulfuric acid is used as a dehydrating agent. It removes hydrogen and oxygen atoms from the carboxylic acid and alcohol to form water. The ester is made up from the fragmented carboxylic acid and alcohol. Heat under reflux means heating the reactants with the Liebig condenser in the vertical position. This allows the mixture of reactants to be heated together for long periods of time without losing either through evaporation. Display diagram of how the reaction happens: H HH H O OHH H C C H+ H O C C H⇌H C C O O O C C H+ HH H HH H HH ethanoic acid ethanol ethyl ethanoate water 250

NES/Chemistry/IGCSE Esters These are a homologous series of organic compounds formed by the reaction of an alcohol with a carboxylic acid in the presence of concentrated sulfuric acid. The simplest esters are colourless liquids, which are immiscible with water and have characteristic pleasant fruity smells. Fats, vegetable oils and margarine are natural polyesters. Esters have the functional group -COO- in the middle of the carbon chain. Functional group O C OH Naming and Drawing Esters Esters have two parts to the molecule: Carboxylic acid part Alcohol part When naming the ester, always put the alcohol part first: Alcohol Name in Ester Methanol Methyl- Ethanol Ethyl- Propanol Propyl- Butanol Butyl- The carboxylic part always goes second: Carboxylic Acid Name in Ester Methanoic acid -methanoate Ethanoic acid -ethanoate Propanoic acid -propanoate Butanoic acid -butanoate  Example 29: butanoic acid and ethanol The ester is called ethyl butanoate 251

NES/Chemistry/IGCSE Naming an ester from a display formula:  Example 30: H OHH HCC OCCH H HH carboxylic alcohol acid part part The ester is called ethyl ethanoate Chemical Properties of Esters Types of reaction: 1. Acid Hydrolysis 2. Alkaline Hydrolysis 1. Acid Hydrolysis Type Of Reaction Hydrolysis General Equation ester + water  carboxylic acid + alcohol Conditions dilute, strong acid - eg HCl Example 31 heat under reflux CH3CH2CH2COOCH3 + H2O  CH3CH2CH2COOH + CH3OH 2. Alkaline Hydrolysis Type Of Reaction Hydrolysis General Equation ester + water  soap + alcohol Conditions dilute, strong alkali - eg NaOH Example 32 heat under reflux CH3CH2CH2COOCH3 + H2O  CH3CH2CH2COONa + CH3OH Note - this time there is a salt made (soap), rather than the carboxylic acid. 252

NES/Chemistry/IGCSE 14.8.1 Polymers Polymers are large molecules made from smaller monomers. There are two types of polymer:  Addition Polymer (see Topic 14.5)  Condensation Polymer Condensation Polymers The monomers used to make condensation polymers are quite complicated. They are: 1. Diols 2. Dicarboxylic acids 3. Diamines 4. Amino Acids 5. Simple Sugars (like a diol) 6. Fatty Acids 7. Glycerol (a triol) 1. Diol These are monomers with two alcohol functional groups.  Example 33: butan-1,3-diol CH2(OH)CH2CH2CH2OH Diols can also be written as where the box represents a carbon chain. 253

NES/Chemistry/IGCSE 2. Dicarboxylic Acid These are monomers with two carboxylic acid functional groups.  Example 34: propandioic acid HOOCCH2COOH where the box represents a Diols can also be written as carbon chain. 3. Diamine These are monomers with two amine functional groups. The amine functional group is -NH2.  Example 35: Ethanediamine H2NCH2CH2NH2 4. Amino Acid These are monomers with one carboxylic acid and one amine functional group.  Example 36: Alanine H2N-R-COOH Where R is used to show a carbon chain. 5. Simple Sugar These are monomers have two alcohol functional groups.  Example 37: Glucose HO-- --OH Where the box represents the rest of the monomer's structure. 254

NES/Chemistry/IGCSE 6. Fatty Acids These are carboxylic acids with a very long carbon chain. They can be saturated, or unsaturated.  Example 38: A fatty acid C17H33COOH 7. Glycerol This is a molecule with three alcohol functional groups.  Example 39: Glycerol R C--OH C--OH C--OH R' 255

NES/Chemistry/IGCSE 14.8.2 Synthetic Polymers Condensation polymerisation is the formation of successive links between small units called monomer molecules to form a long chained macromolecule (polymer) and a small molecule (usually water). There are two different types of synthetic condensation polymers: 1. Terylene - a polyester 2. Nylon - a polyamide Concentrated sulfuric acid is used as the dehydrating agent to remove water, breaking the monomer structures and allowing them to join together. 1. Terylene dicarboxylic acid + diol  Terylene + water As the monomers have functional groups at both ends, they can join together many, many times to produce a polymer.  Example 40: Terylene HOOCC6H4COOH + HOCH2CH2OH  --(--OCC6H4COOCH2CH2O--)-- + H2O Terylene dicarboxylic acid O O diol nC C nH O OH HO OH OO C CO O nO HH n water ester linkage one repeating unit of the synthetic polyester - Terylene 256

NES/Chemistry/IGCSE 2. Nylon dicarboxylic acid + diamine  Nylon + water As the monomers have functional groups at both ends, they can join together many, many times to produce a polymer.  Example 41: Nylon HOOCC6H4COOH + H2NCH2CH2NH2  --(--OCC6H4CONHCH2CH2NH --)-- + H2O Comparison of Nylon and Terylene Nylon Terylene Has an amide link Has an ester link Polyamide Polyester Made from dicarboxylic acid and diamine Made from dicarboxylic acid and diol Used to make clothing Used to make clothing How the polymers join together amide linkage ester linkage OO CN CO H Repeating units of the polymers repeating unit for nylon repeating unit for Terylene OO OO C CN N C CO O H Hn n 257

NES/Chemistry/IGCSE 14.8.3. Natural Polymers These polymers are found as food groups: 1. Carbohydrate 2. Protein - a polyamide 3. Fat - a polyester Concentrated sulfuric acid is used as the dehydrating agent to remove water, breaking the monomer structures and allowing them to join together. 1. Carbohydrate Carbohydrate polymers are made from simple sugar monomers by removing two hydrogen atoms and one oxygen atom. simple sugar  carbohydrate + water Diagram showing three repeating units of carbohydrate: Acid Hydrolysis of Carbohydrate Carbohydrate polymers can be broken down by a process called hydrolysis. Water and acid can be added to a carbohydrate to make simple sugars. carbohydrate + water + hydrochloric acid  simple sugar Enzymes will also decompose carbohydrates into simple sugars. This is how digestion works. There are many different types of sugar and which sugars are in carbohydrates can be identified by chromatography (see Topic 2.2.1). 258

NES/Chemistry/IGCSE 2. Protein Protein polymers are made from amino acid monomers by removing two hydrogen atoms and one oxygen atom. There are 20 different amino acid monomers, which can join together in lots of different combinations to make each protein polymer. amino acid  protein + water Protein can be represented as: Protein polymers have a polyamide link, the same as the synthetic polymer, Nylon. Acid Hydrolysis of Protein Protein polymers can be broken down by a process called hydrolysis. Water and acid can be added to a protein to make amino acid monomers. protein + water + hydrochloric acid  amino acid Enzymes will also decompose protein into amino acids. This is how digestion works. There are 20 types of amino acid which can be identified by chromatography (see Topic 2.2.1). As the dots produced in the chromatography of amino acids are colourless; ninhydrin, a locating agent, is added to give colour so the dots can be seen. 259

NES/Chemistry/IGCSE 3. Fat Fat polymers are made from fatty acid monomers and glycerol monomers, by removing two hydrogen atoms and one oxygen atom. fatty acid + glycerol  fat + water Three fatty acid monomers join with one glycerol monomer to make one fat polymer. Three water molecules are removed for each polymer molecule made. Fat polymers have a polyester link, the same as the synthetic polymer, Terylene. Acid Hydrolysis of Fat Fat polymers can be broken down by a process called hydrolysis. Water and acid can be added to fat to make glycerol and fatty acid monomers. fat + water + hydrochloric acid  fatty acid + glycerol Alkaline Hydrolysis of Fat Fat polymers can be broken down by a process called hydrolysis. Water and alkali can be added to fat to make glycerol and soap monomers. fat + water + sodium hydroxide  soap + glycerol The three fatty acid monomers form their sodium salts with the aqueous sodium hydroxide to produce soap. The type of reaction is the alkaline hydrolysis of fat and the process is called saponification. Soap is the sodium salt of the carboxylic acid in fat. 260

NES/Chemistry/IGCSE Pollution Problems Caused by Polymers Biodegradable materials can be broken down into smaller molecules by micro- organisms Non-biodegradable materials cannot be broken down into smaller molecules by micro- organisms A lot of household rubbish is plastic (polymers). There are biodegradable plastics which decompose and cause minimal problems to the environment. There are non- biodegradable plastics which do not decompose and do cause environmental problems. There are three ways of disposing of plastic waste: 1. Burning 2. Landfill 3. Recycle 1. Burning Burning plastics produces toxic gases such as hydrogen chloride gas, HCl(g) or hydrogen cyanide, HCN(g). 2. Landfill sites Non-biodegradable plastics can be buried in landfill sites, but they quickly fill up and new land for these sites is becoming more expensive and harder to find. 3. Recycling This is a good idea because it:  conserves resources  conserves energy  saves destroying habitats of animals to obtain metal ores from the ground A disadvantage of recycling is that it is costly to separate out all the different types of plastics before recycling can occur. 261

NES/Chemistry/Year 9