Edexcel Chemistry A-level Organic Chemistry I Detailed Notes PDF

Edexcel Chemistry A-level Topic 6: Organic Chemistry I Detailed Notes https://bit.ly/pmt-edu-cc This work by PMT Education is licensed under https://bit.ly/pmt-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Topic 6A: Introduction to Organic Chemistry Hydrocarbons Organic chemistry mainly concerns the properties and reactions of hydrocarbons, compounds that contain only carbon and hydrogen atoms. Hydrocarbons are a series of compounds with similar structures and formulas that can be represented in many different ways. Nomenclature Nomenclature is the set of rules that outline how different organic compounds should be named and how their formulas are represented. Formulas There are many different ways of writing and representing organic compounds: 1. Empirical Formula - The simplest whole number ratio of atoms of each element in a compound. 2. Molecular Formula - The true number of atoms of each element in a compound. 3. General Formula - All members of a homologous organic series follow the general formula. For example, alkanes have the general formula CnH2n+2. 4. Structural Formula - Shows the structural arrangement of atoms within a molecule. For example, CH3CH2COCH3. 5. Displayed Formula - Shows every atom and every bond in an organic compound. 6. Skeletal Formula - Shows only the bonds in a compound and any non-carbon atoms. The vertices are carbon atoms and hydrogen is assumed to be bonded to them unless stated otherwise. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Homologous Series Organic compounds are often part of a homologous series, in which all members follow a general formula and react in a very similar way. Each consecutive member differs by CH2 and there is an increase in boiling points as chain length increases. Example: Each series has a functional group that allows that molecule to be recognised as being able to react chemically in a certain way as a result of that group. Example: Table of functional groups (ignore ethers) https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Naming Compounds Compounds are named according to rules laid out by the International Union of Pure and Applied Chemistry (IUPAC). This ensures each compound is universally named the same which helps to avoid potentially dangerous confusion. As well as being able to name compounds from their structures, you should be able to draw structures from IUPAC names. Stem The prefix of the chemical tells you the length of the longest unbroken chain of carbon atoms in the compound. The first 10 are given below, using alkanes as an example: Functional Groups The ending of the compound’s name tells you the functional group present. If there is more than one functional group present, they are added as a suffix. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc If a halogen is present, it is represented by a prefix: Functional group Prefix Fluorine Fluoro- Chlorine Chloro- Bromine Bromo- Iodine Iodo- Side Chains Carbon side chains that are branches from the longest carbon chain are represented by a prefix at the start of the word. These alkyl groups are made using the stems given above (meth-, eth-, prop-, etc) and the suffix -yl. General Rules 1. Functional groups and side chains are given, if necessary, with the number corresponding to the carbon they are attached to. 2. Numbers are separated by commas. 3. Numbers and words are separated by hyphens. 4. If more than one particular side chain or functional group is present then one of the following prefixes is added: di- (2), tri- (3), tetra- (4), etc. 5. The carbon chain is numbered in ascending order from the end of the chain nearest a functional group. 6. If multiple prefixes are present, they are included in alphabetical order. Examples Example 1: The displayed structure of butan-2,3-diol. This compound only has single carbon-carbon bonds, so is an alkane. Its longest chain of carbon atoms is 4, giving the stem butan-, and it has two alcohol functional groups on carbons 2 and 3. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Example 2: The displayed structure of 3-ethyl,5-methylhexan-2-ol. Example 3: The displayed structure of propanone. Propan-2-one is also correct, but since the C=O can only be in the 2 position for the compound to be a ketone, the number is not necessary. Example 4: The skeletal structure of 1,2-dichloropropane https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Reaction Mechanisms Types of Reactions Reactions can be classified according to what happens to the reactants during the reaction and what the end products are. The main types of reaction are: Addition - In an addition reaction the reactants combine to form a single product. Substitution - In a substitution reaction one functional group is replaced by a different functional group. Oxidation - A species loses at least one electron, and is oxidised. Reduction - A species gains at least one electron, and is reduced. Polymerisation - A reaction in which many small molecules, known as monomers, join together to form a long, repeating molecule called a polymer. Mechanisms Mechanisms show the movement of electrons within a reaction, shown with curly arrows. Example: Mechanisms are used to show the reactions of organic compounds. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Isomerism Isomers are molecules with the same molecular formula but a different arrangement of atoms within the molecule. Structural Isomers Structural isomers have the same molecular formula but a different structural arrangement of atoms. They can be straight chains or branched chains but will have the same molecular formula. Example: Position Isomers Position isomers have the functional group of the molecule in a different position of the carbon chain. Example: https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Functional Group Isomers These have the same molecular formula so but the molecules have a different functional group. Example: Stereoisomers Stereoisomers have the same structural formula but have a different spatial arrangement of atoms and bonds. E-Z isomerism is a type of stereoisomerism, which occurs due to the limited rotation around a double carbon bond. The limited rotation means that groups attached to the C=C can either be ‘together’ or ‘apart’. The E isomer (german for ‘entgegen’ meaning apart) has these groups apart. The Z isomer (german for ‘zusammen’ meaning together) has these groups together on the same side. Example: https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Cahn-Ingold-Prelog (CIP) Priority Rules There is a priority of different groups in molecules that can display E-Z isomerism. The atom or group on each side of the double bond with the higher Ar or Mr is given the higher priority. These groups are used to determine if it is the E or Z isomer. Example: Therefore this molecule is the Z isomer as the highest priority atoms are on the same side (both on top). Cis- and Trans- Isomers Stereoisomers can be named in the same process as above, but instead using Cis- for when the groups are on the same side and trans- for when they are different sides. Cis- and transdiffers from E/Z isomerism in that cis- and trans- can only be used when there are hydrogen atoms to compare the two other groups to. When there are more groups present, you have to assign E/Z isomerism by using the Cahn-Ingold-Prelog (CIP) priority rules described above. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Topic 6B: Alkanes Introduction to Alkanes Alkanes are saturated hydrocarbons where all carbon-carbon bonds are single bonds. They are part of a homologous series with the general formula CnH2n+2. Cycloalkanes are an exception to this general formula but are still saturated hydrocarbons. Fractional Distillation Crude oil is a mixture of different hydrocarbons. It can be separated into the separate molecules by fractional distillation as the different chain lengths of molecules result in them having different boiling points. Crude oil is separated in the following way: 1. The mixture is vapourised and fed into the fractionating column. 2. Vapours rise, cool and condense. 3. Products are siphoned off for different uses. Products with short carbon chains have lower boiling points, meaning they rise higher up the column before reaching their boiling point. Therefore they are collected at the top of the column. Products with long carbon chains have higher boiling points, meaning they don’t rise very far up the column before reaching their boiling point. They condense and are collected at the bottom of the fractionating column. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc The compounds collected from the fractionating column are then broken down further via the method of cracking. Some long-chain alkanes are also converted into branched alkanes and cyclic hydrocarbons in a process known as reforming. These products undergo combustion more efficiently than straight-chain alkanes. Cracking Longer carbon chains are not very useful, so they are broken down to form smaller, more useful molecules. The carbon-carbon bonds are broken in order to do this, which requires quite harsh reaction conditions. There are two main types of cracking which result in slightly different organic compounds. Examples: Thermal Cracking Thermal cracking produces a high proportion of alkanes and alkenes. High temperatures around 1200 K and pressures around 7000 kPa are used to crack the carbon chains. The reaction always forms an alkane, and the remaining atoms form at least one alkene, which have the general formula CnH2n. Catalytic Cracking Catalytic cracking produces aromatic compounds with carbon rings. Lower temperatures around 720 K are used along with normal pressure, but a zeolite catalyst is also used to compensate for these less harsh conditions. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Combustion of Alkanes Alkanes make good fuels as they release a lot of energy when burned. With sufficient oxygen present, they undergo complete combustion to produce carbon dioxide and water. Example: If the oxygen present is insufficient, combustion is incomplete and carbon monoxide or carbon particulates are produced alongside water. Example: Carbon monoxide is a toxic, gaseous product that is especially dangerous to humans as it is odourless and colourless. Carbon monoxide is dangerous because it replaces oxygen in the blood, starving the brain and other organs of oxygen and causing people to suffocate. Oxides of nitrogen and sulfur are also produced as a byproduct of alkane combustion along with carbon particulates from unburnt fuel. In clouds, these oxides can react with water and form dilute acids, which result in acid rain. Catalytic Converters These gaseous products can be removed from systems using a catalytic converter. This uses a rhodium catalyst to convert harmful products into more stable products such as CO2 or H2O. Example: https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Alternative Fuels Alternative fuels are now being developed such as biofuels that release fewer, less harmful products when burned. Carbon dioxide is released during the combustion of fuels. It is a greenhouse gas so causes global warming and contributes to climate change. Ethanol is a common biofuel. It is said to be carbon neutral as the carbon given out when it is burned is equal to the carbon taken in by the crops during the growing process. It is produced by fermentation, where enzymes break down starch from crops into sugars which can then be fermented to form ethanol. It is produced in batches, meaning it is a relatively slow process with a low percentage yield. However, the environmental benefits make it viable. The other advantage of biofuels is that they are sustainable. This means their supply can be maintained at the rate they are being used, so they will not run-out - unlike fossil fuels. Chlorination of Alkanes Alkanes react with halogens in the presence of UV light to produce halogenoalkanes. The UV light breaks down the halogen bonds (homolytic fission) producing reactive intermediates called free radicals. Free radicals are indicated with a dot, as shown below. Free radicals are species containing an unpaired electron which is shown using a single dot. These attack the alkanes resulting in a series of reactions; initiation, propagation and termination. 1. Initiation - the halogen is broken down in the presence of UV light. Cl2 → 2Cl 2. Propagation - a hydrogen is replaced and the Cl radical reformed as a catalyst Cl + CH4 → CH3 + HCl CH3 + Cl2 → CH3Cl + Cl 3. Termination - two radicals join to end the chain reaction and form a stable product. CH3 + CH3 → C2H6 The propagation step can continue many times to result in multiple substitutions, this is a chain reaction. The condition of the reaction can be altered to favour the termination step and limit the number of substitutions, however, the nature of this reaction to produce multiple products limits its use in organic synthesis. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Topic 6C: Alkenes Introduction to Alkenes Alkenes and cycloalkenes are unsaturated hydrocarbons with at least one carbon-carbon double bond. They are part of a homologous series with the general formula CnH2n. Cycloalkanes are saturated and follow this same general formula. Structure and Reactivity The carbon double bond is an area of high electron density making it susceptible to attack from electrophiles (species that are attracted to ∂-areas). It consists of a normal covalent σ bond and a π bond. Example: Bromine water is used to identify an alkene double bond and other unsaturated compounds. Alkenes cause bromine water to change colour from orange-brown to colourless. This is because the C=C bond can ‘open up’ to accept bromine atoms, and thus become saturated. Reactions of alkenes The carbon-carbon double bond in alkenes makes them reactive. During their reactions, the double bond opens up to form single bonds to other atoms. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Alkanes Alkenes can undergo electrophilic addition with hydrogen to produce alkanes. The C=C bond opens up and forms single bonds to each of the hydrogen atoms. This reaction requires a nickel catalyst. Example: This reaction is also known as a hydrogenation reaction. Catalytic hydrogenation is used in the manufacture of margarine from unsaturated vegetable oils. Halogenaoalkanes Halogenoalkanes are organic compounds with single carbon bonds only and halogen functional groups. Alkenes undergo addition reactions with halogens to form di-substituted halogenoalkanes, and with hydrogen halides to form mono-substituted halogenoalkanes. The mechanism for this reaction is given on the following page of these notes. Alcohols Alcohols are organic compounds with a hydroxyl functional group. Alkenes undergo addition reactions with steam to form alcohols. This reaction requires an acid catalyst, such as phosphoric acid. Example: CH2CH2 + H2O → CH3CH2OH Diols, alcohols with two hydroxyl functional groups, can also be formed from alkenes through an oxidation reaction. The double bond is oxidised by acidified potassium manganate(VII) (KMnO4). The manganate ions must be cold, dilute and acidified. Example: CH2CH2 + H2O + [O] → CH2(OH)CH2(OH) https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Electrophilic Addition Alkenes undergo electrophilic addition about the double bond. Electrophiles These are electron acceptors and are attracted to areas of high electron density. Some of the most common electrophiles are: HBr Br2 H2SO4 They can be used in the presence of steam to form alcohols or with hydrogen to produce alkanes from alkenes. Electrophilic Addition Electrophilic addition is the reaction mechanism that shows how electrophiles attack the double bond in alkenes. When the double bond is broken, a carbocation forms. This is a carbon atom with only three bonds, meaning it has a positive charge. Carbocations can have varying stability, with tertiary being the most stable and primary the least. The more stable the carbocation, the more likely it is to form. Therefore in an addition reaction, multiple products can form but the major product will always be the one that is formed via the most stable carbocation intermediate possible. Mechanisms Mechanism: Alkene + Halogen → Dihalogenoalkane The π bond causes the bromine molecule to gain a temporary dipole so that electrons are transferred. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Mechanism: Alkene + Hydrogen Halide → Halogenoalkane Example: Electrophilic addition of hydrogen bromide to ethene Example: Electrophilic addition of hydrogen bromide to propene Hydrogen bromide is polar due to the difference in the electronegativities of hydrogen and bromine. The electron pair in the double bond attracts Hδ+ , forming a covalent bond between carbon and hydrogen. This produces a positively charged carbocation intermediate which attracts the negatively charged bromide ion. The hydrogen joins to the carbon atom which is bonded to the most hydrogen atoms. The bromide ion bonds to the carbon atom which is joined to the most carbon atoms. This is why 2-bromopropane forms more often than 1-bromopropane in the mechanism of propene with hydrogen bromide. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Addition Polymers Addition polymers are produced from alkenes where the double bond is broken to form a repeating unit. Alkenes are short chain monomers which join together to form long chain polymers. Example: The repeating unit must always be shown with extended bonds through the brackets, showing that it bonds to other repeating units on both sides. The energy and resources used to make polymers are large. Polymers are made from alkenes which are obtained from crude oil, a non-renewable resource. The extraction and cracking of crude oil are both high energy processes and additional energy is then needed to convert these alkenes into polymers. Uses of Polymers Polymers are unreactive hydrocarbon chains with multiple strong, non-polar covalent bonds. This makes them useful for manufacturing many everyday plastic products such as poly(ethene) shopping bags. However, the unreactive nature of the bonds in addition polymers means they are not biodegradable and cannot be broken down by species in nature. Disposal of Polymers Addition polymers are non-biodegradable which means disposal of them can be difficult. Waste polymers can be processed in different ways. Some can be recycled, some are used as feedstock for cracking and some are incinerated to produce energy for other industrial processes. Incineration can release toxic gases which must be removed to reduce the impact on the environment. As well as this, scientists are developing biodegradable polymers to overcome these waste issues. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Topic 6D: Halogenoalkanes Introduction to Halogenoalkanes Halogenoalkanes contain polar bonds since the halogens are more electronegative than a carbon atom. This means electron density is drawn towards the halogen, forming ∂+ and ∂regions. Example: Halogenoalkanes can be classed as primary, secondary or tertiary halogenoalkanes depending on the position of the halogen within the carbon chain. Relative Reactivity Reactivity varies depending on the halogen present in the molecule. Electronegativity of the halogens decreases down the group, meaning that a carbon-fluorine bond is much more polar than a carbon-iodine bond. Along with the fact that the carbon-fluorine bond is shorter, this means that the carbon-fluorine bond is much stronger than the carbon-iodine bond. The greater the Mr of the halogen in the polar bond, the lower the bond enthalpy. A lower bond enthalpy means the bond can be broken more easily. Therefore, the rate of reaction increases for halogenoalkanes as you move down the group. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Reactions of Halogenoalkanes To Produce Alcohols Halogenoalkanes can react with aqueous alkali, such as aqueous sodium or potassium hydroxide, to produce alcohols in a nucleophilic substitution reaction. The hydroxide ion acts as a nucleophile. To Produce Alkenes Halogenoalkanes can react with ethanolic potassium hydroxide (KOH) to produce alkenes in an elimination reaction. The hydroxide ion acts as a base. Hydrolysis with Silver Nitrate Halogenoalkanes can be broken down in their reaction with aqueous silver nitrate and ethanol. The water in the solution acts as a nucleophile which leads to the break down of the halogenoalkane, releasing the halide ions into the solution. The halide ions then react with the silver ions from silver nitrate to form silver precipitates. The colour of the precipitate allows you to identify the halide ion present. The rate at which the precipitates forms allows you to identify the relative stability of the halogenoalkanes, because the faster the precipitate forms, the less stable the halogenoalkane, and therefore the more quickly it is hydrolysed. Cl- Br- I- White precipitate (AgCl) Cream precipitate (AgBr) Yellow Precipitate (AgI) Reactivity depends on the strength of the C-X bond (where X is a halogen atom) and not the bond polarity. Bond strength decreases with increasing Mr. Therefore, iodoalkanes would react faster than bromoalkanes and chloroalkanes, and bromoalkanes would react faster than chloroalkanes. To Produce Amines Halogenoalkanes can react with alcoholic ammonia (for example, with ethanolic NH3) to form amines in a nucleophilic substitution reaction. Ammonia acts as a nucleophile. To Produce Nitriles Halogenoalkanes can react with alcoholic potassium cyanide (KCN) to form nitriles in a nucleophilic substitution reaction. The cyanide ion, CN-, acts as a nucleophile. This reaction adds on a carbon atom, so it can be used in synthesis routes to increase the length of carbon chains. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Nucleophilic Substitution Nucleophiles These species are ‘positive liking’. They contain a lone electron pair that is attracted to ∂+ regions of molecules. Some of the most common nucleophiles are: CN:- :NH3 - :OH They must be shown with the lone electron pair indicating they are nucleophiles. Nucleophilic Substitution This is the reaction mechanism that shows how nucleophiles attack halogenoalkanes. Starting from halogenoalkanes, aqueous potassium hydroxide is the reactant used to produce alcohols, potassium cyanide is the reactant used to produce nitriles and ammonia is the reactant used to produce amines. The greater the Mr of the halogen in the polar bond, the lower the bond enthalpy meaning it can be broken more easily. Therefore the rate of reaction for these halogenoalkanes is faster. Nucleophilic substitution reactions can only occur for 1o (primary) and 2o (secondary) alkanes. Mechanism - Formation of alcohols The nucleophile attacks the ∂+ carbon and the electrons are transferred to the chlorine. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Mechanism - Formation of amines The intermediate has a positively charged nitrogen (N+ ). Electrons are transferred to the nitrogen by the loss of a hydrogen atom. Topic 6E: Alcohols Introduction to Alcohols Alcohols contain an -OH functional group and follow the general formula CnH2n+1OH. They can be produced via two main methods of fermentation or hydration. Alcohols are named according to IUPAC rules and have the suffix -ol. Alcohols can be primary (1o), secondary (2o) or tertiary (3o) depending on the position of the hydroxyl group. Example: https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Hydration This method produces alcohols from alkenes in the presence of an acid catalyst, such as phosphoric acid. The reaction is also carried out in aqueous conditions at 300oC and under high pressures. Example: This process has a very high percentage yield as ethanol is the only product. Therefore the hydration method is favoured as an industrial process. Fermentation In this process, enzymes break down the starch in crops into sugars which can then be fermented to form alcohol. This method is cheaper than hydration as it can be carried out at a lower temperature. However, the reaction is carried out in batches, meaning it is a much slower process with a lower percentage yield. Ethanol is a common biofuel produced in this way. It is said to be carbon neutral as the amount of carbon dioxide given out when it is burned is equal to the carbon dioxide taken in by the crops during the growing process. Example: https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Reactions of Alcohols Combustion When burned in air, alcohols react with oxygen to form carbon dioxide and water. Alcohols make good fuels by reacting in this way as lots of energy is also released. Example: Reactions with Halogenating Agents Alcohols can react with halogenating agents via nucleophilic substitution. The -OH group is replaced by a halogen, producing a halogenoalkane. PCl5 is used to produce chloroalkanes. This can be used as a test for alcohols because their reaction with PCl5 produces white steamy fumes that turn damp blue litmus paper red. A reaction mixture of 50% concentrated sulfuric acid and potassium bromide can be used to produce bromoalkanes. The potassium bromide reacts with the sulfuric acid to form HBr. This then reacts with the alcohol to produce the bromoalkane. CH3CH2OH + HBr → CH3CH2Br + H2O A reaction mixture of red phosphorus with iodine can be used to produce iodoalkanes. First, the phosphorus reacts with the iodine to produce phosphorus(III) iodide. This then reacts with the alcohol to form the iodoalkane. 2P + 3I2 → 2PI3 3CH3CH2OH + PI3 → 3CH3CH2I + H3PO3 Elimination Reactions Alkenes can be formed from the dehydration of alcohols, where a molecule of water is removed from the molecule. In order to do this, concentrated phosphoric acid is added as a reagent. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Oxidation of Alcohols Primary and secondary alcohols can be oxidised to produce various products but tertiary alcohols are not easily oxidised. When primary alcohols are heated in the presence of acidified potassium dichromate(VI), they are oxidised to aldehydes. Distillation is required to separate the aldehyde product Example: When heated under reflux conditions, primary alcohols are oxidised further to carboxylic acids. Example: Secondary alcohols can be oxidised in the presence of acidified potassium dichromate to produce ketones. Example: https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Potassium Dichromate (K2Cr2O7) Potassium dichromate(VI) is used in the oxidation of alcohols as the oxidising agent. It is reduced as the alcohol is oxidised. A colour change from orange to green is observed when the alcohol is oxidised with potassium dichromate(VI). Example: Test for Aldehydes Aldehydes are tested for using Benedict’s/Fehling’s solution. A few drops of Fehling’s solution are added and the test tube is gently warmed. If an aldehyde is present a red precipitate will form. If no aldehyde is present the solution will remain blue. Ketones will not give a positive result when added to Benedict’s/Fehling’s solution. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Experimental Techniques There are many different techniques that can be used to prepare and then purify an organic compound. Heating under Reflux Reflux apparatus is used to continually heat the contents of the flask to allow reactions like the oxidation of primary alcohols to proceed all the way to the formation of carboxylic acids. The condenser helps ensure the vapours condense and return to the flask for further heating. This ensures the product vapours can not escape. Separating Funnel A separating funnel is used to separate two liquids with different densities. The mixture is added to the flask and the liquids are allowed to separate into two layers. The tap can then be opened to collect the bottom, denser liquid in one flask and the second, less dense liquid in a second flask. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc Distillation Distillation apparatus is used to separate liquids with different boiling points. The pear-shaped flask is heated and the liquid with the lower boiling point will evaporate first. It rises out of the flask and into the attached tubing which is surrounded by a condenser. The condenser causes the vapour to cool and condense back into a liquid, which is then collected in a separate flask. Drying A compound can be dried by the addition of an anhydrous (contains no water) salt. The anhydrous salt will absorb moisture and water present, thus drying and purifying the compound. A common anhydrous salt used for drying is sodium sulphate. Boiling Point Determination Finding the boiling point of a compound and comparing it to a databook value is a way of testing its purity. The purer a substance, the closer to the databook boiling point value it will be. If a sample has a low purity, the melting/boiling point will take place over a range of temperatures. To determine the boiling point, the substance is packed into a Thiele tube which has an inverted capillary tube in it. The substance is heated to above its boiling point and allowed to cool. When it condenses into a liquid it will be drawn into the capillary tube and the temperature at which this change occurs is taken to be the boiling point. https://bit.ly/pmt-edu https://bit.ly/pmt-cc https://bit.ly/pmt-cc

Edexcel Chemistry A-level Organic Chemistry I Detailed Notes PDF

Document Details

Tags

Related

Summary

Full Transcript

Upgrade to continue