Homologous Series family Each series has a general

Homologous Series (family) • Each series has a general formula. • All members possess the same functional group. It is the functional group that gives the series its characteristic reactions. • There is a gradual change in physical properties from one member to the next. The most common example of this is the increasing melting and boiling points as we go up a series. The reason for this is that the molecules get larger and therefore harder to break. • Members of the same homologous series have similar chemical properties.

Question – How many different ways can be count up to 8? Number of carbons in the hydrocarbon compound; One = Meth Two = Eth Three = Prop Four = But Five = Pent Six = Hex Seven = Hept Eight = Oct

M onkeys E at P eanut B utter P andas H ate H airy O ranges (meth. . . (eth… (prop… (but… (pent… (hex… (hept… (oct… 1 carbon) 2 carbons) 3 carbons) 4 carbons) 5 carbons) 6 carbons) 7 carbons) 8 carbons)

Alkanes Important characteristics of the alkane homologous series; • The names of all alkanes end in ‘ane’ • All bonds are single (saturated) • All alkanes follow the general formula;

Isomers and Naming Isomers have the same chemical formula (same amount of ‘stuff’) but a different structural formula (‘different layout’) For the first three members of the alkanes only one structure is possible butane, C 4 H 10, has two isomers;

Rules for naming branched alkanes; 1. Find the longest carbon chain in the molecule – the name is based on the alkane with this number of carbon atoms. 2. Number the chain to give any branches the lowest possible number(s). 3. Name the branches: methyl (-CH 3), ethyl (C 2 H 5), propyl (-C 3 H 7) etc.

Worked example; Draw and name the isomers of C 5 H 12

Reactions of Alkanes The alkanes are fairly unreactive however they do burn well – therefore their main use is in fuels; • Combustion Example

Cycloalkanes Characteristics • • • The names of all cycloalkanes start with cycloand end in –ane. All bonds in the cycloalkanes are single. (saturated) Cycloalkanes are ring structures First member of the series is cyclopropane. Used in motor fuel, kerosene, diesel, and many other heavy oils. All cycloalkanes follow the general formula;

Alkenes Important characteristics homologous series; of the alkene • The names of all alkenes end in ‘ene’ • At least one C=C double bond (unsaturated) • Therefore 1 st member is ethene. • All alkenes follow the general formula;

Isomers and Naming When naming alkenes we follow the same rules as for the alkanes with one major difference; • the main chain (the longest chain) must contain the double bond, whose position is indicated by a number. • The chain is numbered to make this number as small as possible (the double bond takes priority over any branches. )

Draw and name the isomers of C 5 H 10

Saturated and Unsaturated Hydrocarbons are described as either saturated or unsaturated. ______ and ______ are saturated. They have no double (or triple) carbon to carbon bonds. Every carbon atom is linked to neighbouring atoms by single bonds only (C-C) ____ are unsaturated hydrocarbons. They are unsaturated because each molecule contains at least one carbon to carbon double bond (C=C) Alkenes are more reactive than the alkanes and cycloalkanes because of the carbon to carbon double bond.

Test for Unsaturation • The test for unsaturation is a test to see if a molecule has a double or triple bond. • Bromine is used to test for unsaturation as it rapidly decolourises when added to an unsaturated compound • i. e. if bromine changes colour from orange to colourless you have an alkene. • This is useful for identifying an alkene and a cycloalkane from one another if they have the same chemical formula.

Addition Reactions During the test for unsaturation the bromine ‘adds on’ across the double bond, giving a saturated compound. This is an example of an addition reaction. e. g. Propene + Bromine dibromopropane

Another Example; Pentene + Bromine = bromo… Chlorine = chloro… Fluorine = fluoro… Iodine = iodo… Nitrogen = nitro… Bromine dibromo_____

Another Example; Heptene + Hydrogen _____

Butene + Oxygen

Ethene + Water

Alcohols • The names of all alcohols end in ‘-ol’ • The functional group of the alcohols is –OH (hydroxyl group) • Alcohols are substituted alkanes (as an -H has been replaced with an –OH) • Alcohols are made via hydration of alkenes and fermentation. • Alcohols make useful industrial solvents. • All alcohols follow the general formula;

Isomers and Naming Isomers can result from both branching and varying the position of the -OH group. In naming, the main chain (longest chain) must contain the -OH group, whose position is indicated by a number. Example; Pentan-1 -ol, Pentan-2 -ol, Pentan-3 -ol

Example 2 – Draw the 4 isomers of C 4 H 9 OH

Alcohols as Fuels Alcohols make really good fuels and burn with a clean flame. A reaction (like combustion) which gives out heat to the surroundings is classed as exothermic. The opposite of an exothermic reaction is an endothermic reaction (i. e. heat is taken in. )

Carboxylic Acids • The names of all carboxylic acids end in ‘-oic acid’ • The functional group of the carboxylic acids is -COOH (carboxyl group) • This carboxyl group is always attached to the end carbon. • Carboxylic acids react like other acids • General Formula; Cn H 2 n+1 COOH

Vinegar • Vinegar is dilute ethanoic acid. • Vinegar has been used for years in cooking both as a flavouring and as a preservative. • Vinegar is also a useful cleaning agent and is found in many household products.

Making Esters are compounds formed by a condensation reaction between alcohols and carboxylic acids. In a condensation reaction two molecules join and a small molecule (often water) is removed. Esters are used as flavourings in food and perfumes as well as industrial solvents.

Naming Esters The name of an ester indicates the alcohol and acid which go into making it. • The first part is from the alcohol: eg. -anol becomes -yl. (i. e. ethanol becomes ethyl) • The second part is from the carboxylic acid: e. g. -oic becomes -oate. (i. e. ethanoic becomes ethanoate)

Fuels Calculation We can calculate the energy released by a fuel using the following equation; Eh = c x m x ΔT where: c= m = ΔT = Eh = Specific heat of water, 4. 18 k. J kg− 1 °C− 1 (data book) Mass of water in kg Temperature change of water in °C Energy (k. J)

Worked Example 1 Calculate the amount of energy produced when 0. 5 g of methanol is burned to heat 250 cm 3 of water. The water temperature went up by 2°C.

Worked Example 2 Calculate the amount of energy produced when 200 g of methane is burned to heat 50 cm 3 of water. The initial temperature of water was 25°C and at the end of the experiment the temperature was found to be 65°C.

Worked Example 3 Calculate the amount of energy produced from the following results; Methanol mass before Methanol mass after Mass of water heated Temp rise in water 53. 65 g 53. 46 g 100 g 10°C