Organic Chemistry. AQA Chemistry topic 7

Transcription

1 rganic hemistry AQA hemistry topic 7

2 7.1 arbon ompounds as fuels and feedstock

3 rude il rude oil is a finite resource found in rocks. It s the remains of an ancient biomass consisting mainly of plankton that was buried in the mud. Some questions: 1) What does finite mean? 2) What does biomass mean? 3) ow long ago did the plankton die?

4 ydrocarbons and crude oil rude oil is a mixture of YDRARBNS (compounds made up of carbon and hydrogen). Some examples: Ethane Most of the hydrocarbons in crude oil are called alkanes. Alkanes are chemicals that form a homologous series and only have single carboncarbon bonds, like ethane and butane. Butane

5 General Formulae for Alkanes Instead of circles, let s use letters General empirical formula for alkanes = n 2n+2 Butane (n=4) Methane (n=1) Ethane (n=2) Propane (n=3)

6 Fractional distillation rude oil can be separated by fractional distillation. The oil is evaporated and the hydrocarbon chains of different lengths condense at different temperatures: Fractions with low boiling points condense at the top Fractions with high boiling points condense at the bottom

7 Fuels and Feedstock Due to carbon s ability to form different compounds within the same family, fractions produced by fractional distillation can be used to produce fuels and feedstock for the petrochemical industry: Alkanes as fuels Alkanes used for feedstock to make

8 Properties of Alkanes Alkanes have different properties, depending on the length of the carbon chain. These properties influence the use of each alkane. Ethane Butane Increasing length Longer chains mean 1. More viscous 2. Less flammable 3. igher boiling point Q. Which alkanes are more suitable for use as fuels shorter chain ones or longer chain ones?

9 Burning ydrocarbons ydrocarbons can be burned (combustion) to release energy. ere s what happens during the complete combustion of methane: During this process the carbon and hydrogen are oxidised to produce carbon dioxide and water. Q. Try writing equations to show the combustion of ethane, propane and butane.

10 racking Shorter chain hydrocarbons are in greater demand because they burn easier. They can be made from long chain hydrocarbons by cracking : Butane Ethane For example, this bond can be cracked to give ethane (an alkane) and ethene (an alkene). Ethene Q. an you write a balanced equation for this reaction?

11 Alkenes Alkenes are different to alkanes; they contain DUBLE VALENT bonds. For example: ALKANES Ethane Ethene ALKENES Butane Butene This double bond means that alkenes have the potential to join with other molecules this make them REATIVE.

12 Testing for alkenes Q. ow do you test for an alkene? Bromine water il Bromine goes colourless

13 ow to do racking Method 1 atalytic racking Long chain hydrocarbon Gaseous hydrocarbon eated catalyst Liquid hydrocarbon Method 2 Steam racking The alkanes are heated and vaporised (at very high temperatures) and are then diluted with steam. They are then heated again for a very short time.

14 Uses of alkenes Alkenes can be used to make polymers, the starting material for plastics: Poly(ethene) Poly(propene) Poly(styrene) Poly(chloroethene), PV

15 7.2 Reactions of Alkenes and Alcohols (hemistry only)

16 ALKANES Alkenes recap As we said before, alkenes contain DUBLE VALENT bonds. This means they are unsaturated (they have fewer hydrogen atoms). For example: Ethane Ethene ALKENES Butane Butene This double bond means that alkenes have the potential to join with other molecules this make them REATIVE.

17 General Formulae for Alkenes Ethene (n=2) Propene (n=3) Butene (n=4) General formula for alkenes = n 2n

18 Functional Groups The term functional group refers to the part of a molecule that helps determine that molecule s reactions. For example: Alkenes have the functional group =. This carbon double bond causes the alkene to react in certain ways. Ethene (n=2) Alkenes combust in the same way alkanes do but undergo incomplete combustion, causing a smoky flame.

19 Reactions of Alkenes Most of the reactions of alkenes are addition reactions. In other words, the double bond is broken and new atoms are added to the molecule. l l For example, consider the reaction between butene and chlorine:

20 Reactions of Alkenes 1) With hydrogen (at 150 and with a nickel catalyst) 2) With water (steam, at high temperature and pressure) 3) With halogens at room temperature l 2 l l

21 Alcohols Alcohols are a homologous series with a functional group. Some examples: Methanol (n=1) Methanol is an important raw material used in the manufacture of fuels, adhesives and solvents. Ethanol (n=2) Ethanol can be oxidised using agents or microbes to form ethanoic acid, the main acid in vinegar (a flavouring and preservative). General formula for alkanes = n 2n+1 The next alcohols in this series are propanol and butanol. Write their formula and draw their chemical structure.

22 Reactions of Alcohols 1) Reaction with sodium: Alcohols react with sodium to produce a salt and hydrogen 2) Burning in air and oxidation: Alcohols burn to form carbon dioxide and water. Ethanol + oxygen Alcohols can also be partly oxidised to form carboxylic acids. 3) Added to water: carbon dioxide + water Alcohols do not react with water but small alcohol molecules do dissolve to form a neutral solution.

23 Fermentation Yeast is an example of a micro organism (an enzyme). It is used to help a process called fermentation (breaking down a sugar in the absence of oxygen): Sugar Alcohol + carbon dioxide The alcohol from this process is used in making drinks and the carbon dioxide can be used to make bread rise. Fermentation produces an aqueous solution of ethanol. The best conditions to do fermentation are: 25 to 50 Lots of water Absence of oxygen

24 arboxylic acids arboxylic acids form a homologous series with the functional group. The presence of the gives carboxylic acids their properties. Methanoic acid Ethanoic acid Propanoic acid Some facts about carboxylic acids: 1) They dissolve in water to form weak acidic solutions 2) They react with carbonates to form carbon dioxide 3) They react with alcohols to form esters, e.g. Ethanoic acid + ethanol ethyl ethanoate + water

25 Strength of arboxylic Acids (T only) Recall our definition of the term acid : Acids produce hydrogen ions when they dissolve in water: + - l l arboxylic acids are considered weak acids (p of 2 to 3) because they only partly dissociate into + ions.

26 Synthetic and naturally occurring polymers (chemistry only)

27 Monomers and Polymers Ethene ere s ethene again. Ethene is called a MNMER because it is just one small molecule. We can use ethene to make plastics Step 1: Break the double bond Step 2: Add the molecules together: This molecule is called PLYETENE, and the process that made it is called ADDITIN PLYMERISATIN

28 Another way of drawing it Instead of circles, let s use letters Ethene Ethene Poly(e)thene General formula for addition polymerisation: n n 3 e.g. n 3 n

29 Some examples n n n l l n l l n Br Br n

30 ondensation Polymerisation (T only) ondensation polymerisation involves monomers with two functional groups. When they react small molecules such as water tend to be lost, hence the term condensation. An example, consider reacting a molecule with two functional carboxylic acid groups with another molecule with two functional alcohol groups: arboxylic acid functional groups Alcohol functional groups

31 General Equation for ondensation Polymerisation n n n 2n 2

32 Amino Acids (T only) Amino acids have two different functional groups in a molecule. They react by condensation polymerisation to form polypeptides. For example, consider the polymerisation of glycine: 2 N 2 Glycine (-N 2 -) n + n 2 A polypeptide and water Different amino acids can be combined in the same chain to produce proteins.

33 DNA Some facts: DNA is a large molecule essential for. It encodes genetic for the development and functioning of living organisms. Most DNA molecules are two polymer made up of four different monomers called, in the shape of a double. ther naturally occurring polymers include starch, proteins and. Words nucleotides, instructions, cellulose, chains, life, helix