EDEXCEL GCSE Chemistry - Unit 3 - Topic 5

Flashcards for EDEXCEL GCSE Science Extension Units - Unit 3 Chemistry Topic 5.

This resource has been created with references to the following sources: EDEXCEL GCSE Science Extension Units Student Book, Collins GCSE Chemistry Revision Guide, www.bbc.co.uk/schools/gcsebitesize and www.docbrown.info. 

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What is fermentation?
The conversion of carbohydrates to alcohols and carbon dioxide by yeast or bacteria.
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What conditions are needed for the yeast to make ethanol?
Yeast only makes ethanol if there is no oxygen present. This means air must be kept out of the fermentation container. Keeping oxygen out is called using anaerobic conditions.
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Why does the yeast/glucose mixture have to be kept warm during fermentation?
This is because yeast cells use enzymes to make ethanol and enzymes only work at warm temperatures. 37°C is the best temperature.
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What happens if the yeast/glucose mixture is too hot?
The enzymes are denatured and the active sites are destroyed.
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What happens if the yeast/glucose mixture is too cold?
Fermentation is very slow.
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What is the equation for fermentation of ethanol?
glucose --> ethanol + carbon dioxide (yeast as catalyst) C6H12O6 --> 2C2H5OH + 2CO2
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How does the alcohol level affect the percentage of alcohol produced during fermentation?
When the alcohol level in the mixture gets too high it kills the yeast. Therefore fermentation never gives more than about 15% alcohol.
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How can we get a higher percentage of alcohol?
To get a higher percentage of ethanol, such as to make spirits, the ethanol must be separated from the water by fractional distillation. The water and ethanol separate because they have different boiling points.
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What happens during fractional distillation of ethanol?
When the temperature reaches 78°C the liquid ethanol turns to vapour and moves to the cold condenser. The vapour condenses back to liquid and runs into the collecting vessel. Everything else remains in the flask.
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What are the uses of ethanol?
Ethanol is used as a fuel or fuel additive, as a solvent and as a reactant in many industrial chemical processes.
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How can ethanol be produced in a chemical reaction?
By combining ethene with steam.
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What is the equation for the reaction of ethene with steam?
ethene + steam --> ethanol C2H4 + H2O --> C2H5OH
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What is a homologous series?
A family of compounds which have the same general formula and similar chemical properties, but have different numbers of carbon atoms and different physical properties.
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What are alkanes?
A homologous series of hydrocarbons found in crude oil containing only hydrogen and carbon, with single covalent bonds.
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What is the general formula for alkanes?
CnH2n+2
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Name the first three alkanes and give their molecular formulas.
(1). Methane, CH4 (2). Ethane, C2H6 (3). Propane C3H8
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What are alkenes?
A homologous series of hydrocarbons found in crude oil with double carbon to carbon covalent bonds.
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What is the general formula for alkenes?
CnH2n
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Name the first three alkenes and give their molecular formulas.
(1). Ethene, C2H4 (2). Propene, C3H6 (3). Butene, C4H8
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How can you test for alkenes?
Bromine water is an orange solution of bromine. It becomes colourless when shaken with an alkene. Alkenes can decolourise bromine water.
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What is the equation for the reaction of bromine with ethene?
ethene + bromine --> dibromoethane C2H4 + Br2 --> C2H4Br2
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What are the functional groups of: (1) Alkenes, (2) Alcohols, (3) Carboxylic acids, (4) Esters?
(1). Alkenes = (C=C) (2). Alcohols = hydroxyl group (-OH) (3). Carboxylic acids = carboxyl group
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What is the general formula for carboxylic acids?
CnH2nO2
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Name the first three carboxylic acids and give their molecular formulas.
(1). Methanoic acid, HCOOH (2). Ethanoic acid, CH3COOH (3). Propanoic acid, CH3CH2COOH
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What are carboxylic acids?
All carboxylic acids have a –COOH functional group, and have similar reactions as a result. They are weak acids because this functional group is only partly ionised in solution.
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What is the general formula of alcohols?
CnH2n+1
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Name the first three alcohols and give their molecular formulas.
(1). Methanol, CH3OH (2). Ethanol, C2H5OH (3). Propanol, C3H7OH
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What is the reason for the trend in physical properties?
The increasing length of the carbon chain in a homologous series is the reason for the trend in physical properties.
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What are the dangers of alcoholic drinks?
Drinking too much alcohol damages your liver and makes you more likely to get heart disease and cancer.
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What are the UK Government recommendations for alcohol consumption?
Women should drink no more that 2-3 units a day and men should drink no more that 3-4 units a day. Children under 15 should never be given alcohol.
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What are some of the ethical issues associated with alcohol?
Alcohol affects your brain and changes people's behaviour. People who have been drinking are more likely to be involved in violence or accidents in the home or the streets. Drinking causes many days of work to be missed each year.
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How can ethanol be oxidised to form ethanoic acid using chemicals?
The addition of chemical oxidising agents - such as acidified potassium dichromate.
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How can ethanol be oxidised to form ethanoic acid using enzymes? (2 methods)
(1). The action of microbes in aerobic conditions (in the presence of oxygen). This happens on a small scale when a bottle of wine is left open and exposed to air. (2). On a commercial scale, it is achieved in a fermenter using acetic acid bacteria.
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What is vinegar?
Vinegar is an aqueous solution containing ethanoic acid. Ethanoic acid is formed from the mild oxidation of the ethanol (which is an alcohol).
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What is ethanoic acid an example of?
Ethanoic acid is an example of a carboxylic acid. Carboxylic acids are weak acids. They turn blue litmus paper red and universal indicator red/orange.
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What happens when bromine is reacted with unsaturated compounds?
Bromine Br2 is used to test for saturation. An addition reaction happens at the C=C double bond, producing a dibromo compound. The observed change is that bromine is decolourised.
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How is margarine made?
Liquid oils can be hardened into solid fats by hydrogenation. The C=C double bonds in the oils are reacted with hydrogen using a nickel catalyst.
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What are esters?
Esters are compounds with a low boiling point that have a sweet smell. They are used in perfumes and also as artificial flavourings in foods.
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What are polyesters?
Polymers formed from very many monomers joined by an ester bond. The polymer can be melted and moulded or spun into fibres to make cloth.
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How are soaps made?
When fats are heated with alkali the ester bonds in the molecule break down. The products are soaps and glycerol.
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What are soaps?
Soaps are the sodium or potassium salts of carboxylic acids which have long chains of carbon atoms. Common chain lengths are 16 or 18 carbon atoms.
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What happens during dehydration of alcohols?
Alcohols can be converted to alkenes by a dehydration reaction. Two atoms oh hydrogen and one atom of oxygen are removed from the alcohol molecule and a double bond forms between the carbon atoms. A catalyst is required - often Aluminium oxide Al2O3.
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How are esters formed?
Carboxylic acids and alcohols react together to form compounds called esters. The reaction is called an esterification and uses a catalyst of concentrated sulphuric acid.
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What are the products of an esterification of ethanoic acid and ethanol?
Ethyl ethanoate and water.
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What is the equation for the reaction of ethanoic acid with a base?
Ethanoic acid + sodium hydroxide --> sodium ethanoate + water
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What is the equation for the reaction of ethanoic acid with a carbonate?
Ethanoic acid + sodium carbonate --> sodium ethanoate + carbon dioxide + water
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What is the equation for the reaction of ethanoic acid with a metal?
Ethanoic acid + magnesium --> magnesium ethanoate + hydrogen
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Other cards in this set

Card 2

Front

What conditions are needed for the yeast to make ethanol?

Back

Yeast only makes ethanol if there is no oxygen present. This means air must be kept out of the fermentation container. Keeping oxygen out is called using anaerobic conditions.

Card 3

Front

Why does the yeast/glucose mixture have to be kept warm during fermentation?

Back

Preview of the front of card 3

Card 4

Front

What happens if the yeast/glucose mixture is too hot?

Back

Preview of the front of card 4

Card 5

Front

What happens if the yeast/glucose mixture is too cold?

Back

Preview of the front of card 5
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