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Why do we cook food?
To kill microbes, to improve the texture, to improve the taste and to make the food easier to digest.
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What changes occur to an egg when it is cooked?
The shape of the protein molecules change. This process is irreversible and is called denaturing.
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What changes occur to a potato when it's cooked?
The cell walls of the potato rupture resulting in loss of rigid structure and softer texture. The starch grains swell up and spread and the potato is easier to digest.
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Why do cakes rise?
Baking powder contains sodium hydrogencarbonate. When this is heated during cooking it breaks down into sodium carbonate, carbon dioxide and water. The carbon dioxide gas makes the cake rise.
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What is a thermal decomposition reaction?
Thermal decomposition is a chemical reaction which uses heat to break down a chemical substance into smaller substances.
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What are the main groups of food additives?
Flavourings, emulsifiers and stabilizers, preservatives and antioxidants and colourings.
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What do antioxidants do?
Antioxidants are used to stop food reacting with oxygen in the air.
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What do emulsifiers do?
They stop oil and water from seperating.
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What do stabilizers do?
They maintain the texture of the food.
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What does immiscible mean?
When two liquids DON'T mix.
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What does hydrophilic mean?
The end of the emulsifier molecule that is attracted to water.
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What does hydrophobic mean?
The end of the emulsifier molecule that is attracted to oil.
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What is fractional distillation?
Crude oil is a mixture of hydrocarbons and each of the hydrocarbons have different boiling points. The oil is split into useful parts called fractions and each fraction has slightly different properties and uses.
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What are the properties of fractions?
As the boiling point of the fraction increases; the colour gets darker, it gets less runny and more vicious, it gets less flammable and harder to ignite and it gets smokier.
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What is catalytic cracking?
When large hydrocarbons are broken down into smaller, more useful hydrocarbons using heat and a catalyst.
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What is an alkane?
The simplest hydrocarbons form a series of compounds known as alkanes. They are saturated hydrocarbons.
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What is the general formula for alkanes?
CnH2n+2 where n is a number.
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What is an alkene?
They are unsaturated hydrocarbons and have fewer hydrogen atoms than alkanes.
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Why are alkenes more reactive than alkanes?
Alkenes have a double bond between a pair of carbon atoms. The double bonds are more reactive than single bonds making the alkenes chemically more reactive.
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How can you use a monomer to make a polymer?
You break the double bond so that many more monomers can join together. This process is called polymerisation.
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What are fuels?
A fuel is something that can be burned to release heat and light energy, e.g. oil, wood, coal and gas.
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What makes a good fuel?
Toxicity, Energy value, Availability, Cost, Usability, Pollution and Storage.
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What is combustion?
Combustion is a rapid reaction between a substance and oxygen that releases heat and light energy.
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What is the equation for fuel and oxygen?
Fuel + oxygen --> carbon dioxide + water
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What is incomplete combustion?
If there is a shortage of air, incomplete combustion of hydrocarbons takes place. Instead of producing just carbon dioxide and water, incomplete combustion also produces carbon monoxide and/or carbon. It also releases less energy than complete combus
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What is nitrogen oxides?
It's formed in the internal combustion engine by oxidation of part of the air, it causes photochemical smog.
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What is carbon monoxide?
It's formed from the incomplete combustion of fossil fuels and is a poisonous gas.
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What is sulfur dioxide?
It is formed from the burning of fossil fuels and causes acid rain.
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What is the reaction of a catalytic convertor?
Carbon monoxide + nitrogen oxide --> carbon dioxide + nitrogen
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What is a catalyst?
A catalyst speeds up the reaction without being used up.
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What is a catalytic convertor?
It's a small metal box that's fitted on the exhaust pipe, it reduces pollution significantly and has a ceramic honeycomb structure which lets gases easily pass through.
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What are some properties of perfume?
They have to be insoluble (can't dissolve in water), non-toxic, non-irritant, unreactive and volatile (evaporate easily.
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What components are paints made up of?
They're made up of pigments (gives the paint its colour), binder (liquid polymer that hardens to form a continuous layer when the paint dries) and solvent (dissolves the binding medium and makes the paint more fluid).
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What is a colloid?
A paint is a colloid which are mixtures that visually appear to be a solution. In a colloid, the dispersed phase is made of very small particles or droplets that are evenly dispersed throughout the liquid.
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What are thermochromic pigments?
Pigments that change colour as the temperature changes.
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What are phosphorescent pigments?
Pigments that can absorb light and store energy when lights shine on them. When light is turned off they release the energy slowly in a form of light.
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What changes occur to an egg when it is cooked?



Card 3


What changes occur to a potato when it's cooked?


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Card 4


Why do cakes rise?


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Card 5


What is a thermal decomposition reaction?


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