Chemistry C1

OCR Gateway C1

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Food Additives

Additives make food last longer and look and taste better

  • Food colours- make more attractive
  • food enhancers- enhance flavour
  • antioxidants- stop fats reacting with oxygen found in margarine and lard
  • emulsifiers- help water and oil mix in mayonnaise

Antioxidants stop food from reacting with oxygen

  • oxygen can discolour food and make it go off
  • found in margarine and lard

Emulsifiers- Help oil and water mix

  • Hydrophillic end likes water so latches onto it
  • Hydrophobic end hates water so is attracted to the oil
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Food Packaging

Food goes off if its stored for a long time due to the action of mould bacteria and it produces waste products that smell and taste bad

Active and intelligent packaging- can change the product inside

  • widgets in beer cans release gas when can is opened to make frothy
  • can tell us when food has gone off
  • self heating cans can heat contents- exothermic reactions
  • self cooling cans use evaporation
  • can remove water from inside the packet e.g. silica gel
  • prevent the action of harmful free radicals
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Cooking and chemical change

  • Enhance flavours
  • make easier to digest
  • Kill bacteria
  • prevent food poising

Cooking causes a chemical change- not reversible, new product is formed, energy change

Eggs and meat= protein

  • change shape when heated
  • energy from cooking breaks some chemical bonds allowing molecule to form in a different shape so its a more edible texture

Potatoes= Carbohydrates

  • surrounded by cellulose cell wall which humans can't digest so cooking breaks down this wall
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Baking powder

when heated, undergoes thermal decomposition

thermal decomposition= when a substance breaks down into simpler substance when heated

baking powder contains sodium hydrogencarbonate

word equation=

Sodium hydrogencarbonate ----> sodium carbonate+ carbon dioxide+ Water

Symbol equation

2NaHCO3 -----> Na2CO3 + CO2 + H20

test for carbon dioxide: can be detected using limewater- Co2 turns limewater cloudy when its bubbled through

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Perfumes

Natural perfumes= essential oils

Synthetic perfumes= alcohol reacted with organic acid

Esters can be made by heating carboxylic acid with and alcohol (esterification)

Acid + Alcohol ------> Ester + Water

Perfumes must be:

  • non toxic
  • evaporate easily (volatile)
  • doesn't react with water (sweat)
  • doesn't irritate skin
  • insoluble in water
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Testing perfumes

Advantages of testing cosmetics on animals:

  • get an idea whether likely to irritate or be toxic to humans
  • results happen quicker
  • no one would volunteer if it was human testing

Disadvantages of animal testing:

  • pain or suffering caused to animals
  • may not be exactly the same reaction on humans
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Kinetic Theory and Forces between particles

Solids:

  • Strong forces of attraction, which holds them in fixed positions in a lattice arrangement
  • particles don't move so keep definite shape and volume, but vibrate, the hotter the solid the more they vibrate

Liquids:

  • same force of attraction but they're free to move past each other
  • don't keep a definite shape and will flow to fill a container
  • particles are constantly moving with random motion, hotter more movement

Gases:

  • No force of attraction, they're free to move and travel in straight lines and only interact when collide, don't keep definite shape or volume
  • constantly move with random motion, hotter the gas the more pressure or the more it expands
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How we smell

When a liquid is heated the heat energy goes to the particles which makes them move faster

some particles move faster than others

fast-moving particles at the surface will overcome the forces of attraction from the other particles and escape- Evapouration

how easily a liquid evaporates= volatility

evaporated particles drifting  in the air and smell receptors in the nose pick up the chemical so you smell it

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Solutions

Solute= the substance that's being dissolved

solvent= the liquid dissolving into

solution= the mixture of the solute plus the solvent

soluble= means it will dissolve, insoluble= won't dissolve

Nail varnish is insoluble in water

  • molecules in nail varnish are strongly attracted to each other, this attraction is stronger than the attraction between the nail varnish and the water molecules
  • the molecules of water are strongly attracted to each other, this attraction is stronger than the attraction between the water molecules and the nail varnish
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Polymers

Plastics are long chains of small molecules called monomers joined together, usually carbon based

Addition polymers are made under high pressure and in the presence of a catalyst= POLYMERISATION

  • alkenes have double bonds which are broken to form long saturated chains with no double bonds

ethene -----> polyethene           Propene ------> polypropene

Forces between molecules determine the properties of plastics

Thermoplastics= weak intermolecular forcesstretched/ softened easily

Thermosets= strong covalent bonds, higher melting points and can't be stretched as cross links hold the chains together, rigid

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Polymers and their uses

Polyethene=  strong and rigid- plastic milk bottles

easily melted- plastic bags

polystyrene= CO2 blown into melted polystyrene, a stable solf is made-cups

Polyester- form thin fibres when polymer is melted and forced through a narrow hole- spun and woven into fibres for cloth

polypropene- ropes and garden furniture

plastic= non biodegradable= durable, won't decay, dissolve or break apart

ways of disposal= putting in land fill- wasting land and takes long time,burning- releases poisonous gases, re using= expensive and its difficult to recycle

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Polymers as clothing

Nylon:

  • synthetic polymer
  • hard wearing
  • easily coloured
  • protects from UV radiation
  • waterproof
  • keeps water vapour in making wearer uncomfortable

Gore-tex

  • is breathable
  • made by laminating fabrics with expanded PTFE onto fabrics like polyester and nylon made with tiny holes so water vapour can escape
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Alkanes and Alkenes

Alkanes= saturated

  • atoms joined together by a single covalent bond
  • bond formula= CnH2n+2
  • won't decolourise bromine water
  • burn cleanly
  • won't form polymers

Alkenes= unsaturated

  • have double bonds
  • general formula= CnH2n
  • Decolourise bromine water
  • produce soot
  • form polymers
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Hydrocarbons

= compounds of carbon and hydrogen only

meth=1 (can only be methane)

eth=2

prop= 3

but= 4

pent= 5

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Fractional distillation of crude oil

fossil fuels= crude oil, coal and gas- non renewable, finite resources (take millions of years to be replaced)

crude oil= mixture of different hydrocarbon compounds

crude oil is formed of dead plants and animals and is separated using a fractioning column

  • oil is heated until most of it has turned into gas, the liquid (bitumen) is drained off
  • hot at bottem, cooler at the top
  • shorter hydrocarbons have lower boiling points
  • makes use oh the fact different fractions have different boiling points

order of fractions from bottom:

bitumen, oil, diesel, paraffin, naphtha,petrol, LPG

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Hydrocarbon properties

large molecules at the bottom:

  • high boiling points
  • don't flow easily
  • don't ignite easily
  • residue used for bitumen in roads

small molecules at the top:

  • low boiling points
  • very volatile
  • flow easily
  • ignite easily
  • e.g. refinery gases, petrol for cars

bonds in crude oil- strong covalent bonds between carbons and hydrogen's

intermolecular forces of attraction between hydrocarbon molecules are strong

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Cracking

= splitting up long chains of hydrocarbons

  • when a large alkane molecules are split into smaller alkanes and an alkene
  • happens when large molecules are passed over a catalyst at high temperatures and broken into smaller alkanes and an alkene

supply of larger molecules making up the fuel oils is greater than demand so they convert it into much needed fuels

matching supply with demand

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Fuels from crude oil

problems with oil

  • transporting- ships sometimes crash causing oil slicks, damaging wildlife like birds feathers stop being waterproof and they die of cold, seals are poisoned, cleaning beaches is expensive and time consuming
  • burning fossil fuels produces green house gases
  • crude oil resources are non renewable

using more fossil fuels all the time:

  • provides fuel for modern transport
  • population increase
  • underdeveloped countries becoming more industrialised
  • greater use of electrical equipment
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choosing the best fuel

can be remembered using the word TEACUPS

T oxicity

E nergy value

A vailability

C ost

U ease of Use

P ollution

S torage

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Burning Fuels- complete combustion

Complete combustion- needs plenty of oxygen

  • carbon dioxide and water are produced
  • clean and non-poisonous
  •  hydrocarbon + oxygen ----> carbon dioxide + water
  • releases lots of energy
  • gas burns with a blue flame
  • you can show a fuel burns to give Co2 and H2O by....
    • water pump draws gases from the burning hexane through apparatus
    • water collects in the cooled U-tube can show its water by checking boiling point
    • the limewater turns milky when the gas is bubbled through showing carbon dioxide is present
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Burning Fuels- Incomplete combustion

Incomplete combustion= not safe- there is not enough oxygen

  • carbon dioxide, water, carbon monoxide and carbon are produced
  • produces less energy
  • produces a smoky yellow flame
  • Hydrocarbon+oxygen--> carbon dioxide+water+carbon monoxide+carbon
  • carbon monoxide= colourless, odourless and poisonous gas that is very dangerous
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Energy Transfers in Reactions

exothermic reactions= gives out energy, rise in tempurature

bond formation is exothermic

endothermic reactions= takes in energy, fall in tempurature

bond breaking is endothermic

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Measuring energy content of fuels

Calorimetric method- reduce heat loss as much as possible

1. reduce draught when heating water

2. put fuel in spirit burner and weigh

3. measure out 200cm3 of water into a copper calorimeter

4. take the initial temperature then light wick of burner

5. stir water every now and then

6. when the heat burner has made temperature rise by about 20-30'C blow out spirit burner and take note of highest temperature

7. reweigh spirit burner and fuel

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Calculations to find energy output

Energy transferred(J)= mass of water (g) times specific heat capacity of water (4.2) times temperature change

Energy given out per gram (J/g)= Energy transferred (J)

Mass of fuel burned (G)

to compare fuels you most repeat several times using different fuel

to keep fair everything should be the same- same apparatus, same amount of water, should start and finish at the same time

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