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How big are atoms?
- Very small
- Too small for the eye to see, even with a microscope
What is the charge of the nucleus in an atom?
What is the charge of the electrons which orbit the atom?
If atoms form bonds, what do they make?
Molecules or compounds
If an atom loses an electron, what charge does it get?
If an atom gains an electron, what charge does it get?
What are charged atoms called?
What happens if a positive and negative ion meet?
- They become attracted to each other
- They join together
- This is called an ionic bond
What are the two main types of bond?
Ionic and Covalent
What is a covalent bond?
Where two atoms are linked by a shared pair of electrons
How many carbon and hydrogen atoms are there in METHANE?
What is molecular formula?
- Shows the number and type of atoms in the molecule.
- Eg. CH4
What is displayed formula?
- Shows the atoms and covalent bonds as a picture.
- Eg. H-O-H
What is the molecular formula for Carbon Dioxide?
What is the molecular formula for Hydrogen?
What is the molecular formula for Water?
What is the molecular formula for Oxygen?
What is the molecular formula for Carbon Monoxide?
What is the molecular formula for Hydrochloric Acid?
What is the molecular formula for Calcium Chloride?
What is the molecular formula for Magnesium Chloride?
What is the molecular formula for Sodium Carbonate?
What is the molecular formula for Calcium Carbonate?
What is the molecular formula for Sulfuric Acid?
What is the molecular formula for Magnesium Sulfate?
Give 4 examples of additives.
- Food colours
- Flavour enhancers
Why is food colouring an effective additive?
They make the food look more appetising
Why are flavour enhancers an effective additive?
They bring out the taste and smell of food without adding a taste of their own
Why are antioxidants an effective additive?
They help to preserve food
Why are emulsifiers an effective additive?
- They help the oil and water to blend together in foods such as salad cream and ice cream.
- Oil and water naturally separate into two layers - with oil on top, emulsifiers help stop the two liquids separating out
What are emulsifiers made up of?
- Lots of droplets of one liquid suspended in another liquid.
- Emulsifiers are molecules with one part attracted to water and another attracted to oil
What is the part of an emulsifier that is attracted to water called?
What is the part of an emulsifier that is attracted to water oil called?
How do the two parts of an emulsifier molecule bond?
- hydrophilic part - bonds to the water molecules
- hydrophobic part - bonds to the oil molecule
- when you shake oil, water and emulsifier - oil forms droplets surrounding by a coating of the emulsifier - with hydrophilic bit facing out
why cook food?
- easier to digest
- kill off microbes
- some foods poisonous unless cooked
cooking eggs and meets...
- sources of protein
- protein changes shape when heated
- some chemical bonds break
- irreversible change to give edible texture
- called denaturing
- potatoes are plants
- each potato cell is surrounded with rigid cell wall made of cellulose.
- humans cant digest cellulose
- cooking ruptures / breaks down cells walls
- also makes starch grains inside cells swell up and spread out
- makes softer / easier to digest
What happens to baking powder when heated?
- undergoes thermal decomposition
- thermal decomposition is when a substance breaks down into simpler substances when heated
- many thermal decompositions are helped with a catalyst.
- Different to chemical reactions as only one substance
- baking powder contains sodium hydogencarbonate
What is the word equation for thermal decomposition within baking powder?
sodium hydrogencarbonate --> sodium carbonate + carbon dioxide + water
What is the symbol equation for thermal decomposition within baking powder?
2NaHC03 ---> Na2CO3 + CO2 + H2O
How does baking powder help in baking cakes?
The carbon dioxide makes the cake rise
How is carbon dioxide detected?
When CO2 is bubbled through limewater is turns the limewater cloudy
What are esters?
- Organic compounds
- formed by reaction of an alcohol with a carboxylic acid.
- All contain the functional group -COO-
- They are volatile
- become vapours easily
- have distinctive "fruity" smell
- used in perfume / airfresheners - apple smell, flowery, like jasmine
Are esters natural or synthetic (man-made)?
What is esterification?
- Ester can be made by heating carboxylic acid with alcohol.
- Acid catalyst is usually used (e.g. concentrated sulphuric acid).
- Acid + Alcohol --> Ester + Water
Give an example of how esterification can be done?
- Mix 10 cm3 of a carboxylic acid such as ethanoic acid..with
- 10 cm3 of of an alcohol such as ethanol
- add 1 cm3 of concentrated sulphuric acid to the mixture
- heat gently for 5 minutes
- tip mixture into 150 cm3 of sodium carbonate solution (to neutralise the acids)
- the fruity smelling product is ester
What properties does a substance need to be used as a perfume?
- easily evaporates - so particles reach nose
- non-toxic doesn't seep thro' skin & poison you
- doesn't react with water - cos of sweat
- doesn't irritate skin
- insoluble in water - so doesn't wash off every time you get wet
Properties of solids?
- strong forces of attraction between particles
- held in fixed position in a very regular lattice arrangement
- particles do not move from their position
- definite shape and volume
- particles vibrate, as heated vibrate faster -and expand
Properties of liquids?
- some force of attraction between particles
- free to move past each other
- do tend to stick to each other
- do not keep definite shape, flow to bottom of container
- keep same volume
- constantly moving with random motion
- get hotter - move faster - and expand
Properties of gases?
- no force of attraction between particles
- free to move
- travel in straight lines
- only interact when they collide
- do not keep definite shape or volume
- will fill any container
- as bounce off walls of a container they exert a pressure
- move constantly in random directions
- get hotter -move faster - either expand or pressure increases
What is volatility (or how volatile something is)
- when liquid is heated the heat energy makes particles move faster
- some particles move faster than others
- fast-moving particles at the surface overcome forces of attraction and escape
- this is evaporationhow easily a liquid evaporates is called its volatility
- for perfume particles to reach smell receptors in your nose perfume needs to be quite volatile
Danger of volatile liquids?
- petrol is a liquid as particles held together
- petrol is smelly not as smelly as teenage girls from West End
- smell means particles constantly escaping
- therefore petrol particles in the air and flame could cause fire
Effects of chemical study?
- are you still studying?
- if so, and learn all of these you will get
- a A STAR!!!
Solution, solvent, solute, soluble, solubility, insoluble... what are all these 'sol' words about?
- solution is a mixture of a solute and a solvent which do not separate out
- solute is substance being dissolved
- solvent is the liquid it's dissolving into
- soluble means it can be dissolved
- insoluble means it will not dissolve
- solubility is a measure of how much will dissolve
What happens when making a solution?
- add a solid ( a solute ) to a liquid ( the solvent )
- the bonds holding the solute molecules together sometimes break
- the molecules mix with the molecules in the liquid
- examples -
- water common solvent
- brine is a solution of salt and water
- evaporate off the solvent (water) to see the solute (salt) again.
Why is nail varnish insoluble?
- molecules of nail varnish are strongly attracted to each other
- this attraction is stronger than attraction between nail varnish molecules and water molecules
- the water molecules are strongly attracted to each other.
- This attraction is stronger than their attraction to nail varnish molecules
- therefore the two substances are more attracted to themselves and do not form a solution
Why is nail varnish soluble in acetone?
- the attraction between the acetone and nail varnish molecules is stronger than their attraction to themselves.
- Acetone is nail varnish remover
What does paint contain?
- solvent - thins paint so easier to spread
- pigment - gives the paint colour
- binding medium - liquid carries the pigment, holds them together, when goes solid sticks pigment to surface
What are colloids?
- really tiny particles of one kind of stuff dispersed (mixed in with) another kind of stuff
- they are mixed in - not dissolved
- can be solid, droplets of liquid, or bubbles of gas
- they don't separate or settle to the bottom as particles are so small
- paint is a colloid - particles of pigment (usually solid) dispersed in liquid
What are emulsion paints?
- water based i.e. the solvent is water
- binding agent usually acrylic or vinyl acetate polymer
- dries when solvent evaporates
- leaves binder and pigment in thin solid film
- fast drying
- do not produce harmful fumes
What are oil-based paints?
- traditional gloss & artists' oil
- binding material is oil
- solvent is an organic compound that will dissolve oil
- dry in two stages - 1) solvent evaporates 2) oil is oxidised by oxygen in air
- slower drying
- are glossy, waterproof, hardwearing
- harmful fumes
- used outside or metal painting
what are thermochromic pigments?
- change colour or become transparent when heated or cooled
- different pigments change at different temps therefore can be used for thermometers etc
what are phosphorescent pigments?
- absorb light
- store energy in molecules
- release as light over a period of time
What are polymers?
- lots of small molecules called monomers join together
- called polymerisation
- usually need high pressure and a catalyst
- plastics are usually polymers - usually carbon based and their monomers are often alkenes
What do the monomers that make up addition polymers have?
A double covalent bond
what are molecules with at least one double covalent bond between carbon atoms called?
what are molecules with no double bond between carbon atoms called
what is addition polymerisation?
- lots of unsaturated monomer molecules (alkenes) open up their double bonds
- then join together
- form polymer chains
what is cracking?
- turning long alkene molecules into smaller alkane and alkene molecules
- type of thermal decomposition
why do you need lots of heat and a catalyst for cracking?
need to break strong covalent bonds
why is cracking used?
- longer molecules are in things like diesel and lubricating oils
- smaller molecules are petrol and kerosene (jet fuel)
- more demand for smaller molecules
Cracking also produces lots of ****** molecules which can be used to make ********
Cracking also produces lots of alkene molecules which can be used to make polymers
What conditions are needed for cracking?
- Hot - 400°C to 700°C
- Catalyst - powdered aluminium oxide
How is cracking done?
- vaporised hydrocarbon passes over catalyst
- long chain molecules spilt apart on the surface of the catalyst
- e.g. paraffin (ten C atoms) to Octane (8 C atoms) - paraffin in crude oil, octane used in petrol
- ethene also produced and used in making plastics
What does crude oil provide?
- The energy needed to do lots of vital things; generating electricity, heating homes etc
- The fuel for most transport
- The raw materials needed to make various chemicals, including plastics
What are the cons of crude oil?
- It will run out eventually
- We are trying to find new ways to run our things rather than solely relying on crude oil
What are the political problems of crude oil?
- As the stocks lower, the price will increase
- Countries with the most oil and natural gas will have power over the other countries
- ^Could cause political conflicts or wars
- It will become harder for countries which don't have the oils and gases to get them
- We may have to rely on politically unstable countries but then our supply could be cut off at any time
What are the environmental problems of crude oil?
- Oil tanker crashes can lead to huge amounts of oil being released into the sea. The oil floats on the water and the waves spread it out onto big oil slicks
- Covers sea birds' feathers and stops them being waterproof. The water soaks into their feathers and they die of cold. The oil also means they can't fly
- Detergents used to clean up oil (break it into tiny droplets, making it easier to disperse) but some of these harm wildlife. Can be toxic to marine creatures like fish and shellfish
What should we consider when choosing the best fuel?
- Energy value
- Ease of use
What is complete combustion?
The complete combustion of hydrocarbons in oxygen will produce only carbon dioxide and water as waste products
What is incomplete combustion?
- When there isn't enough oxygen
- Gives carbon monoxide and carbon as waste products
- Produces a smoky yellow flame
What is phase 1 of the evolution of the atmosphere?
- Volcanoes gave out steam and carbon dioxide
- Earths surface was originally molten
- Eventually cooled and a thin crust formed but volcanoes kept erupting
- When things settled down it was mostly carbon dioxide and water vapour (which later condensed to form the oceans)
- There was very little oxygen
What is phase 2 of the evolution of the atmosphere?
- A lot of early carbon dioxide dissolved into the oceans
- Green plants evolved over most of the Earth
- ^As they photosynthesised they removed carbon dioxide and produced oxygen
- The amount of oxygen in the air built up and much of the carbon dioxide eventually got locked up in fossil fuels and sedimentary rocks
- Nitrogen gas was put into the atmosphere by ammonia reacting with oxygen and denitrifying bacteria
- Nitrogen isn't very reactive so the amount increased because it wasn't breaking down
What is phase 3 of the evolution of the atmosphere?
- Build up of oxygen in the atmosphere killed off early organisms that couldn't tolerate it
- It did allow the evolution of more complex organisms that made use of the oxygen
- The oxygen created the ozone layer which blocked the harmful rays of the sun and enabled even more complex organisms to develop
- Virtually no carbon dioxide left now
What is today's atmosphere like?
- Just right for us
- 78% nitrogen
- 21% oxygen
- 0.035% carbon dioxide
- Varying amounts of water vapour
- Noble gases (mainly argon)
What is the carbon cycle?
- Respiration, combustion and decay of plants and animals add carbon dioxide and remove oxygen
- Photosynthesis adds oxygen and removes carbon dioxide
- These processes would balance out but humans have messed up the cycle
- The balance of gases has been affected
What is acid rain?
- Caused by sulfur dioxide and oxides of nitrogen
- When fossil fuels are burned they release mostly carbon dioxide
- They also release other harmful gases - especially sulfur dioxide and various nitrogen oxides
- The sulfur dioxide comes from sulfur impurities in the fossil fuels
- The nitrogen oxides are created from a reaction between nitrogen and oxygen in the air, caused by the heat of the burning (can happen in the internal combustion engines of cars)
- When these gases mix with clouds they form dilute sulfuric acid and dilute nitric acid
- This falls as acid rain
- Power stations and internal combustion engines in cars are the main causes
What is photochemical smog?
- A type of air pollution caused by sunlight acting on oxides of nitrogen
- Oxides combine with oxygen to produce ozone
- Ozone can cause breathing difficulties, headaches and tiredness
What is carbon monoxide?
- A poisonous gas
- Can stop blood carrying oxygen around the body
- Can lead to fainting, coma or death
- Formed when petrol or diesel in car engines is burnt without enough oxygen - incomplete combustion
How can we control atmospheric pollution?
- Catalytic converters on motor vehicles reduce the amount of carbon monoxide and nitrogen oxides getting into the atmosphere
- Normally a mixture of platinum and rhodium
- Helps unpleasant exhaust gases from the car react to make things that are less immediately dangerous
- Carbon monoxide + nitrogen oxide = nitrogen + carbon dioxide