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Year 8 - Triplet 2 Revision (Chemistry (Properties of Metals (Metals can…
Year 8 - Triplet 2 Revision
Biology
The Human Digestive System
Mouth - Teeth and enzymes in saliva are used to break down food
Oesophagus - Transports food particles to the stomach. Also a protective mechanism
Stomach - Contains highly concentrated hydrochloric acid to break down food and kill harmful bacteria which may have been ingested
Small Intestine - Breaks down food further and useful nutrients are absorbed
Large Intestine - Absorbs water into the blood leaving faeces, which are mainly fibre
Rectum - Holds faeces until they are expelled
Anus - Where faeces leave the body
Digestion is the break down of large, insoluble molecules into small, soluble molecules so that they can be absorbed into the body
Enzymes
Enzymes are catalysts released into our digestive system to break down large, insoluble molecules into small, soluble ones that can be absorbed into the bloodstream
We make a different enzyme for each food substance that needs breaking down because the shape of the enzyme's active site has to be the right shape for the molecule
Carbohydrates >
Carbohydrase (Enzyme)
> Glucose
Proteins >
Protease
> Amino acids
Lipids >
Lipase
> Fatty acids + Glycerol
If we heat up enzymes, the shape of the active site changes and they are denatured
Enzymes can also become denatured as a result of a change in pH
The enzyme in our saliva is called amylase. When it is mixed with starch, the starch is broken down into glucose
Some enzymes are more effective at certain pH levels, for example, catalase (found in the liver and also in potatoes), works best at pH 8.
Absorption
Diffusion is the net (overall) movement of particles from an area of high concentration to an area of low concentration
Particles move towards the area of low concentration by colliding with each other and the "walls" of the "container", until equilibrium is reached
We need nutrients (eg glucose, amino acids, fatty acids and glycerol, as well as vitamins and minerals) to be absorbed quickly into our bloodstream
The most important nutrient we need is glucose as our cells need this to release energy from respiration
The 3 principles of fast diffusion
Make it happen over a large surface area
Make it happen over a short distance
Keep a steep concentration gradient
Our small intestine is adapted for fast diffusion of nutrients into the bloodstream
Chemistry
The Periodic Table
'Staircase' separates metals and non-metals
Metals are on the left
Non-metals are on the right
Horizontally are groups
Vertically are periods
History of the Periodic Table
1669 - Hennig Brand discovers phosphorous when trying to make gold from urine
1789 - Antoine Lavoisier wrote a set of 'simple substances'; an early periodic table
1863 - John Newlands divided the elements into groups based on their characteristics
1869 - Dmitri Mendeleev arranged the periodic table almost as it is today
Alkali Metals
Lithium
Appearance
Grey on outside
Soft
Shiny when cut
Stored under oil
Reaction with air
Shiny surface went dull and grey
Oxidised (reacted with oxygen) slowly
Lithium + Oxygen > Lithium Oxide
4Li + O₂ > 2Li₂O
Reaction with water
Slowly fizzed
Releases a colourless gas (hydrogen)
Lithium + Water > Lithium Hydroxide + Hydrogen
2Li + 2H₂O > 2LiOH + H₂
Floats
Sodium
Appearance
Grey on outside
Very soft
Shiny when cut
Stored under oil
Reaction with air
Shiny surface went dull and grey
Oxidised quicker than Lithium
Sodium + Oxygen > Sodium Oxide
4Na + O₂ > 2Na₂O
Reaction with water
Fizzed
Released hydrogen
Sodium + Water > Sodium Hydroxide + Hydrogen
2Na + 2H₂O > 2NaOH + H₂
Floats
Moved around
Became a ball
Potassium
Appearance
Dull green on outside
Very soft
Shiny when cut
Stored under oil
Reaction with air
Shiny surface went dull green
Oxidised very fast
Potassium + Oxygen > Potassium Oxide
4K + O₂ > 2K₂O
Reaction with water
Released sparks
Released hydrogen
Potassium + Water > Potassium Hydroxide + Hydrogen
2K + 2H₂O > 2KOH + H₂
Floats
Moved around
Became a ball
Burned with a purple flame
Properties of Metals
Metals can be found in the periodic table - They are found on the left-hand side and make up most of it
Metals conduct electricity - Because they contain free electrons which can carry an electric current from one end to another
Metals conduct heat - Because they have particles which are very close together which also helps to transfer vibrations by colliding with each other. They also contain free electrons which help to transfer thermal energy
Metals are strong and tough - Because they have strong bonds that hold them together
Metals are shiny when polished - Because they reflect light, especially when they have just been polished or just cut
Metals are malleable - Because they have layers of atoms that can roll over each other without shattering
Metals are ductile - Because they have layers of atoms that can roll over each other without shattering
Metals have high melting and boiling points - Because a lot of heat energy is needed to break the bonds that hold the atoms together
Metals have high densities - Because they contain a lot of particles in a small volume
Metals make alloys when mixed with other metals - Lighter, weaker metals can be mixed with heavier, stronger ones to create a metal that is light and strong.
Some metals are magnetic - Only iron, nickel and cobalt are attracted to magnets
Metals are sonorous - When you hit them they make a sound
Properties of Non-metals
Non-metals can be found in the periodic table - They are found on the right-hand side
Non-metals are poor conductors of electricity -They are electrical insulators because the atoms are arranged so that electrons can't pass through - one exception is graphite
Non-metals are poor conductors of heat - Heat doesn't travel very well through them because the particles don't pass on vibrations well.
Non-metals are not strong or hard-wearing - The forces between the particles in non-metals are weak; they break easily. Also, atoms are easily scrubbed off - so they wear away quickly.
Non-metals are dull - They don't reflect light very well because their surfaces aren't as smooth as metals.
Non-metals are brittle - Their structures are held together by weak forces
Non-metals have low melting points and boiling points - The forces holding the particles together are very weak; this means they melt and boil easily. At room temperature, most non-metals are gases or solids. Only one is a liquid.
Non-metals have low densities - Becuase they don't have very many particles packed into a certain space.
Non-metals are not magnetic - Only a few metals are magnetic, so all non-metals are most definitely non-magnetic.
Oxides
Formed when elements react with oxygen. For example:
4Na + O₂ > 2Na₂O
Sodium + Oxygen > Sodium Oxide
Physics
Types of energy
Chemical potential energy is stored in fuels and food. It is released in chemical reactions such as combustion and respiration
Elastic potential or strain energy is stored when materials are stretched, compressed or twisted
Gravitational potential energy is stored in objects at a high level
Kinetic energy is possessed by any moving object: the bigger or faster, the more energy
Heat or thermal energy is the energy of particles and increases as heat does
Sound energy is carried by sound waves, caused by vibrations in particles (transfer of energy)
Light energy is carried by the part of the electromagnetic spectrum we see (transfer of energy)
Electrical energy is carried by charged particles
Magnetic energy occurs in magnetic materials and electromagnets
Energy can't be created or destroyed, but is converted from one form to another.
Energy Efficiency
% Efficiency = Useful energy output / Energy Input × 100
To show energy efficiency, we use something called a Sankey Diagram
Sankey Diagram rules:
In exams, they will be drawn to scale using graph paper
The energy input is always on the left
The wasted energy always curls away from the diagram
The useful energy is always horizontal
How to draw Sankey diagrams:
Energy Transfer
Heat travels through materials by conduction
This involves vibrating particles passing the vibrations (heat)
Materials that let heat travel easily are called conductors
Materials that do not let heat travel through them are called conductors
Convection is when heated particles collide with each other and move away from the heat source, carrying energy
Radiation is when objects radiate invisible waves of heat; they do not have to be touching
Renewable Energy Resources
Biomass
Comes from the chemical potential energy stored in dead plants
Involves burning dead plants to produce heat energy
Renewable
No special equipment required
Large areas needed to grow trees
Tidal
Comes from the sea's tide
Water is released at low tide and the pressure turns a turbine
Renewable
No pollution
Reliable - there are 2 tides per day
Cheap to run
Expensive to build
Can cause local flooding
Geothermal
Comes from heat from hot rocks in the Earth's mantle
Involves using steam from the core to generate electricity
Renewable
No pollution
Doesn't damage the environment
Very few places in the world where you can do this
Expensive
Hydroelectric
Comes from kinetic energy from a river
Involves the energy from the water spinning a turbine
Renewable
No pollution
Can choose when energy is produced
Expensive
Can ruin environment
Wave
Comes from the power of the sea's waves
Involves using machines that bob up and down on waves to create power
Renewable
No pollution
Lots of machines required
Expensive
Ugly
Can be damaged easily in a storm
Wind
Comes from the wind
Involves the wind turning turbines, which then generate electricity
Renewable
No pollution
Cheap and easy to build
Can be ugly and noisy
Only works if it's windy
Solar
Comes from heat and light from the sun
Involves light being absorbed into solar panels, and converted into electricity
Renewable
No pollution
Can be expensive
Only works if it's sunny
Fossil Fuels (Non-renewable)
Come from finite resources underground
Involves fuels being burned in a boiler to heat and water to create steam, which is then used to drive turbines and generate electricity
Easily available
Cheap
Lots of energy is produced
Non-renewable (only finite amounts available)
Lots of pollution
