# Chemistry

Percentage composition
AR of element times number of them /Divided By/ MR of compound *Times 100*
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Ar
Ar is the relative atomic mass and is normally the top number
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Mr
Relative molecular mass, the sum of all Ar of a compound
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Isotope relative abundance
Ar = (mass of isotope 1 *times* relative abundance) + (mass of isotope 2 *times* abundance) /divided by/ Sum of abundances
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Moles equation
Moles = Mass /Divided by/ Mr
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Calculating mass
1. write balanced equation 2. work out moles of known element mass 3. write down ratios (big numbers in equation) 4. Rearrange mole equation to Mass = Moles * Mr
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Empirical formula
1. work out % or mass 2. Ar 3. Percentage /Divided by/ Ar 4. Divide by smallest
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Percentage Yields
Percentage Yield = Actual Yield /Divided by/ theoretical yield *Times* 100
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Separation - Filtration
Involves separating components of a mixture according to size, with small particles going through the filter, which leaves the larger particles
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Separation - Evaporation
Separates mixtures of solids and liquids by evaporating the liquid. Mixture is heated so liquid evaporates leaving the solid
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Separation - Distillation
Used to separate liquids that have different boiling points. When one reaches its boiling point it will evaporate and then be condensed, separating the two
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Separation - Chromatography
Separates substances according to their solubility in a particular solvent
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Atomic Number
Number of protons in nucleus
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Mass number
Total of protons + neutrons
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Group Number
Indicates the number of electrons in the outer shell
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Period Number
How many shells
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Group 1 - Lithium
Soft, silvery metal. Lightest metal, least reactive alkali metal but still has to be stored in oil
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Group 1 - Sodium
Silvery white metal, not found in nature because of reactivity. Stored in mineral oil to prevent it reacting with air
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Group 1 - Potassium
Silvery grey metal, has to be stored in oil, but can sometimes react with oxygen that dissolves in the oil
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Group 1 - Rubidium
Silvery metal, very reactive. If it has contact with air it bursts into flames
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Group 1 - Caesium
Explodes violently on contact with water and can only be handled in a inert atmosphere
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Group 1 - Francium
Highly reactive, radioactive and unstable. Only 30g on earth at a time
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Group 1 - Properties (Alkali metals)
React with oxygen to form oxides, react with water to form hydroxides and hydrogen, react with chlorine and bromine to form Bromide and chloride. Get more reactive down the group
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Group 1 - Flame test
Lithium - Red, Sodium - Yellow, Potassium - Lilac, Calcium - Brick Red, Barium - Apple Green
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Group 7 - Flourine
Pale yellow gas. Highly toxic and explosive. Despite this very small quantities are needed by the human body (fluorides)
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Group 7 - Chlorine
Greenish - yellow gas, reactive and toxic, used to disinfect water and clean swimming pools
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Group 7 - Bromine
Reddish - brown liquid at room temp, is reactive and toxic
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Group 7 - Iodine
Found in its toxic form in salts, essential in human body
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Group 7 - Astatine
One of the rarest elements on earth, highly radioactive and breaks down too quickly to be observed
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Group 7 - Properties (Halogens)
Increase reactivity up the group
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Group 7 - Iron wool test
Chlorine - Iron glows brightly and a blackish - brown deposit is formed, Bromine - Iron glows slightly and brown residue is left, Iodine - Needs strong heating for a reaction
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Group 7 - Tests for Halogens
Silver nitrate test - White, chloride - Pale Yellow, bromine - Yellow was iodine
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Reactivity of alkali metals and halogens explained
Group 1 only have one electron in the outer shell and group 7 have seven. This means that for group 1 it is easier to lose one than gain seven, and for group 7 it is easier to gain one than lose seven
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Group 0 - Noble Gases
Helium, Neon and Argon. Very unreactive
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Whats in water
Ions, mainly magnesium, calcium and chloride, microorganisms and pollutants
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Ways to save water
Having quick showers, re-use water for plants, don't leave water running and ensure dishwasher/washing machines are full before use
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Abstracting water
Obtaining water for human use, e.g. dams/reservoirs, underground pumps, desalination and collecting rain water
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Public water supply/treatment
Water from natural sources goes to a reservoir to be stored and allow solids to settle. Filtration removes small particles, chlorination kills bacteria, the water is stored in a tank or water tower and then goes out for public use
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Stages of treatment of water - Sedimentation
Larger insoluble particles are removed by allowing them to settle on the bottom of a tank
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Stages of treatment of water - Filtration
Smaller insoluble particles are removed by passing through a water filter
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Stages of treatment of water - Chlorination
Chlorine is added. It is poisonous to many bacteria and kills them.
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Fluoridation - Process
Fluoride is added to drinking water to prevent tooth decay. This can happen naturally, through picking up magnesium and calcium ions through rocks or can be added by hand
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In children fluoride helps make the enamel more resistant, fluoride reduces the ability of plaque bacteria to form acid
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If teeth are exposed to high levels of fluoride then dental fluorosis can occur (white blotches on enamel), fluoridation could be rendered useless as 90% of toothpastes have fluoride in them
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Desalination – Process
Desalination is the process of removing salt from water, usually to make it drinkable. It is called reverse osmosis. The sea water is pushed through a filter at high pressure to remove the salt.
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Uses a lot of energy, to produce the high pressure needed, costs more than other processes, very expensive because of the energy required, many countries can not afford it, and some do not have a coastline
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Easy to transport as next to sea, can make huge quantities safe to drink, renewable
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Distillation
Separating two liquids, by using the different boiling points. Once the liquid with the lower boiling point has evaporated and becomes vapour, goes into the condenser which turns it back into liquid
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Solubility curves
How much of a solute dissolves in a solvent. The graph shows this out of g/100g solvent (usually water)
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Hard and soft water
Water can be 'hard' or 'soft' depending on where it is from and if it has dissolved calcium and magnesium ions in it
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Temporary hard water
Contains calcium hydrogencarbonate and/or magnesium hydrgencarbonate. When the water is boiled the hardness is removed with the formation of solid calcium carbonate
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Temporary hard water - Boiled equation
Ca(HCO3) --> CaCO3 + H2O + CO2
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Permanent hard water
Boiling does nor soften. Contains chlorides and/or sulphates of calcium and magnesium
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Softening hard water - Boiling
Boiling, used for temporary hard water, easy and cheap, however it produces limescale, only practical for small quantities and only works on temporary hard water
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Softening hard water - Adding sodium carbonate
Adding sodium carbonate, used for both types of hard water, its cheap, however it produces limescale, only practical for small quantities
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Softening hard water - Ion exchange
Ion exchange, used for both types, no limescale is produced and can be used for large quantities. However it is expensive and ions need to be rerplaced
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Structure of the earth
Inner core - hottest part of the earth, mostly iron. Outer core - liquid layer, temperatures almost as high as inner core. Mantle - Thickest layer of earth, semi-molten rock. Crust - Thin layer of solid rock
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Destructive plate boundary
One plate is subdued under the other to form magma, this forms volcanoes. Oceanic plate is forced under the continental
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Constructive plate boundary
Plates move away from each other, magma is released which cools to create rock
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Conservative plate boundary
Plates slide past each other. Generating earthquakes. No volcanoes present as no rock melts
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Gas in atmosphere
Nitrogen - 78.1%, Oxygen - 20.9%, Argon - 0.9%, Carbon Dioxide - 0.035, Other - 0.065%
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Carbon cycle - Photosynthesis
Plants absorb CO2 and produce oxygen
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Carbon cycle - Respiration
Animals produce and release CO2
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Carbon cycle - Combustion
Some plants and animals do not decay but instead form fossils and have carbon in them. When they are burnt they release CO2
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Carbon cycle - Decomposition
Decomposers, e.g. microbes and fungi break down the remains of dead animals and plants releasing CO2 through respiration
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Tests for gasses in the air
Oxygen -Glowing splint will re-light, Carbon Dioxide - Bubble through water, lime water will turn cloudy, Hydrogen - Lighting a splint, makes a squeaky pop sound
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Acid Rain - Sulphur equation
Sulphur Dioxide + Water --> Sulphurous acid / SO2 + H2O --> H2SO3
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Acid Rain - Nitrogen equation
Nitrous oxides + Water --> Nitric acid / NO2 + H2O --> HNO3
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Acid Rain
Burning fossil fuels causes acid rain as it releases Sulphur dioxide and Nitrous oxides into the atmosphere, which react with water to form acid rain
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Measuring the rate of a reaction
The rate of reaction means how much product (usually mass or volume) is produced in a set time (usually per second)
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Explanation of rate of reaction
A chemical reaction occurs when particles collide with on another. The collision needs energy to work. Lots of particles move at high speeds and lots of collisions happen, however only a small amount are successful.
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Factors affecting rate of reaction - Temperature
Higher temp = higher rate of reaction. Higher temperature means that the particles move quicker, faster particles mean more energy for each collision and a higher collision frequency means higher reaction rate
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Factors affecting rate of reaction - Concentration of Reactants
Increasing concentration increases the number of particles, in the same volume. More particles per unit means there will be more collisions and higher collision frequency means higher rate of reaction
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Factors affecting rate of reaction - Surface area
Increasing surface area allows more reactants to collide with each other with enough energy, and more collisions cause a higher collision frequency, so higher rate of reaction
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## Other cards in this set

### Card 2

Ar

#### Back

Ar is the relative atomic mass and is normally the top number

Mr

### Card 4

#### Front

Isotope relative abundance

Moles equation