Chemistry (IGCSE coordinated science)
Terms in this set (143)
What is the difference between an atom and a molecule?
An atom is only one atom
A molecule is two or more atoms bonded together.
What does filtration seperate?
A liquid and an insoluble solid
What does crystallisation seperate?
A soluble solid in solution
What can chromotography seperate?
A mixture of coloured compound
What does distillation seperate?
Why is it important that pharmaceutical drugs are as pure as possible?
This reduces the chance of unecessary side effects and helps to ensure an accurate dose in each tablet.
How do we test if a substance is pure or not?
The purity of something can be tested using data from its melting and boiling point.
What is the effect of impurity to the boiling of the substance
The presence of an impurity usually lowers the melting point and raises the boiling point
evidense of a chemical reaction:
- color change
- temperature change
- not easy to reverse
What is a physical change?
Whe no new substance is formed and the cnage is easily reversed
EXP: phase transformation (melting, boiling)...
What is a chemical change?
When a new substance is formed, but it is difficult to reverse
EXP: burning, rusting, any reaction
What is an element?
Substance that only has one type of atom
What is a compound?
Pure substance made up of two or more elements bound together
What is a mixture?
Matter that formed from two or more elements/ compounds physically intermingled
What is a atoms goal in life?
To get a noble gas outer shell configuration
What is an atom made up of?
Electrons, a nucleus (full of protons and neutrons)
Whats an electrolyte?
A liquid or solution that conducts electricity by movement of ions
What is the Atomic number?
The number of protons in the nuclues of an atom
What is the mass number?
the total number of protons and neutrons in a nucleus
What are isotopes?
Atoms that have same number of protons but different numbers of neutrons
What is an ion?
Ions are particles formed when atoms gain or lose electrons
In what kind of structure are ions held together?
A lattice structure, which is a regular arrangement of alternating positive and negative ions held together by electrostatic attraction.
h and cl
N=-N (triple bond)
Properties of ionic compounds
- High melting and boiling points
- Low volatility
- Usually solid state
- Usually soluble in water
- Conduct electricity when molten or dissolved
(ions are free to move and carry charge)
Properties of Simple Convalent compounds
- Low melting and boiling points; high volatility
- More soluble in organic solvents than water
- Do not conduct electricity
(no ions present)
What is a convalent structure?
Non-metals that share electrons
Talk about Graphite
- a form of carbon
- each carbon atom is joined to three other carbon atoms, forming a giant convelant structure
- these layers formed slide over each other, so it is quite soft.
- it is used in pencils, and as a lubricant
- it conducts eletricity
What is a lubricant?
a substace used to reduce friction between two surfaces
Talk about Diamond!
- A form of carbon
- Each carbon atom is joined to four other carbon atoms
- As a result, diamond is very hard and has a high melting point
- It does not conduct electricity
Talk about Silica (silicon IV oxide)
Silica, which is found in sand, has a similar structure to diamond.
It is also hard and has a high melting point.
But it contains silicon and oxygen atoms, instead of carbon atoms.
What is relative atomic mass?
Is the average value for the isotopes of the element
For example: for chlorine it is 35.5 because it contains two different isotopes
What is relative molecular mass? (M = molecular mass = mass of 1 mole)
Is the sum of the relative atomic masses
eg, what is relative atomic mass of water (H2O)?
What is a mole?
A unit for amount of substance.
One mole contains avogrado's number or particles (atoms, molecules, ions or electrons) in a substance
What is the molar gass volume at room temperature and pressure?
24 dm^3 or 24000 cm^3
moles = mass/molar mass
concentration of solution formula
conentration of solution= number of moles of solute dissolved/ total volume of solution
Remember trick- REDCAT
IN electrolysis, where does reduction take place?
reduction always happens at the cathode
Remember trick- ANOX
IN electrolysis, where does reduction take place?
Oxidation always happens at the anode
what is ELECTROLYSIS?
The chemical effect of electricity on ionic compounds, causing them to break up into smaller, simpler substances, usually elements
- Positively charged ions (ANODE) move to the negative electrode (CATHODE) during electrolysis. They receive electrons and are reduced
- Negatively charged ions (ANIONS) move to the positive electrode (ANODE) during electrolysis. They loose electrons and are oxidised
The products of the electrolysis of Molten lead (II) bromide
lead and bromine
The products of the electrolysis of aqueos copper chloride
copper metal and chloring gas
The products of the electrolysis of dilute sulphuric acid
hydrogen gas and oxygen gas
The products of the electrolysis of aqueaus copper (II) Sulphate
copper and Oxygen
Rule for what is produced at the anode if in solution:
Attract - ions (anions)
If halogens (Cl, Br, I) are present they are present
If no halogens are present, Oxygen is produced
Rule for what is produced at the cathode if in solution:
Attract + ions (cations)
If the cations are more reative than hydrogen, then hydrogen is produced.
If + ions are less reactive than hydrogen, then the ion is produced.
Talk about the purification of copper
- the extraction of copper is done by reduction with carbon
- the copper produced is not pure enough to be used as a condutor, so it is purified using electrolysis.
- The positive electrode (anode) is made of inpure copper, which is to be purified
- the negative electrode (cathode) is a bar of pure copper
- the electrolyte used is copper (II) sulphate
- copper ions leave the anode ad are attracted to the cathode, where they are deposited as copper atoms
- The pure copper cathode increases greatly in size, while the anode dwindles away.
- the impurities left at the anode form a sludge beneath it
What is electroplating?
- This is done by electrolysis
- It is useful for covering a cheaper metal with a more expensive one
- the negative electrode should be the object that is to be electroplated
- The positive electrode should be the metal that you want to coat the object with
- the electrolyte should be a solution of the coating metal, like its metal nitrate or sulphate.
The extraction of aluminium
Aluminium is the most abundant metal on earth
Despite this, it is expensive, largely because of the amount of electricity used to extract it.
Aluminium ore is called bauxitite
The bauxitite is purified to yield a white powder: aluminium oxide, through white aluminium can be extracted
The extraction is done by electrolysis
But first, the aluminium oxide must be made molten so that electricity can pass through it.
Aluminium has a very high melting point, so it would be expensive to melt it. Instead, It is dissolved in molten cryolite, an aluminium compound with a lower melting point than aluminium oxide. The use of this reduces energy costs.
What is Brine?
A solution made from consentrated aqueos sodium chloride (salt).
What is the electrolysis of brine used to manufacture?
chloring, hydrogen, and sodium hydroxide
What is an endotheric reaction?
a reaction that takes in energy from its surroundings. (ussually as heat- making things grow colder) eg. electrolysis, thermal decomposition of calcium carbonate
What is an exothermic reaction?
A reaction that transfers energy to its surroundings (ussually transferred as heat- making things warmer) eg. burning, neutralisation between acids and alkali's
What effects rate of reaction?
- particle size (surface area)
- adding a catalyst
How does particle size affect rate of reaction?
the larger the surface area, the faster the rate of reaction is because it increases the chance of particles coliding with each other
How does consentration affect rate of reaction?
A higher consentration means that there are more particles in a given area, so there are more collisions
How does adding a catalyst affect rate of reaction?
Adding a catalyst speeds up the rate of reaction, as it lowers the amount of energy needed for a reation to take place
how does temperature affect rate of reaction?
A higher temperature, gives particles more energy to move , so they collide more often.
What is a practical method of measuring rate of reaction?
- react two things together in a flask
- record the time it takes for the syringe to fill up with a certain amount of gass
- repeat the experiment, changing a factor affecting rate of reaction and see how it affects the previous time
Rate of reaction in a flour mill
Flour is produced in a flour mill
flour particles are small, so have a large suface area
if there is alot of flour in the air, a small spark can cause an explosion between flour and oxygen
Rate of reaction in a coal mine
In a coal mine, the air is filled with flammable gasses.
If the gasses reach a certain consentration, they can form an explosion with air.
what is oxidation?
If something is oxidised, it gains oxygen or looses electrons
What is reduction?
when something is reduced, it looses oxygen or gains electrons
What is a redox reaction?
A combination of two chemical reactions- oxidation and reduction.
An example of this is rusting
when iron looses electrons, it is oxidised
and oxygen gains electrons, it is reduced
What is an acid?
Have a Ph less than 7, turn blue litmus paper red, and turn universal indicator anything ranging from yellow-red
What is a base?
Have a ph more than 7. They are ussualy metal oxides or metal hydroxides. they will turn red litmus paper blue and universal indicator anything from blue- purple
what is an alkali?
A base dissovled in water
What does an acid produce when dissolved in water?
What does an alkali produce when dissolved in water?
what does an acid and metal produce?
a salt and hydrogen
What does an acid and base produce?
salt and water
What does an acid and carbonate produce?
salt and water and carbon dioxide
What kind of salt does hydrochloric acid make?
What kind of salt does sulphuric acid make?
What kind of salt does nitric acid make?
Importance of ph in air
Burning fossil fuels releases gasses into air, like nitrogen oxides and sulphur dioxide. They react with water and air, leading to acid rain, which erodes buildings and negatively affects soil and water.
Importance of ph in water
Factory waste if often acidic, and can leak into water. To prevent this from happening it needs to be neutrlise. Slacked lime can be used for this.
Importance of ph in soil
Soil is used to grow crops, so it is important that it is neutral. If it happens to be acidic or alkaline, the crops tend to grow poorly. Bases can help neutralise acidic soil, like slasked lime.
Non metals and oxygen form...
Metals and Oxygen from...
Test for carbonate
add dilute acid; effecvesence and carbon dioxide will be produced if present
Test for chloride`
acidify with dilute nitric acid, then add aquos silver nitrate; a white percipitate will be produced if present.
Test for nitrate
add aqeous sodium hydroxide, then aluminium foil; warm carefully; ammonia will be produced if present
Test for sulphate
acidify with dilute nitric acid, then add aqueous barium nitrate; a white percipitate will be produced if present
effect of aquoeous sodium hydroxide on ammonium.
ammonia produced on warming
effect of aquoeous sodium hydroxide on copper (II)
light blue percipitate, insoluble in excess
effect of aquoeous sodium hydroxide on Iron (II)
green percipitate, insoluble in excess
effect of aquoeous sodium hydroxide on zinc
white percipitate, soluble in excess, giving a colourless solution
effect of aquoeous aqueous ammonia on ammonia
effect of aquoeous aqueous ammonia on copper
light blue pericipitate, soluble in excess giving a dark blue solution
effect of aquoeous aqueous ammonia on iron
green percipitate, insoluble in excess
effect of aquoeous aqueous ammonia on zinc
white precipitate, soluble in excess giving a colourless solution
Test for ammonia
turns damp red litmus paper blue
test for carbon dioxide
turns limewater milky
test for chlorine
bleaches damp litmus paper
test for hydrogen
'pops' with a lighted splint
test for oxygen
relights a glowing splint
the characteristics of elements change from_________ to __________ across a period
the characteristics of elements change from metallic to non-metallic across a period
Properties of group 1 (alkali metals)
- most normal metal properties
- relatively soft (low densities)
- Have low melting and boiling points, the melting point decreases as you go down the group (lithium has the lighest, ect.)
- they react vigourously with cold water, forming hydrogen gas and a metal hydroxide
- the speed and violence of the reaction increases down the group, they will fiz and melt into a ball (sodium may and potassium will produce a flame)
-the solutions produced are highly alkaline (they are alkali metals after all!)
- Do NOT react them with acid, as they will cause an explosion.
flame colours for sodium
flame colour for calcium
flame colour for potassium
flame colour for copper
flame colour for lithium
Properties for group 7 (the halogens)
- they get less reactive down the group
- they become darker down the group (flourine is a pale yellow, chlorine is a greenish yellow, bromine is red-brown, iodine is black with a purple vapour
- Melting and boiling points increase down the group (at room temperature, flourine and chlorine are gasses, bromine is a liquid and iodine is a solid)
- A halogen can displace a halide ion from below it.
What are the transition elements?
A collection of metals having high densities, high melting points and formng colour compounds, and which, as elements and compounds, often act as catalysts.
What is a general use of the noble gasses?
the noble gasses are used to provide an inert atmosphere
What is helium used for?
baloons, deep sea diving, body scanners
What is neon used for?
red advertising signs
What is argon used for?
Light bulbs, extraction of titanium
What is the use of krypton?
laser to operate on eyes
Properties of metals
shiny, solid (except mercury), high density, strong, malleable, ductile, good conductors of heat and electricity, sonorous, some are magnetic
Properties of non-metals
dull appearance, half gasses, half solids (only bromine is a liquid), low density, weak, brittle, not ductile, bad conductors of electricity and heat, make a dull sound when hit, none are magnetic
What are alloys?
a mixture of two elements, one being a metal. Alloys have different properties to the metals that they contain. This makes them more useful than pure metals alone. Alloys are often harder than the metals that they contain. Alloys contain different sizes of atoms, which distorts the regular arrangement of atoms. This makes it harder for atoms to slide over each other, making alloys harder than pure metal.
list the reactivity series
pottassium, sodium, calcium, magnesium, zinc, iron, hydrogen, copper
Why is hydrogen included in the reactivity series?
because it can be used to extract metals.
What substance do zinc and iron react well with, as they don't react with water?
Metals below carbon in the reactivity series can be reacted how?
Zinc, iron and copper are all present in their ores as oxides. Each of these oxides is heated with carbon to obtain the metal. The metal looses oxygen and is therefore reduced. The carbon gains oxygen and is therefore oxidised. only metals below carbon in the rectivity series can be extracted this way, as carbon is more reactive than them, so therefore displaces them.
Describe the process for the extraction of iron
Iron is extracted in a huge container called a blast furnace. Iron ores such as hemotite contain iron oxide. In this reaction, the iron oxide is reduced to iron, and the carbon is oxidised to carbon dioxide. In a blast furnace, it is so hot that carbon monoxide can be used to reduce the iron oxide in the place of carbon
iron ore (haematite) (contains iron, a compound that contains iron)
coke (contains carbon) (burns in air to produce heat and reacts to form carbon monoxide, which is needed to reduce the iron oxide.)
limestone (calcium carbonate) (helps to remove acidic impurities from the iron by reacting with them to form molten slag)
air (oxygen) (allows coke to burn, and so produces heat and carbon monoxide)
Uses of aluminium
- the low density and strength of aluminium makes it perfect for use in the aircraft industry. An alloy of aluminium called duralumin if often used instead of pure aluminium because of its improved properties.
- easy shaping and corrosion resistance make it ideal in food containers
What is Galvanising?
a method of rust prevention
the steel object is coated with a thin layer of zinc
this stops oxygen and water reaching the metal underneath.
it also acts as sacrificial protection as zinc is more reactie than iron, so it oxidises in preferance to the iron object
tests for water
- white anhydrous copper(II) sulphate turns blue if water is present
- blue anhydrous cobalt (II) chloride turns pink if water is present
describe the purification of water
1. FILTRATION the water is filtered through specially prepared layers of sand and gravel to remove different sized insoluble solids
2. CHLORINATION chlorine is added to the water to kill microbes and any water borne pathogens
What is air made up of?
the air is 78% nitrogen, 21% oxygen, and 1% other gasses including water vapour, noble gasses (argon) and carbon dioxide
How do we obtains different things from air?
- the air is filtered to remove dust, and then is cooled in stages until it reaches -200 degrees celcius
- now its a liquid
- water vapour condenses and is removed using absorbant filters
- cabon dioxide is removed at -79 degrees when it freezes
- oxygen liquefies at -183 degrees
- nitrogen liquefies at -196 degrees
- oxygen and nitrogen are then seperated by fractional distillation
what is water used for at home?
drinking, washing, cooking and cleaning
what is water used for in industry?
as a coolant, solvent, and raw material
how is the common air pollutant, carbon monoxide, produced?
incomplete combustion of the fuel in car engines
how is the common air pollutant, oxides of nitrogen, produced?
formed by the heat and pressure found in car engines
how is the common air pollutant, sulphur dioxide, produced?
sulphur impurities in fuel burn
what do catalytic converters do about the oxides of nitrogen produced?
carbon monoxide + nitrogen monoxide -> nitrogen + carbon dioxide
what is carbon monoxide?
a poisonous gas
it kills you
what forms acid rain?
oxides of nitrogen and sulphur dioxide
What effects does acid rain have on the enviroment?
- killing plants and aquatic life
- eroding stonework
- corroding metals
carbon dioxide is formed by .....
- as a product of respiration
- as a product of the reaction between an acid and a carbonate
- as a product of thermal decomposition
- as a product of complete combustion of carbon-containing substances
raw materials needed for the Haber process?`
- hydrogen gas (obtained by reacting natural gas (methane) with steam or by cracking hydrocarbons
-nitrogen gas (obtained by fractional disstillation of liquid air)
conditions necessary for the haber process
-A high temperature (about 450 degrees)
- a high pressure (about 200 atmospheres)
- an iron catalyst
the reaction for the haber process
what is rusting?
A reaction involving air and water:
iron+oxygen+water->hydrated iron (III) oxide
the hydrated iron (III) oxide is the familiar orange-brown rust we find on steel objects
Methods of rust prevention
- use an alloy of iron that does not rust like stainless steel
- galvanising (the iron or steel object is coated with a thing layer of zinc. This stops oxygenand water reaching the metal underneath, but also acts as sacrificial protection as zinc is more reactive than iron, so it oxidises instead)
- sacrificial protection (magnesium and zinc are often used as sacrificial metals, they loose their electrons in preference to iron)
What kind of fertilisers do plants need?`
NPK ferlilisers- ones that contain: nitrogen, phosphorus and potassium
Nitrate is needed for building proteins and growth, phosphate for respiration and growth,and potassium for respiration and photosynthesis
ammonia can be displaced from its salt by warming it with an alkali.
basically if ammonium saltsis reacted witha strong base, ammonia will be produced along with water and a salt. eg:
as you can see, the ammonia is displaced by the salt cation.
The thermal decomposition of limestone
When limestone (calcium carbonate) is heated, at about 1000 degrees, it undergoes thermal decompotion. It looses carbon dioxide and turn into quick lime (calcium oxide)
calcium carbonate -> calcium oxide + carbon dioxide
what is quick limes uses?
it reduces the acidity of lakes and soil that have become acidic due to acid rain. It is faster than powdered limestone, but it more expensive. Slaked lime dissolves in water to form lime water.
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