Chemistry paper 1
Types of substances
Giant Covalent Structures.
Properties of Ionic compounds
Ionic bonds are bonds between a metal and a non metal.
Ionic compounds have regular structures / Giant ionic lattice in which strong electrostatic attraction between oppositely charged ions forms a bond.
They have high melting and poiling points becasue alot of energy is required in the breaking of storng bonds.
They can not conduct electricity when they are solid.
When dissolved in water , they have the ability to conduct electricity because the ions are free to move.
When they dissolve in water , they form an aqueos solution.
Properties of Simple Molecular Compounds.
They consist of small molicuoles gaseous or liquid molecules.
They have a low melting and boiling point.
The substances contain weak intermolecular forces.
These intermolecular forces increase with the size of the molecules.
They can not conduct electricity because small molecules do not have an overall charge.
They are usually two non metals Bonded together. in the sharing of electrons.
Substances that make up a giant covalent structure have high melting points and boiling points.
They are usually made from non metals.
All the atoms are linked together by strong covalent bonds.
Some Giant Covalent bonds have the ability to conduct electricity
Properties of metals
Metals Consist of Giant structures of atoms arranged in a regular pattern.
The sharing of electrons allows for metalic bonding to occure.
The electrons on the outer shell are Delocolised.
Metals have high boiling and melting points.
Metals can conduct heat and electricity.
The layers of atoms in a metal are able to slide of each other.
Metals are malleable.
Summary
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Regular arrangement due to strong electrostatic forces between oppositely charged ions.
Can conduct elelctricity when molen or in an aqous solution.
High melting and boiling points
Summary
Low melting and boiling points due to weak intermolecular forces.
Strong covalent bonds.
Poor conductors.
Allotropes of carbon.
Diamond
Graphite.
Contains 4 Carbon atoms covalently bonded.
High melting and boiling points due to the strength of the covenant bonds.
They can not conduct electricity.
Contains 3 Carbon atoms covalently bonded to another.
The Carbons are arranged in a Hexegonical pattern.
The layers of Graphite are able to slide over each other due to no covalent bonds between them.
They contain a delocalized electron.
It can conduct electricity.
Uses of diamond.
Cutting tools due to it being very hard and possesing a rigid structures
Uses of Graphite
They can be used in electrodes due to their ability of conducting electricity.
They can be used as Lubricant due to them being able to slide over each other because of their weak intermolecular forces.
states of matter and mixtures.
Pure substances :
Mixtures
A mixture consists of 2 or more elements which are not chemically bonded together.
The chemical properties of a each substances in a mixture is unchanged.
A pure substance is a substance which only consists of one single element or compound and is not mixed with another substance.
A pure substance is a substances in its natural state.
A Pure substance melts/boils at a specific temperature and not over a range.
You can distinguish if a substance is pure on not depending on whether it ranges in temperature.
Methods of seperation.
Simple distillation
Used to separate a pure liquid from a mixture of liquids.
When the liquids have different boiling points , simple destination can be used,
You can separate ethanol from water using simple distillation.
Ethanol has a lower boiling point compared to water and so it will evaporate first. the gases is caught in a cooling jacket and it begins to condense. A separated Ethanol is separated from the water.
Sequence of events.
Heating => evaporation of mixture => cooling of gas => condensing of gas.
Fractional distillation
Oil is commonly separated within a fractionating column.
Fractioning distillation separates mixtures that have a range of boiling and melting points.
Method
Oil is heated in the fractoling columb and the oil evaporates and condesenes at the number of differnet temperature.
The many hydrocarbons are separated into fractions each of which contain molecules with similar number of carbon atoms.
The fractionating column works continuously , heated crude oil is then piped in at the bottom. the vaporized oil then rises up the column and the various fractions are constantly tapped off at the different levels where they condense.
Fractions can be processed to produced fuels and feed stock in the petrochemical industry.
Filtration
Crystallization
It is used to separate produce a precipitate from an insoluble salt.
Method
You would carry filtration out by adding a filter to the solution then leaving behind the precipitate on the filter paper.
Crystilsation is used to produce a soluble salt from the solution it is dissolved in.
Method
Allow the solution to cool.
The solid will come out of the solution and the crystals will start to grow.
Warm the solution in an open container allowing the solvent to evaporate.
Paper Chromatography
Paper chromatography is sued to separate mixtures to give information to help identify substance.
it involves two parts : the stationary and mobile faze.
The Rf value = distance moved by the substance / distance moved by the solvent.
Different compounds have different Rf values in different solvents. they can be used to help identify compounds.
A pure substance will produce one single spot whilst an impure substance will produce more than one spot.
Chemical changes
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Acids And Bases
Electroliyc process.
When ionic substances are melted or dissolved , the ions are free to move about the liquid solution. this is called an electrolyte.
Electrolisis.
Electrolysis is the process of breaking down substances with electrical energy. this involves passing a current though substances that are molten or a solution. This means that it can be broken down into elements.
During electrolysis , Positively charged ions (known as cations) travel to the negatively charged electrode (the cathode) and negatively charged ion (anions) travel to the positively Charged electrode.
The formations of electrolysis.
When you have an ionic solution which is not molten , the solution will contain the ions that make up the solution and the ions in water (H+ AND OH-)
Rules
Hydrogen is always produced at the cathode unless the ions of the Products are less reactive then hydrogen. if the metal is less reactive , then it is always produced.
Oxygen from the hydroxide will always be produced at the anode unless the ionic A halide is present. if a halide is present , then the halide is always produced.
The reactivity series.
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Silver
Hydrogen
Lead
Iron
Zink
Carbon
Aluminum
Magnisium
Calcium
Sodium
Potassium.
Ironic compounds are molten ad are very simple to predict
The positive ions go to the cathode
The negative ions go to the anode
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: Oxidation is the loss of electrons
Reduction is the gain of electrons
Occurs at the anode.:
Occurs at the cathode.
Explain the formation of products in the electrolysis pf cupper solution . using copper electrodes , and how electrolysis can be used to purify copper.
Set up
The anode is made from an inpure copper
Cathode is made from a pure copper
The solution is coppper sulphate.
Observations
Cupper ions from the anode to the cathode. as this happens , they will gain electrons and they will discharge as pure copper.
Impurities begin to sludge up at the bottom of the anode.
The cathode will increase in mass as it gains more pure copper , whilst the anode will lose its mass as the ions are lost.
Extracting metals and equilibria
Deducing the reactivity of some metals.
Most reactive
Fairly reactive
Least reactive
The most reactive metals will react with water.
The products of this are Hydroxides (An alkiline solution is formed.)
2K + 2H2O -> 2KOH + H
Fairly reactive metals react with acids.
Acid + metal -> salt + hydrogen
Almost all metals react with Oxygen, However , the only metal that does not react with oxygen is gold.
These metals don't react with anything.
Observations
Therefore , you are able to deduce how reactive some metals are by seeing if they react with water , acid and oxygen. For these experiments , if you can see bubbles forming , it means that hydrogen is produced.
Visual observations
The more reactive metal will gradually disappear as the less reactive metal coats the surface of the more reactive metal.
Redox reactions
The less reactive metals forms an atom to form as it negative ions are being displaced therefore gaining electrons and therefore being reduced
More of the reactive metals forms a positive cations as they displace less reactive metals losing one electron and therefore being oxidized. It will form an ion as it replaces the less reactive ion.
The reactivity series.
Metals can be arranged in their reactivity series.
Metals potassium, sodium, lithium, calcium, magnesium, zinc, iron and
copper
Processes of extraction
Non conventional
Phytoextraction
Bacterial extraction
Some compounds absorb metals through their compounds.
They concentrate the compounds into their leaves and shoots.
When the plants are burned , they produce ash which contains the metal compounds.
Some bacteria absorbs a metal compound.
Scrap iron can then be used to obtain metals from leachates.
They produce a solution called leachate which contains metal compounds.
Concentional.
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Carbon reduction
Mining
Electrolysis
It is very expensive due to the large amounts of energy needed to melt the compounds and to produce the electrical current needed to electrolyze the compound. it is used for metals more reactive then carbon.
Carbon reduction can only occur when the metals extracted are less reactive then carbon.
Most metals are found in the earth in the form of compounds. For this , they require chemical reactions to be separated since they have been reacted with other elements.
When metals react with other substances , metal ions begin to form.
The reactivity of a metal simply describes it tendency to form ions with the more reactive being the one that can easily make an ion.
Reduction and Oxidation
Oxidation is gain of oxygen and reduction is loss of oxygen.
Evaluate the advantages.
Recycling is important to achieve sustainable development. It requires less energy to melt down compounds and remold metal than it does to extract from the earth.
Mining ores is bad for the environment as it causes large quarries to be created.
Recycling allows waste to be reused , saving money and helping the environment.
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