Chemistry Module 2

All of Module 2. 

Chemistry Module 2

Structure and Bonding - 1.1 Chemical Bonding

Elements react to achieve a full outer shell. This is also why we have 2+ subsets etc. Magnesium which has a 2+ subset, has two extra electrons in it's outer shell and needs to emit them to have a stable outer shell. 

Covalent Bonding

Two non-metallic atoms come together. Atoms share pairs of electrons.

Ionic Bonding 

  • Metallic and Non-metallic react to produce ionic compounds
  • Metals lose electrons to become positive ions. 
  • Non-metals gain electrons to become negative ions.
  • Oppositely charged attract. 
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Chemistry Module 2

Structure and Bonding - 1.2 Ionic Bonding

Ionic Bonding holds oppositely chargeed ions in a strong giant Ionic Lattice.

Strong electrostatic forces of attraction act in all directions

The amount of each element depends on the amount in each outer shell. If they both need to lose/gain the smae amount then the amount in the lattice will be split 50:50. However if one needs two and the needs just one to have a full outer shell, then there will be twice as many of the element that requires one than the element that requires two so as to compensate. 

We can use Dot and cross diagrams to represent the atoms and ions involved. In these we only show the outermost electronic shells. 

Look at diagram p 41

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Chemistry Module 2

Structure and Bonding - 1.3 Formulae of Ionic Compounds

Due to an equal amount of positive and negative forces, Ionic Compounds are neutral.

This is pretty much telling you how to do stuff you've already figured out a method to do. (Your clever little naming the columns and rows method ;)) so yeah, you're set. 

Insert pretty picture to cheer you up. Flowers, Daisies, Unicorns, izzy Renfrew or any other friend if you're reading this don't panic!!!! You'll be great! and I know this in advance ;) 

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Chemistry Module 2

Structure and Bonding - 1.4 Covalent Bonding

The atoms of non-metals need to gain electrons to gain stable strucutres. So they share paired electrons. Since the shared pair strongly attracts the two atoms they pretty much join. 

Atoms in Group 7 need to gain 1 elecron so they only form 1 shared pair.

Atoms in Group 6 need to gain 2 eletrons so they form two shared pairs. 

etc. (it only goes to Group 4)

Covalent Bonds only join in individule (simple) molecules structures or Giant molecules. You'll do more on this at a later card, so don't worry if you're trying to form a picture in your mind now. The minute you se it you'll remember it anyway. 

We can draw Covalent bonds via the circular atom method or the line method both are picure on p42.

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Chemistry Module 2

Structure and Bonding - 1.5 Metals

toms in metals are all the same size so they form giant structures in which atoms are arranged in regular layers. 

Bonding

When metal atoms pack together the electrons in the highest level the outer electrons delocalise and can move freely between atoms. This produces a sea of delocalised electrons between the positively charged ions (in lattic formation). The opposite charges keep this structure together. 

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Chemistry Module 2

Strucutre and Properties - 2.1 Giant Ionic Structures

Ionic Structures are Giant Ionic Lattices held together by strong electrostatic forces of attraction. 

They are solids at room temperature so a lot of energy is needed to overcome the forces holding them together making them difficult to melt. Ionic solids have high melting and boiling points

Plot Twist

However when they are molten, the ions are free to move which means they can carry an electrical charge. 

Also since some Ionic Structures dissolve in water, the solutions can carry charge because they are now free to carry charge. 

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Chemistry Module 2

Structure and Properties - 2.2 Simple Molecules

Atoms in a molecule are held together by strong covalent bonds.. However these only act between the atoms within the molecule and so simple molecules have little attraction for each other. Substances made of simple molecules have relatively low melting and boiling points. They do not carry charge so do not conduct electricity because they have no overall charge. 

Intermolecular Forces

The forces keeping molecules together are weak intermolecular forces. These are easily overcome when melted or boiled. Those with the smallest molecules (H(2), Cl(2), CH(4)) have the weakest intermolecular forces and are gases at room temperature. Larger molecules have stronger attractions and so may be liquids at room temperature or solids at room temperature. 


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Chemistry Module 2

Structure and Properties  - 2.3 Giant Covalent Structures

 Atoms of some elements can form several covalent bonds. These atoms can join together in Giant Covalent Structures (sometimes called macromolecules). Every atom in the structure is joined to others by strong covalent bonds.It takes an enormous amount of energy to break them up. 

Diamond

An example of a giant lattice. Since it is made of Carbon, every atom joins to 4 others (the number of atoms carbon needs to have a stable structure). Silicon Dioxide (Silica) has a similar structure.

Graphite

This is bonded in layers. The atoms are bonded to three other carbon atoms to form a sheet of hexagons (Fullerenes). The sheets are held together by weak intermolecular forces, the final electron from Carbon is delocalised and they form a sea of delocalised electrons. This means Graphite can carry charge. Graphite can be written with due to the layers and weak forces. Fullerenes are also used in drug deliver yinto the body, lubricants, catalysts and reinforcing materials. 

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Chemistry Module 2

Structure and Properties - 2.4 Giant Metallic Structures

These are arranged in layers. If a force is applied to one of these layers, the strucutre can be moved into a new position without breaking apart (malleable). It can be bent or stretched into a new shape. 

This makes it useful for making wires, rods and sheet materials

Alloys are mixtures of metals (metals with other elements). THe different sizes distorts the layers in the metallic structure and make it more difficult for them to slide over each other, thus making them harder materials

Shape Memory Alloys- These can be bent into different shapes but upon being heated return to                                       the original shape. 

Due to the delocalised electrons in metals, they can carry charge. 

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Chemistry Module 2

Structure  and Properties - 2.5 The Properties of Polymers

 Properties depend on the monomer used to make it, and the conditions used to carry out the reaction. Polypropene softens at a higher temperature than polyethene and high density (HD) polyethene ae made using different catalysts and different reaction conditions. HD polyethene has a higher softening temperature and is stronger than LD polyethene. 

Thermosoftening Polymer

It is made up of individual polyer chains all tangled up together. When it is heated it becomes soft and hardens as it cools, this means it can be reheated and reshaped over and over again. e.g. polyethene

Thermosetting Polymer

They do not melt or soften at high temperatures. They set hard when first moulded because strong covalent bonds form cross-links between their polymer chains. The strong bonds hold them in position. 

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Chemistry Module 2

Structure and Properties - 2.6 Nanoscience

    When atoms are arranged into very small particles they behave differently to ordinary materials made up of the same atoms. A nanometre is one billionth of a metre (or 10 (-9)) and nanoparticles are a few nanometres in size. Their very small size give them very large surface areas and new properties that can make them very useful materials. 

  • Nanotechnology uses nanoparticles as highly selective sensors, very efficient catalysts, new coatings, new cosmetics and to give construciton materials special properties. 
  • If they are used more and more there is a greater risk of them finding their way into the air and our bodies. THis could have unpredictable consequences on our health and the environment. 
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Chemistry Module 2

How Much? - 3.1 The Mass of Atoms

Protons and Neutrons have the same mass so the relative mass of both of them individually is +1. Therefore the mass of an atom is the number of protons and neutrons combined. This is called the MAss Number

Electrons have relatively no mass and so we say they weigh nothing. 

Atoms of the same element all have the same Atomic Number. THe number of protons and electrons in an atom must always be the same but there can be different amounts of neutrons. Atoms of same element with different neutron amounts are called Isotopes. 

Number of Neutrons = Mass - Atomic

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Chemistry Module 2

How Much? - 3.2 Masses of Atoms and Moles 

Relative Atomic Masses - Since atoms are much too small to weigh we use these. They are                                               shown in the periodic table. The relative atomic mass of an element in                                         grams is called one Mole of atoms of an element. 

The relative atomic mass of an element is an average value that depends on the isotopes the element contains. However when rouded to a whole number it is often the same as the mass of the main isotope of the element. 

Relative Formula Mass

This is found by adding up the Relative Atomic Masses of the elements involved. The answer is one mole of that substance. Using moles is useful when we need to work out how much of a substance reacts or how much produc we will get. 

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Chemistry Module 2

How Much? - 3.3 Precentages and Formulae

We can calculate the percentage build up of any element in any compound by  dividing the element's mass number by the total mass number and timesing the result by 100%. 

Empirical Formula

This is the simplest ration of atoms or ions in a compound. It is the formula used for Ionic compounds but for covalent compounds it is not always the smae as the molecular formula. e.g. molecular formula of Ethane is C(2)H(6) but it's empirical formula is CH(3). We can calculate it by

  • Dividing the mass of each element in a 100g of the compound (using its Atomic mass) to give a ratio of atoms. 
  • Then convert this to the simplest whole ratio. 

If you're confused there are really good notes on Empirical formula in your exercise book. 

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Chemistry Module 2

How Much? - 3.4 Equations and Calculations

This is all reactive mass calculations and the notes in the book are ridiculously complicated so either write down notes from your book or just memorise them . 

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Chemistry Module 2

How Much? - 3.5 The Yield of a Chemical Reaction

Yield - How much you actually produce

Percentage Yield - The amount made with the maximum amount that coudl be actually made. 

Percentage Yield = amount of product collected      (x100)

                  maximum amount of poduct possible

For example - A student collected 2.3g of Magnesium Oxide from 2.0 g of Magnesium.

Theoretically - 2Mg + O(2) = 2MgO so 48 g of Mg should give 80g MgO and so 2.0g of Mg should give 2 x 80/48 = 3.33g MgO.

Percentage Yield = 2.3    x 100 = 69%

                            3.33

This happens because reactions can not go until completion, or other reactions may happen or some may be lost in transfer of vessels. High yield reactions produce little waste. 

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Chemistry Module 2

How Much? - 3.6 Reversible Reactions

f the producs of a chemical reaction can react to produce the reactants the reaction can go in both directions. This is called a reversible reaction. 

An example is 

Ammonium Chloride =(weird double arrow thingy) Ammonia + Hydrogen Chloride

When Ammonium Chloride decomposes it produces these two. When Ammonia and hydrogen chloride are cooled they reac to produce Ammonia Chloride.

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Chemistry Module 2

How Much? - 3.7 Analysing Substances

Food Additives - Substances that are added to foods to improve its qualities. They can be natural                           products or synthetic chemicals. 

Foods can be checked by chemical analysis to ensure only safe, permitted additives have been used. The methods used include paper chromatography and mass specrometry. 

Paper Chromatography can be used to analyse the artificial coloours in food. A spot of colour is put onto the paper and the solvent is allowed to move through the paper. THe colours move different distances depending on solubility. 

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Chemistry Module 2

How Much? - 3.8 Instrumental Analysis

Modern instrumental methods are very rapid, effective and sensitive using only a small sample. Computers process the data from the instrument to give meaningful results almost instantly. 

However one must be trained to hadle the equipment and it is often very expensive. 

Samples for analysis are often mixtures than need to be separated. These require Gas Chromatography linked to a Mass Spectrometer. 

In this the material is carried through a long coiled cloumn packed with particle sof solid. tHe different parts of the material travel through at different rates through the column and come out at different times. The amount of substance leaving the column is recorded against time and shows the compounds in the mixtures retention times. These retention times can be compared with the results for known substances to help identify the compounds in a mixture. 

The output can be linked directly to a mass spectrometer which gives further data that a computer can use quickly to identify the individual components. 

A MAss specrometer can give the relative mass of a compound. For an individual compound the peak with the larges mass corresponds to an ion with just one electron removed. THis peak is called the molecular ion peak and is furthest to the right on a mass spectrum. 

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Chemistry Module 2

Rates and Energy - 4.1 How Fast?

The rate of a reaction can be found by measuring how much of a reacant is used/how much of a product has formed and the time taken. 

Rate of Reaction = Amount of Reactant Used         OR    amount of product formed

                                         Time                                                Time

The rate of a reaction can be foudnat any given time from the gradient or slope of the line on a graph. THe steeper the gradient the faster the reaction was at the time. 

A graph can be produced by measuring the mass of gas released or the volume of gas produced at intervals of time. Other possible ways include measuring changes in the colur, concentration or pH of a reaction mixture over time. 

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Chemistry Module 2

Rates and Energy - 4.2 Collision Theory and Surface area

Collision Theory - this states reactions can only happen if particles collide. however they must also collide with enough energy to change into new substances. The minimum energy they need to react is called the activation energy.

Factors that increase the chance of collisions or the energy of particles will increase the rate of reaction.

  • Temperature. Increases the energy. More frequent succesfull collisions. Increase rate
  • Concentration. Increases number of succesful collisions. Increase rate
  • Pressure of Gases. Increase number of sucessful collisions. Increase rate
  • Surface area. Increase number of succesful collisions. Increase rate
  • Using a catalyst. Increase energy. Increase number of succesful collisions. Increase rate. 

Breaking larger pieces of solid into smaller pieces increases the surface area, this means there are more collisions at the same time. So a powder reacts faster than large lumps of a substance. 


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Chemistry Module 2

Rates and Energy - 4.3 The Effect of Temperature

Increasing the temperature of a substnace, increases the amount of energy the particles have. This means they speed up and there are more frequent succesful collisions. This increases the rate of reaction. They collide more frequently with more energy. 

A small change in tempertaure makes a big difference. 

Increase of 10 degrees C can halve the time taken for the reaction to complete.

Likeise a decrease of 10 degrees C can double the time taken for the reaction to complete. 

Then theres a lovely picture which basically reiterates everything I just said. 

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Chemistry Module 2

Rates and Energy - 4.4 The Effect of Concentration or Pressure

The particles in a solution are moving around randomly. If you increase the concentration there are more particles dissolved in the same volume. This means collisions are more frequent and so rate of reaction speeds up. 

Increasing concentration therefore increases the rate of reaction in a solution.

Lovely picture inserted on page

Likewise the same happens if we increase the pressure in a gas. There are more particles in the sma e amount of space so more frequent collisions occur. 

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Chemistry Module 2

Rates and Energy - 4.5 The Effect of Catalysts

Catalysts change the rates of reactions. They are used to speed up reactions. 

They work by lowering the activation energy of the reaction so that more of the collisions result in a reaction. 

Although the catalyst changes the rate of the reactioin, it is not used up and does not react itself. It is left so it can be reused.

Catalysts that are solids are used in forms that have large surfaace areas to make them as effective as possible. 

Catalysts often work with only one type of reaction and so different reactions need different catalysts. 

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Chemistry Module 2

Rates and Energy - 4.6 Catalysts in Action

    Whilst catalysts are expensive they are economical because they don't get used up. They are used in many industrial processes because they can reduce the energy and the time needed for reactions. This helps to reduce costs and reduce impacs on the environment. If fossil fuesl are burned to provide energy for industrial reactions using catalysts will help to conserve resources and reduce pollution. 

Many catalysts in industry involve transition metals and compounds. Some of these are toxic and harmful if they get in to the environment. 

Nanoparticles offer possibilities for developing, new , highly efficient catalysts that work at ordinary temperatures.  If they replace traditional catalysts, they will reduce energycosts even further. 



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Chemistry Module 2

Rates in Energy - 4.7 Exothermic and Endothermic Reactions

Exothermic

Reactions that transfer energy (particularly heat) to the surroundings. Temperature increases. Examples of exothermic reactions include

  • Combustion (burning fuels)
  • Oxidation reacns (respiration)
  • Neutralisation reactions involving Acids and bases 

Endothermic

These reactions take energy in from the surroundings. Some cause a decrease in temperature, others require a supply of energy. When some solid compounds are mixed with water the temp. decreases beacuse endothermic chsnges happen as they dissolve. 

Thermal decomposition reactiosn need to be heated continuously to keep the reaction going. IT is endothermic. 

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Chemistry Module 2

Rates and Energy - 4.8 Energy and Reversible Reactions 

In reversible reactions the energy involved is equal in both the forward and reverse reactions. However they are opposite enrgy transfers. If it is exothermic in the forward reaction it must be endothermic in the reverse reaction. 

Example

When blue copper sulphate crystals are heated the reaction is endothermic.

Blue Crystals (Hydrated Copper Sulphate) = White Powder (Anhydrous Copper sulphate) + Water

CuSO₄.5H₂O = CuSO₄ + 5H₂O

When water is added to anhydrous copper sulphate the reaction is exothermic. 

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Chemistry Module 2

Rates and Energy - 4.9 Using Energy Transfers from Reactions

Exothermic

  • Hand warmers and self-heated cans use exothermic reactions. In some hand warmers and cans the reactants are used up so they cannot be used again. Other hand warmers use a reversible reaction so they can recrystillised again and again.

Endothermic

  • Come chemical ice packs. These contain ammonium nitrate and water that are kept separate. When mxed to gether the ammonium nitrate dissolves and takes energy in from  the surroundings. The cold pack can be used to keep drinks cool or on any injuries. The reaction is a reversible one but not in the pack, so this can't be reused. 
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Chemistry Module 2

Salts and Elecrolysis - 5.1 Acids and Alkalis

Acids

  • Substances that produce H(+) ions (aq) when added to water. This forms an aqueous solution. 
  • Hydrogen ions make solutions acidic and these have a pH of less than 7. 

Bases and Alkalis

  • Bases react with acids and neutralise them.
  • Alkalis are bases that dissolve in water and make alkaline solutions. These have pH of more than 7. 
  • Alkalis produce OH(-) (aq) in the solution.
  • Universal Indicator = Blues/Purples
  • Phenolphthalein - Pink  
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Chemistry Module 2

Salts and Electrolysis - 5.2 Making Salts From Metals or Bases

Acids will react with metals that are above Hydrogen in the reactivity series, but reactions of acids with very reactive metals are too violent to be done safely. 

When metals react with acids they produce a Metal Salt and Hydrogen Gas. 

Acid + Metal = Metal Salt + Hydorgen 

Metal oxides and metal hydroxides are bases. When an acid reacts with a base, a neutralisation reaction occurs. Metal salt and water are produced

Acid + Base = Metal Salt + Water

  • These reactions are used to make salts
  • A metal or a base that is insoluble in water is added a little at a time to the acid until all of the acid has reacted. The mixture is then filtered to remove the excess solid reactant leaving a solution of the salt. The solid salt is made when water is evaporated from the solution forming crystals. 
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Chemistry Module 2

Salts and Electrolysis - 5.3 Making Salts from Solutions

Soluble Salts are produced from reacting an acid with an alkali.

Acid + Alkali = Salt + Water

We can represent the neutralisation reaction between any acid and any alkali by this equation.

H(+) (aq) + OH(-) (aq) =H(2)O (l)

Since there is no visible change when we react an acid with an alkali we must use an indicator or a pH meter to show when the reaction is complete. The solid salt can be obtained from the solution via crystallisation. Ammonium Salts are used as fertilisers

We can make soluble salts by mixing solutions of soluble salts that ocntain the ions needed. For example, we can make Lead Iodide by mixing solutions of Lead Nitrate and Potassium Iodide. The Lead Iodide forms a precipitate that can be filtered from the solution, washed with distilled water and dried. 

Some pollutants such as metal ions can be removed from water by precipitation. The water is treated by adding substances that react with the pollutant metal ions dissolved in the water to form insoluble salts. 


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Chemistry Module 2

Salts and Electrolysis - 5.4 Electrolysis

The process that uses electricity to break down ionic compounds into elements. When electricity is passed through a molten ionic compound or a solution containing ions, electrolysis takes place. The substance that is broken down is called the electrolyte.

  • The circuit has two electrodes (one positive, one negative) that make contact with the electrolyte. The electrodes are made with an inert substance that doens't react with the electrolyte.
  • The ions in the electrolyte move to the electrodes where they are discharged to produce elements.
  • Positively charged ions move to the negative electrode where they form metals or hydrogen depending on the electrolyte
  • Negatively charged ions are attracted to the positive electrode where they lose their charge to form non-metallic elements
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Chemistry Module 2

Salts and Electrolysis - 5.4 Electrolysis

The process that uses electricity to break down ionic compounds into elements. When electricity is passed through a molten ionic compound or a solution containing ions, electrolysis takes place. The substance that is broken down is called the electrolyte.

  • The circuit has two electrodes (one positive, one negative) that make contact with the electrolyte. The electrodes are made with an inert substance that doens't react with the electrolyte.
  • The ions in the electrolyte move to the electrodes where they are discharged to produce elements.
  • Positively charged ions move to the negative electrode where they form metals or hydrogen depending on the electrolyte
  • Negatively charged ions are attracted to the positive electrode where they lose their charge to form non-metallic elements
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Chemistry Module 2

Salts and Electrolysis - 5.5 Changes at the Electrodes

Negative Electrode

  • Positively charged ion
  • Gain electrons to become neutral atoms
  • Gaining is called reduction. RIG (Reduction is gain). THey have been reduced
  • Ions with a single positive charge gain one electron. 2 positive charge gain two electrons
  • Water contains H(+) and OH(-) ions. Hydrogen can be formed here if the metal is more reactive than it. However it must be a solution. 

Positive Electrode

  • Negatively charged ion
  • Loses electrons to become neutral atoms.
  • Losing is called Oxidation. OIL (Oxidising is loss). They have been oxidised. 
  • Some non-metals combine to form molecules. Bromine forms Br(2)
  • Oxygen is produced if solution is aqueous. 

MAKE SURE YOU CAN DO HALF EQUATIONS. P64

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Chemistry Module 2

Salts and Electrolysis - 5.6 The Extraction of Aluminium 

ince Aluminum is more reactive than Carbon it must be extracted from its Ore via Electrolysis. It's ore contains aluminium oxide which must be purified and then melted so that it can be electrolysed. Aluminium Oxide melts at over 2000 degrees C which would need a lot of energy so it is mixed with another compound cryolite so that the mixture melts at about 850 degrees C. The mixture can be electrolysed now and it produces aluminium and oxygen. 

Aluminium Oxide = Aluminium + Oxygen

  • Cryolite remains in the cell and fresh aliuminium oxide is added as aluminium and oxygen are produced. 
  • At the negative electrode aluminium ions are reduced to aluminium atoms by gaining elecrons. The molten aluminium metal is collected from the bottom of the cell.
  • At the positive electrode oxide ions are oxidised to from oxygen atoms by losing electrons and the oxygen atoms form oxygen molecules. 

Negative Electrode - Al(3+) (l) + 3e(-) = Al(l)

Positive Electrode - 2O(2-) (l) = 2O(2) (g) + 4e(-)

Since the positive electrodes are made of Carbon, the oxygen reacts with the carbon due to high temperatures producing Carbon dioxide. This means the electrode burns away over time and has to be replaced. 

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Chemistry Module 2

Salts and Electrolysis - 5.7 Electrolysis of Brine

Brine is a solution of Socium Chloride in water. Solution contains

  • Sodium Ions - Na(+) (aq)
  • Chloride Ions - Cl(-) (aq)
  • Hydrogen Ions - H(+) (aq)
  • Hydroxide Ions - OH (-) (aq) 

When electrolised Hydrogen forms at the negative electrode and chlorine is produced at the positive electrode. the solution left is a solution of Sodium ions and hydroxide ions (NaOH (aq)) 

Positive - 2Cl(-) = Cl(2) + 2e(-)

Negative - 2H(+) + 2e(-) = H(2)

Sodium hydroxide is a strong alkali and has many uses including soap making, paper making, making bleach, neutralising acids and controlling pH. 

Chlorine is used to kill bacteria in drinking water and in swimming pools and to make bleach, disinfectants and plastics. Hydrogen is used to make margarine and hydrochloric acid.

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