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What happens when two or more elements react together?
Compounds are formed. The atoms of the elements join together by sharing or transferring electrons to achieve stable electronic structures. Atoms of noble gases have stable electronic structures and are unreactive.
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What is covalent bonding?
When atoms of non-metallic elements join together by sharing electrons. Substances with covalent bonding are called molecules. Atoms of group 7 are missing 1 electron + so form 1 covalent bond, group 6 form 2 bonds etc.
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Describe the bonding in covalent bonding?
Atoms of non-metals need to gain electrons to achieve stable electronic structures, they can do this by sharing with other atoms. Each shared pair of electrons strongly attracts the two atoms. Substances held together by cov bond are called molecules
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What are ionic compounds?
Metals + non-metals. Metal atoms lose electrons to form pos ions. Non-metals gain electrons to form neg ions. The oppositely charged ions attract each other (ionic bonding). The ions have the stable electronic structure of noble gases = neutral.
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Describe ionic bonding
Oppositely charged ions are held together in giant, regular structures (all ions pack together neatly). Strong electrostatic forces of attraction act in all directions and each ion is held in place by the surrounding oppositely charged ions.
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What are macromolecules?
A covalent bond only acts between the 2 atoms it bonds to each other & so, many covalently bonded substances consist of small molecules. Some atoms that can form several bonds (i.e. Carbon) can join together in giant covalent structures (macromolecul
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How are the atoms arranged in metals?
Atoms all the same size, form giant structures in which layers of atoms are arranged in regular patterns.
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Describe metallic bonding?
The electrons in the highest energy level (outer electrons) delocalise + can move freely between atoms producing a lattice of pos ions in a ‘sea’ of moving electrons. The delocalised electrons strongly attract the pos ions + hold the structure togeth
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Why do ionic solids/compounds have high melting & boiling points?
They have a giant structures in which many strong electrostatic forces hold the ions together. This means that they are solids at room temperature. A lot of energy is needed to overcome the ionic bonds to melt the solids.
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Why can ionic substances conduct electricity when molten or when dissolved in water?
As the ions are free to move allowing them to carry electrical charge, so the liquids conduct electricity. Some ionic solids dissolve in water because water molecules split up lattice + ions are free to move in the solutions and so can conduct electr
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What are the properties of simple molecules?
Strong covalent bonds between atoms within molecule but weak intermolecular forces between molecules (overcome when melted/boiled) = low melting/boiling points. Molecules have no overall charge = can’t carry electrical charge.
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Why do substances with giant covalent structures have high melting/boiling points?
As every atom in the structure is joined to another by strong covalent bonds. It takes an enormous amount of energy to break down the lattice.
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Describe the structure in diamonds?
Regular 3-dimensional giant structure. Every carbon atom is covalently bonded to 4 other carbon atoms making diamond hard and transparent. Silicon dioxide (silica) has a similar structure.
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Describe the structure of graphite?
C atoms are covalently bonded to 3 other C atoms in giant flat 2-D layers. As there are no covalent bonds between the layers, they slide over each other, making graphite slippery + grey. 1 electron from each atom is delocalised (graphite can conduct.
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Describe the structure of fullerenes?
Large molecules formed from hexagonal rings of carbon atoms which join together to form cage-like shapes with different number of carbon atoms some of which = nano-sized. Uses = drug delivery into body, lubricants, catalysts, + reinforcing materials.
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Why are alloys harder than pure metal and how can they can be used?
Metals atoms arranged in layers making them soft --> malleable and ductile. Alloys=mixtures of metals + the different sized atoms distort the layers + make it more difficult for the layers to slide over each other. ieShape memory alloys=dental braces
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Why are metals good conductors of electricity?
As they have delocalised electrons which move throughout the giant metallic lattice and can transfer energy quickly.
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Why do LD (Low Density) and HD poly(ethene) have different properties?
Made using different reaction conditions; different structures + differently shaped molecules. HD polyethene has a higher softening temperature and is stronger than LD polyethene.
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Describe the structure and main properties of thermosoftening polymers.
Thermosoftening polymers consist of tangled polymer chains with weak intermolecular forces which are easily overcome heated so that they melt and harden when they cool. This means that it can be heated to mould and remould into a shape.
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Describe the structure and main properties of thermosetting polymers.
Thermosetting polymers do not melt/soften when heated and set hard when first moulded because strong covalent bonds form cross-links between their polymer chains holding them in position.
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Explain why, in terms of structure, carbon dioxide is a gas, even at low temperatures.
Carbon has weak intermolecular forces and is made of small molecule and therefore has a low melting and boiling point. Therefore Carbon dioxide is a gas a room temperature and low temperatures.
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What is a nanoparticle?
Particle a few nanometres in size made of a few hundred atoms with large surface areas & small sizes = new properties as they behave differently to normal materials..
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What are the advantages of using nanotechnology?
Nanoparticles can be used in nanotechnology as highly selective sensors, very efficient catalysts, new coatings, new cosmetics i.e. sun screens, deodorants + for constructions materials.
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What are the advantages of using nanotechnology?
Increased use of nanoparticles increases risk of them finding their way into the air and our bodies = unpredictable consequences for our health + environment. More research needed.
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What is the mass number?
Protons + neutrons. As the mass of an electron is miniscule compared to the mass of protons + neutrons.
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What are isotopes?
Atoms of an element with different numbers of neutrons, They have the same proton number but different mass numbers
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What is the mass of one mole of a sodium atoms?
23g- the relative atomic mass of an element in grams is called one mole of atoms of the element.
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Why is the relative mass of chlorine not a whole number?
It has two main isotopes and the relative mass is an average value of the 2.
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How do you work out the percentage of an element in a compound e.g % of oxygen in H2O?
Total relative mass of element in compound/Relative mass of compound * 100. E.g Answer= Total relative mass of 0 in h20/Relative mass of h20 * 100 = ((16/18)*100) =89%.
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Calculate the Mr of calcium chloride
CaCl2 Ar of Ca = 40, Ar of Cl =35.5 so Mr = 40 + (35 x 2) = 111
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What is the formula for calculating the amount of moles in a substance?
Moles = Mass/Mr
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How do you calculate the mass of chemicals involved in reactions?
1) Write a balanced formula, 2) use the equation Moles = Mass/Mr to work out the amount of moles in the ‘known’ compound, 3) Work out the moles of the known compound, 4) Work out the unknown mass using the same formula.
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What are the steps involving finding the empirical formula of a compund?
1) List the atoms in the compound. 2) list the mass of each atom. 3) list the realative formula mass of each atom .4) work out the moles using the formula (don’t round your answers). 5) divide each by the smallest fom 4). 6) Round if within 0.1.
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What is the equation for percentage yield?
Percentage yield= actual yield/theroretical yield * 100
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What is Ar?
Relative atomic masses are used as atoms are too small to weigh – Ar of element in grams = mole. 3The Ar of an element is often the same as the mass number of the main isotope of the element.
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What is the Mr of a substance?
Relative formula mass is found by adding up the relative atomic masses of the atoms in its formula. Ar of element ÷ Mr of the compound × 100
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What is empirical formula?
The simplest ratio of the atoms/ions in a compound – formula used for ionic compounds but isn’t always the same as molecular formula for covalent compounds
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How can we calculate the empirical formula of a compound from its percentage compositions?
Mass of each element in 100g ÷ Ar then convert this to the simplest whole number ratio.
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Why is it not usually possible to get 100% yield from a chemical reaction?
Reactions may not go to completion, other reactions may happen, some product may be lost when separated/collected
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Why should chemical manufacturers use reactions with high yields?
To help conserve resources, reduce waste and/or pollution
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What methods can be used to analyse the colours in food and why are they used?
Paper chromatography and mass spectrometry are used to ensure only safe, permitted additives are used.
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How is paper chromatography used and why?
To analyse artificial colours in food. A spot of colour is put onto paper and a solvent is allowed to move through the paper. The colours move different distances depending on their solubility.
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What can gas chromatography linked to mass spectrometry do?
Analyse mixtures that need to be separated so that the compound can be identified.
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How is gas chromatography carried out?
The mixture is carried by a gas through a long column packed with particles of a solid and individual compounds travel though the column at different speeds and so come out different times.
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What is recorded in GC-MS analysis?
The amount of substance leaving the column at different times is recorded against time and shows the number of compounds in the mixture and their retention times.
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What can the retention times of output from the gas chromatography column be compared with?
The results for known compounds to help identify the compounds in the mixture and be linked to a mass spectrometer (GC-MS) to give the relative molecular mass of a compound.
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How is the relative molecular shown in a mass spectrum?
From the molecular ion peak or the peak with the largest mass (furthest to the right in the spectrum)
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What is the effect of adding a mass spectrometer in gas chromatography?
It would identifiy the suubstance for you instead of you having to compare the substance rentention time to known substances.
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What an you work out from a mass spectrum?
You can work out the molecular mass by looking at the molecular ion peak which is for an indivaul compund the peak with the largest mass.
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What is the benefit of using a mass spectrometer?
It can identify chemical quickly, accurately and it can detect very small quanitites (sensitive) but it usually very expensive and requires training to use.
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What does the number of peaks on a gas chromatograph show
It shows the number of compunds present.
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How do you find the rate of reaction?
By measuring how much of a reactant is used or how much of a product is formed + time taken or how much time taken for a certain amount of reactant to be used or product to be formed (gas given off or amount of solid to appear in a solution).
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How can you use a graph of amount of product against time to tell us the rate of the reaction at a given time?
The steeper the GRADIENT the faster the reaction at that time. A graph can be produced by measuring the overall gas released or gas produced at intervals of time. Also by measuring changes in colour, concentration or pH of a reaction mixture over tim
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What are the two different equations for rate of reaction?
Amount of reactant used ÷ time. Amount of product formed ÷ time
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What does the collision theory state?
That reactions can only happen if particles collide with enough energy; activation energy – minimum energy to react.
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What can increase the chance of collisions/energy of particles to increase the rate of reaction?
Increasing: Temperature , concentration of solutions, pressure of gases, surface area of solids (powder) + using catalyst.
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Why do powders react faster than large pieces of solid?
As new surfaces are exposed and so increases the S.A. increasing the frequency of collisions. The finer the powder, the faster the reaction.
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How does increasing the temperature increase the rate of reaction?
It increases the speed of the particles in a reaction so that they collide more often with more energy. At ordinary temps a rise of 10oC will roughly double the rate of reaction + decrease will roughly half the rate of reaction-->why we freeze/refrig
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How can increasing the concentration or pressure increase the rate of reaction?
As increasing the concentration of reactants in solutions or pressure of reacting gases increases the particles frequency of collisions between particles as there are more particle in the same volume.
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How do catalysts speed up the rate of a chemical reaction (most do)?
By lowering the activation energy of the reaction do that more of the collisions result in a reaction, but different reactions often need different catalysts and are used in solid forms with large SA for maximum efficacy + can be used again.
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What are the advantages of using catalysts in industrial processes?
Reusable, don’t often need to replaced. Can reduce the energy and time needed for reactions helping reduce costs + impact on environment. May help conserve resources + reduce pollution if fossil fuels are burned to provide energy for the industrial r
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What is the disadvantage of using many of the catalysts used in industry?
They often involve transition metals and their compounds, some of which are toxic and may cause harm if released into the environment.
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Give examples of how finding new and better catalysts is a major area of research for the chemical industry?
Nanoparticles (larger S.A.) + enzymes (biological catalysts). If they replace traditional ctalysts they can further reduce energy costs.
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What are exothermic reactions?
Reactions that transfer energy to the surroundings, often heating up the surroundings and so increasing in temperature. Combustion (i.e. burning fuels), oxidation reactions (respiration) + neutralisation reactions (involving acids + bases)-Handwarmer
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What are endothermic reactions?
Reactions that take energy from surroundings. Some cause decrease in temp + others require a supply of energy. Thermal decomposition reactions need to be heated continuously – happen as the solid compounds dissolve in water- i.e.chemical icepacks
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What do reversible reactions involve?
The forward and reverse reactions involve equal + opposite energy transfers i.e. a reversible reaction that’s exothermic in one direction must be endothermic in the other direction. Waters added to androhynous copper sulphate = exothermic.
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How are exothermic reactions used in hand-warmers and self-heating cans?
If they use reactions such as the oxidation of iron or the reaction of CaO with water they are non-reusable. Other hand-warmers use reversible reactions i.e. crystallisation of a salt. Once used a pack can be heated in boiling water to re-dissolve th
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How can endothermic reactions be used to cool things (i.e. sports injuries + drinks)?
In a cold pack that be used on sports injuries. Some contain water and ammonium nitrate which are kept separated, when mixed the ammonium nitrate dissolves + takes in energy from surroundings. Reaction = reversible outside pack –non-reusable.
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What are acids and alkalis?
Substances that produce H+ ions when they are added to water with pH values of less than 7. Alkalis are bases that dissolve in water to = alkaline solutions. Produce hydroxide ions OH- (aq) in solution with pH values greater than 7.
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What are aqueous solutions, bases and indicators?
Aqueous solutions: substance dissolved in water. Bases: react with acids + neutralise them. Indicators have different colours in acidic + alkaline solutions – Universal indicators.
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What metals will acids react with?
Those above hydrogen in the reactivity series but when very reactive metals (i.e. Na, K etc.) are involved, the reactions are too violent to be done safely. When metals react with acids they produce a salt + hydrogen gas H2SO4 + Zn -> ZnSO4 + H2.
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What happens when metals react with bases?
Metal oxides/hydroxides = bases. Acid + base -> neutralisation takes place-> salt + water produced. (2HCL + MgO --> MgCl2 + H2O). Insoluble metal/base added a little at a time until all acid is reacted, mixture filtered leaving salt solution. Sulfat
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How can we make a soluble salt?
By reacting acid and an alkali. (i.e. HCl(aq) + NaOH(aq)--> NaCl(aq) + H2O(l)). Neutralisation reaction: H+(aq) + OH-(aq) --> H2O(l)) No visible change when acids react with akalis --> need to use pH meter/indicator. Obtain salt by crystallisation.
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How can we make insoluble salts?
By mixing solutions of soluble salts that contain ions needed i.e. we can make lead iodide by mixing solutions of lead nitrate + potassium iodide - forms a precipitate that can be filtered from the solution, washed with distilled water + dried.
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How can some pollutants i.e metals ions be removed from water?
By precipitation- water treated by adding substance that react with the pollutant metal ions dissolved in the water to dorm insoluble salts
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What is electrolysis?
Process that uses electricity to break down ionic compounds into elements -when electricity is passed through a molten ionic compound/solution containing ions. Substance broken down called electrolyte.
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What is reduction?
Gaining electrons (i.e. when positive ions reach neg electrode they gain to become neutral atoms). Ions with 1+ charge gain 1 electron, 2+ charge gain 2 electrons.
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What is oxidation?
Losing electrons (i.e. at positive electrode, neg ions lose electrons to become neutral atoms). Some non-metal atoms combine to for molecules i.e. Br.
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How can we represent the changes at electrodes by half equations i.e. lead bromide?
At neg electrode: Pb 2+ + 2e- --> Pb. At pos electrode 2Br- --> Br2 + 2e-.
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Water contains H and OH ions. What happens when solutions of ions in water are electrolysed?
H produced at neg electrode if other pos ions in the solution are those of a metal more reactive than H. O2 usually produced from aqueous solutions at pos electrode, but if solution contains high concentration of halide ion then a halogen will be pro
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Why must aluminium be extracted from its ore by electrolysis?
More reactive than carbon. Ore contains Al oxide-must be purified, then melted to be electrolysed. Al2O3 melts at over 2000oC – requires a lot of energy. Mix with ionic compound (cryolite)-->melts at 850oC. Electrolysed at lower temp, produces Al+O2.
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What is the overall reaction in the electrolysis cell (extraction of aluminium)?
Aluminium Oxide --> Aluminium + Oxygen. 2Al2O3(l) --> 4Al(l) + 3O2(g). The cryolite remains in the cell + fresh aluminium oxide is added as aluminium and oxygen are produced.
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Why do the positive electrodes used in the cell (for the extraction of aluminium) need to be replaced regularly?
As they’re made of carbon. At high temperatures of the cell the O2 reacts with the Carbon electrodes to produce CO2. The carbon electrodes gradually burn away.
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What happens at the electrodes during electrolysis of aluminium oxide (and cryolite)?
At neg electrode, Al ions are reduced to Al atoms by gaining electrons. The molten aluminium metal is collected from the bottom of the cell. At pos electrode, oxide ions are oxidised to O atoms by losing electrons + the O atoms form O2 molecules.
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What are the half equations for electrolysis (extraction aluminium)?
At neg electrode: Al3+¬(l) + 3e- --> Al(l). At pos electrode: 2O2-(l) --> 2O2(g) + 4e-
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What is Brine?
A solution of sodium chloride in water. The solution contains sodium ions Na+(aq), Chloride ions Cl-(aq), hydrogen ions H+(aq) and hydroxide ions, OH-(aq).
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What is produced when brine is electrolysed?
Hydrogen is produced at the neg electrode from the hydrogen ions (2H+ + 2e- --> H2). Chlorine is produced at the pos electrode from the Chloride ions (2Cl--->Cl2 + 2e-) – leaving a solution of sodium ions + hydroxide ions, NaOH(aq).
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Why is the electrolysis of brine an important industrial process?
Sodium hydroxide = strong alkali (making soap, paper, bleach, neutralising acids + controlling pH). Cl2 used to kill bacteria in drinking water + swimming pools + to make bleach, disinfectants+plastics. H2 used to make margarine + HCl.
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Why is the electrolysis of brine an important industrial process?
Sodium hydroxide = strong alkali (making soap, paper, bleach, neutralising acids + controlling pH). Cl2 used to kill bacteria in drinking water + swimming pools + to make bleach, disinfectants+plastics. H2 used to make margarine + HCl.
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What is electroplating and what are the half equations for nickel electroplating?
Electroplating uses electrolysis to put a thin coating of metal onto an object, Gold, silver + chromium plating are often used. At positive nickel electrode: Ni(s)-->Ni2+(aq) + 2e-. At negative nickel electrode to be plated: Ni2+(aq) + 2e--->Ni(s).
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Name 4 reasons why electroplating is used?
To: make the object look more attractive, protect the metal object from corroding, increase the hardness of a surface + reduce costs by using a thin layer of metal instead of the pure metal.
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Card 2

Front

What is covalent bonding?

Back

When atoms of non-metallic elements join together by sharing electrons. Substances with covalent bonding are called molecules. Atoms of group 7 are missing 1 electron + so form 1 covalent bond, group 6 form 2 bonds etc.

Card 3

Front

Describe the bonding in covalent bonding?

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Preview of the front of card 3

Card 4

Front

What are ionic compounds?

Back

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Card 5

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Describe ionic bonding

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