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Flashcards by lauramarypowell, updated more than 1 year ago
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Created by lauramarypowell
almost 9 years ago
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| Question | Answer |
| What are thermosoftening polymers? | 1) Thermosoftening polymers consist of individual polymer chains that are tangled together. The forces between the chains are easily overcome as they are easy to melt e.g. plastic, when they cool the polymer hardens into a new shape, you can melt these plastics and remould them as many times as you like. 2) There are weak intermolecular forces between all of the polymer chains in a thermosoftening polymer so the individual chains are able to slide over each other. |
| What are thermosetting polymers? | 1) Thermosetting polymers consist of polymer chains that are joined together by cross-links between them which hold the chains together in a solid structure. Thermosetting polymers have strong intermolecular forces. 2) the polymer doesn't soften when it's heated. Thermosetting polymers are tough, they're strong, hard and rigid. |
| How does the way a polymer is made affect its properties? | 1) The starting materials and reaction conditions will both affect the properties of a polymer. 2) Two types of polyethene can be made using different conditions: - Low density (LD) polyethene is made by heating ethane to about 200 degrees centigrade under high pressure. It's flexible and is used for bags and bottles. - High density (HD) polyethene is made at a lower temperature and pressure (with a catalyst). It's more rigid and is used for water tanks and drainpipes. |
| How does a reversible reaction mean that the yield is less than 100%? | 1) The reaction is reversible. A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants. This means that the reactants will never be completely converted to products because the reaction goes both ways. Some of the products are always reacting together to form the original reactants this will mean a lower yield. |
| What are two other reasons for the yield always being less than 100%? | 1) When you filter a liquid to remove solid particles you always lose a bit of liquid or a bit of solid. So some of the product may be lost when it's separated. 2) Things don't always go exactly as planned sometimes there can be unexpected reactions happening which use up the reactants this means there's not as much reactant to make the product you want. |
| Why is thinking about the percentage yield important? | Thinking about percentage yield is important for sustainable development. Sustainable development is about making sure we don't use resources faster than they can be replaced - there needs to be enough or future generations too. So for example using as little energy as possible to create the highest product yield possible means the resources are saved. A low yield means wasted chemicals (not very sustainable). |
| How can artificial colours be separated using paper chromatography? Use this example a food colouring might contain one dye or a mixture of dyes how can you tell? | 1) Extract the colour from a food sample by placing it in a small cup with a few drops of solvent (can be water, ethanol, salt water etc.) 2) Put spots of the coloured solution on a pencil baseline on filter paper. (don't use pen because it might dissolve in the solvent and confuse everything.) 3) Roll up the sheet and put it in a beaker with some solvent but keep the base line above the level of the solvent. 4) The solvent seeps up the paper taking the dyes with it. Different dyes form spots in different places. 5) Watch out though - a chromatogram with four spots means at least four dyes, not exactly four dyes there could be five with two of them making a spot in the same place. It can't be three dyes though because one dye can't split into two spots. |
| What are the advantages of using a machine to analyse unknown substances? | 1) Very sensitive - can detect even the tiniest amounts of substances. 2) Very fast and tests can be automated. 3) Very accurate. |
| How does gas chromatography do? | Gas chromatography can separate out a mixture of compounds and help you identify the substance present. |
| How does gas chromatography work? | 1) A gas is used to carry substances through a column packed with a solid material. 2) The substances travel through the tube at different speeds so they're separated. 3) The time they take to reach the detector is called the retention time. It can be used to help identify the substances. 4) The recorder draws a gas chromatograph. The number of peaks shows the number of different compounds in the sample. 5) The position of the peaks shows the retention time of each substance. 6) The gas chromatography column can also be linked to a mass spectrometer. This process is known as GC-MS and can identify the substances leaving the column very accurately. 7) You can work out the relative molecular mass of the substances from the graph it draws. You just read off from the molecular ion peak. |
| Name three different reactions with three different rates. | 1) One of the slowest is the rusting of iron. 2) A moderate speed reaction is a metal (like magnesium) reacting with acid to produce a gentle stream of bubbles. 3) A really fast reaction is an explosion where it's all over in a fraction of a second. |
| What four things does the rate of a reaction depend on? | 1) Temperature. 2) Concentration - (or pressure for gases). 3) Catalyst. 4) Surface area of solids - (or size of solid pieces). |
| How can the rate of reaction be worked out? | The rate of reaction can be observed either by measuring how quickly the reactants are used up or how quickly the products are formed. It's usually a lots easier to measure products forming. The rate of reaction can be calculated using the following formula: Rate of reaction = Amount of reactant used or amount of product formed divided by time. |
| There are other ways that the rate of reaction can be measured tell me about precipitation. | 1) This is when the product of the reaction is a precipitate which clouds the solution. 2) Observe a mark through the solution and measure how long it takes for it to disappear. 3) The quicker the mark disappears the quicker the reaction. 4) This only works for reactions were the initial solution is feather see - through. 5) The result is very subjective - different people might not agree over the exact point when the mark 'disappears'. |
| There are two more ways tell me about change in mass first. | 1) Measuring the speed of a reaction that produces a gas can be carried out on a mass balance. 2) As the gas is released the mass disappearing is easily measured on the balance. 3) The quicker the reading on the balance drops, the faster the reaction. 4) Rate of reaction graphs are particularly easy to plot using the results from this method. 5) This is the most accurate of the three methods that can be used because the mass balance is very accurate. But it has the disadvantage of releasing the gas straight into the room. |
| The last one how can the rate of reaction be measured by the volume of gas given off? | 1) This involves the use of a gas syringe to measure the volume of gas given off. 2) The more gas given off during a given time interval the faster the reaction. 3) A graph of gas volume against time elapsed could be plotted to give a rate of reaction graph. 4) Gas syringes usually give volumes accurate to the nearest millimetre, so they're quite accurate. You have to be quite careful though - if the reaction is too vigorous you can easily blow the plunger out of the end of the syringe. |
| How would you do the reaction of hydrochloric acid and marble chips to show the effect of increasing surface area and concentration if you increase the concentration of acid? | 1) Measure the volume of gas evolved with a gas syringe and take readings at regular intervals. 2) Make a table of readings and plot them as a graph. You choose regular time intervals and time goes on the x-axis and volume goes on the y-axis. 3) Repeat the experiment with exactly the same volume of acid and exactly the same mass of marble chips, but with different marble use big chips, small chips. 4) Then repeat with the same mass of powdered chalk instead of marble chips. |
| Look at the graph on pg 60 for reaction of hydrochloric acid and marble ships describe what it is showing. | 1) Using finer particles means that the marble has a larger surface are. 2) A larger surface area causes more frequent collisions so the rate of reaction is faster. 3) Line 4 shows the reaction if a greater mass of small marble chips is added. The extra surface area gives a quicker reaction and there is also more gas evolved overall. |
| How would you use the experiment of magnesium metal and dilute HCl for rates of reaction? | 1) This reaction is good for measuring the effects of increased concentration. 2) This reaction gives off hydrogen gas, which we can measure with a mass balance at certain times. 3) In this experiment time also goes on the x-axis and volume goes on the y-axis. |
| How would you do the reaction of magnesium metal with dilute HCl? | 1) Take readings of mass at regular time intervals. 2) Put the results in a table and work out the loss in mass for each reading. Plot a graph. 3) Repeat with more concentrated acid solutions, but always with the same amount of magnesium. 4) The volume of acid must always be kept the same too - only the concentration is increased. 5) The graphs that you draw should show the same pattern - a higher concentration giving a steeper graph, with the reaction finishing much quicker. |
| What does the experiment of Sodium Thiosulfate and HCl involve? | 1) These two chemicals are both clear solutions. 2) They react together to form a yellow precipitate of sulfur. 3) The experiment involves watching a black mark disappear through the cloudy sulfur and timing how long it takes to go. 4) The reaction can be repeated for solutions at different temperatures. In practice, that's quite hard to do accurately and safely (it's not a good idea to heat an acid directly). The best way to do it is to use a water bath to heat both solutions to the right temperature before you mix them. 5) The depth of the liquid must be kept the same each time. 6) The results will of course show that the higher the temperature the quicker the reaction and therefore the less time it takes for the mark to disappear. 7) This reaction can also be used to test the effects of concentration. 8) Put the results in a table. |
| How is the decomposition of hydrogen peroxide a good reaction for showing the effect of different catalysts? | The decomposition of hydrogen peroxide is: 2H202 (aq) ↔ 2H20(l) + O2 (g). 1) This is normally quite slow but a sprinkle of manganese (IV) oxide catalyst speeds it up no end other catalysts which work are found in a) potato peel and b) blood. 2) Oxygen gas is given off which provides an ideal way to measure the rate of reaction using a gas syringe. 3) Then draw the results on a graph time in seconds on the x-axis and vol. of gas in centimetres cubed on the y- axis. 4) Better catalysts give a quicker reaction, which is shown by a steeper graph which levels off quickly. 5) This reaction can also be used to measure the effects of temperate or of concentration of the H2O2 solution. The graphs will look just the same. |
| What three things increase collisions? | 1) High temperature increases collisions: - When the temperature is increased the particles are moving quicker, they're going to collide more often. 2) High concentration (or pressure) increases collisions: - If a solution is made more concentrated it means there are more particles of reactant knocking about between the water molecules which makes collisions between the important particles more likely. - In a gas increasing the pressure mean the particles are more squashed up together so there will be more frequent collisions. 3) Larger surface area increases collisions: - If one of the reactants is a solid then breaking it up into smaller pieces will increase the total surface area. This means the particles around it in the solution will have more area to work on, so there'll be more frequent collisions. |
| How can increasing the temperature cause faster collisions? | Higher temperature also increases the energy of the collisions because it makes the particles move faster. Reactions only happen if the particles collide with enough energy. The minimum amount of energy needed by the particles to react is known as the activation energy. At a higher temperature there will be more particles colliding with enough energy to make the reaction happen. |
| What is a catalyst? | A catalyst is a substance which speeds up a reaction without being changed or used up in the reaction. |
| How do catalysts help reduce costs in industrial reactions? | 1) Catalysts are very important for commercial reasons - most industrial reactions use them. 2) Catalysts increase the rate of reaction, which saves a lot of money simply because the plant doesn't need to operate for as long to produce the same amount of stuff. 3) Alternatively, a catalyst will allow the reaction to work at a much lower temperature. That reduces the energy used up in the reaction (the energy cost), which is good for sustainable development and can save a lot of money too. |
| What are the disadvantages of using catalysts in industry? | 1) They can be very expensive to buy, and often need to be removed from the product and cleaned. They never get used up in the reaction though, so once you've got them you can use the over and over again. 2) Different reactions use different catalysts, so if you make more than one product at your plant, you'll probably need to buy different catalysts for them. 3) Catalysts can be 'poisoned' by impurities, so they stop working, e.g. sulfur impurities can poison the iron catalyst used in the Haber process (used to make ammonia for fertilisers). That means you have to keep you reaction mixture very clean. |
| What is an exothermic reaction? | An exothermic reaction is one which transfers energy to the surroundings, usually in the form of heat and usually shown by temperature rise. |
| What are examples of exothermic reactions and how are they useful? | 1) The best example of an exothermic reaction is burning fuels - also called combustion. This gives out a lot of heat. 2) Neutralisation reaction (acid + alkali) are also exothermic. 3) Many oxidation reactions have lots of everyday uses. For example sons hand warmers use exothermic oxidation of iron in air (with a salt solution catalyst) to generate heat. Self heating cans of hot chocolate and coffee also rely on exothermic reactions chemicals and their bases. |
| What is an endothermic reaction? | An endothermic reaction is one which takes in energy from the surroundings usually in the form of heat and is usually shown by a fall in temperature. |
| Give an example of an endothermic reaction and their uses. | 1) Endothermic reactions are much less common. Thermal decompositions are a good example: CaCO3 = CaO+ CO2 heat must be supplied to make calcium carbonate decompose to make quicklime. 2) Endothermic reactions also have everyday uses. For example, some sports injury pack use endothermic reactions - they take in heat and the pack becomes very cold. More convenient that carrying ice around. |
| How can reversible reactions be endothermic and exothermic give an example? | In reversible reactions if the reaction is endothermic in one direction it will be exothermic in the other direction. The energy absorbed by the endothermic reaction is equal to the energy released during the exothermic reaction. A good example of this is the thermal decomposition of hydrated copper sulfate. 1) If you heat blue copper (II) sulcate crystals it drives the water off and leaves which anhydrous copper (II) sulcate powder. This is endothermic. 2) If you then add a couple of drops of water to the white powder you get the blue crystals back again. This is exothermic. |
| Describe the pH scale | 1) The pH scale is a measure of how acidic or alkaline a solution is. 2) The strongest acid is pH 0. The strongest alkali has pH 14. 3) A neutral substance has pH 7. |
| Give a few examples and where they would be on the pH scale. | 1) Car battery acid, stomach acid is around pH 1. 2) Vinegar, lemon juice is around pH 3. 3) Acid rain is around pH 4. 4) Normal rain has a pH of about 5. 5) Pure water is neutral pH 7. 6) Washing-up liquid is about pH 9. 7) Pancreatic fluid is about pH 10. 8) Soap powder has a pH of about 11. 9) Bleach has a pH of about 12. 10) Caustic soda ( drain cleaner) has a pH of about 14. |
| What does an indicator do? | The dye in the indicator changes the colour depending on whether it's above or below a certain pH. Universal indicator is a combination of dyes which gives the colours of the pH scale. It's very useful for estimating the pH of a solution. |
| What is an acid, a base and an alkali? | 1) An acid is a substance with a pH of less that 7. Acids form H+ ions in water. 2) A base is a substance with a pH of greater than 7. 3) An alkali is a base that dissolves in water. Alkalis form OH- ions in water. 4) So, H+ ions make solutions acidic and OH- ions make them alkaline. |
| What is neutralisation? | 1) The reaction between acids and bases is called neutralisation: acid + base = salt + water. 2) Neutralisation can also be seen in terms of H+ and OH- ions like this: H+ (aq) + OH- (aq) = H2O (l). 3) When an acid neutralises a base (or vice versa), the products are neutral i.e. they have a pH of 7. An indicator can be used to show that a neutralisation reaction is over (the universal indicator will go green). |
| What do these symbols tell you: (s), (l), (g), (aq)? | 1) (s) means solid. 2) (l) means liquid. 3) (g) means gas. 4) (aq) means dissolved in water. 5) E.g. 2Mg(s) + O2 (g) = 2MgO (s) |
| What is the typical experiment of acid + metal? | 1) Remember Acid + Metal = Salt + Hydrogen. 2) The typical experiment is putting magnesium, aluminium, zinc, iron and copper in different test tubes with some dilute HCl. 3) The more reactive the metal, the faster the reaction will go - very reactive metals (e.g. sodium) react explosively. 4) Copper doesn't react with dilute acids at all - because it's less reactive than hydrogen. 5) The speed of reaction is indicated by the rate at which the bubbles of hydrogen are given off. 6) The hydrogen is confirmed by the burning splint test giving the notorious squeaky pop. 7) The name of the salt produced depends of which metal is used and which acid is used. |
| What salts will hydrochloric acid alway produce? | 1) Hydrochloric acid will always produce chloride salts: - 2HCl + Mg = MgCl2 + H2 (Magnesium chloride) - 6HCl + 2Al = 2AlCl3 + 3H2 (Aluminium chloride) - 2HCl + Zn = ZnCl2 + H2 (Zinc chloride) |
| What type of salt will sulphuric acid always produce? | Sulfuric acid will always produce sulcate salts: - H2SO4 + Mg = MgSO4 + H2 (Magnesium sulfate) - 3H2SO4 + 2Al = Al2 (SO4)3 + 3H2 (Aluminium sulfate) - H2SO4 + Zn = ZnSO4 + H2 (Zinc Sulfate) |
| What does nitric acid produce? | 1) Nitric acid produces nitrate salts when neutralised. 2) Nitric acid reacts fine with alkalis to produce nitrates, but it can play silly devils with metals and produce nitrogen oxides instead. |
| What happens when acid reacts with metal oxides and hydroxides? | 1) Some metal oxides and metal hydroxides dissolve in water. These soluble compounds are alkalis. 2) Even bases that won't dissolve in water will still react with acids. 3) So, all metal oxides and metal hydroxides react with acids to form a salt and water. 4) Acid + Metal Oxides = Salt + Water. 5) Acid + Metal Hydroxide = Salt + Water. |
| How does the combination of metal and acid decide the salt? | 1) Hydrochloric acid + copper oxide forms copper chloride + water. 2) Hydrochloric acid + sodium hydroxide forms sodium chloride + water. 3) Sulfuric acid + zinc oxide forms zinc sulfate + water. 4) Sulfuric acid + calcium hydroxide form calcium sulfate + water. 5) Nitric acid + magnesium oxide forms magnesium nitrate + water. 6) Nitric acid + potassium hydroxide forms potassium nitrate + water. 7) The symbol equations are all pretty much the same here are two: - H2SO4(aq) + ZnO(s) - ZnSO4 (aq) + H2O (l) - HNO3(aq) + KOH(aq) - KNO3 (aq) + H2O (l) |
| How can ammonia be neutralised to make fertiliser? | - Ammonia dissolves in water to make an alkaline solution. - When it reacts with nitric acid, you get a neutral salt - ammonium nitrate: NH3 (aq) + HNO3 (aq) - NH4NO3 (aq) Ammonia + Nitric acid - Ammonium nitrate. - This is a bit different from most neutralisation reactions because there's NO WATER produced - just ammonium salt. - Ammonium nitrate is an especially good fertiliser because it has nitrogen from two sources, the ammonia and the nitric acid. |
| How do you make salts using a metal or an insoluble base? | 1) You need to pick the right acid, plus metal or insoluble base (a metal oxide or metal hydroxide). E.g. if you want to make copper chloride, mix hydrochloric acid and copper oxide. E.g. CuO(s) + 2HCl(aq) - CuCl2 (aq) + H2O (l) 2) You add the metal, metal oxide or hydroxide to the acid - the solid will dissolve in the acid as it reacts. You will know when all the acid has been neutralised because the excess solid will just sink to the bottom of the flask. 3) Then filter out the excess metal, metal oxide or metal hydroxide to get the salt solution. To get pure, solid crystals of the salt, evaporate some of the water (to make the solution more concentrated) and then leave the rest to evaporate slowly. This is called crystallisation. |
| How do you make salts using an alkali? | 1) You have to add exactly the right amount of alkali to just neutralise the acid - you need to use an indicator to show when the reaction's finished. Then repeat using exactly the same volumes of alkali and acid so the salt isn't contaminated with indicator. 2) Then just evaporate off the water to crystallise the salt as normal. |
| Tell me about make insoluble salts - precipitation reactions. | 1) If the salt you want to make is insoluble you can use a precipitation reaction. 2) You just need to pick two solutions that contain the ions you need. E.g. to make lead chloride you need a solution which contains lead ions and one that contains chloride ions. So you can mix lead nitrate solution ( most nitrates are soluble) with sodium chloride solution ( all group 1 compounds are soluble). Pb(NO3)2 (aq) + 2NaCl(aq) - PbCl2(s) + 2NaNO3(aq) 3) Once the salt had precipitated out (and is lying at the bottom of your flask), all you have to do is filter it from the solution wash it and then dry it on filter paper. 4) Precipitation reactions can be used to remove poisonous ions (e.g. lead) from drinking water. Calcium and magnesium ions can also be removed from water this way - they make water "hard", which stops soap lathering properly. Another use of precipitation is in treating effluent (sewage) - again unwanted ions can be removed. |
| What is electrolysis? | Electrolysis mean "splitting up with electricity". 1) If you pass an electric current through an ionic substance that's molten or in solution, it breaks down into the elements it's made of. This is called electrolysis. 2) It requires a liquid to conduct the electricity call the electrolyte. 3) Electrolytes contain free ions - they're usually the molten or dissolved ionic substance. 4) In either case it's the free ions which conduct the electricity and allow the whole thing to work. 5) For an electrical circuit to be complete, there's got to be a flow of electrons. Electrons are taken away from ions at the positive electrode and given to other ions at the negative electrode. As ions gain or lose electrons they become atoms or molecules and are released. |
| How is oxidation and reduction involved in electrolysis? | 1) Reduction is the gain of electrons. 2) On the other hand, oxidation is a gain of oxygen or a loss of electrons. 3) So reduction and oxidation don't have to involve oxygen. 4) Electrolysis always involves an oxidation and reduction. |
| Tell me about the electrolysis of molten lead bromide. | When a salt (e.g. lead bromide) is molten it will conduct electricity. 1) Positive ions are attracted to the negative electrode ( cathode). Here they gain electrons (reduction). Lead is produced at the cathode. 2) Negative ions are attracted to the positive electrode (anode). Here they lose electrons (oxidation). Bromine is produced at the anode. 3) At the negative electrode (cathode), one lead ion accepts tow electrons to become one lead atom. 4) At the positive electrode (anode), two bromine ions lose one electron each and become one bromine molecule. |
| What is produced at the cathode and anode? | 1) The metal is produced at the cathode. 2) The non-metal is produced at the anode. |
| What are the names of the different ions that go to each electrode? | 1) Because positive ions go to the cathode they are called cations. 2) Because negative ions go to the anode they are called anions. |
| How can reactivity affect the products formed by electrolysis? | 1) Sometimes there are more than two free ions in the electrolyte. For example, if a salt is dissolved in water there will also be some H+ and OH- ions. 2) At the negative electrode (cathode), if metal ions and H+ ions are present, the metal ions will stay in solution if the metal is more reactive than hydrogen. This is because the more reactive an element, the keener it is to stay as ions. So, hydrogen will be produced unless the metal is less reactive than it. 3) At the positive electrode (anode), if OH- and halide ions (Cl-, Br-, I-) are present then molecules of chlorine, bromine or iodine will be formed. If no halide is present the oxygen will be formed. |
| Tell me about the electrolysis of NaCl (l). | 1) The main ions present in sodium chloride are Na+ and Cl-, but there are also a few H+ and OH- ions present because water is very slightly ionised. 2) The Na+ and H+ ions are attracted to the negative electrode (cathode). Here the H+ ions pick up electrons since hydrogen is less reactive than sodium. The hydrogen ions gain electrons (reduction) to form hydrogen atoms, which then pair up to form hydrogen molecules. 3) The Cl- ions are attracted to the positive electrode (anode). Here they lose one electron each (oxidisation) to form chlorine atoms. These atoms pair up to form chlorine molecules. Chlorine gas is given off at the anode. 4) The sodium stays in the solution because they're more reactive than hydrogen. Hydroxide ions from water are also left behind. This means sodium hydroxide (NaOH) is left in solution. |
| What are the uses of the products formed in the electrolysis of sodium chloride solution? | Chlorine: Purifying water, making PVC plastic and is used in the production of bleach. Hydrogen: Making margarine or ammonia. Sodium Hydroxide: It is a very strong alkali and is used widely in the chemical industry, e.g. to make soap. |
| What do half equations show and how do you make them? | Half equations show the reactions at the electrodes. The main thing is to make sure the number of electrons is the same for both half-equations. For the electrolysis of sodium chloride the half equations are: Negative electrode: 2H+ + 2e- = H2 Positive electrode: 2Cl- = Cl2 +2e- or 2Cl- - 2e- = Cl2. And for the electrolysis of molten lead bromide the half equations would be : Pb2+ + 2e- = Pb and 2Br- = Br2 +2e-. |
| How is electrolysis used to remove aluminium from its ore? | 1) Aluminium's a very abundant metal, but it is always found naturally in compounds. 2) Its main ore is bauxite, and after mining and purifying, a white powder is left. 3) This is pure aluminium oxide, Al2O3. 4) The aluminium has to be extracted from this using electrolysis. |
| How is aluminium extracted using electrolysis? | 1) Al2O3 has a very high melting point of over 2000 degrees centigrade so it would be expensive to melt. 2) Instead the aluminium oxide is dissolved in molten cryolite (a less common ore of aluminium). 3) This brined the temperature down to about 900 degrees centigrade which makes it much cheaper and easier. 4) The electrodes are made of carbon (graphite), a good conductor of electricity. 5) Aluminium forms at the negative electrode (cathode) and oxygen forms at the positive electrode (anode). Negative electrode: Al3+ +3e- = Al Positive electrode: 2O2- = O2 +4e- 6) The oxygen then reacts with the carbon in the electrode to produce carbon dioxide. This means that the positive electrode (anode) has to be replace every once in a while. 7) This takes place in a steel container. |
| How does electroplating use electrolysis? | 1) Electroplating uses electrolysis to coat the surface of one metal with another metal, e.g. you might want to electroplate silver onto a brass cup to make it look nicer. 2) The negative electrode (cathode) is the metal object you want to plate and the positive electrode (anode) is the pure metal you want it to be plated with. You also need the electrolyte to contain ions of the plating metal. (The ions that plate the metal object come from the solution, while the positive electrode keeps the solution topped up). Example: To electroplate silver onto a brass cup, you'd make the brass cup the negative electrode (to attract the positive silver ions), a lump of pure silver the positive electrode and dip them in a solution of silver ions, e.g. silver nitrate. |
| What are some of the different uses for electroplating? | 1) Decoration: Silver is attractive, but very expensive. It's much cheaper to plate a boring brass cup with silver, than it is to make the cup out of solid silver - but it looks just as pretty. 2) Conduction: Metals like copper conduct electricity well - because of this they're often used to plate metals for electronic circuits and computers. |
| How is electrolysis used to purify copper? | 1) The following ions are present in copper sulphate solution: Cu2+, SO42- (from CuSo4) H+ , OH- (from water). 2) The H+ ions and Cu2+ ions are attracted to the cathode but Cu gains electrons (reduction) more easily so that the copper is deposited. Cu2+ + 2e- = Cu. 3) At the anode rather than the sulphate or hydroxide ions releasing their electrons, the atoms in the copper anode release their release their electrons (oxidisation) and form ions that then enter the solution. Cu = Cu2+ + 2e-. 4) Therefore, at the cathode, copper ions from solution are being deposited, and the cathode increases mass. At the anode the copper atoms from the anode are going into the solution as copper ions. The concentration of copper ions in the solution remains unchanged. |
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