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141 Cards in this Set
- Front
- Back
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What are electrolytes? |
Ionic |
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How does the charge move through the molten liquid? |
By the movement of ions |
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What happens when the ions reach the electrode in electrolysis? |
They are discharged and turned into atoms or molcules |
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What happens if the electrolyte solidifies? |
The ions are in a fixed positions and cannot move and the current cannot flow |
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What is electrolysis? |
The flow of charge by moving ions.These moving ions discharge at electrodes. |
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What can be written as half equations? |
The reactions that take place at the electrodes in the electrolysis of electrolyes |
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In the electrolysis of electrolytes, what is the reaction at the cathode? |
Na+ + e- -> Na |
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In the electrolysis of electrolytes, what happens at the cathode? (3) |
-The sodium chloride splits up into ions, so the ions are free to move -the positive Na+ ions migrate towards the negative cathode -Each Na+ ion gains one extra electron from the cathode |
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In the electrolysis of electrolytes, what is the reaction at the anode? |
2Cl- - 2e- -> Cl2 |
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In the electrolysis of electrolytes, what happens at the anode? (3) |
-The negative Cl- ions migrate to the positive anode -The Cl- ions are discharged as chlorine gas -Two Cl- ions each gain one electron and combine to form a chlorine molecule |
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What happens if sodium hydroxide NaOH solution is electrolysed? |
Hydrogen is formed at the cathode and oxygen is formed at the anode |
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What happens if sulphuric acid H2SO4 solution is electrolysed? |
Hydrogen is formed at the cathode and oxygen is formed at the anode |
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What happens if copper(II) sulphate CuSO4 solution is electrolysed with carbon electrodes? |
Copper is farmed at the cathode and oxygen is formed at the anode |
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What does the amount of substance formed during electrolysis vary with? |
Time and current - it increases with increasing time and current |
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What are the substances produced at the electrodes? |
Discharged ions |
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What affects the number of ions discharged? |
The amount of charge transferred |
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What is the electrode reaction at the cathode in the electrolysis of NaOH or H2SO4? |
2H+ + 2e- -> H2 |
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What is the electrode reaction at the anode in the electrolysis of NaOH or H2SO4? |
4OH- - 4e- -> 2H2O + O2 |
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What happens in the electrolysis of sodium hydroxide? |
Hydrogen is made rather than sodium, as sodium is much higher in the reactivity series so hydrogen is discharged in preference. |
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What is the electrode reaction in the electrolysis of CuSO4 with carbon electrodes at the cathode? |
Cu2+ + 2e- -> Cu |
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What is the electrode reaction in the electrolysis of CuSO4 with carbon electrodes at the anode? |
4OH- - 4e- -> 2H2O + O2 |
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How can the amount of substance formed be calculated? |
By ratios |
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Why are fuel cells used in spacecraft? (4) |
-The water produced is not wasted, the astronauts drink it -They are lightweight; normal batteries ar heavier so the spacecraft can use the saving to carry a bigger payload -They are compact -There are no moving parts |
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Why is the car industry developing fuel cells? (4) |
-There are no carbon emissions when fuel cells are used in cars -Fossil fuels are non renewable so car manufacturers are researching alternatives that are renewable and cause less pollution -The main product of a hydrogen power fuel cell is water, which is not a pollutant -There is a large source of hydrogen available by decomposing water |
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What are fuel cells especially useful for? |
Mobile energy sources |
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What are the advantages of hydrogen-oxygen fuel cells?(6) |
-There is direct energy transfer. Energy is converted directly from chemical energy in the fuel into electrical energy. This energy does not have to be converted into heat first. -There are fewer production stages. Every new stage in any process increases the energy losses. In the fuel cells themselves the energy conversion is all done in a single stage. -Thereare more efficient as there are fewer stages and almost all the energy is converted -They are less polluting. A hydrogen-oxygen fuel cell produces water and no nitrogen oxides. -Fuel cells last longer than conventional rechargeable batteries before they need to be replaced -Fuel cells weigh less than the current style of batteries in electric vehicles |
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What are the two problems with hydrogen-oxygen fuel cells? |
-Poisonous catalysts are used that have to be disposed of at the end of the life time of the cell -Fossil fuels are burnt to produce the hydrogen and oxygen needed |
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When is energy released from fuel? |
When the fuel reacts with oxygen in the air. The reaction is exothermic. |
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If the fuel cell uses hydrogen, what is the reaction? |
2H2 + O2 -> 2H2O |
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What happens when hydrogen reacts with oxygen by burning? |
The chemical energy is given out as heat. |
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What does a fuel cell convert chemical energy directly into? |
Electrical energy, there is no heat |
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What is the overall reaction in a hydrogen-oxygen fuel cell? |
2H2 + O2 -> 2H2O with electrons being exchaged from the cathode to the anode |
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What is shown in an energy level diagram? |
When the fuel reacts and some of the chemical energy as a store inside them is given out. |
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What is the oxidation reaction at the negative electrode when hydrogen releases electrons? |
2H2 -> 4H+ + 4e- |
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What is the reduction reaction at the positive electrode as electrons are taken in? |
4H+ + O2 + 4e- -> 2H2O |
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What is a redox reaction? |
A reaction where electrons are gained and lost |
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What is the equation for rusting? (an example of a redox reaction) |
iron + oxygen + water -> hydrated iron(III) oxide |
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What does galvanising do? |
Protect iron from rusting by covering it with a layer of zinc |
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How does galvanising work? |
-The layer of zinc stops water and oxygen from reaching the surface of the iron -Zinc is also a sacrificial metal, as it is more reactive than iron |
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When is a substance oxidised? |
If it loses electrons. An oxidising agent takes electrons away from a substance |
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When is a substance reduced? |
If it gains electrons. A reducing agent pushes electrons onto another substance so that it gains. |
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What happens when iron rusts? |
The oxygen is the oxidising agent; it takes electrons from the iron. The electrons go onto the oxygen, so the oxygen has been reduced. |
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What happens when a word equation for displacement is written? |
The more reactive metal 'swaps places' with the less reactive metal. |
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What does displacement happen with? |
Reactive metals and compounds of a less reactive metal. |
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How do all metals react? |
By pushing off electrons and turning it into ions (oxidation). These electrons are forced onto the ions of other metals thatare not so reactive. Metal atoms that gain these electrons are reduced. |
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What is the pattern of displacement reactions? |
Reactive metal element + less reactive metal compound -> Reactive metal compound + less reactive metal element |
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Give an example of sacrificial protection. |
Iron can be coated in a thin layer of zinc or magnesium which are more reactive than iron and so lose electrons in preference to iron. |
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What is the molecular formula for ethanol? |
C2H5OH |
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How is ethanol made? |
By fermentation |
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What is the word equation for the fermentation of ethanol? |
Glucose -> ethanol + carbon dioxide |
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What is the balance symbol equation for fermentation? |
C6H12O6 -> 2C2H5OH + 2CO2 |
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How is ethanol made by the fermentation of glucose solution? |
The reaction is catalysed by the enzymes in yeast. This will only happen if there is no oxygen present. The dilute liquid produced undergoes fractional distillation to produce ethanol. |
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What is the general form of alcohols? |
Cn H2n+1 OH |
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What happens if the temperature is too low in fermentation? |
The enzymes in yeast are inactive |
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What happens if the temperature is too high in fermentation? |
The enzymes in yeast are denatured |
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What happens if air is present in fermentation? |
There is a different reaction, producing ethanoic acid instead of ethanol |
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What is the order of the alcohols? |
Methanol, ethanol, propanol, butanol, pentanol |
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How can ethanol by fermentation be used? |
As fuel. It is a renewable fuel because the plants that make the sugar for the process can be grown very quickly. |
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How can ethanol that is used in industry also be made? |
From ethene. Ethanol made in this way is a non renewable fuel because the ethene it is made from comes from comes from fossil fuels. These fossil fuels cannot be replaced and are a finite resource. |
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What is the reaction to make ethanol from ethene known as? |
A hydration reaction because water is added to the ethene molecule: ethene + water -> ethanol |
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How is ethanol made from ethene? |
Ethene and steam are passed over a hot phosphoric acid catalyst |
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What is the balanced symbol equation for the hydration reaction to make ethanol from ethene? |
C2H4 + H2O -> C2H5OH |
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Why are the conditions of ethanol production better by fermentation? (2) |
-35oC less energy needed, compared to the hot catalyst needed by hydration. -sustainable and not from a finite resource like hydration |
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What process is fermentation? |
Batch |
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What process is hydration? |
Continuous |
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Why are the conditions of ethanol production better by hydration? (2) |
-Relatively pure on production, fermentation needs fractional distillation -high yield and atom economy compared to fermentations low yield and atom economy |
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Where is the ozone layer? |
In the stratosphere |
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What does the ozone in the stratosphere do? |
Absorbs most of the uv radiation from the sun |
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What happens as the layer of ozone gets more depleted? |
More UV light gets to earths surface |
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What dos scientists know about CFC molecules? |
The move slowly upwards into the stratosphere and attack the ozone layer |
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Why is the use of CFCs a global problem? |
Society agrees that CFCs deplete the ozone layer |
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What can CFCs be replaced with? |
Alkanes or HFCs which will not damage the ozone layer |
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Why is uv radiation absorbed by the ozone layer? (3) |
-The uv part of the electromagnetic spectrum has exactly the right frequency to make ozone molecules vibrate -The energy of the uv radiation is converted into movement energy inside each molecule -The thicker the ozone layer, the more uv radiation is absorbed |
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When were CFCs discovered? |
In the 1930s |
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Why were scientists originally excited by CFCs? |
The substances were inert |
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What happened in the 1970s? |
Scientists linked the depletion of the ozone layer with CFCs |
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What does uv radiation from the sun do in the stratosphere? |
Break down CFC molecules to give highly reactive chlorine atoms. |
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What is a single chlorine atom called? |
A chlorine radical |
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What do chlorine radicals do? |
React with ozone molecules, turning the ozone back into oxygen gas and depleting the ozone layer |
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Why can chlorine atoms keep reacting with ozone molecules? |
They are regenerated |
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Why do CFCs last a long time? |
UV light breaks down CFCs very slowly. |
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What is the equation for uv light breaking down CFCs? |
CF2Cl2 -UV> CF2Cl + Cl. (dot is a radical) |
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Why are HFCs safer than CFCs? |
They do not contain chlorine so cannot make chlorine radicals. |
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What does uv radiation cause? |
Radicals. Each set of radicals sets off a chain reaction. One chlorine radical causes the breakdown of more than 100k ozone molecules. |
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What are the three stages of the chain reaction of chlorine radicals? |
-UV light breaks a bond in CFC molecules to form chlorine radicals -Chlorine radicals react with ozone molecules, creating more chlorine radicals -Cl. + Cl. -> Cl2 |
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How long do CFCs last before they are broken down by uv radiation? |
20 to 50 years |
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Why are CFCs a huge issue? |
They will continue to deplete the ozone long after they have been banned. |
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When is hard water formed? |
When rainwater dissolves some of the rock that it flows over. |
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Why is some rainwater slightly acidic? |
It may contain dissolved carbon dioxide. |
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What are some rock forms of calcium carbonate? |
Chalk, limestone and marble. |
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What do rock forms of calcium carbonate do? |
React with water and carbon dioxide to form calcium hydrogencarbonate. |
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What does calcium hydrogencarbonate do? |
Dissolves to form temporary hard water |
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What is the equation for the formation of temporary hard water? |
Calcium carbonate + carbon dioxide + water -> calcium hydrogencarbonate |
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When is permanent hardness produced? |
When calcium sulphate rock dissolves. |
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How can water hardness be measured? |
By how much soap is needed to produce a lather. |
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What happens when a soap flake is shaken in a water sample? (3) |
-Calcium ions in the water react with the soap and turn it into scum -Eventually as more flakes are added and the mixtured is shaken, the soap reacts with all of the calcium ions -After that, any more soap produces a stable later for the first time. The number of soap flake needed is a measure of water hardness. |
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How is temporary hardness removed? |
By boiling. The calcium hydrogencarbonate decomposes easily in hot water to form calcium carbonate water and carbon dioxide |
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What does heating do? |
Remove the soluble calcium ions from the water by changing them into insoluble calcium carbonate |
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Why is permanent hardness not affected by heating? |
Calcium sulphate is too stable |
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What are ion exchange resins? |
A way of removing temporary and permanent hardness |
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How do ion exchange resins work? |
The water flows over beads of solid resin which trap calium ions on the surface and exchangin them for sodium ions. |
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When does thermal decomposition occur? |
When water is boiled |
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What does thermal decomposition do? |
Softens temporary hardness |
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What is the equation for temporary hardness being removed by thermal decomposition? |
Ca(HCO3)2 -> CaCO3 + CO2 + H2O |
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What can washing soda soften? |
Both temporary and permanent hard water |
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What is washing soda? |
Sodium carbonate, Na2CO3 |
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What happens when washing soda dissolves? |
It reacts with the calcium sulphate in the water to form insoluble calcium carbonate, so locking up the calcium ions |
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What is the equation for washing soda dissolving? |
CaSO4 + Na2CO3 -> Na2SO4 + CaCO3 |
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What are fats and oils? |
Esters. They have chains of carbon atoms |
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What is the fat saturated? |
If the carbon chains contains no double bonds |
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When is the oil unsaturated? |
If the carbon chain contains some double bonds |
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What is the test for unsaturation? |
Bromine water goes from orange to colourless if the compound is unsaturated |
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What is one industrial use of vegetable oil? |
To make margarine. Vegetable oil is unsaturated. |
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How are double carbon bonds turned into single bonds using hydrogen? (3) |
-The first stage is to harden the oils to turn them into saturated compounds -Hydrogen is boiled through the oil at about 200oC using a nickel catalyst -The hydrogen reacts with the carbon double bonds and turns them into single bonds |
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Which oils come from plants? |
Unaturated fats and oils |
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Which oils come from animals? |
Saturated fats and oils |
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What does polyunsaturated mean? |
The compound contains more than one double bond between carbon atoms |
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Who have lower levels of the type of cholesterol that causes heart disease? |
People whose diet is rich in unsaturated fats and oils |
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What is bromine? |
An orange liquid. |
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When does bromine react? |
In an addition reaction with the carbon double bonds in the chain. |
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Describe what happens in an addition reaction with bromine. |
The reaction uses up the bromine molecules, making a dibromo compound. This compound is colourless. Saturated compounds cannot react with bromine since they have no carbon double bonds. |
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What are oil and water? |
Immiscible liquids. They do not dissolve in each other, but disperse into tiny droplets to form an emulsion. |
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What is milk? |
An oil in water emulsion |
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What are cold cream and margarine? |
Water in oil emulsions |
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How can fats and oils be split up? |
Using hot sodium hydroxide to make soap and glycerol |
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What is the word equation for splitting fats and oils? |
Fat + sodium hydroxide -> soap + glycerol |
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What is saponification? |
The reaction of splitting up natural oils with alkalis |
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What happens when an ester reacts with sodium hydroxide? |
Saponification occurs. |
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What is the saponification of esters? |
The ester forms one glycerol molecule and three soap molecules. The reaction is really the reaction of alkaline water so it is a hydrolysis reaction. |
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Why should clothes be washed at 40oC instead of higher temperatures? (3) |
-Its good for the environment -Heating water needs energy so the lower the temperature the less greenhouse gases put into the atmosphere as less energy is used -its good for coloured clothes as dyes are damaged in higher temperatures |
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What does a detergent do? |
Lifts grease stains offinto the water |
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What are thee two parts of a detergent molecule? |
A hydrophilic head (dissolves in water) and a hydrophobic tail (dissolves in grease) |
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What happens when clothes are washed? |
Dirt is lifted off the clothes and put into water. If the dirt is made from oil or grease it will not dissolve in water. |
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What do detergents do? |
Remove fat or oil stains by forming strong intermolecular bonds with both the oil and the water. |
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What bonds does the hydrophobic end form? |
Strong intermolecular bonds with molecules of oil and grease |
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What bonds does the hydrophilic end form? |
Strong intermolecular bonds with water |
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Why must some fabrics be dry cleaned? |
Some fabrics will be damaged if they are washed in water. |
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What does a dry cleaning machine do? |
Washes clothes in an organic solvent. Dry does not mean that no liquids are used, it means that the liquids used are not water |
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What do grease based stains dissolve in? |
Dry cleaning solvent. The solvent molecules surround the grease molecules and pullthem from the fabric |
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How do solvent remove grease? (3) |
-Grease forms intermolecular forces with other molecules of grease -Solvent forms intermolecular forces with other molecules of solvent -Molecules of solvent forms intermolecular forces with molecules of grease |
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Why ant molecules of water form intermolecular forces with molecules of grease? |
The attractive forces are too strong between themselves |
