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48 Cards in this Set
- Front
- Back
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What s hard water caused by?
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Hard water is caused by Ca2+ and Mg2+ ions.
in some places water usually flows over rocks and through soils that contain Magnesium and calcium ions. |
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What causes temporary hardness?
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when calcium carbonate (chalk or limestone) reacts with acid rain to form calcium hydrogencarbonate which is soluble and dissolves in water, releasing calcium ions
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What causes permanent hardness?
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dissolved calcium sulphate, magnesium sulphate ions.
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How can temporary hardness be gotten rid of?
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Boiling the hard water will decompose calcium hydrogen-carbonate to the insoluble calcium carbonate precipitate (lime-scale), water and calcium carbonate.
this wont work for permanent hardness as heating a sulphate ion does nothing. |
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How can both types of hardness be gotten rid of?
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water supply is fed through an ion exchange resin which exchanges the magnesium and calcium ions that runs through it with sodium and hydrogen ions. this removes the hardness from the water.
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What is a resin?
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A solid polymer that is insoluble in water.
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The resin equation for Calcium ions
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Ca+2(aq) + Na2 Resin(s)=====>2Na+(aq) + Ca Resin(s)
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What is electrolysis?
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Uses D.C electricity to decompose a compund
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What is a electrolyte?
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an ionic substance that either molten or dissolved in water.
The free ions conduct electricity. |
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How do they gain or lose electrons?
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Electrical current requires a flow of electrons. the electron are taken away from ions at the positive anode and given to the ions at the negative cathode.
As ons gain or lose electrons they become atoms or molecule and are released. |
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Explain the electrolysis of molten sodium chloride?
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Half equation Of NaCL
Cathode= Na+ + e- =====> Na Anode= 2Cl- ============>2e- + Cl2 At cathode, Na+ is reduced to become Na atom. At Anode, Cl- is oxidised to become cl2 molecule |
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Oxidation and reduction
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Oxidation
Is Loss of electrons Reduction Is Gain of electrons |
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Uses of sodium
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Na can be use in street lamps and a coolant in some nuclear reactor.
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Explain the electrolysis of molten sodium chloride?
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Half equaion of PbBr2
Cathode=Pb2+ +2e- =======> Pb Anode=2Br- ============>Br2+2e- At Cathode Pb2+ is reduced to Pb atom At Anode, Br- is oxidised to become Br2 molecule |
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difference between molten and dissolved ionic salts
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molten only contains the ions of the salt. dissolved contains sal ions as well as hydrogen+ and hydroxide- ions
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which are discharged at the anode?
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the simplest ions are dischargeed eg. cl- is dischargged rather than oh- and oh- is discharged rather than so4-2.
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Which are discharged at the cathode.
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a metal that is less reactive than H+. e.g.. copper is less reactive than H+ s it will be discharged at the cathode. however Na+ is more reactive than H+ so hydrogen will be discharged rather than Na+.
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Describe what will be discharged at the anode and cathode of dissolved sodium chloride.
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The ions present are Na+ Cl- OH- H+.
Chlorine will be discharged at the anode as it is a simpler ion than hydroxide. hydrogen will be discharged at the cathode as sodium s more reactive than hydrogen. |
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why is graphite used as an electrode?
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it is inert and unreactive so doesn't take part in the reaction
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copperis purifyed by elecrolyis why?
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It is unreactive and can be obtained very easily from its ore by reduction with carbon. but copper produced isn't pure enough to sue in electrical conductors.
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What is at the cathode and anode durng the purification of copper.
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Cathode= a thin piece of pure copper and more pure copper gets added to it
Anode= a big lump of impure copper which will dissolve. |
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Give an example of the electrolyte?
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copper sulphate soluton containg cu2+ ions (aq)
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Explain the electrolysis?
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The electrical current pulls electrons off copper atoms at the anode causing them to dissolve the solution as cu2+ ions. oxidation.
Then the electrons are deposited at the cathode nearby the cu+ ions turning them into copper atoms. reduction. the impurities are dropped at the anode as sludge whilst pure copper atoms bond to the cathode. |
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Write the half equation?
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cathode= cu2+(aq)+++2e- =====> cu(s)
Anode== cu2======>2e- + cu2+ |
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what is electroplating?
What is usually at the cathode? What is at the cathode? |
-applying a metal coating to the surface of a metal using electricity
-Its the object you're going to electroplate. -It is the bar of metal used for plating |
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Explain how to electroplate silver onto a brass cup?
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The cathode is the brass cup
the anode is a bar of pure silver the electrolyte is silver nitrate solution the silver ions from the electrolyte move towards the cathode and metal gets deposited onto the brass cup. the anode keeps he silver ions in the solution topped up. |
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Why metals are electroplated?
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-for decoration and to improve the appearance of the metals-making them look shiny and attractive.
-to prevent corroding and the metals used for protection are unreactive so don't corrode easily. |
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what is the half equation at the cathode and anode for electroplating?
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cathode Ag+ ++ e- ======Ag
anothe Ag=====Ag+ ++e- |
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What are the steps to a titration?
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Rinse pipette with alkali and burette with acid
Measure alkali using a pipette into a conical flask add a few drops of indicator place flask on a white tile fill the burette with acid add acid to flask until the mixture change colour repeat experiment. |
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Why does the mixture change colour?
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When it has all be neuralised
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When is phenolphthalein used and what colour does it change?
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It s used for a strong acid and weak alkali. it changes from goes from pink in alkali to colourless in acid.
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When is methyl orange used and what colour does it change to?
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Strong acid and weak alkali. it changes from >>>>>>>>>>
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What is equilibrium?
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-rate of forward reaction is the same as the rate of backward reaction
-but there is no overall change in concentration of each substance as they reach a balance and stay there. -reversible reaction |
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Why must a reversible reaction take place in a closed system?
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so that a state of equilibrium will be reached and none of the products and reactants will escape.
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What 2 factors do the "position of equilibrium depend on?"
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Temprature and pressure
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How does temperature affect the equilibrium yield?
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Lower temperature favours/ equilibrium shifts to the right forward reaction as it is exothermic so give out heat and therefore the yield increases.
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How does pressure affect the yield?
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higher pressure favours the reacion/ equillibrum shfts to the -------..........--------use book
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What does raised pressure and temperature mean?
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Increased rate of reaction and equilibrium is reached faster.
but this also changes the position of equilibrium therefore less product is made. |
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What does a catalyst do?
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Speeds up both the forward and backward reaction by the same amount.
Means reaction reaches equilibrium quicker. you still make the same amount of product as you would without the catalyst-doesn't change the equilibrium position. doesnt affet the % yield |
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What is a reversible reaction?
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one where the products of reaction can react with each other and convert back to original reactants. the reaction can go both ways.
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Where can nitrogen and oxygen be obtained from
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Nitrogen can be obtained from the air as there is 78% whilst the hydrogen can be obtained from natural gas.
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Some thing about the reacton
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It is reversible therefore the reaction can occur in both directions and not all of the nitrogen and hydrogen will convert into ammonia. it also reaches dynamic equilibrium.
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What are the conditions needed to produce ammonia?
why must a compromise be made? |
temperature- 450 degrees
Pressure- 200 atm Catalyst-iron -because it is a reversible reaction |
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Why do higher pressure favour the forward reaction.
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because there are 4 molecules of gas on the left-hand side for every two molecules on the right. this is why the pressure is set as highest % yield. without making the plant too expensive.
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why is lower better
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the forward reaction is exothermic, meaning that increasing the temperature will move the equilibrium the wrong way-away from ammonia and towards the n2 H2. so the yield would be greater at lower temperature.
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what is the problem with lower temperature
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slower rate of reaction (equilibrium is reached more slowly). so they temp. is increased anyway to get a faster rate of reaction. 450 is a compromise to get an acceptable yield in an acceptable time.
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How is ammonia formed?
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Ammonia is formed as a gas, but as t cools in the condenser, it liquefies and is removed.
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What is ammonia used for?
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-to make nitrogenous fertilisers
-these are used to increase plant growth -but when fertillisers enter rivers, they can cause eutrophication. |
