A Redox reaction is where electrons are being transferred
- Oxidation is loss of electrons, and reduction is the gain of electrons. so a REDOX reaction is where reduction and oxidation occur at the same time
- this means that the electrons are being transferred
- an oxidising agent accepts electrons and gets reduced
- a reducing agent donates electrons and gets oxidised
- one example is when chlorine gas is passed into a solution of iron (II) salt. the iron is oxidised into Iron (III) and the Fe2+ looses an electron to make Fe3+. Chlorine is the oxidising agent
- example: iron atoms reacting with dilute acid. iron atoms loose electrons, theyre oxidised by the hydrogen ions. and hydrogen ions gain electrons. theyre reduced by the iron atoms
Displacement reaction are redox reactions
- a more reactive metal will displace a less reactive one
- an example is with iron in a solution of Tin(II) sulphate. and we end up with iron sulphate and tin metal. the iron looses 2 electrons and the tin ion gains 2 electrons to become a tin atom.
- the metal ion always gains electrons and the metal atom always looses electrons.
Fermentation produces ethanol
- the general formula of an alcohol is CnH2n+1OH. And the general naming system is replace the final 'e' with 'ol'. fermentation converts sugars (glucose) into ethanol. the reaction is done by enzymes found in yest.
- the temperature needs to be carefully controlled. too cold and yest is inactive, too hot and enzymes will denature. optimum is between 25' and 50'. oxygen is also needed to convert ethanol to ethanoic acid used in vinegar. fractional distillation used to get ethaonic acid back to pure ethanol.
- Hydration. Ethene + Water (Steam) = Ethanol. C2H4 + H2O = C2H5OH. the conditions are 300', a pressure of 70 atmposheres and catalyst of phosphoric acid
Fermentation vs. Hydration
- Fermentation = batch process (slow and ineffeicient). Ethene = continuous (Quicker) but requires harsher conditions. Fermentation uses a renewable fuel of sugar, but hydration uses crude oil. fermentation isn't pure, hyrdration is. Fermentation has a low atom economy. Low yield in both, but the excess reactants from hydration can be reused which can make the yeild up to 95%.
Rusting of iron
Rusting of iron is a Redox reaction
- Iron will rust if in contact with air and water. the rust is a form of hydrated iron(III) oxide
- Iron + Oxygen + Water = Hydrated Iron(III) oxide
- iron looses electrons, each atom looses 3 electrons and is oxidised to Fe3+
- oxygen gains electrons and each one gains 2 electrons and is reduced to O2-
- rusting of iron can be prevented by mixing it with other metals to make alloys. steels are alloys of iron with carbon and other metals. most common is stainless steel.
- painting is ideal for large and small structures - it provides a barrier between metal and oxygen/water. it's also practical and aesthetic. greasing is ideal to prevent rust on moving parts
- tin plating is where a coat of tin is applied. the tin acts as a barrier. this will only work as long as the tin remains intact, if it's scratched then the iron behind it may rust, which is why you shouldn't buy tins with dents or scratches
- you can also prevent rusting using the sacrificial method. a more reactive metal is put on top of the iron. Galvanising is where a coat of zinc is used. the zinc will loose electrons in preference to the iron. also blocks of metal can be bolted and they will loose electrons in preference.
- But these are NOT displacement reactions
Detergents have a hydrophilic head and hydrophobic tail
- hydrophobic tail clings onto oil, and the head clings onto water, meaning that they can be mixed together to lify oily dirt out of fabric
Dry cleaning uses solvents to remove stains
- Dry cleaning is cleaning that use other solvents rather than water. these solvents are much better than detergants at removing oil and grease stains and will clean stains that won't dissolve in water
- the solvent can completeley dissolve the oil and grease removing the stains.
- there are weak intermolecular forces between the solvent molecules, and also between the molecules of grease.
- when the solvent is applied to the clothes, intermolecular forces are formed between solvent and grease, so grease is surrounded by molecules of solvent.
- when the solvent is removed the grease is removed and clothes are left clean.
Washing clothes at lower temperatures saves energy
- biological detergants contain enzymes which work best at lower temperatures, which mean that the washing can be done at lower temperatures which saves energy. also lower temperatures means you can wash more delicate fabric
Electrolysis mean splitting up with electricity
- electric current is passed through a molten or dissolved ionic compound, causing it to decompose. this creates a flow of charge through the electrolyte
- the posotive ions will move towards the -ve Cathode and gain electrons, the negative ion will move towards the +ve anode and loose electrons
- as ions gain or loose electrons they become atoms or molecules and are discharged from the soloution at the electrodes
It may be easier to discharge ions from water rather than solute
- there are both Hydrogen [H+] and hydroxide ions [OH-] from the water in aqueous soloutions
- it can be easier to discharge the ion from the water rather than the ones from the solute. so H+ and OH- are discharged, and the rest of the solution remains in the beaker. meaning hyrdrogen is produced at the cathode, and oxygen produced at the Anode.
- Example: a soloution of Aqueous sulfuric acid (H2SO4) contains SO4(2-), H+ and OH-.
- hydrogen ions from either water or sulfuric acid can accept electrons coming from the cathode. meaning hydrogen gas is produced 2H+ + 2e- = H2
- Hydroxide ions from water can lose electrons easier then sulfate ions. so oxygen is produced at the anode. 4OH- - 4e- = 02 + 2H2O
Even More Electrolysis
Amount of electrons & Amount of product
- the amount of product made depends on no. of electrons transferred. more electrons means more product
- This cna be done by electrolysing for more time. or increasing the current
- Generally, the amount of charge measured in Coulombs (Q) can be calculated through current multiplied by time.
Examples for using Q = It, to work out amount of product formed
- in electrolysis, a current of 2.0A is passed through for 40 seconds. calculate charge. this would be done by Q = It. 2 x 40 = 80.
- experiment A: 0.5A ... 100 seconds
- experiment B: 1A ... 50 seconds
- experiment C: 2A ... ?
- we can find out the charge from experiment A by doing 0.5 multiplied by 100 to get 50. then re-arrange to find out the time taken withn experiment C. 50 divided by 2 = 25. so the answer is 25 seconds
Copper sulphate can be electrolysed to form copper and oxygen
- cathode starts as carbon and gets coated with copper. the reaction is Cu2+ + 2e- = Cu.
- at the anode, hydroxide ions are discharged from the solution and converted to oxygen and water. the reaction is 4OH- - 4e- = O2 + 2H2O
- copper ions are easier to discharge then H+ ions. they're attracted to the anode and are reduced to copper atoms
- hydroxide ions are oxidised to oxygen and water at the anode
In molten ionic solids, there's only one source of ions
- ionic solid can't be electrolysed because the ions are fixed and can't move
- molten ionic liquids can electrolyse as the electrons are free to move. they are always broken into their elements
- positive metal ions are reduced to atoms at the cathode.
- Negative ions are oxidised to make atoms at the anode
Way more Electrolysis
Hydrogen and Oxygen give out energy when they react
- hydrogen and oxygen react to produce water. this reaction is exothermic so it releases energy - which can be shown on an energy level diagram
- the higher a line is on the diagram, the more energy
- when bonds are formed excess energy is given out
Fuel cells use fuel and oxygen to produce electrical energy
- a fuel cell is a cell that's supplied with fuel and oxygen and uses the energy given out to produce efficient electrical energy. Example: hydrogen-oxygen fuel cell, which involves a redox reaction
- the electrolyte is a soloution of potassium hydroxide. electrodes are a porous carbon with a catalyst.
- hydrogen goes in at the anode compartment. oxygen goes in at the cathode compartment
- at the -ve Cathode, oxygen gains electron and reacts with water from the electrolyte to make OH- ions. [O2 + 4e- + 2H2O = 4OH-] the oxygen gas is being Reduced. OH- ions move to the +ve anode.
- also at the anode hydrogen combines with hydroxide ions to produce water to produce water and electrons. the hydrogen gas is oxidised. [2H2 + 4OH- = 4H2O + 4e-]
- the electrons being moved flow through an external unit from the anode to the cathode, this is the electric circuit.
- this is the overall reaction: Hydrogen + Oxygen = Water. OR 2H2 + O2 = 2H2O
CFC's and the Ozone Layer
There are lots of posotives to CFC's (Chlorofluorocarbons)
- they are organic molecules containing carbon, chlorine and fluorine
- CFC's are non toxic, Non flammable, un-reactive, insoluble, and have low boiling points
- they were used a coolants in fridges and air conditioning systems, and propellants in aerosol spray cans
But then came THE TRUTH!
- in 1974 it was found they destroyed Ozone, then in 1985 they found decreasing levels of Ozone in the atmosphere over antarctica
- measurements in the upper atmosphere have shown high levels of the compounds formed when CFC's break down
- O3 absorbs UV light from the sun and breaks down into an oxygen molecule and an oxygen atom. these two can then react again to form O3. so the cycle repeats
- Less ozone means more UV can pass through causing sunburn and skin cancer
- scientists' view on CFC's caused a lot of concern, their evidence and research into the damage that CFC's can cause needed to be evaluated and peer reviewed by other scientists.
- in 1978 USA, Canada, Sweden, and Norway banned use of CFC's. After the hole was discovered most countries got together and totally banned use of CFC's.
More Fuel cells
Advantages & Disadvantages
- more efficient than power stations or batteries. can be up to 80% if the heat is used
- direct energy transfer, less energy loss due to minimal stages
- no moving parts to go wrong
- no pollutants produced
- producing the hydrogen requires a lot of energy and burns fossil foils causing pollution
- Hydrogen fuel cells contain a poisonous catalyst which have to be disposed. takes up time and money and damages environment
Uses in Spacecraft and Cars
- hydrogen and oxygen readily available on the spacecraft. can drink the water produced
- lightweight, compact, and no moving parts, and no waste products
- the car industry is developing fuel cells, they don't produce any conventional pollutants. no carbon dioxide, nitrogen oxide, sulfur dioxide or carbon monoxide.
- Hydrogen can be obtained by decomposing water, of which there is a large amount available
- this fixes the issue with worries about fossil fuels polluting
- also fixes problems to do with non-renewable sources as we always have enough water to electrolyse
More CFC's and the Ozone Layer
(Chlorine) Free Radicals
- a covalent bond can break unevenly to make two ions (negative and positive) or it can break evenly, and each atom gets 1 of the shared electrons. this makes a free radical
- these free radicals are very reactive, and can be made when CFC's come into contact with ultraviolet light.
- these chlorine free radicals can then react with ozone which makes an oxygen molecule and chlorine oxide. which then reacts with ozone to make 2 oxygen molecules and a chlorine free radical. which then reacts with more ozone ect.. it's a chain reaction
- this means that the ozone is being broken down but the reactants can't make ozone again, so it's being depleted. but CFC's must react with UV before it becomes harmful.
CFC's remain in the stratosphere for a long time, but there are safe alternatives.
- they are not very reactive and only react with a few chemicals in the atmosphere, and only break down to chlorine in the stratosphere with lots of UV.
- so even though they have been banned the ozone will continue to deplete but just at a lower rate
- Alkanes is an alternative, they dont react with ozone so theyre safer
- HFC's can also be used. the compounds are very similar however there is no chlorine which means that the ozone won't be depleted.
Hardness Of Water
Consequences and Causes
- hard water won't form a lather with soap, it will only form a scum, so you need softer water or more soap. also form limescale. (Calcium Carbonate) in pipes. limescale can take in heat meaning it takes longer to boil, and it can block pipes if it builds up
- Hard water contains Calcium ions (Ca2+) and or Magnesium ions (Mg2+). these dissolve into the water when it passes over rocks containing these ions.
- magnesium sulfate and calcium sulphate dissolve in water
- calciumcarbonate can react with acids to dissolve in water, rainwater is acific from CO2, meaning it can react with rainwater to make calcium hydrogencarbonate which is soluble
- Carbon dioxide + water + calcium carbonate = Calcium Hydrogencarbonate
Temporary Hardness can be removed by boiling
- temporary hardness = hydrogencarbonate. Permenant = dissolved calcium sulfate
- Boiling breaks down calcium hyrdrogencarbonate into CaCO3 which is insoluble, so the hardness has been removed. but this wont work for permenant.
- both types can be removed by adding washing soda, sodium carbonate (Na2CO3).
- calcium ions join to carbonate ions to make an insoluble precipitate of calcium carbonate.both types can also be removed with an 'ion exchange resin' which sodium ions and swaps them for Mg or Ca Ions
Fats and Oils
They can come from animals or plants
- animal fats = lard (pork) blubber (Whale) ghee (butter) and cod liver oil. plants include walnut, coconut, olive and soya oil.
- At room temp, fats are solid and oils are liquid. fats and oils are esters (from an acid and an alcohol) specifically glyxerol reactign with fatty acids. these are important for the chemical industry, E.G - paints, machine lubricants, and also alternative to crude oil
- Milk is an oil in water emulsion (Oil droplets in water) and butter is a water in oil emulsion (Droplets of water in oil)
Uses of Vegetable oils, fats, and other oils
- vegetabel oils like rapeseed and soybean oil can be processed and turned into fuels. an example is biodiesel - it has similar properties to diesal and burns in the same way. it can be used just like diesel
- vegetable oils react with alkali to make soap
- natural fats and oil are boiled with sodium hydroxide, the hot sodium hydroxide splits up fats and oils to produce soap and glycerol - this is called saponification
- fat or oil breaks up to release glycerol and fatty acids (called hydrolysis - breaking up with water) then fatty acids react with sodium hydroxide to make soap. fat + sodium hydroxide = Soap + Glycerol
More Hardness Of Water
Comparing the hardness of water samples
- Method: Add 100cm3 of water to a conical flask. add 1cm3 soap soloution to the water. put a bung in and then shake
- Repeat unti a good lasting lather has formed (lasts at least 30secs) and then record the amount of soap used
- this method was carried out using Distilled water, local tap and foreign tap.
- fresh samples were used and then they were boiled and then repeated. From our table of results here is what we can tell:
- Distilled water contains little/no hardness as minimum soap was used
- imported water contains more hardess than the local water as more soap was needed to lather
- Local water contains only temporary hardness as all the hardness is removed by boiling it - as same amount of soap was needed for boiled as distilled
- imported contains both temporary and permenant as you still need 8cm3 after boiling
Using Plant Oils
Unsatured oild contain double bonds - C=C
- Monosaturated fats contain one C=C double bond somewhere in the carbon chain, whereas polysatured fats contain more than one C=C double bond. We can test for this using bromine water:
- an unsaturated oil or fat will react and decolorise bromine water, an addition reaction occurs and a colourless Dibromo compound is formed.
- Saturated oils or fats have no double bond to react so it stays orange from bromine
Unsaturated oils can be Hydrogenated
- they are liquid at room temperature and can be hardened by reacting them with carbon with a nickel catalyst at 60'. this is called hydrogenation, the hydrogen reacts with the double bonded carbons and opens out the double bond.
- margerine is made from partially hydrogenated vegetable oil, turning all the double bonds into single bonds would make it too hard, but partially makes it soft and spreadable.
Vegetable oils in foods can affect health
- saturated fats increase cholesterol which can block up arteries increasing blood pressure. natural unsaturated oils reduce the amount of cholesterol. partially hydrogenated oil increases bad cholesterol and decreases good cholesterol. which can lead to heart disease.