Chemistry 3 - QWC's

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  • Created on: 05-04-14 11:31

Haber Process of making Ammonia

The Haber Process is used to make ammonia gas. Ammonia gas is made by reacting together nitrogen gas with hydrogen gas. The nitrogen comes from the air & the hydrogen is obtained from natural gas. The reaction between nitrogen & hydrogen is a reversable reaction, this means that the reaction can go forwards & backwards at the same time. When the rate of the forwards reaction & backwards reaction are equal, the reaction will be in 'equilibrium'.

If we change the temperature of pressure, the position of the equilibrium will change, by either forwards or backwards going faster. If we increase temperature, the reaction will decrease the temperature so the reaction will go backwards & the yield of ammonia will decrease. However, if we increase temperature the rate of reaction will also increase. In this reaction the temperature causes a problem between the yield of ammonia & the rate. As the rate of & yield of ammonia require different temperatures, a moderature temperature is used (400-500'c). Also to increase rate an iron catalyst is used, this will have no effect on the yield of ammonia. If we increase the pressure, the reaction will decrease the pressure by going forwards more. This will increase the yield of ammonia. This is why the reaction uses a high pressure (200-300 atmsopheres).

The unreacted nitrogen & hydrogen are recycled through the system, this allows the yield of ammonia to be relativly low. Even though the iron catalyst is used in the process is can become poisoned by impurities & cause the the catalyst to stop working properly.

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Contact Process of making Conc H2SO4

The raw materials used in making Conc H2SO4 are sulfur, air & water. Firstly, burn the sulfur in the air to produce sulfur dioxide gas.

Secondly, the sulfur dioxide is reacted with more air to form sulfur trioxide, this is a reversable reaction.

If we increase the temperature the reaction will decrease the temperature by going backwards more, this will decrease the yield of sulfur trioxide. But if we increase the temperature we increase the rate. Because the yield of sulfur trioxide require different temperatures a moderate temperature is used (400-500'c) & a vanadium (v) oxide catalyst is added to increase the rate. This catalyst can get poisoned by impurities & stop working. If we increase the pressure the reaction will decrease the pressure by going forwards more, which will increase the yield of sulfur trioxide & the rate. The pressure used is 1 atmosphere because this will give a 95% of sulfur trioxide yield & a high rate. The cost of using a higher pressure isn't balanced by the profit from a higher yield.

Finally, the sulfur trioxide is then absorbed into the concentrated sulfuric acid to produce a mixture called oleum. The oleum is then added to water to give Conc H2SO4. The sulfur trioxide can't be added directly to the water as it is too dangerous & highly exothermic.

Conc H2SO4 can act as a dehydrating agent.

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Advantages & disadvantages of fertilisers

A fertiliser is a substance that is used to put nutrients back into the soil for a healthy plant growth. There are a number of advantages & disavantages to using man-made fertilisers.

The main disadvantage to using such fertilisers is that it causes water pollution called eutrophication. This is because manufactured fertilisers are water soluble & can be washed by the rain into rivers & other water courses. This contributes to the nitrate pollution of water. The increase in nutrients encourages microscopic plants (algae) to grow, these plants will cover the surface of the water blocking out the sunlight from the plants that live deeper in the water. The plants at the bottom of the water will die because they can't photosynthesis & algae have short lives so they will die too. The bacteria will start to decompose the decaying plants, but because the bacteria respire a lot of oxygen the oxygen level will in the water will fall rapidly. This then causes the fish & other animal life to die due to the lack of oxygen in the waterAnother disadvantage is that the intensive farming used to support the use of fertilisers can result in the loss of habitats & can threaten the range of biodiversity.

However there are advantages to the use of man-made fertilisers. One is because the fertilisers produced by the chemical industry allows intensive farming of arable lands & so enable farmers to produce large yields of stable food crops yearly. This helps to keep down the price of food & avoids a shortage of food.

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What are the uses of Ethanol

Ethanol is a type of alcohol. Ethanol has 3 main uses.

One, it can be used as a solvent (meth, which is a mixture of ethanol & methanol).

Two, ethanol is the alcohol in all alcoholic drinks. Alcohol can result in problems in the human body; drinking an excessive amount of alcohol over a long period of time can cause liver failure & cancers, even drinking excessive amounts of alcohol over a short period of time can cause memory loss, dizziness, vomiting, aggression & depression. The taxes the Government put on alcohol brings in large amounts of money but this is more than balanced by the cost to the NHS or police for dealing with alcohol related problems.

Thirdly, ethanol can be used as a fuel. Ethanol can be produced from sugar cane by a process called fermentaion. When the sugar cane grows carbon dioxide is removed from the air by photosynthesis, but when the ethanol is then burnt the carbon dioxide is put back. This is why ethanol is classed as a carbon neutral fuel. Brazil uses ethanol in place of petrol as a fuel, mainly becuase the climate & land area allows for huge amounts of sugar cane to be grown.

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Differences & similarities between acid strength

An acid is a substance that produces hydrogen ions.

A strong acid will completely dissociate (break apart) into hydrogen ions, while a weak acid will only partically dissociate into hydrogen ions.

The pH scale measures the hydrogen ion concenetration.

The stronger the acid the more higher the concentration of hydrogen ions & the lower the pH.

The weaker the acid the weaker the concentration of hydrogen ions & the higher the pH.

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Describe the reactions of limestone

Limestone is calcium carbonate (CaCO3).

When limestone is heated, a strong chemical reaction called thermal decomposition occurs (the limestone will glow, giving out a light called 'lime light'):

Calcium carbonate (limestone)Calcium oxide (quicklime) + Carbon dioxide

When the calcium oxide (quicklime) is added to water an exothermic reaction occurs. There is enough heat produced to make the water boil:

Calicum oxide (quicklime)WaterCalcium hydroxide (slaked lime)

If the calcium hydroxide (slaked lime) is dissolved in water, it forms a solution of calcium hydroxide called limewater.

When the carbon dioxide is bubbled into limewater the limewater will turn milky due to the insoluble calcium carbonate & water. If the carbon dioxide is to continue bubbling into the milky limewater, the milkiness will disappear due to this reaction:

Calcium carbonate + Water + Carbon dioxideCalcium hydrogen carbonate (soluble, colourless solution)

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Compare the differences between metal carbonates

To investigate the thermal stabilities of metal carbonates, heat is required.

When sodium carbonate is heated bubbles are seen in the limewater being slowly releasedThe air in the tube expands when heated which causes bubbles to be seen in the limewaterThe limewater does not turn milky & the bubbles stop. The bubbles stop because the sodium carbonate does not decompose when heated. This is why sodium carbonate is thermally stable.

Copper II carbonate is a green solid that undergoes thermal decomposition when it is heated. When heated, bubbles can be seen in the limewater (no milkiness) & the solid stays green. The air in the tube expands causing the bubbles to be seen. The bubbles are now produced more quickly, & the limewater turns milky & the green solid turns black. Copper II carbonate is not thermally stable.

Calcium carbonate is a white solid that undergoes thermal decomposition when it is heated. When heated, bubbles can be seen in the limewater (no milkiness) & the solid stays white. The bubbles are now produced more quickly & the limewater turns milky & the solid stays white.

Calcium carbonate has to be heated more strongly than Copper II carbonate because it is thermally stable.

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Describe the chemical testings for positive metal

Firstly, flame tests can be used. From the Group 1 ions; lithium has a red flame, sodium has a yellow flame & potassium has a lilac flame. From Group 2; calcium has a brick red flame (orange-red/red). Copper II ions burn with a green flameSecondly, sodium hydroxide solution can be added to a solution of the metal ion. Iron II ions go from pale green to making a precipiate of dark green, which is due to the iron II hydroxide.

Iron II ions + Sodium hydroxide solution → Iron II hydroxide

Iron III ions go from yellow to a brown precipiate due to the iron III hydroxide.

Iron III ionsSodium hydroxide solution → Iron III hydroxide

Copper II ions go from a blue solution to making blue precipiate due to the copper II hydroxide.

Copper II ionsSodium hydroxide solution → Copper II hydroxide

In all these precipiation reactions there are "spectator ions", which are the ions that are not seen.

Copper II ions + Sodium hydroxide solution → Copper II hydroxide + Sodium sulfate (spectator ions)

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Explain what Atomic Spectroscopy is

Atomic Spectroscopy is basically a flame test, but using a machine.

It can be used to identify the metal ions present & it can also measure the concentration of the metal ions.

It can do this because the frequency of light emitted by the metal is used to identify & meausre the concentration of the metal ions present.

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Describe the chemical testings for negative metal

When a halide ion (Group 7) is dissolved in distilled water it forms a solution.

The reagents are silver nitrate & nitric acid.

The chloride ion makes a white precipiate.

The bromide ion has a cream precipiate.

The iodide ion has a yellow precipiate.

Siver nitrate solution + Halide X → Silver haliade X

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Describe the chemical testings for molecular ions

When a sulfate ion is reacted with barium chloride solution & hydrochloric acid, barium sulfate is produced which is a white solid. However if the sulfate ion is in a solid, the solid has to dissolve in water to make a solution.

Barium chloride + Sulfate → Barium sulfate

The reaction between a carbonate ion & hydrochloric acid will work if it is a solid or a solution. When these two chemicals react, bubbles are given off. This gas given off will turn limewater milky, this means that the gas is carbon dioxide.

Calcium carbonate + hydrochloric acid → Calcium chloride + Water + Carbon dioxide

The reaction between an ammonium ion & sodium hydrogen solution will work if it is a solid or a solution. To get these two chemicals to react they have to be heated first, bubbles are then seen. This gas that is given off will turn damp litmus paper blue, this means that the gas is ammonia.

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Describe some organic testings

An organic test on an alkene (C=C) would involved adding bromine water to the alkene & watching the colour change from orange/brown to colourless. This is because of the bromine ion.

Alkene + Bromine waterX (colourless)

To alcohol (R-OH) add potassium dichromate (VI) or add sulfuric acid. The observation seen is that the alcohol will turn from orange to green. In tis reaction the alcohol is oxidised to a carboxylic acid.

Alcohol + Potassium dichromate (VI)X (green)

Alcohol + Sulfuric acidX (green)

To a carboxylic acid (R-COOH) add sodium hydrogen carbonate solution or sodium carbonate solution. In this test bubbles will be seen, this gas will turn limwater milky so this means that this gas is carbon dioxide.

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Explain what Infra-red Spectroscopy is

Infra-red spectroscopy can be used to identify the bonds present in an organic molecule. The different bonds present in the molecules will show a different infra-red spectroscopy. However, this can be a problem as it will only work if the chemical bonds differ from eachother as their infra-red spectroscopy will be the same.

The infra-red spectroscopy is now used in the breath test for drink driving. The bond they look for is the C-H bond, this is because the O-H bond of alcohol is also found in water.

The old test for drink driving was blowing into a bag through a tube that contained potassium dichromate (VI) crystals. The crystals would then turn green if there was alcohol present in the breath.

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How to prepare salt by neutralization

Salt = Potassium sulfate

Acid = Sulfuric acid

Alkai = Potassium hydroxide 

1. measure 25.0 cm3 of potassium hydroxide solution using a pipette & place in conical flask with a few drops of indicator

2. add sulfuric acid (from burette) until indicator changes showing that neutralization has occured

3. repeat 1.& 2. so indicator changes when 1 drop of sulfuric acid is added

4. repeat 3. to get three results of volumes of sulfuric acid within 0.1 cm3 of eachother

5. repeat titration without using indicator & adding volume of sulfuric acid found in 4.

6. heat "neutral" solution to evaporate water & leave to make a solid - potassium sulfate salt

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Ethanol can be made from sugars by a fermentation reaction.

Glucose → Ethanol + Carbon dioxide

C6H12O16 → 2CH3CH2OH + 2CO2

To make the fermentation reaction to work, enzymes are needed. The enzymes used are found in yeast (an enzyme is a bilobical catalyst produced by living cells). The optinum temperature of yeast is at about 30'c, this is when the yeast is working at its best.

The ethanol is removed from the fermentation reaction mixutre by a process called distillation.

Ethanol has a lower boiling point than water so the ethanol will be distilled off first.

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