Term
| What is the composition of air? |
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Definition
Air is a mixture of gases with different boiling points – so it is a mixture of variable composition.
The composition of air is based on:
The Composition of Air %
Oxygen - 21
Nitrogen- 78
Carbon Dioxide- 0.04
Water Vapour- Varies (0.03)
Argon and other noble gases- 0.93 |
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Term
| What experiment did we carry out to measure the amount of air present in the air? |
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Definition
| To measure the amount of oxygen present in the air, a sample of lab air is passed repeatedly over some copper metal. There will be a colour change (pink – black) to the copper, as the metal is oxidised. So this means, that when you put, say 100cm³, at the start of the experiment, you will only be left with 79cm³ do to 21% is oxygen and so has reacted with the copper – removed. Copper only reacts with oxygen, so the remaining gas volume doesn't keep on getting smaller. |
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Term
| What are the tests for the oxygen, carbon dioxide and water? |
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Definition
Oxygen: Put a glowing splint in the test tube, if it re-lights, oxygen is present.
Carbon dioxide: Lime water goes cloudy when you put a bung through full of carbon dioxide.
Water (vapour): You put the droplets on blue cobalt paper, if it goes pink, water is present. You could also put the droplets in white copper sulphate, because if water is present, it will go blue. |
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Term
| What is the name of the process that separates air into its different components? |
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Definition
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Term
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Definition
It works by:
1) Air is filtered
2) Water vapour and carbon dioxide gases are removed - otherwise, when the air is cooled, they would solidly block the pipes.
3) Air is compressed (and so gets hot) and then cooled.
4) Air is allowed to expand rapidly which cools it sufficiently to turn it into a liquid.
5) Gas mixture is fed into the fractionation tower. Gases are separated according to their boiling points.
This means that dry air, free from carbon dioxide, can be liquefied and then fractionally distilled to obtain oxygen and nitrogen. |
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Term
| Other facts about the fractionation of air |
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Definition
-The expansion energy made is used to drive the turbine to produce electricity - to operate the compressor.
-Liquid oxygen collects at the bottom and is a colourless liquid.
-The other gases extracted are supplied in cylinders, or for larger items, it is stored in refrigerated tanks.
-Oxygen can be used for metal cutting, steel making.
-Nitrogen can be made for storing food, as there is an inert (unreactive) atmosphere.
-Argon is used to fill light bulbs. |
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Term
| What happens when we burn elements in air? |
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Definition
| Elements burn in the air to form oxides which are acidic, alkaline or basic. |
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Term
| When we dissolve metal oxides in water, what is the pH of the solution formed? |
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Definition
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Term
| When we dissolve non-metal oxides in water, what is the pH of the solution formed? |
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Definition
| They form acids. However, not all oxides are soluble in water, therefore the metal oxides which are insoluble are called base. |
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Term
| Why are these oxidation reactions? |
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Definition
| It is because the substances are burning in air, they are reacting with oxygen. The oxidation reactions involve the addition of oxygen to the element. |
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Term
| How could we tell water is pure? Describe an experiment you could use. |
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Definition
| Natural waters contain dissolved solid salts, which can be distilled (removed) to get pure water. You could test different samples over a beaker of hot water, to evaporate the water, this means that there may be solids left over. |
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Term
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Definition
| Desalination is an important method o obtaining water for domestic use in some countries. It is the large scale purification of water and uses large amounts of energy and needs specialised equipment. The water is therefore more expensive than traditionally sourced water. |
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Term
| How can we obtain pure water by distillation? |
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Definition
Distilled water is pure water because it only contains 1 compound H20. Dissolved substances have been removed in the distillation processes.
Distillation involves evaporation followed by condensation. |
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Term
| What is the point of distillation? |
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Definition
It makes undrinkable water palatable but is only economic in countries where:
there is a small shortage of water
there is access the sea without long pipes
the expense of lots of heat can be afforded |
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Term
| What stages does water have to undergo before it's fit to drink? |
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Definition
It has to evaporate and then condense again. it is heated by a flame, and the vapour entering the condenser (boiling point) is 100oc. The tubing on the condenser is connected to the water supply at its lower end because it's cold and so fills up without air bubbles in liquid surrounding the condenser.
the distillate could be checked with the water tests. |
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Term
| What is rusting and what metal does it affect? |
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Definition
Rusting is when the iron corrodes (oxidises) with oxygen in the air and water.
Iron + oxygen --> hydrated iron (III) oxide.
It affects iron, and its alloys, like steel. |
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Term
| What methods can be used to prevent rusting? How do they work? |
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Definition
Painting:Painting/ greasing stops moisture and oxygen getting to the iron. Medium cost, and it protects fairly well.It's easier to put on, but this means it rusts if it is scratched.
Greasing: A low cost, with protection fair. It is easy to put on, but it is also easily removed.
Tin plating: There is a medium cost, but has good protection. No particular advantages, but it rusts if scratched.
Chromium plating: Costs a lot, but has good protection, and looks good too. But it also rusts if scratched.
Galvanising: Where you coat it with zinc. It has a medium cost but is very good at protecting the iron, as it protects the iron even if it is scratched. |
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Term
| What is sacrificial protection? |
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Definition
| Sacrificial Protection:When metals that are higher than iron in the reactivity series coat the iron. This is done because as zinc and magnesium are more reactive than iron, any oxygen present will react with these metals rather than the iron: zinc and magnesium sacrifice themselves for iron. |
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