Chemistry Topic 25, 26, 27

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T25- What are the relative percentages of nitrogen, oxygen, argon and carbon dioxide in the air?
N- 78% O- 21 % Argon- 1% Carbon dioxide- 0.04%
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T25- What are two methods of proving the percentage of oxygen in the air?
Heating copper or reacting iron with oxygen and water to form rust.
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T25- Explain the heating copper method
Heat an excess of copper between two syringes and the markers on the syringes will tell you how much oxygen has been used up. If starting with 100cm^3 of air, you will end up with roughly 80 cm^3 of air, meaning that 20% has been used up, so O2=20%
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T25- Explain the rusting method
Soak some iron wool in acetic acid will will catalyse the reaction. Place in test tube, and invert the test tube in water. Mark the starting position of the water. As the oxygen reacts to form rust, the water will rise to fill the air.
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T25- How would you work out the percentage of oxygen in the air from the rusting method?
Fill water up to the starting point and end point marked on the test tube, and in turn pour each of these into a measuring cylinder to record the volumes. Change in volume/initial volume.
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T25- What is the first step of the contact process?
Burning sulphur in air S + O2 ---> SO2
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T25- What is the second step of the contact process?
The sulphur dioxide is oxidised to form sulphur trioxide: 2SO2 + O2 2SO3
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T25- What are the conditions for step two and why?
450 degrees C, 2 atmospheres and catalyst: V2O5. There are 3 mol of reactants for 2 mol of products. The reaction is exothermic, but reducing temperatures to try to increase the yield slows the reaction down too much. With V2O5, 99% yield.
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T25- What are three uses of sulphuric acid?
1) fertilisers 2) Detergents 3) Paints as it can make titanium oxide, a white pigment.
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T26- How can you produce oxygen in a lab?
The decomposition of hydrogen peroxide: 2H2O2 ----> O2 + 2H2O. Use the catalyst Manganese IV oxide.
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T26- How can the oxygen be collected?
Water displacement or in a gas syringe.
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T26- Describe the reaction of Magnesium with oxygen
Burns with bright white light. White powder produced, alkaline in water.
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T26- Describe the reaction of carbon with oxygen
ONLY IF STRONGLY HEATED. Burns with yellow/orange flame. Produces carbon dioxide which is acidic in water.
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T26- Describe the reaction of sulphur with oxygen
Burns with pale blue flame. Produces sulphur dioxide which is acidic in water.
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T26- When should upward/downward delivery be used?
Downward- (test tube faces up,) gases heavier than air. Upward- (test tube faces down,) gases lighter than air.
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T27- What are two ways to produce carbon dioxide in a lab?
Hydrochloric acid and calcium carbonate, CO2 collected in syringe. Decomposition of metal carbonate.
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T27- What is the chemical equation for the reaction of HCl and calcium carbonate?
2HCl (aq) + CaCO3 (s) ---> CaCl2 (aq) + H2O (l) + CO2 (g)
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T27- Define thermal decomposition.
Breaking down a substance into simpler substances by heating.
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T27- What is the general word equation for this type of decomposition?
Metal carbonate ---> Metal oxide + carbon dioxide.
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T27- Explain this experiment involving Copper II carbonate
Copper oxide is black. Copper carbonate is green. Collected via downward delivery.
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Card 2

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T25- What are two methods of proving the percentage of oxygen in the air?

Back

Heating copper or reacting iron with oxygen and water to form rust.

Card 3

Front

T25- Explain the heating copper method

Back

Preview of the front of card 3

Card 4

Front

T25- Explain the rusting method

Back

Preview of the front of card 4

Card 5

Front

T25- How would you work out the percentage of oxygen in the air from the rusting method?

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