Essay about Chemistry: Oxygen and Marks

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Chemistry 1
Question 1
1.1 The fundamental ideas in chemistry

Group 1 elements burn vigorously when heated in oxygen.
(a) Complete these diagrams to show the electronic structures of sodium and oxygen atoms. (2 marks)
(b) Write the word equation that describes the reaction between sodium and oxygen. (1 mark)
(c) Write the balanced equation for this reaction, including the state symbols. (3 marks)
(d) Why are the elements in group 0 unreactive? (1 mark)
Question 2
1.2 Limestone and building materials

When limestone is heated to make cement it first reacts to produce lime (calcium oxide).
(a) Write a word equation using chemical names for what happens when limestone is heated. (1 mark)
(b) Write the chemical formula for: (i) limestone (1 mark) (ii) lime (1 mark)
(c) Write a balanced equation with state symbols for what happens when limestone is heated. (2 marks)

Water reacts with lime to form slaked lime (calcium hydroxide).
(d) Write a word equation for this reaction using chemical names. (1 mark)
(e) Write a balanced equation with state symbols for this reaction. (3 marks)
(f) Farmers use slaked lime for liming the soil. Why is it necessary to lime some soils? (1 mark)
Question 3
1.3 Metals and their uses

Copper can be obtained from solutions of copper salts by electrolysis or by displacement using scrap iron. It can also be extracted by phytomining.
(a) Draw an arrow on the following reactivity series (reactivity decreases down the list) to show where copper should be placed. (1 mark) sodium calcium magnesium aluminium carbon zinc iron
(b) Write a word equation for the displacement of copper from copper sulfate solution by iron. (1 mark)
(c) Write a balanced equation with state symbols for this reaction. (3 marks)
(d) Explain why copper is produced at the negative electrode during electrolysis. (2 marks)
(e) What is phytomining? (2 marks)
(f) Predict the method of extraction used to obtain calcium from its ore and explain your answer. (2 marks)
Question 4
1.4 Crude oil and fuels

Crude oil is a mixture of compounds, mainly hydrocarbons.
(a) What is a hydrocarbon? (1 mark)
(b) The table gives the boiling points of four hydrocarbons.

Hydrocarbon
Boiling point in °C
P
174
Q
–161
R
125
S
–42

Which of these hydrocarbons are gases at room temperature (20°C)? (1 mark)
(c) Which of these hydrocarbons has the largest molecules? (1 mark)
(d) Fractional distillation can be used to separate crude oil into fractions. Describe how this process works. (3 marks)
(e) Draw the structure of ethane, C2H6, showing all the bonds. (1 mark)
(f) Write a balanced equation for the complete combustion of ethane. (3 marks)
(g) The use of hydrocarbons as fuels can lead to acid rain. Explain how this arises. (3 marks)
Question 5
1.5 Other useful substances from crude oil

The cracking of large molecules involves their thermal decomposition.
The diagram shows an apparatus that can be used to crack hydrocarbons in the laboratory.

(a) What is thermal decomposition? (2 marks)
(b) Why is the porous pot included in the apparatus? (2 marks)
(c) Complete the equation below for the cracking of the molecule C20H42. (1 mark) C20H42  C3H6 + _____________________
(d) What chemical test would you use to show that the gas, propene, was an alkene? (3 marks)
(e) Draw the structure of the propene (C3H6) molecule, showing all the bonds. (2 marks)
(f) Explain what is meant by polymerisation. (2 marks)
(g) Use a diagram to show the formation of poly(propene). (3 marks)

Crude oil is used to produce many useful fuels, but oil reserves are being used up. One way to conserve crude oil reserves would be to increase the production of bio-fuels.
Ethanol can be produced for use as a bio-fuel. Cars can be powered by ethanol or ethanol–petrol mixtures.
Sugar cane can be fermented to give a mixture of water (boiling point 100°C) and ethanol (boiling point 78°C).
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