AS & A Level Chemistry - 9701 Paper 2 2010 Winter Zone 2

In 1814, Sir Humphrey Davy and Michael Faraday collected samples of a flammable gas, A, from the ground near Florence in Italy. They analysed A which they found to be a hydrocarbon. Further experiments were then carried out to determine the molecular formula of A.
(a) What is meant by the term molecular formula?
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Davy and Faraday deduced the formula of A by exploding it with an excess of oxygen and analysing the products of combustion.
(b) Complete and balance the following equation for the complete combustion of a hydrocarbon with the formula C_xH_y.
$C_xH_y + \left( x + \frac{y}{4} \right) O_2 \rightarrow$ ................................. + .................................
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(c) When $10\text{cm}^3$ of A was mixed at room temperature with $50\text{cm}^3$ of oxygen (an excess) and exploded, $40\text{cm}^3$ of gas remained after cooling the apparatus to room temperature and pressure. When this $40\text{cm}^3$ of gas was shaken with an excess of aqueous potassium hydroxide, KOH, $30\text{cm}^3$ of gas still remained.
(i) What is the identity of the $30\text{cm}^3$ of gas that remained at the end of the experiment?
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(ii) The combustion of A produced a gas that reacted with the KOH(aq). What is the identity of this gas?
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(iii) What volume of the gas you have identified in (ii) was produced by the combustion of A?
..............................cm$^3$
(iv) What volume of oxygen was used up in the combustion of A?
..............................cm$^3$
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(d) Use your equation in (b) and your results from (c)(iii) and (c)(iv) to calculate the molecular formula of A. Show all of your working.
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(a) Write an equation for the formation of ammonia in the Haber process.
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(b) The Haber process is usually carried out at a high pressure of between 60 and 200 atmospheres (between $60 \times 10^5$ Pa and $200 \times 10^5$ Pa).
State two further important operating conditions that are used in the Haber process.
For each of your conditions, explain why it is used.
condition 1 .....................................................................................................................................
reason .................................................................................................................................................
condition 2 .....................................................................................................................................
reason .................................................................................................................................................

(c) State one large-scale use for ammonia, other than in the production of nitrogenous fertilisers.
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(d) The uncontrolled use of nitrogenous fertilisers can cause environmental damage to lakes and streams. This is known as `eutrophication`.
What are the processes that occur when excessive amounts of nitrogenous fertilisers get into lakes and streams?
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(e) (i) Outline how each of these pollutants may be formed in an internal combustion engine.
CO ..............................................................................................................................................
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NO ..............................................................................................................................................
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(ii) State the main hazard associated with each of these pollutants.
CO ........................................................................................................................
NO ........................................................................................................................

(f) (i) What metal is most commonly used as the catalyst in a catalytic converter?
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(ii) Construct one balanced equation for the reaction in which both CO and NO are removed from the exhaust gases by a catalytic converter.
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(a) Explain what is meant by the following terms.
(i) hydrocarbon .................................................................................................................
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(ii) fractional distillation .............................................................................................
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(b) Undecane, $\text{C}_{11}\text{H}_{24}$, is a long chain hydrocarbon which is present in crude oil. Such long chain hydrocarbons are ‘cracked’ to produce alkanes and alkenes which have smaller molecules.
(i) Give the conditions for two different processes by which long chain molecules may be cracked.
process 1 .............................................................................................................
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process 2 .............................................................................................................
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(ii) Undecane, $\text{C}_{11}\text{H}_{24}$, can be cracked to form pentane, $\text{C}_{5}\text{H}_{12}$, and an alkene. Construct a balanced equation for this reaction.
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(c) (i) Draw the three structural isomers of pentane.

isomer B    isomer C    isomer D
(ii) The three isomers of pentane have different boiling points.
Which of your isomers has the highest boiling point?
isomer .........
Suggest an explanation for your answer.
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(d) Define the term standard enthalpy change of combustion.
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(e) (i) Use relevant data from the Data Booklet to calculate the amount of heat released in this experiment.
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(ii) Use the data above and your answer to (i) to calculate the relative molecular mass, $M_{r}$, of E.
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(f) Deduce the molecular formula of E.
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Halogenoalkanes have many chemical uses, particularly as intermediates in organic reactions. Three reactions of 1-bromobutane, CH₃CH₂CH₂CH₂Br, are shown below.
(a) For each reaction, state the reagent and solvent used.
reaction 1 reagent .....................................................
solvent ...........................................................
reaction 2 reagent .....................................................
solvent ...........................................................
reaction 3 reagent .....................................................
solvent ...........................................................

(b) When 1-iodobutane, CH₃CH₂CH₂CH₂I, is reacted under the same conditions as those used in reaction 1, butan-1-ol is formed. What difference, if any, would there be in the rate of this reaction compared to the reaction of 1-bromobutane? Use appropriate data from the Data Booklet to explain your answer.
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Dichlorodifluoromethane, CCl₂F₂, is an example of a chlorofluorocarbon (CFC) that was formerly used as an aerosol propellant. In September 2007, at the Montreal summit, approximately 200 countries agreed to phase out the use of CFCs by 2020.
(c) State two properties of CFCs that made them suitable as aerosol propellants.
1. ................................................................................
2. ................................................................................

(d) When CFCs are present in the upper atmosphere, homolytic fission takes place in the presence of ultraviolet light.
(i) What is meant by the term homolytic fission?
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(ii) Suggest an equation for the homolytic fission of CCl₂F₂.
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(e) The most common replacements for CFCs as aerosol propellants are hydrocarbons such as propane and butane. Suggest one disadvantage of these compounds as aerosol propellants.
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The gaseous hydrogen halides HCl, HBr and HI, may be prepared by reacting the corresponding sodium salt with anhydrous phosphoric(V) acid, H_3PO_4.
When the sodium halide NaX was used, the following reaction occurred and a sample of gaseous HX was collected in a gas jar.
NaX + H_3PO_4 → NaH_2PO_4 + HX
A hot glass rod was placed in the sample of HX and immediately a red/orange colour was observed.

(a) What is the identity of NaX?
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(b) What gas, other than HX, would be formed if concentrated sulfuric acid were used with NaX instead of phosphoric(V) acid?
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(c) Suggest why phosphoric(V) acid rather than concentrated sulfuric acid is used to make samples of HX from the corresponding sodium salt.
Explain your answer.
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