AS & A Level Chemistry - 9701 Paper 2 2014 Summer Zone 2

(a) Explain what is meant by the term nucleon number.
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(b) Bromine exists naturally as a mixture of two stable isotopes, $^{79}\text{Br}$ and $^{81}\text{Br}$, with relative isotopic masses of 78.92 and 80.92 respectively.

(i) Define the term relative isotopic mass.
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(ii) Using the relative atomic mass of bromine, 79.90, calculate the relative isotopic abundances of $^{79}\text{Br}$ and $^{81}\text{Br}$.

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(c) Bromine reacts with the element $A$ to form a compound with empirical formula $ABr_3$. The percentage composition by mass of $ABr_3$ is $A, 4.31$; $ ext{Br, 95.69}$.

Calculate the relative atomic mass, $A_r$, of $A$.
Give your answer to three significant figures.

$A_r$ of $A$ = ........................ [3]

(d) The elements in Period 3 of the Periodic Table show different behaviours in their reactions with oxygen.

(i) Describe what you would see when separate samples of magnesium and sulfur are reacted with oxygen.
Write an equation for each reaction.

magnesium
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sulfur
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(ii) Write equations for the reactions of aluminium oxide, $Al_2O_3$, with
sodium hydroxide,
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hydrochloric acid.
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(e) Phosphorus reacts with chlorine to form $PCl_5$.
State the shape of and two different bond angles in a molecule of $PCl_5$.

shape of $PCl_5$ ..................................................................................................................
bond angles in $PCl_5$ ............................... ............................... [2]

A 6.30 g sample of hydrated ethaneedioic acid, $H_2C_2O_4·xH_2O$, was dissolved in water and the solution made up to 250 cm³.
A 25.0 cm³ sample of this solution was acidified and titrated with 0.100 mol dm^-3 potassium manganate(VII) solution. 20.0 cm³ of this potassium manganate(VII) solution was required to react fully with the ethanedioate ions, $C_2O_4^{2-}$, present in the sample.
(a) The $MnO_4^-$ ions in the potassium manganate(VII) oxidise the ethanedioate ions.
(i) Explain, in terms of electron transfer, the meaning of the term oxidise in the sentence above.
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(ii) Complete and balance the ionic equation for the reaction between the manganate(VII) ions and the ethanedioate ions.
2$MnO_4^-$ (aq) + 5$C_2O_4^{2-}$ (aq) + ........$H^+$ (aq) → .........(aq) + 10$CO_2$(aq) + ........$H_2O$(l) [3]
(b) (i) Calculate the number of moles of manganate(VII) used in the titration.
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(ii) Use the equation in (a)(ii) and your answer to (b)(i) to calculate the number of moles of $C_2O_4^{2-}$ present in the 25.0 cm³ sample of solution used.
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(iii) Calculate the number of moles of $H_2C_2O_4·xH_2O$ in 6.30 g of the compound.
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(iv) Calculate the relative formula mass of $H_2C_2O_4·xH_2O$.
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(v) The relative formula mass of anhydrous ethaneedioic acid, $H_2C_2O_4$, is 90.
Calculate the value of $x$ in $H_2C_2O_4·xH_2O$.
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(a) The bar chart below shows the variation of melting points of the elements across Period 3.

In each of the following parts of this question you should clearly identify the interactions involved and, where appropriate, explain their relative magnitudes.
(i) Explain the general increase in melting point from Na to Al.
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(ii) Explain the variation of melting points from P to Ar.
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(iii) Explain why Si has a much higher melting point than any of the other elements in the period.
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(b) The graph below shows the variation of the first ionisation energies across Period 3.

(i) Explain why the first ionisation energy of Ar is greater than that of Cl.
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(ii) Explain why the first ionisation energy of Al is less than that of Mg.
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(iii) Explain why the first ionisation energy of S is less than that of P.
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(a) Give the names of one physical process and one chemical process carried out during the processing of crude oil.
physical process .............................................................
chemical process ............................................................

(b) Alkanes and alkenes can both be obtained from crude oil.
(i) Explain why alkanes are unreactive.
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(ii) State the bond angles in a molecule of
ethane, ............................................................
ethene. ............................................................
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(iii) State the shape of each molecule in terms of the arrangement of the atoms bonded to each carbon atom.
ethane ....................................... ethene .......................................
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(iv) Explain why these molecules have different shapes in terms of the carbon-carbon bonds present.
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(c)
(i) Use a series of equations to describe the mechanism of the reaction of ethane with chlorine to form chloroethane. Name the steps in this reaction.
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(ii) Write an equation to show how butane could be produced as a by-product of this reaction.
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A hydrocarbon, P, with the formula $C_6H_{12}$ readily decolourises bromine.
On reaction with hot, concentrated, acidified potassium manganate(VII) solution a single organic product, Q, is obtained.
Q gives an orange precipitate when reacted with 2,4-dinitrophenylhydrazine, 2,4-DNPH reagent, but has no reaction with Tollens' reagent.
(a) (i) Explain these observations.
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(ii) Draw the skeletal formula of P and give its name.

name of P .................................................................................................................................[2]
(iii) Draw the skeletal formula of Q and give its name.

name of Q .................................................................................................................................[2]

(b) There are several structural isomers of P that also decolourise bromine, but only four of these structural isomers exhibit geometrical (cis-trans) isomerism.
Give the structures of any three structural isomers of P that exhibit geometrical (cis-trans) isomerism.

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