No questions found
The composition of atoms and ions can be determined from knowledge of atomic number, nucleon number and charge.
(a) Complete the table.
| atomic number | nucleon number | number of electrons | number of protons | number of neutrons | symbol |
|---|---|---|---|---|---|
| 3 | 2 | 6_3Li^+ | |||
| 23 | 11 | ||||
| 26 | 32 |
(b) Boron occurs naturally as a mixture of two stable isotopes, $^{10}B$ and $^{11}B$. The relative isotopic masses and percentage abundances are shown.
| isotope | relative isotopic mass | abundance / % |
|---|---|---|
| $^{10}B$ | 10.0129 | 19.78 |
| $^{11}B$ | to be calculated | 80.22 |
(i) Define the term relative isotopic mass.
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(ii) Calculate the relative isotopic mass of $^{11}B$.
Give your answer to six significant figures. Show your working.
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598
589
600
Explain why nitrogen gas is so unreactive.
(b) Despite the low reactivity of $N_2$, oxides of nitrogen occur in the atmosphere through both natural and man-made processes.
(i) Explain why oxides of nitrogen can be produced by internal combustion engines. [2]
(ii) State and explain, using a suitable equation, how oxides of nitrogen produced by internal combustion engines can be prevented from reaching the atmosphere. [2]
(iii) State the role of nitrogen dioxide, $NO_2$, in the formation of acid rain by oxides of sulfur. Write suitable equations to explain this role.
role ..................................................................................................................................................................................................................................................
equation 1 .........................................................................................................................................................................................................................................
equation 2 ......................................................................................................................................................................................................................................... [3]
(iv) Suggest an equation to show how $NO_2$ can contribute directly to acid rain. [1]
(c) Explain how the uncontrolled use of nitrate fertilisers on land can lead to a severe reduction in water quality in rivers.
591
521
569
The hydrogen halides, HCl, HBr and HI, can undergo thermal decomposition. In a sealed container an equilibrium is established according to the equation shown.
$2HX(g) \rightleftharpoons H_2(g) + X_2(g)$ (where $X = Cl, Br$ or $I$)
(a) Some bond energies are shown in the table.
[Table_1]
Use these data to calculate a value for the enthalpy change, $\Delta H$, for the thermal decomposition of hydrogen bromide, $HBr$, according to the equation shown.
$$\Delta H = \text{......................... kJ mol}^{-1}$$ [1]
(b) At a temperature of 700 K a sample of HBr is approximately 10% decomposed. Changing the temperature affects both the rate of decomposition of HBr and the percentage that decomposes.
The Boltzmann distribution for a sample of HBr at 700 K is shown. $E_a$ represents the activation energy for the reaction.
(i) Using the same axes, sketch a second curve to indicate the Boltzmann distribution at a higher temperature. [2]
(ii) With reference to the curves, state and explain the effect of increasing temperature on the rate of decomposition of HBr.
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................................................................................................................... [3]
(iii) The decomposition of HBr is endothermic.
State the effect of increasing temperature on the percentage of HBr that decomposes. Use Le Chatelier's principle to explain your answer.
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(iv) At 700 K HBr is approximately 10% decomposed but hydrogen iodide, HI, is approximately 20% decomposed.
Explain this difference with reference to bond strengths and the factors that affect them.
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................................................................................................................... [3]
(c) At temperatures above 1500 K, HCl will decompose.
A sample of 0.300 mol of HCl decomposed in a sealed container.
The resulting equilibrium mixture was found to contain $1.50 \times 10^{-2}$ mol of $Cl_2$.
(i) Calculate the amounts, in mol, of $H_2$ and HCl present in the equilibrium mixture.
$$H_2 = \text{.......................... mol}$$
$$HCl = \text{.......................... mol}$$ [2]
(ii) Calculate the mole fraction of each gas in the equilibrium mixture.
mole fraction of $HCl = \text{..........................}$
mole fraction of $H_2 = \text{..........................}$
mole fraction of $Cl_2 = \text{..........................}$ [1]
(d) In another experiment under different conditions, an equilibrium mixture was produced with mole fractions for each species as shown.
[Table_2]
(i) Write the expression for the equilibrium constant, $K_p$, for the decomposition of HCl.
$2HCl(g) \rightleftharpoons H_2(g) + Cl_2(g)$
$$K_p = \text{....................................}$$ [1]
(ii) Explain why the total pressure of the system does not need to be known for $K_p$ to be calculated for this experiment.
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................................................................................................................... [1]
(iii) Calculate the value of $K_p$ for this experiment.
$$K_p = \text{..........................}$$ [1]
531
512
527
(a) The hydrocarbons A, C_4H_{10}, and B, C_4H_8, are both unbranched.
A does not decolourise bromine.
B decolourises bromine and shows geometrical isomerism.
(i) Draw the skeletal formula of A. [1]
(ii) The hydrocarbon A, C_4H_{10}, has a branched isomer.
Suggest why unbranched A has a higher boiling point than its branched isomer.
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(iii) Give the structural formula of B.
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(iv) Explain why B shows geometrical isomerism.
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(v) Draw the mechanism of the reaction of B with bromine, Br_2.
Include all necessary charges, dipoles, lone pairs, and curly arrows. [4]
(vi) Explain the origin of the dipole on Br_2 in this mechanism.
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(b) The alcohols C and D are isomers of each other with molecular formula C_4H_{10}O. Both isomers are branched.
When C is heated under reflux with acidified potassium dichromate(VI) no colour change is observed.
When D is heated under reflux with acidified potassium dichromate(VI) the colour of the mixture changes from orange to green and E, C_4H_8O_2, is produced.
E reacts with aqueous sodium carbonate to form carbon dioxide gas.
(i) Identify C, D and E. [3]
(ii) Write the equation for the reaction between E and aqueous sodium carbonate.
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(c) The isomers F and G, C_5H_{10}O, both form an orange precipitate when reacted with 2,4-DNPH.
F is unbranched and reacts with alkaline aqueous iodine to produce a yellow precipitate.
G does not react with alkaline aqueous iodine. It contains a chiral centre and produces a silver mirror when warmed with Tollens' reagent.
(i) Name the yellow precipitate produced by the reaction between F and alkaline aqueous iodine.
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(ii) Give the structural formula of F and of G.
F ...................................................................................................................
G .................................................................................................................. [2]
(iii) Explain the meaning of the term chiral centre.
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(d) H and I are isomers with molecular formula C_2H_4O_2. The infra-red spectra of isomers H and I are shown.
(i) Identify the bonds responsible for the principal peaks above 1500 cm^{-1}in each spectrum.
spectrum of H ...............................................................................................
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spectrum of I ................................................................................................
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(ii) Name H and I.
H ...................................................................................................................
I ................................................................................................................... [2]
549
572
561
