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(a) (i) Describe and explain the variation in the thermal stabilities of the carbonates of the Group 2 elements.
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(ii) Suggest and explain a reason why sodium carbonate is more stable to heat than magnesium carbonate.
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(b) Sodium hydrogencarbonate, NaHCO$_3$, and potassium hydrogencarbonate, KHCO$_3$, decompose on heating to produce gases and the solid metal carbonate.
(i) Write an equation for the decomposition of KHCO$_3$.
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(ii) Predict which of NaHCO$_3$ or KHCO$_3$ will decompose at the lower temperature. Explain your answer.
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(c) (i) Use the data in the table below, and relevant data from the Data Booklet, to calculate the lattice energy, $\Delta H^{\text{⦵}}_{\text{latt}}$ of potassium oxide, K$_2$O(s).
| energy change | value / kJ mol$^{-1}$ |
|---|---|
| enthalpy change of atomisation of potassium, $\Delta H^{\text{⦵}}_{\text{at}}$ K(s) | +89 |
| electron affinity of O(g) | -141 |
| electron affinity of O$^{2-}$(g) | +798 |
| enthalpy change of formation of potassium oxide, $\Delta H^{\text{⦵}}_{\text{f}}$ K$_2$O(s) | -361 |
$\Delta H^{\text{⦵}}_{\text{latt}} =$ ext{............................ kJ mol$^{-1}$} [3]
(ii) State whether the lattice energy of Na$_2$O would be more negative, less negative or the same as that of K$_2$O. Give reasons for your answer.
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(a) Complete the table to show how both AgNO$_3$(aq) and NH$_3$(aq) could be used to distinguish between solutions of NaCl(aq) and NaI(aq).
Important information for this question
• In this question (pr) means 'a solution in propanone'.
• Sodium iodide is soluble in propanone giving Na$^+$(pr) and I$^-$(pr).
• Sodium chloride is insoluble in propanone.
The reaction between 2-chlorobutane and sodium iodide in propanone is shown.
$ \text{CH}_3\text{CH}_2\text{CHClCH}_3\text{(pr)} + \text{Na}^+(\text{pr}) + \text{I}^-(\text{pr}) \rightarrow \text{CH}_3\text{CH}_2\text{CHICH}_3\text{(pr)} + \text{NaCl(s)} $
The rate of this reaction can be investigated by measuring the electrical conductivity of the reaction mixture. The electrical conductivity changes as the reaction progresses due to the precipitation of the NaCl produced.
(b) (i) Suggest how the electrical conductivity will change as the reaction proceeds. Explain your answer.
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(ii) Describe a suitable method for studying the rate of this reaction at a temperature of 40°C, using the following.
• an electrical conductance meter which measures the electrical conductivity of solutions
• solutions of known concentrations of 2-chlorobutane in propanone and sodium iodide in propanone
• stopclock
• access to standard laboratory equipment
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(c) The rate of this reaction was measured at different initial concentrations of the two reagents.
The table shows the results obtained.
(i) Deduce the order of reaction with respect to each of \text{[CH}_3\text{CH}_2\text{CHClCH}_3\text{]} and \text{[I}^- \text{]}.
Explain your reasoning.
order with respect to \text{[CH}_3\text{CH}_2\text{CHClCH}_3\text{]} ..................................................
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order with respect to \text{[I}^- \text{]} ..................................................
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(ii) Write the rate equation for this reaction, stating the units of the rate constant, k.
rate = .......................................................... \text{ mol dm}^3 \text{s}^{-1}
units of k = ..........................................................
[1]
(iii) Calculate the relative rate for experiment 4.
relative rate for experiment 4 = ...........................................
[1]
(d) (i) Suggest the mechanism for the reaction of 2-chlorobutane with iodide ions. Draw out the steps involved, including the following.
• all relevant lone pairs and dipoles
• curly arrows to show the movement of electron pairs
• the structure of any transition state or intermediate
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(ii) This reaction was carried out using a single optical isomer of 2-chlorobutane.
Use your mechanism in (i) to predict whether the product will be a single optical isomer or a mixture of two optical isomers. Explain your answer.
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(e) (i) State the number of peaks that would be seen in the carbon-13 NMR spectrum of \text{CH}_3\text{CH}_2\text{CHClCH}_3.
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(ii) There are two isomers of \text{CH}_3\text{CH}_2\text{CHClCH}_3 that have fewer peaks in their carbon-13 NMR spectra than \text{CH}_3\text{CH}_2\text{CHClCH}_3.
Draw the structures of the isomers and state the number of peaks for each isomer.
isomer 1 .................................................. number of peaks = ..................................
isomer 2 .................................................. number of peaks = ..................................
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(a) In a molecule of $\text{SOCl}_2$ the sulfur atom has four bonds.
Draw a 'dot-and-cross' diagram of $\text{SOCl}_2$. Show the outer shell electrons only.
(b) When $\text{SOCl}_2$ is reacted with a carboxylic acid to produce an acyl chloride, two acidic gases are formed.
$\text{SOCl}_2(l) + \text{RCO}_2\text{H}(l) \rightarrow \text{RCOCl}(l) + \text{SO}_2(g) + \text{HCl}(g)$
A 1.00 g sample of a carboxylic acid $\text{RCO}_2\text{H}$ was treated in this way, and the gases were absorbed in 60.0 cm$^3$ of 0.500 mol dm$^{-3}$ NaOH(aq), an excess.
(i) Write equations for the reactions between
NaOH and HCl, ...........................................................
NaOH and $\text{SO}_2$. .......................................................
[2]
(ii) Calculate the total number of moles of NaOH that reacted with the $\text{SO}_2$ and HCl.
moles of NaOH = ............................... [2]
(iii) Calculate the number of moles of $\text{RCO}_2\text{H}$ that produced the $\text{SO}_2$ and HCl.
moles of $\text{RCO}_2\text{H} = ...............................$ [1]
(iv) Hence calculate the $M_r$ of the carboxylic acid, $\text{RCO}_2\text{H}$.
$M_r \text{RCO}_2\text{H} = ...............................$ [1]
(v) The R group contains carbon and hydrogen only.
Suggest the molecular formula of $\text{RCO}_2\text{H}$.
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(c) The following synthetic route shows how a carboxylic acid can be converted into an amine.
$\text{CH}_3\text{CO}_2\text{H} \xrightarrow{\text{SOCl}_2} \text{CH}_3\text{COCl} \xrightarrow{\text{NH}_3} \text{CH}_3\text{CONH}_2 \xrightarrow{\text{step 3}} \text{CH}_3\text{CH}_2\text{NH}_2$
(i) Suggest a reagent for step 3.
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Angelic acid, $\text{C}_5\text{H}_8\text{O}_2$, is a natural product isolated from the roots of the angelica plant.
• Angelic acid reacts with $\text{H}_2$ + Ni to form T, $\text{C}_5\text{H}_{10}\text{O}_2$.
• T undergoes the above synthetic route to form the amine U, $\text{C}_5\text{H}_{13}\text{N}$.
• U can also be made by reacting 1-bromo-2-methylbutane with ammonia.
Both angelic acid and T exist as stereoisomers.
(ii) Suggest structures for angelic acid, T and U.
[Image]
[3]
(iii) State the type of stereoisomerism shown by angelic acid and T.
angelic acid ..............................................................
compound T .......................................................... [1]
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(a) A number of isomers with the formula $\text{Cr(H}_2\text{O)}_6\text{Cl}_3$ exist. Their general formula is $[\text{Cr(H}_2\text{O)}_{6-n}\text{Cl}_n]\text{Cl}_{3-n}\cdot n\text{H}_2\text{O}$. Each isomer contains a six co-ordinated Cr(III) ion in an octahedral complex. Water molecules not directly bonded with the Cr atom are held in the crystal lattice as water of crystallisation. The Cr–Cl bond is not easily broken and so chloride bonded with the Cr(III) ion in the complex does not react.
1.00 g samples of three of the isomers, A, B and C, were dissolved in separate samples of water. An excess of AgNO$_3$(aq) was added to each and the mass of AgCl(s) formed was measured.
$$\text{Ag}^+\text{(aq)} + \text{Cl}^-\text{(aq)} \rightarrow \text{AgCl(s)}$$
The number of moles of AgCl(s) formed was calculated. The table shows the results.
| isomer | moles of AgCl formed from 1.00 g of isomer |
|---|---|
| A | 3.75 $\times$ 10$^{-3}$ |
| B | 7.50 $\times$ 10$^{-3}$ |
| C | 1.13 $\times$ 10$^{-2}$ |
$M_r$ $\text{Cr(H}_2\text{O)}_6\text{Cl}_3$ = ............................. [1]
(ii) Use the data in the table above to calculate the value of n for each of the isomers, A, B and C. Complete the table below with the values of n and the molecular formula of each isomer, in the style of the general formula given above.
Show your working for at least one calculation of n.
| isomer | n | molecular formula |
|---|---|---|
| A | ||
| B | ||
| C |
(b) Two isomers have the same shape and their formula is $\text{Ni(R}_3\text{P)}_2(\text{CN})_2$, where $R = \text{CH}_3$. Only one of these isomers has a dipole moment.
(i) Name the type of isomerism shown by $\text{Ni(R}_3\text{P)}_2(\text{CN})_2$.
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(ii) Draw structures of these two isomers.
isomer 1 isomer 2 [1]
(iii) State which isomer has a dipole moment. Explain your answer.
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(a) 1,2-diaminoethane, en, $\text{H}_2\text{NCH}_2\text{CH}_2\text{NH}_2$, is a bidentate ligand.
(i) What is meant by the terms bidentate and ligand?
bidentate ...................................................................................................................
ligand ...................................................................................................................
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(a) 1,2-diaminoethane, en, $\text{H}_2\text{NCH}_2\text{CH}_2\text{NH}_2$, is a bidentate ligand.
(ii) There are three isomeric complex ions with the formula $[\text{Cr(en)}_2\text{Cl}_2]^+$.
Complete the three-dimensional diagrams of the isomers in the boxes.
You may use $\text{N}\hspace{0.1cm} \text{N}$ to represent en.
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(b) Copper forms complexes with NH$_3$ and en according to equilibria 1 and 2.
equilibrium 1 \hspace{0.5cm} Cu$^{2+}$(aq) + 4NH$_3$(aq) $\rightleftharpoons$ [Cu(NH$_3$)$_4$]$^{2+}$(aq)
equilibrium 2 \hspace{0.5cm} Cu$^{2+}$(aq) + 2en(aq) $\rightleftharpoons$ [Cu(en)$_2$]$^{2+}$(aq)
(i) Write the expressions for the stability constants, $K_{stab1}$ and $K_{stab2}$, for equilibria 1 and 2. Include units in your answers.
$K_{stab1}$ = .......................................................... units = ...............................
$K_{stab2}$ = .......................................................... units = ...............................
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(b) Copper forms complexes with NH$_3$ and en according to equilibria 1 and 2.
(ii) An equilibrium is set up when both en and NH$_3$ ligands are added to a solution containing Cu$^{2+}$(aq) as shown in equilibrium 3.
equilibrium 3 \hspace{0.5cm} [Cu(NH$_3$)$_4$]$^{2+}$(aq) + 2en(aq) $\rightleftharpoons$ [Cu(en)$_2$]$^{2+}$(aq) + 4NH$_3$(aq)
Write an expression for the equilibrium constant, $K_{eq3}$, in terms of $K_{stab1}$ and $K_{stab2}$.
$K_{eq3}$ = ......................................................................................................
[1]
(b) Copper forms complexes with NH$_3$ and en according to equilibria 1 and 2.
(iii) The numerical values for these stability constants are shown.
$K_{stab1}$ = 1.2 $\times$ 10$^{13}$ \hspace{0.5cm} $K_{stab2}$ = 5.3 $\times$ 10$^{19}$
Calculate the value of $K_{eq3}$ stating its units.
$K_{eq3}$ = .......................................................... unit = ................................................
[2]
(c) $\Delta S^o$ values for equilibria 1 and 2 differ greatly, as can be seen in the table. All values are at a temperature of 298 K.
[Table_1]
(i) Explain why $\Delta S^o_{eq2}$ is so different from $\Delta S^o_{eq1}$.
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(c) $\Delta S^o$ values for equilibria 1 and 2 differ greatly, as can be seen in the table. All values are at a temperature of 298 K.
(ii) Calculate $\Delta G^o_{eq2}$ at 298 K.
$\Delta G^o_{eq2}$ = ...................................................... kJ mol$^{-1}$
[2]
(c) $\Delta S^o$ values for equilibria 1 and 2 differ greatly, as can be seen in the table. All values are at a temperature of 298 K.
(iii) What conclusion can be made about the relative feasibility of equilibrium 1 and 2?
Explain your answer.
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(c) $\Delta S^o$ values for equilibria 1 and 2 differ greatly, as can be seen in the table. All values are at a temperature of 298 K.
(iv) Using data from the table, suggest a value of $\Delta H^o$ for equilibrium 3.
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(c) $\Delta S^o$ values for equilibria 1 and 2 differ greatly, as can be seen in the table. All values are at a temperature of 298 K.
(v) State the type of reaction that is occurring in equilibrium 2.
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The table lists some organic acids and their $pK_a$ values.
\[ \begin{array}{|c|c|c|} \hline \text{acid} & \text{formula} & pK_a \\ \hline \text{ethanoic acid} & \text{CH}_3\text{CO}_2\text{H} & 4.76 \\ \text{chloroethanoic acid} & \text{CICH}_2\text{CO}_2\text{H} & 2.86 \\ \text{aminoethanoic acid (glycine)} & \text{H}_2\text{NCH}_2\text{CO}_2\text{H} & 9.87 \\ \hline \end{array} \]
(a) (i) State the relationship between $pK_a$ and the strength of an acid.
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(ii) State the mathematical relationship between $pK_a$ and the acidity constant $K_a$.
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(iii) Give reasons for why the $pK_a$ value for chloroethanoic acid is smaller than that for ethanoic acid.
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(b) (i) Use the zwitterionic structure for aminoethanoic acid (glycine) in aqueous solution to write an equation for its dissociation giving $\text{H}^+(aq)$ ions.
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(ii) Calculate the pH of a $0.100 \text{ mol dm}^{-3}$ solution of aminoethanoic acid.
pH = .................................. [2]
(iii) A $10.0 \text{ cm}^3$ sample of $0.100 \text{ mol dm}^{-3}$ aminoethanoic acid (glycine) was titrated with $0.100 \text{ mol dm}^{-3}$ NaOH. After $20.0 \text{ cm}^3$ of NaOH, an excess, had been added, the pH was found to be 12.5.
Using the following axes, sketch a graph showing how the pH changes during this titration.
[Graph Image]
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Compounds W, X, Y and Z are isomers of each other with the molecular formula C₈H₇ClO. All four isomers contain a benzene ring. Only one of the isomers contains a chiral centre. The results of six tests carried out on W, X, Y and Z are shown in the table.
[Table_1]
(a) Use the experimental results in the table above to determine the group(s), in addition to the benzene ring, present in the four isomers W, X, Y and Z. Complete the table below, identifying the group(s) present in each isomer.
[Table_2]
(b) Isomers W, X, Y and Z all have the molecular formula C₈H₇ClO.
(i) Use the information in (a) to suggest a structure for each of these isomers and draw these in the boxes.
[Boxes for W, X, Y, Z]
(ii) Draw a circle around the chiral centre in one of the above structures.
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(a) The amino acid tyrosine can be synthesised from phenol by the route shown.
(i) Name the mechanism occurring in the following steps.
step 1 ............................................................................................................................
step 2 ............................................................................................................................ [2]
(ii) What \textit{type of reaction} is occurring in step 3?
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(iii) Suggest reagents and conditions for each of the following steps.
step 1 ............................................................................................................................
step 2 ............................................................................................................................
step 3 ............................................................................................................................
step 5 ............................................................................................................................ [5]
(iv) Draw the structures of the products of the reactions of tyrosine with an \textit{excess} of each of the following reagents.
with NaOH(aq)
with HCl(aq)
with Br_2(aq)
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(b) The dipeptide phe-tyr has the following structure.
A mixture of this dipeptide (phe-tyr) and its two constituent amino acids (phe and tyr) was
subjected to electrophoresis in a buffer at pH 12. At the end of the experiment the following
results were seen. Spots R and S remained very close together.
The three spots are due to the three species phe, tyr and phe-tyr.
(i) Which species is responsible for spot P? Explain your answer.
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(ii) Suggest why the other two species give spots R and S that are so close together.
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