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A Group 2 metal combines with bromine to form a crystalline solid, MBr_2. Excess aqueous AgNO_3 is added to a solution of MBr_2 and a precipitate forms. The mixture is filtered. The precipitate is dried and the mass of the precipitate is recorded.
(a) State the formula and colour of the precipitate.
[2]
(b) Complete the equation to represent the reaction between MBr_2 and AgNO_3.
......MBr_2 + ......AgNO_3 \rightarrow ............................................................
[1]
(c) A 0.250 g sample of pure MBr_2 contains 8.415 \times 10^{-4} mol MBr_2.
Calculate the relative formula mass, M_r, of MBr_2. Use this to identify M.
Show your working.
M_r = .............................
M = .............................
[3]
(d) A sample of MBr_2 is dissolved in water. Chlorine gas is then bubbled into the solution.
(i) Describe the observations for this reaction.
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[1]
(ii) Name the type of reaction that occurs when MBr_2 reacts with chlorine gas.
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[1]
(e) Compound Y is a pure \textbf{insoluble} solid which contains halide ions.
A single reagent is added directly to compound Y to determine the halide ion present.
Identify the reagent added. State the observation which would confirm that Y contains bromide ions.
reagent ..................................................................................................................
observation .........................................................................................................
[2]
(f) Separate 1.0 g samples of three different magnesium salts are tested in order to identify the anion present in each sample.
(i) Explain how the action of heat is used to identify which sample is:
\begin{itemize}
\item MgCO_3
\item Mg(NO_3)_2
\item MgO
\end{itemize} .................................................................................................................................
[3]
(ii) Complete the electron configuration of the magnesium cation present in these salts.
1s^2 .....................................................................................................................
[1]
(g) A sample of MgCO_3(s) is distinguished from a sample of Mg(OH)_2(s) by adding a small amount of each solid to HCl(aq).
State one similarity and one difference in these two reactions.
similarity ..................................................................................................................
difference ...................................................................................................................
[2]
593
538
512
The strength of interaction between particles determines whether the substance is a solid, liquid or gas at room temperature.
(a) Lithium sulfide, Li₂S, is a crystalline solid with a melting point of 938°C. It conducts electricity when it is molten.
(i) Give the formulae of the particles present in solid lithium sulfide.
................................................................................................................................................. [1]
(ii) Explain, in terms of the structure of the crystalline solid, why lithium sulfide has a high melting point.
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(b) Carbon monoxide, CO, is a gas at room temperature and pressure. It contains a coordinate bond.
(i) Explain what is meant by coordinate bond.
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(ii) Draw a 'dot-and-cross' diagram to show the arrangement of outer electrons in CO.
Show the electrons belonging to the C atom as x.
Show the electrons belonging to the O atom as •.
................................................................................................................................................. [2]
(c) Nitrogen, N₂, is also a gas at room temperature and pressure. Neither CO nor N₂ is an ideal gas.
(i) State two assumptions that are made about the behaviour of particles in an ideal gas.
1 ...............................................................................................................................................
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2 ...............................................................................................................................................
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(ii) Explain why N₂ does not behave as an ideal gas at very high pressures.
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(iii) Complete the table by naming all the types of intermolecular forces (van der Waals') in separate samples of N₂(g) and CO(g).
| N₂(g) | CO(g) | |
|---|---|---|
| number of electrons per molecule | 14 | 14 |
| presence of a dipole moment | ✗ | ✓ |
| boiling point /°C | –195.8 | –191.5 |
| intermolecular forces (van der Waals') |
(iv) Suggest why the bond in a molecule of CO contains a dipole moment.
................................................................................................................................................. [1]
594
545
509
A large excess of 2-bromo-2-methylpropane is added to 0.0010 mol of NaOH(aq), which contains a few drops of phenolphthalein indicator. A stopwatch is started as soon as the substances are mixed. The time taken for the pink colour to disappear is recorded. The experiment is repeated at different temperatures, keeping all concentrations and volumes of reagents constant.
[Table_1]
(a) Explain what is meant by the term rate of reaction.
.......................................................................................................................................................................................... [1]
(b) The graph shows the energy distribution of molecules in a sample of 2-bromo-2-methylpropane at 25°C.
$E_a$ represents the activation energy for the reaction.
[Graph_1]
(i) Label the graph to show the proportion of 2-bromo-2-methylpropane molecules which have sufficient energy to react. [1]
(ii) Use the same axes to sketch the distribution of energies of molecules in a sample of 2-bromo-2-methylpropane at 50°C. [2]
(iii) State the effect of an increase in temperature on $E_a$ for this reaction.
.......................................................................................................................................................... [1]
(c) (i) Draw the mechanism to show the reaction of 2-bromo-2-methylpropane with OH⁻(aq). Show the intermediate formed in this reaction. Include all charges, partial charges, lone pairs and curly arrows as appropriate.
[Diagram_1]
[3]
(ii) Name the mechanism for this reaction.
.......................................................................................................................................................... [1]
(d) The original experiment is repeated at 25°C with 2-chloro-2-methylpropane instead of 2-bromo-2-methylpropane. All other variables remain constant. Predict the effect of using 2-chloro-2-methylpropane compared to 2-bromo-2-methylpropane on the time taken for the pink colour to disappear. Explain your answer.
.......................................................................................................................................................................................... [2]
563
533
527
(a) The table shows the structural formulae of four compounds, A, B, C and D, with molecular formula $C_4H_8$.
(i) Complete the table by giving the systematic name of A, B, C and D.
(ii) Explain what is meant by stereoisomerism.
.................................................................................................................................
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(b) W is an alkene with formula $C_4H_8$. It reacts with HBr to form two possible carbocations, $CH_3C^+ (H)(CH_2CH_3)$ and $H_2C^+CH_2CH_2CH_3$.
(i) Identify W as compound A, B, C or D.
.....................................................................................................................................
(ii) Draw the skeletal formula of the major organic product formed when HBr reacts with W. Explain why this is the major organic product.
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(c) A sample of propan-1-ol reacts with concentrated sulfuric acid to form propene. Identify the role of concentrated sulfuric acid in this reaction.
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(d) Alcohol Y reacts completely when warmed with acidified $Cr_2O_7^{2-}$ to form Z.
Z is distilled from the reaction mixture as soon as it is made. Tollens’ reagent is added to a sample of Z and warmed. A silver mirror forms.
(i) Name the type of reaction that occurs when Y reacts to form Z.
.................................................................................................................................
(ii) Identify with a tick (✓) the functional group(s) present in Z.
579
517
552
S is a secondary alcohol with molecular formula $C_{4}H_{10}O$.
(a) Draw the displayed formula of S.
(b) S is converted to V in a three-step reaction sequence.
In step 1, the secondary alcohol S reacts with $PBr_{3}$ to produce T, which has molecular formula $C_{4}H_{9}Br$.
(i) Give the systematic name of T.
................................................................................................................................. [1]
(ii) Name the type of reaction that occurs in step 1.
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(iii) State the reagent(s) and conditions for step 2.
.................................................................................................................................
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(iv) Step 3 involves heating $C_{4}H_{9}CN$ with dilute acid to form V.
Complete the equation for this reaction.
.....$C_{4}H_{9}CN + .....H^{+} + .....H_{2}O \rightarrow$ ......................................................... [2]
(v) An unlabelled sample contains either S, T or U.
The sample produces the infrared spectrum shown.
Explain how this spectrum confirms that the unknown sample contains U.
In your answer identify one relevant absorption in the infrared spectrum and the bond that corresponds to this absorption in the region above $1500 \text{cm}^{-1}$.
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................................................................................................................................. [1]
518
596
568
