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Atoms with nuclei containing an odd number of protons tend to have fewer isotopes than those with an even number of protons.
(a) Gallium has two stable isotopes, $^{69}$Ga and $^{71}$Ga.
(i) Complete Table 1.1 to show the numbers of protons, neutrons and electrons in the two stable isotopes of gallium.
Table 1.1
[Table_1]
[2]
(ii) Define relative atomic mass.
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[2]
(iii) The relative atomic mass of gallium, $A_r$, is 69.723.
The relative isotopic masses of $^{69}$Ga and $^{71}$Ga are:
$^{69}$Ga, 68.926; $^{71}$Ga, 70.925.
Use this information to calculate the percentage abundance of $^{69}$Ga in elemental gallium.
Show your working.
Assume that the element contains only the $^{69}$Ga and $^{71}$Ga isotopes.
Give your answer to four significant figures.
percentage abundance of $^{69}$Ga = ................................. %
[2]
(b) Potassium also has two stable isotopes. Both isotopes have the same chemical properties.
(i) Explain why both isotopes of potassium have the same chemical properties.
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[1]
(ii) State the full electronic configuration of an atom of potassium.
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[1]
(iii) The first, second and third ionisation energies of potassium are 418, 3070 and 4600 kJ mol$^{-1}$, respectively.
Use this information to explain why potassium is in Group 1.
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[2]
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Magnesium shows reactions typical of a Group 2 metal.
(a) Draw a labelled diagram to show the bonding in magnesium metal.
(b) Fig. 2.1 shows some reactions of magnesium and its compounds.
(i) Identify the other products of reactions 1 and 2.
reaction 1 ..............................................................
reaction 2 .............................................................. [2]
(ii) Reaction 3 is used to form a precipitate of Mg(OH)₂ from MgCl₂(aq).
State why Ca(OH)₂(aq) would not form a precipitate of Ba(OH)₂ from BaCl₂(aq). [1]
(iii) State the type of reaction that occurs in reaction 4. [1]
(c) 1 cm³ of MgCl₂(aq) is placed in a test-tube. A few drops of AgNO₃(aq) are added, followed by 1 cm³ of dilute NH₃(aq).
State in full what is observed in this experiment. [2]
(d) When 1 cm³ of MgCl₂(aq) is added to 1 cm³ of Br₂(aq) in a test-tube, the solution remains orange.
Explain this observation. [1]
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Some of the common chlorides of Period 3 elements are shown in the list.
NaCl MgCl_2 AlCl_3 SiCl_4 PCl_5
(a) From this list, identify:
(i) all the chlorides that have giant ionic structures in the solid state
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(ii) all the chlorides that react vigorously with water to form strongly acidic solutions
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(iii) the chloride that dissolves in water to form a neutral solution
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(iv) the chloride formed from the element with the highest melting point.
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(b) NaCl is one product of the reaction of chlorine gas and cold aqueous sodium hydroxide.
Identify the other products.
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(c) PCl_5 reacts with alcohols to form chloroalkanes.
(i) Identify this type of reaction.
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(ii) Draw the structure of the organic product formed in the reaction of an excess of PCl_5 with butane-1,3-diol.
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(d) Sulfur, S_8, reacts with chlorine to form several different chlorides. The most common are S_2Cl_2 and SCl_2. SCl_2 forms when sulfur reacts with an excess of chlorine.
reaction 1 S_8(s) + 4Cl_2(g) \rightarrow 4S_2Cl_2(l) \Delta H_r = -58.2 kJ mol^{-1}
reaction 2 S_2Cl_2(l) + Cl_2(g) \rightleftharpoons 2SCl_2(l) \Delta H_r = -40.6 kJ mol^{-1}
(i) SCl_2 is a cherry-red liquid that reacts vigorously with water to form an acidic solution.
Use this information to deduce the bonding and structure shown by SCl_2.
Explain your answer.
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(ii) Calculate the enthalpy change of formation, \Delta H_f, of SCl_2(l). You may find it useful to use Hess’s Law to construct an energy cycle.
enthalpy change of formation of SCl_2(l), \Delta H_f = ................................... kJ mol^{-1} [2]
(iii) State the effect of a decrease in pressure on the position of equilibrium in reaction 2.
Explain your answer.
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Fig. 3.1 shows the two structural isomers of S_2Cl_2.
(iv) Define the term structural isomer.
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(v) Suggest a value for the Cl-S-S bond angle in isomer I. Explain your answer.
bond angle = .................................... °
explanation ..............................................................................................................
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(vi) Draw a dot-and-cross diagram to show the bonding in isomer II. Show outer shell electrons only.
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(a) Complete Table 4.1 to:
• identify a reagent that could distinguish between the compounds in each pair
• give the positive result of the chemical test and identify which compound shows this result.
Use a different reagent for each test. [8]
[Table_1]
(b) C1 has melting point −94°C and boiling point +49°C.
Explain these properties by referring to the type of van der Waals’ forces between molecules. [2]
(c) Draw the structure of the cis isomer of C2. [1]
(d) C2 forms a polymer when heated gently.
(i) Identify the type of polymer that forms from C2.
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(ii) Draw one repeat unit of the polymer formed from C2. [2]
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(a) (i) M reacts with hot concentrated acidified KMnO4(aq) to form N, C6H10O3, in reaction 1. Draw the structure of N.
(ii) N is reduced by NaBH4 to form 5-hydroxyhexanoic acid in reaction 2. Construct an equation for reaction 2 using molecular formulae. In the equation, use [H] to represent one atom of hydrogen from the reducing agent.
(iii) Reaction 2 is a nucleophilic addition. Suggest why reaction 2 creates a mixture of two organic compounds.
(iv) Draw lactone P, the product of reaction 3.
(b) A student monitors the progress of reaction 2 using infrared spectroscopy. Use Table 5.1 to suggest why it is difficult to distinguish between N and 5-hydroxyhexanoic acid using infrared spectroscopy.
[Image_1: Table 5.1]
(c) Unknown lactone Q is analysed using mass spectrometry. Table 5.2 shows information from the mass spectrum. Use these data to deduce the structure of Q. Show your working.
[Image_2: Table 5.2]
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