Periodic table, elements and physical chemistry June 2023, Question 8 1 mark
Which compound requires the most energy to convert one mole into its gaseous ions?
A NaF
B Na2O
C MgF2
D MgO
Your answer
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Topic questions Energy changes Enthalpy of solution & hydration
Enthalpy of solution & hydration
5 questions · 55 marks · about 1 hour
Enthalpy of solution and hydration questions
TopicEnthalpy of solution & hydration▾
OCR H432 Enthalpy of solution and hydration 5 questions
Unified chemistry June 2022, Question 5 10 marks
This question is about energy changes.
(a)
[6]
* A student plans to determine the enthalpy change of hydration of calcium ions.
The student finds the information below from data tables.
The student carries out an experiment to find the enthalpy change of solution of calcium chloride.
Student’s method:
• Weigh a bottle containing calcium chloride and weigh a polystyrene cup.
• Add water from a measuring cylinder to the polystyrene cup and measure its temperature.
• Add the calcium chloride, stir the mixture, and measure the maximum temperature of the final solution.
• Weigh the empty bottle and weigh the polystyrene cup with the final solution.
Mass readings
Temperature readings
Calculate the enthalpy change of solution of calcium chloride and determine the enthalpy change of hydration of calcium ions.
Show your working, including an energy cycle linking the energy changes.
Assume that the density and specific heat capacity, c, of the solution are the same as for
water.
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(b)
Internal combustion engines have historically used fuels obtained from crude oil as a source of power.
The environmental effects of fossil fuel use can be reduced by blending petrol with biofuels such as ethanol.
A fuel is being developed using a 1:1 molar ratio of octane and ethanol.
(b)(i)
[1]
Write the equation for the complete combustion of this fuel.
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(b)(ii)
[3]
Calculate the energy released, in kJ, by the complete combustion of 8.00 kg of this fuel.
cH(C8H18) = –5470 kJ mol–1; ∆cH(C2H5OH) = –1367 kJ mol–1.
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Periodic table, elements and physical chemistry November 2021, Question 16 14 marks
This question is about magnesium and magnesium halides.
(a)
[3]
Magnesium has metallic bonding and is a good conductor of electricity.
Describe, with the aid of a labelled diagram, the metallic bonding in magnesium and explain why magnesium conducts electricity.
Include the correct charges on the particles in your diagram.
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(b)
The 12 successive ionisation energies of magnesium are shown in Table 16.1.
(b)(i)
[1]
Write an equation to represent the fourth ionisation energy of magnesium.
Include state symbols.
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(b)(ii)
[1]
Explain how the successive ionisation energies provide evidence that magnesium is in Group 2 of the periodic table.
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(b)(iii)
[1]
Electrons occupy orbitals.
In Table 16.2 below, add a tick (✓) below the ionisation numbers that are responsible for removing an electron from a full orbital in a magnesium atom.
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(c)
The enthalpy change of solution for magnesium fluoride, MgF2, can be determined indirectly using an energy cycle based on the enthalpy changes below.
(c)(i)
[1]
Explain what is meant by enthalpy change of solution.
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(c)(ii)
[2]
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(c)(iii)
[1]
Calculate the enthalpy change of solution of MgF2.
enthalpy change of solution =........ kJ mol–1
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(c)(iv)
[4]
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Periodic table, elements and physical chemistry June 2019, Question 16 15 marks
Sir Humphry Davy discovered several elements including sodium, potassium, magnesium, calcium and strontium.
(a)
[1]
Explain which block in the Periodic Table sodium and magnesium belong to.
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(b)
[2]
A sample of magnesium, Ar= 24.305, is found to consist of three isotopes. The accurate relative isotopic masses and % abundances of two of the isotopes are shown in the table.
| Isotope | Relative isotopic mass | % abundance |
| 24 Mg | 23.985 | 78.99% |
| 25 Mg | 24.986 | 10.00% |
Determine the relative isotopic mass of the third isotope of magnesium in the sample.
Give your answer to 5 significant figures.
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(c)
A student adds an excess of calcium oxide to water in a test tube. In a separate test tube, the student adds an excess of strontium oxide to water.
(c)(i)
[1]
Write the equation for the reaction of calcium oxide with water.
State symbols are not required.
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(c)(ii)
[1]
Suggest the approximate pH of the two solutions formed in the test tubes.
pH with calcium oxide........
pH with strontium oxide........
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(d)
The table below shows enthalpy changes involving potassium, oxygen and potassium oxide,
(d)(i)
[4]
The incomplete Born–Haber cycle below can be used to determine the lattice enthalpy of potassium oxide.
In the boxes, complete the species present in the cycle. Include state symbols for the species.
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(d)(ii)
[2]
Calculate the lattice enthalpy of potassium oxide.
lattice enthalpy =........ kJ mol−1
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(e)
A similar Born–Haber cycle to potassium oxide in (d) can be constructed for sodium oxide.
(e)(i)
[2]
The first ionisation energy of sodium is more endothermic than that of potassium.
Explain why.
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(e)(ii)
[2]
The lattice enthalpy of sodium oxide is more exothermic than that of potassium oxide.
Explain why.
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Periodic table, elements and physical chemistry June 2018, Question 16 15 marks
This question is about enthalpy changes.
(a)
Table 16.1 shows enthalpy changes that can be used to determine the enthalpy change of hydration of fluoride ions, F –.
(a)(i)
[2]
Explain what is meant by the term enthalpy change of hydration.
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(a)(ii)
[4]
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(a)(iii)
[2]
Calculate the enthalpy change of hydration of fluoride ions, F –.
enthalpy change of hydration =........ kJ mol–1
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(a)(iv)
[2]
Predict how the enthalpy changes of hydration of F – and C l – would differ.
Explain your answer.
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(b)
Fluorine reacts with steam as shown in the equation below.
Average bond enthalpies are shown in the table.
| Bond | Average bond enthalpy / kJ mol–1 |
| O–H | +464 |
| O=O | +498 |
| H–F | +568 |
(b)(i)
[2]
Explain what is meant by the term average bond enthalpy.
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(b)(ii)
[3]
Calculate the bond enthalpy of the F–F bond.
bond enthalpy =........ kJ mol–1
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