Equilibria, Energetics and Elements - Exam Questions

Define 'lattice enthalpy'
The energy associated with the formation of one mole of an ionic lattice from its gaseous ions in their standard states.
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Why is the enthalpy change of hydration of chloride ions exothermic?
Hydration involves bonds forming.
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Why is the enthalpy of hydration of magnesium ions more exothermic than calcium ions?
Magnesium has a smaller atomic radius so a larger charge density, therefore magnesium has a stronger attraction for the water molecules than calcium.
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What is the definition of a transition element?
Forms an ion with a partially filled d orbital (also form coloured compounds, variable oxidation states)
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Define standard electrode potential
The e.m.f of a half cell compared with a standard hydrogen half cell measured at 298K, will solution concentrations of 1 moldm3 and gas pressures of 100kPa
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State 2 properties of Fe2+, other than the ability to form complex ions, that are typical of an ion of a transition element
Form coloured compounds
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Explain how ligand substitutions allow haemoglobin to transport oxygen in the blood
O2 binds to Fe2+ ion (haem group) by donating an electron pair instead of water when the concentration of oxygen is high. It is then released (substituted for water) again when needed in tissues
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What important factor does the student need to consider when choosing the most suitable indicator for an acid-base titration?
That the pH range of the indicator is as close as possible to the pH of the equivalence point (vertical section of graph)
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Suggest reasons for the differences between enthalpy changes of solution of KF (-15) and RbF (-24)
Atomic radius increases down a group, therefore K+ ions are smaller than Rb+ but have the same charge = greater charge density. The lattice enthalpy of KF is more -ve than RbF = affects enthalpy change of solution > than enthalpy change of hydration
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If copper is a transition element and zinc is not, suggest 2 differences between compounds containing Zn2+ and Cu2+ ions
Cu2+ compounds will be coloured where as Zn2+ not, Cu2+ may be catalytic where as Zn2+ are not
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Colour change when hexa-aquacobalt undergoes ligand substitution with chlorine
pink to blue
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Observations that would be made as ammonia is added drop by drop until in excess to hexa-aqua copper complex
It is a pale blue solution that forms a light blue precipitate with ammonia then when it is in excess, redissolves to a dark blue solution
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Card 2

Front

Why is the enthalpy change of hydration of chloride ions exothermic?

Back

Hydration involves bonds forming.

Card 3

Front

Why is the enthalpy of hydration of magnesium ions more exothermic than calcium ions?

Back

Preview of the front of card 3

Card 4

Front

What is the definition of a transition element?

Back

Preview of the front of card 4

Card 5

Front

Define standard electrode potential

Back

Preview of the front of card 5
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