Edexcel Chem Unit 1 - Question. Watch

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Tealer
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Solubilities of hydroxides + sulphates in groups 1 + 2.

Sulphates solubility decreases as group two is descended.

In contrast hydroxides solubility increases as group 2 is descended.

Do we need to know why?
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hornblower
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(Original post by Tealer)
Solubilities of hydroxides + sulphates in groups 1 + 2.

Sulphates solubility decreases as group two is descended.

In contrast hydroxides solubility increases as group 2 is descended.

Do we need to know why?
Yes, definitely. Group II solubility questions are common.

You need to know about lattice energies and enthalpies of solution and hydration.
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lgs98jonee
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(Original post by hornblower)
You need to know about lattice energies and enthalpies of solution and hydration.
not in unit 1 edexcel btw
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hornblower
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(Original post by lgs98jonee)
not in unit 1 edexcel btw
I'm certain it is in unit one.
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MalaysianDude
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(Original post by Tealer)
Solubilities of hydroxides + sulphates in groups 1 + 2.

Sulphates solubility decreases as group two is descended.

In contrast hydroxides solubility increases as group 2 is descended.

Do we need to know why?
i think you would have to explain that as sulphates are large molecules and hydroxide are smaller molecules,the degree of polarising affects the solubility
thats pretty much it in unit 1
but as you reach unit 4
you`ll have to explain it by using the ideas of the enthalphy of hydration and the lattice enthalphy to obtain the enthalphy of solution to explain the process
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meawinner
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you dont need to know the explanation for it in unit one as this is specifically said in the specification. Though u need to know why abt the thermal stability of carbonates and nitrates of grp 1 and 2
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FidoDiDo
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(Original post by Tealer)
Solubilities of hydroxides + sulphates in groups 1 + 2.

Sulphates solubility decreases as group two is descended.

In contrast hydroxides solubility increases as group 2 is descended.

Do we need to know why?
Solubility affected by 2 factors :
A)Heat of lattice dissociation
B)Heat of hydration

As u descend down the group solubility decrease for the Sulphate becuz ..
as the cation gets larger its Charge density decrease .. so this decrease the enthalpy of Hydration.[not enough energy to compensate with the enthalpy of lattice dissociation]
As u descend down the group solubility of hydroxides increase this is becuz the cations are getting larger .. the Hydroxide and Cation cannot approach Close together .. so there is a decrease in enthalpy of Lattice dissociation.
[easier to separate ions]
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john !!
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Thermal stability increases down the groups because further down the cation is less polarising, so there is less weakening distortion, which means more energy is needed to break the bond.
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FidoDiDo
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(Original post by mik1a)
Thermal stability increases down the groups because further down the cation is less polarising, so there is less weakening distortion, which means more energy is needed to break the bond.
Yup the percentage of ionic bonds found in a compound of group 2 increases down the group.
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Sahir
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(Original post by FidoDiDo)
Solubility affected by 2 factors :
A)Heat of lattice dissociation
B)Heat of hydration

As u descend down the group solubility decrease for the Sulphate becuz ..
as the cation gets larger its Charge density decrease .. so this decrease the enthalpy of Hydration.[not enough energy to compensate with the enthalpy of lattice dissociation]
As u descend down the group solubility of hydroxides increase this is becuz the cations are getting larger .. the Hydroxide and Cation cannot approach Close together .. so there is a decrease in enthalpy of Lattice dissociation.
[easier to separate ions]
Hmm, for edexcel.. i'm sorry, dunno what board you're on, but we've been taught: this is UNIT 4 btw..

Trend in solubility of G2 hydroxides:
1. Cation ionic radius increases, charge remains the same.. therefore charge density decreases.
2. Hydroxide anions have a comparatively small ionic radius.
3. Lattice Enthalpy is significantly less exothermic, as a result.
3. Hydration enthalpy less exothermic
4. Enthalpy of solution less endothermic.. hence the group 2 hydroxides are more soluble down group.

Trend in solubility of G2 sulphates:
1. Cation ionic radius increases, charge remains the same.. therefore charge density decreases.
2. Sulphate anions have a comparatively large ionic radius.
3. Lattice Enthalpy is slightly less exothermic, as a result.
3. Hydration enthalpy slightly less exothermic
4. Enthalpy of solution more endothermic.. hence the group 2 sulphate is less soluble.
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