it depends on the polarising power of the the metal actually even i dont know much about the hydroxide slubility as we have to consider the fact of hydrogen bonding .
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Chemistry: Post your doubts here!
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OH- is a relatively small anion, so it contributes little to the lattice enthalpy but to a greater extent to the hydration enthalpy.
As we descend down G-II the cation size increases and the lattice enthalpy decrease (becomes less exothermic). This happens to a large extent as the OH- has little contribution.
The increase in cation size also means that the hydration enthalpy decreases (becomes less exothermic) but this happens to a smaller extent as the OH- ion owing to it's relatively smaller size releases a greater portion of the energy as it interacts with water.
ΔHsol = ΔHhyd - ΔHlatt
If initially ΔHhyd was -60 it decreases supposedly to -40
If ΔHlatt was -60 it has a greater decrease, to suppose -20
so ΔHsol = -40 - (-20) = -20
Following this trend ΔHsol becomes more negative down the group and the solubility increases.
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We need to consider the equation : ΔHsolution = ΔHhydration - ΔHlattice
Solubility of the compound depends on the ΔHsolution , if it is positve, the solution isnt very soluble as energy has to be put in to dissolve it. Likewise, if it is negative, the solution is more soluble.
As we go down the group , both hydration and lattice enthalpies decrease.But these two fall at different rates and that is what decides whether overall solution enthalpy gets postive or negative.
Hydration enthalpies fall because the water molecules are less attracted to the positive ion ,as it gets bigger down the group
Lattice enthalpies fall because the distance between the centre of the positive and negative ion increases, so their attraction and thus enthalpy falls.
For hydroxides:
The lattice enthalpy falls faster than the hydration enthalpy ,overall solution enthalpy gets more negative and so the hyrdoxide gets more soluble down the group.
For sulpahtes/carbonates:
The hydration enthalpy falls faster than the lattice enthalpy , solution enthalpy gets overall more positive and so the sulphate gets more insoluble down the group.
littlecloud11 and KurayamiKimmi
I have a small problem, when you say lattice enthalpy decrease, like from -60 to -20 ( I know it is just an example) but like mathematically speaking -60 increase to -20 not decrease. I am really sorry for bothering, (I got the point that it become less exothermic) but how decrease?
(or does it mean, that when latt decrease, means become less exothermic?)
Thank you soo much, I understood everything else said, (and seems same thing to sulphate but a bit opposite).
May Allah S.W.T grant you the highest grades, in this life and hereafter. May Allah S.W.T shower his blessing upon you and your parents. Aameeen!!!!
Thank you, aloooooot...MUCH appreciated.
A star, check these posts! We got answers, Alhamdulilah.
I have a small problem, when you say lattice enthalpy decrease, like from -60 to -20 ( I know it is just an example) but like mathematically speaking -60 increase to -20 not decrease. I am really sorry for bothering, (I got the point that it become less exothermic) but how decrease?
(or does it mean, that when latt decrease, means become less exothermic?)
Thank you soo much, I understood everything else said, (and seems same thing to sulphate but a bit opposite).
May Allah S.W.T grant you the highest grades, in this life and hereafter. May Allah S.W.T shower his blessing upon you and your parents. Aameeen!!!!
Thank you, aloooooot...MUCH appreciated.
A star, check these posts! We got answers, Alhamdulilah.
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Decrease is just the conventional way of saying that the value gets less exothermic. Even though mathematically it's the reverse. I know this can get confusing. Just remember that both values get less exothermic or become more positive.
You're welcome.
Okay, now it is no longer confusing, Alhamdulilah!!! Jazaki Allah khairan!!!!! Thankss Alottttt!! The exams are so close, thank you for giving some of your time!! May Allah S.W.T make the exam easy for you. Aameen!!!!!Decrease is just the conventional way of saying that the value gets less exothermic. Even though mathematically it's the reverse. I know this can get confusing. Just remember that both values get less exothermic or become more positive.
You're welcome.
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If lattice enthalpy decreases from -60 to -20 , it does become more positive , which in turn means that it becomes less exothermic and therefore the "exothermic-ness" of lattice enthalpy has fallen as going down the group .
Jazaki Allah khairan, littlecloud explained that just now, but repetition makes a fact stick to ones head, so thank you soooo much!!!!! Again your exams are close too, so thank you for giving me some of your time. May Allah S.W.T make the exam easy for you too, Aameen!!!!!!!
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ummm okay *freaks out* this is an A2 concept ryt? not an AS one??
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yea its a2 lol xD
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ohh *phew* thanks
lmao my first reaction was the same i thought u guys wouldnt undestand it so i didnt tell looks like phyzacs like to go ahead like me
yupo i realised it the moment i saw the word lattice enthalpy
can you go to phy thread and solve the question i posted plsssss looks like others are busy
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ah sorry but my as physics is very weakcan you go to phy thread and solve the question i posted plsssss looks like others are busy
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hahha ryt!!?!!lmao my first reaction was the same i thought u guys wouldnt undestand it so i didnt tell looks like phyzacs like to go ahead like me
yupo i realised it the moment i saw the word lattice enthalpy
yeah i made the connecction with the lattice energy when my panic finallly sank a bit but until then i had already posted the question so i said 'oh well..'
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hahha ryt!!?!!
yeah i made the connecction with the lattice energy when my panic finallly sank a bit but until then i had already posted the question so i said 'oh well..'
Well the word Lattice energy was enough.. and I stopped reading after that.. cuz Lattice Energy will be like the first chapter we study in A2
It's 18th Chapter in the book.. and First 17 are in AS level.. Physics is tougher than chemistry..!
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hmm...Well the word Lattice energy was enough.. and I stopped reading after that.. cuz Lattice Energy will be like the first chapter we study in A2
Physics is tougher than chemistry..!
yeah u know wat actually now that my chem is prepared like satisfactorily prepared... it does seem like physics is much tougher becasue there are umpteen possibilities of questions being made on phy concepts ... chem has that but not to that extent.... i agree with u and A star
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http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_2.pdf
Variant 1, Q.4 a the last box when you add k2Cr2O7/H+. Also b)ii)
also Q.5. a)
Variant 1, Q.4 a the last box when you add k2Cr2O7/H+. Also b)ii)
also Q.5. a)