Why Solubility of alkali metal carbonates increases down the group but for alkaline earth metals decreases down the group?

Answer 1

as we move down the group solubility of sulphates decrease,for alkaline earth metals because down the group, size of cation increase, thus hydration energy decreases,and thus solubility of sulphates decrease.

Answer 2

Heat of Hydration means the energy released when a substance makes new chemical bonds with water (or parts of water molecules).

In the reaction,

M + 2H2O --> M(OH)2 + H2,

the water molecule is split at the surface of the metal:

H2O --> H+ + OH-

This is because the outer 2 electrons of each metal atom, being held only loosely, travel easily to the surface and are attracted by the hydrogen ends of the polarised water molecules.

(Please ignore the spacer dots in the following diagram! e- means electron in the metal. The d+ and d- show the polarisation of the water molecule.)

.............. d+ H

e- ===> ...... \

...................... O 2d-

..................... /

.............. d+ H

This initial step happens more readily as you go down the group, since outer electrons are held much more weakly.

But then, as the somewhat positively charged hydrogen atom releases its electron completely onto the oxygen causing the formation of hydroxide ions, the latter are attracted lessby the nuclei of lower Group 2 metals than by those of higher ones, because of electron shielding and a greater distance to the nucleus.

The net result is that when M(OH)2 is formed, the bonds between the metal ion and the hydroxide ion are longer (towards the bottom of the group), so that less energy had been released in forming them, i.e. the heat of hydration is less.

Answer 3

Elements from the bottom can lose electrons easily.

Answer 4

because down the group the cation becomes gets larger so the hydration energy decreases. so the solubility decreases

Answer 5

it decreases