A question of chemistry

[bttay]

Magnesium Sulphate - MgSO4.7H2O
Calsium Nitrate - Ca(NO3)2.4H2O

Both compounds have one common property that is they liquefy when come into contact with moisture in the air. I suppose this is due to the H2O molecules that easily bond with other water molecules (Correct me if I am wrong).

My question is: If that is the case, does liquefied compound become heavier due to bonding with more H2O molecules? In other words, will 1g of MgSO4.7H2O weight more than 1g after it has liquefied?

Thanks.

[dx]

I suppose what u meant is: when moisture come into contact with those salts, they turn into liquid form. So yes, the total weight increase, however weight of the salt remain the same.
Example:
MgSO4.7H2O(solid) 1g + moisture (say 0.1g) = total 1.1g (liquid)
So now u have to weight 1.1 g in order to get 1g of MgSO4.7H2O.

Btw, I have yet to collect Ca(NO3)2 from you. I will find time to get it.

Cheers !

[geoffrey]

The term for this is hygroscopic. Yes Ca(NO3)2 is very hygroscopic, keep it in a dry place and seal tight. Don't buy too much to keep too. It will affect your calculation if you are weighing a known amount for mixing with water.

[bttay]

OIC. In that case, I should mix them with water before they all melt.

dx: No problem. It is still in my office, dry.[] My colleague thought that I keep sugar in plastic bags.