Hydrogel (super absobent polymers) Question 5, 9701/41/O/N/13

Tan Zhao Xuan asked me about “coordination bonds to Na+ ions”
I have read many moons ago that Mg2+ ions form complex aqua ions just like the more familiar d-block ions do.

We don’t learn aqua coordination complexes of s-block ions so if you look at the mark scheme, you may be surprised to see one mark for showing a dative bond from O in H2O to Na+ ions. Maybe you could have drawn a similar diagram to the one I give below, which is a bit more simple than the one stated in the mark scheme. It has an ion-dipole, Na+ and H2O respectively instead of the coordinatate bond.

The point about hydrogels is that water can bond into a very hydrophilic group repeatedly occurring throughout the structure of the polymer. In this case, interposing between the polymer chain and the Na+ counter ion.

9071 - 2013 winter paper 41 Q5 d i)

Please remember when drawing hydrogen bonds that it’s there is a straight line inbetween the three atoms of the hydrogen bond. e.g. O-H……..O  (or alternatively  H-O………..H) The dotted line represents the hydrogen bond. You can see this on my sketch between the O- of the carboxylate and the O-H in the water molecule.

I’m sure my diagram would get full marks.


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