[Nat360]

Hi Everyone.
I am in high school and I am completing an assignment on a topic of my choice. For this, I have chosen to investigate the effects of saline concentration and pH levels on the absorption of water in sodium polyacrylate.

As many would know, sodium polyacrylate is a super-absorbent polymer which means it can absorb around 1000 times its own mass in water. Since the absorption is very high, I needed some help with formulating a method.

These are my current ideas:
1. Use a very small amount of sodium polyacrylate and finding how much water it absorbs by filtering out the water and measuring the mass increase.
2. Measuring the rate of absorption, however my teacher has advised against this.

Any recommendations? 
Thanks for all your help in advance.
 

[Corribus]

Gravimetric method (weighing it) is the standard way to do it.

[Nat360]

Gravimetric method (weighing it) is the standard way to do it.

Thanks for your reply. Should I connect a vacuum to it, so maximum amount of unabsorbed water is removed?

[Borek]

Thanks for your reply. Should I connect a vacuum to it, so maximum amount of unabsorbed water is removed?

Depending on how long the vacuum is applied you can also remove absorbed water (absorption is an equilibrium process).

Doesn't mean vacuum is out of the question, but you will need to do some testing to make sure your method/procedure gives reproducible results - and you need to keep in mind that what you are measuring is not the absolute value, but some proxy. That can be enough for your project though.

[Corribus]

Surface evaporation does happen faster than loss of absorbed water but it is hard to exclude the latter while completing the former. I would still just dry the surface as best you can with a lint free cloth. This will just be a source of your error.