Hi, Mr. Alseny Bah

Answer your Q1: NaOH 96% usually means 96 wt% NaOH and 4 wt% water. Aqueous solutions of strong alkalis, like NaOH will attack glass, with time. This is the reason why one must to avoid to store and keep NaOH, KOH, etc solutions in glassware long times. Better to store it in plastic bottles, like polyethylene or polypropylene flasks. So, usually, there is no SiO2 (silicate) in pure (analytical reagent grade) sodium hydroxide solutions. However, if one stored aqueous hydroxide solutions in glass, some small amount of silicate will be present, yes.

Reply your Q2: usually, most of the published papers does not account the sodium from NaOH solution, to the geopolymer total mix. But, to include the amount of water of sodium hydroxide solution is mandatory, regarding the water/binder ratio. Hope you find it helpful. Best. Antonio

Thank you so much Dr. Antonio for your help

kind regards

You are welcome. One more thing, Alseny: I did not realize, that 96 wt% of NaOH plus only 4 wt% water is not possible to prepare in real lab, since the solubility limit of NaOH in water is ~ 52.6 wt%. Most common impurity of NaOH is sodium carbonate (Na2CO3). Regards.

We should generally take not fully specified % concentrations as wt% ― where wt is often omitted or can be substituted by either wt., wt/wt, wt./wt., or m/m.

Commercial (technical grade) caustic soda (sodium hydroxide) pellets of [min.] 96 [wt]% specified purity, usually determined by titrimetric assay, typically contain H2O as main impurity. Sodium carbonate is another common impurity found in technical grade caustic soda (usually less than 2 wt%, on delivery). Please refer to the supplier analysis note (often given in dry basis); if available.

This standard may help:

ASTM E291 - 18, "Standard Test Methods for Chemical Analysis of Caustic Soda and Caustic Potash (Sodium Hydroxide and Potassium Hydroxide)"; https://www.astm.org/Standards/E291.htm

You may want to check also this somewhat related RG discussion: https://www.researchgate.net/post/Can_granular_sodium_hydroxide_be_dried_in_an_oven