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Take 70 gm chitosan in 100ml of 10% acetic acid solution.

use ultrasound to dissolve

I do agree with both responses and I will like to add that, Chitosan should fully dissolve in acidic solutions, thus a 100mL 10% acetic acid should be sufficient to dissolve 70gm of Chitosan. Also I will not recommend sonication of chitosan (see the reference below), but rather you can start by weighing out the chitosan into a flask and adding a given volume of your acidified water (say 50mL) and constantly stirring on a magnetic stirrer. you can add some more acidified water to make up to volume but stirring usually helps to dissolve the chitosan fully and the dissolved chitosan should yield a transparent solution.

you can check Article Synthesis and Characterization of Fatty Acid Grafted Chitosa...

Article Degradation of chitosan by sonication in very-low-concentrat...