Ketene will convert the water to acetic acid first, then acetic anhydride production will begin. In short, you'll need more acetone.

technically, you COULD use 90 percent, sure, the ketene will first react with that water to form acetic acid, then when no more water is present it will acetylate the acetic acid, forming the anhydride. The issue however is that you increase the likelihood of polymerization products with water present, it is better to use dry acetic acid. Glacial. Otherwise, you will have to remove contaminants with distillation.

ケトンに塩化カルシウムは使えないから、水酸化ナトリウムあたりじゃないかな？

so, increase surface area of bubbles lights off cover flask in aluminium foil 120g --> 204g = 100% yield ive heard 600*C is where it starts to happen, but higher temperature is better? the acetone doesnt seem to be splitting perfectly into ketene

@@WeebRemover4500 all that will help but it won't "split perfectly into ketene" there aren't many reactions in high energy complex chemistry that are 100 percent, there's all sorts of things going on. Think of it like this, at the atomic level, the shape of the electronic fields that are the place where the true interaction begins, those surfaces, or areas, are curved and large, and there is a lot of points along that curved area of field density for attraction and repulsion, this gives rise to the chances of different reactions and thus products to occur, this is especially so with molecules like acetone and ketene, with their carbonyl groups and the alpha hydrogens all offering areas of resonance , higher and lower charge areas, it's actually quite complex what is going on down there at that level, given that level of complexity and high energy you will never get 100 percent yield from this reaction, not ever. With a known quantity of acetic acid, you can keep bubbling in Ketene and periodically stopping the process and weighing your flask with the acetic in it, when it finally gets to the theoretical weight for that molar amount of acetic anhydride, you stop. This way you have converted all the acetic acid that you started with, there will be some minor contamination, which is why you then distill it, then you have your acetic anhydride, as much as possible, and fairly pure.