[Alex koosha]

In the materrials and methods of one article is mentioned that: A specific amount of citric acid and the catalyst sodium hypophosphite (50 % w/w, on weight of citric acid used) was dissolved in the starch solution.

My question is how much citric acid and sodium hypophosphite I need to weigh on the balance?

p.s: In one part of article is written: films were cast from 3 % starch and cross-linked using 5 % (w/w) citric acid.



Is my answer correct? 50 % w/w so we need to weigh 50 g or mg of citric acid + 50 g or mg of sodium hypophosphite. But why in another part of article mentioned 5 % of citric acid was used? I am confused.

[Arkcon]

I would be best for us if you wrote or copied the entire text block.  I'd suspect once you did that, you might even have an "Oh, I see ..." moment.

You've mentioned starch in this and other threads, and you've said you can make a film from 3% starch and 5% citric acid.  You've also said the catalyst is 50% of the weight of citric acid.  If I assume the balance is water, you have a fine proportional recipe.

You're asking the common noob lab question -- but how much do I weigh, I'm only given percents.  That's true.  But how many grams you need will depend on how much film you intend to make.  And we can't know that.

At a guess, I'd make 100 mls, so the percents are easy to figure.  If that's 5 times too much, you can do better next time.  If that's one third too small, you can make twice as much again and pool.  On a level, not planning first is wasteful.  But this is starch, citric acid and sodium hypophosphite, not Grub's catalyst.

[Alex koosha]

So it is ok If we say I want to make 3 % of starch so I weigh 3 gram of starch. Then 5 % of citric acid which is 1.28 gram then catalyst 50 % which becomes 0.64 gram. Then I will add 96.23 gram of water. Am I right?

[Alex koosha]

Here is copy and paste from the article:


A specified amount of citric acid and the catalyst sodium hy- pophosphite (50% w/w, on weight of citric acid used) was dissolved in the starch solution. The starch solution containing the cross-linking agent and catalyst was heated to 90 °C.

Also from another part of article copy and paste:

Films were cast from 3% starch and cross-linked using 5% (w/w) citric acid and cured at 165 °C for 5 min.

[aga]

The full article would be better.

It would (hopefully) contain All of the relevant data.

[Alex koosha]

Here you can read the full article

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1024&context=textiles_facpub

[Furanone]

Commonly, for experiments designed like this a stock solution of starch will be prepared of double so 6% (wt/wt so 6 g of starch in 94 g of water), and then a stock solution of the highest amount of citric acid solution will be made in double as well (so 10% citric acid wt/wt with 5% sodium hypophosphite). Then the two stock solutions can be added in 50:50 ratio to get a final 3% starch and 5% citric acid (with 2.5% catalyst). Then for lower concentrations of citric acid and catalyst, smaller amounts can be added with water bringing up the volume so 50% starch solution to 25% citric/catalyst to 25% water for a final 3% starch, 2.5% citric acid and 1.25% catalyst solution.

If 15% glycerol is desired to be held constant, then there would be 15% glycerol in each stock solution as well as 15% glycerol in the dilution water so that glycerol content never changes no matter how much starch solution, citric acid+catalyst solution or dilution water is added to mix.

But another suggestion to be 100% clear about the methodology is to email the authors since you have their papers with their contact information. Most of the time they will be most helpful if you ask them for clarification.

[billnotgatez]

@Alex koosha

Are you doing this for a high school project?

[Alex koosha]

No, this is for bachelor's project. I posted in another thread but someone moved my post into the high school thread