# Homework Help: What is the right amount of citric acid and sodiumhypophosphite?

1. Feb 6, 2016

### Cyrus the great

1. The problem statement, all variables and given/known data

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.
2. Relevant equations

3. The attempt at a solution

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!

Last edited: Feb 6, 2016
2. Feb 7, 2016

### Cyrus the great

I calculated like this. 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?

3. Feb 7, 2016

### Cyrus the great

Any feedback?