The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Role of acids in lemon and salt used to remove rust from clothes

I am undertaking International Bacchalaureate course. I am doing my Extended Essay as required in this course. My Extended Essay is on removing rust from clothes using lime and salt. I am using limes, lemon and orange as the lime. But, I don't know what are the equations involved and what role are the acids in those lime and the salt are playing as it was proven succcess in my experiment. (they are able to remove rust from clothes) Are pH value and amount of salt influence the rate of reaction? hope you can answer all these question. May God give you easeness in encountering this question. Hope to hear from you ASAP.

Thanx so much and good luck!

Jere
student - Selangor, Kajang, Malaysia
2004

I'm sure that by this time in your academic career you understand that every explanation of a physical phenomena is a simplification, Jere. A simplified explanation that suits me because it accounts for a lot, but which others might feel inadequate or even misleading, is that the acid in the limes (H+anion-), makes hydrogen ions (H+) available. These H+ ions, being positively charged, want to combine with oxygen items to form the stable compound water. As they combine with the oxygen atoms of the metal oxide (the rust), the metallic portion of the metal oxide is thus freed to enter the solution as a soluble positively charged ion and float away. Thus any acid dissolves rust.

In the case of limes, which contain citric acid and ascorbic acid and other acids, the 'citric' anion is a good chelator. Again in simple terms, this anion 'surrounds' the iron ion it encounters in a physical way that makes it difficult for the iron to reach and react with other ions; by doing so it means that the iron will not readily precipitate back out of solution even as the pH goes higher. In the presence of citrates the iron can stay soluble at higher pH (less acidic condition) than would be the case with simpler mineral acids like sulfuric or hydrochloric acid.

I don't really understand why salt makes the limes so much more effective myself, although I know it does. I think it's the Cl- anion rather than the Na+ cation which helps speed the reaction. My suspicion, but I haven't been motivated to research it, is that the Cl- replaces some of the O-- in the rust, by common ion effect, converting the rusts to far more soluble ferric and ferrous chloride.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

Thanx so much you have been very helpful

Can you please give the balanced equation of titration of citric acid s against sodium hydroxide. I'm a bit confuse because ctric acids does not ionize fully, right?

Hope you can help me. thanx good luck.

Jere
mara - Kajang, Selangor, Malaysia
2004