Difference in reaction between ferrous bisglycinate, ferrous gluconate, and ferrous fumarate

[sabrinasmith]

I am doing an experiment and received much lower results for the titrated iron content when using ferrous fumarate and bisglycinate versus ferrous gluconate. It was titrated using potassium permanganate. 

I need to be able to:

1. List the stoich reactions for each compound when they were reacted with dilute (1.0M) sulphuric acid to create Fe2+ ions

2. Explain why ferrous gluconate gave me the most accurate iron content results when compared to the listed amount on the bottle

Any insight is appreciated!

[exchemist]

2 hours ago, sabrinasmith said:

I am doing an experiment and received much lower results for the titrated iron content when using ferrous fumarate and bisglycinate versus ferrous gluconate. It was titrated using potassium permanganate. 

I need to be able to:

1. List the stoich reactions for each compound when they were reacted with dilute (1.0M) sulphuric acid to create Fe2+ ions

2. Explain why ferrous gluconate gave me the most accurate iron content results when compared to the listed amount on the bottle

Any insight is appreciated!

Well I don't know the answer to this offhand, so perhaps we can work it out between us. Can you do the first part? 

[studiot]

Ok so the fumarate and gluconate are acid ferrous (ironII) salts, whereas the bisglycinate is a chelate complex.

I don't know how you prepared your solutions, but the salts will have water of crystallisation.
For example the gluconate will probably be the dihydride.

All this will affect the apparent molecular or equivalent weight in titration.

Some interesting data about these here, but not necessarily your answers since we don't do your homework, just try to help.

https://www.sabm.org/wp-content/uploads/2019/01/2A2-PhysiciansGuideOralIron.pdf

[exchemist]

9 minutes ago, studiot said:

Ok so the fumarate and gluconate are acid ferrous (ironII) salts, whereas the bisglycinate is a chelate complex.

I don't know how you prepared your solutions, but the salts will have water of crystallisation.
For example the gluconate will probably be the dihydride.

All this will affect the apparent molecular or equivalent weight in titration.

Some interesting data about these here, but not necessarily your answers since we don't do your homework, just try to help.

https://www.sabm.org/wp-content/uploads/2019/01/2A2-PhysiciansGuideOralIron.pdf

Gluconic acid is a bidentate ligand for Fe II as well, though. Gluconate seems to have the highest 1st pKa. Not sure if that's relevant.