Predict whether Fe(OH)2 will dissolve, precipitate, or do neither after:
(a) water is added --> dissolve
(b) Fe(OH)2 is added--> neither
(c) Solid Fe(NO3)2 is added--> precipitate
(d) Solid KNO3 is added---> neither
I'm given the answers...but no explanation. I am not sure how to solve these problems. Can someone help me out? I haven't been able to get a hold of my professor....thanks!
After that long discussion below, I won't go into much detail here. Actually, with what I answered below on the HCN = H2O problem, these should go well for you
(a) water is added --> dissolve
Fe(OH)2(s) + H2O ==> Fe^+2 + 2OH^-
So adding water moves the reaction to the left and the ppt dissolves.
(b) Fe(OH)2 is added--> neither
Adding more solid to a saturated solution can't make it dissolve more
(c) Solid Fe(NO3)2 is added--> precipitate
Addition of Fe(NO3)2 is adding Fe^+2 to the solution, that shifts the reaction to the left and causes more solid (ppt) to form.
(d) Solid KNO3 is added---> neither
KNO3 isn't involved in the reaction so it has no effect.
Certainly! I'll be happy to explain how to solve the problem.
In order to predict whether Fe(OH)2 will dissolve, precipitate, or do neither in each scenario, we need to consider the solubility rules.
(a) When water is added: In general, Fe(OH)2 is insoluble in water. However, there are exceptions for hydroxides of Group 1 metals and ammonium hydroxide. Since Fe(OH)2 is not one of those exceptions, it will not dissolve in water.
(b) When Fe(OH)2 is added: Fe(OH)2 is already in the form of a solid, so it will not dissolve any further or precipitate. Therefore, it will do neither.
(c) When solid Fe(NO3)2 is added: Fe(NO3)2 is a soluble salt in water. When it dissociates, it forms Fe2+ and NO3- ions. When Fe2+ ions come into contact with OH- ions from Fe(OH)2, they can react to form an insoluble precipitate, Fe(OH)2. So, when solid Fe(NO3)2 is added, Fe(OH)2 will precipitate.
(d) When solid KNO3 is added: KNO3 is a soluble salt in water. It dissociates into K+ and NO3- ions. These ions do not react with Fe(OH)2, so no precipitation or dissolution will occur. Therefore, it will do neither.
I hope this helps! If you have any more questions, feel free to ask.