[JadenErius]

Hello everyone, its my first time posting here so I am not quite sure this topic belongs here. I'm a High school student so I assume my questions will be around here. Anyway onwards to my question:

An experiment where an Iron nail that is laced with magnesium as a sacrificial anode is placed into an electrolyte (Sodium Chloride).
According to my teacher; she says that hydrogen gas bubbles will be released due to the oxidation of magnesium metal to Magnesium Ions and the subsequent reduction of hydrogen ions in water to hydrogen gas.
The question is; why doesn't the magnesium ions combine with the remaining hydroxide ions left behind from the ionization of water and release of the hydrogen ions to form a white precipitate namely Magnesium Hydroxide?
My teacher has been unable to answer this question.

P.S. Is it against the rules to post multiple new topics that contain different questions in a very short time frame?

[aeacfm]

may be the solution is acidic !!!!!

[aeacfm]

 i mean like what happen in the pitting theory (adsorption theory ) as the rust
(Fe(OH)2 ) dissolved by the acidic media (although it is  sea water the same component of your electrolyte ) but the action of chloride becomes acidic and disslove the hydroxide so you cant see the ppt you may try another electrolyte and i think you will see the ppt..

[JadenErius]

but for a solution to be acidic it will need the hydroxonium ions which are not present in this solution as hydrogen ions have been discharged to form hydrogen gas. The solution is also tested with phenolphthalein indicator and it shows that it is alkali. The Iron does not rust due to the presence of the sacrificial anode (magnesium)

[Borek]

I doubt solutions pH goes high enough to precipitate Mg(OH)₂. Phenolphthalein gets pink at about pH 9, for the Mg(OH)₂ precipitation you need pH around at least 12 (probably more as concentration of Mg²⁺ is quite low in your solution).

[JadenErius]

Hmmm, so it has something to do with the chemical equilibrium and the solubility of product? Is that the reason why Magnesium Hydroxide does not precipitate out?

[Borek]

Yes.

[JadenErius]

ah ok well question solved =D