[ajax0604]

A multiple choice question states that calcium metal is placed in a solution of magnesium chloride. One of the answer choices says that magnesium ions will be reduced and calcium will be oxidised which I thought was the right answer but there is another choice which says that water will be reduced producing hydrogen gas and calcium will be oxidised. This also seems likely, possibly more likely than the first choice because water is a better oxidant compared to magnesium ion on the electrochemical series. Could both reactions occur simultaneously? Thank you.

[Borek]

What would happen to metallic magnesium?

[ajax0604]

Magnesium metal won't react with calcium ions but it could react slowly with water to produce hydrogen gas and insoluble magnesium hydroxide?

[Borek]

Haven't you just answered your own question?

[ajax0604]

Then this multiple choice question has more than one possible answer

[Borek]

No. Magnesium metal doesn't exist in the solution - so it won't be created. Calcium will react with water, yielding the most stable product directly.

[ajax0604]

I see. So when calcium reacts with water to produce hydrogen gas and hydroxide ions, the hydroxide ions will react with the magnesium ions to form magnesium hydroxide.

[Borek]

Whether Mg(OH)₂ will precipitate depends on the concentrations, but that's more or less correct way of thinking.