In chemistry we did a lab examining iron nails corroding in agar. One of the nails was wrapped in zinc, and the nail did not rust. A whitish substance appeared around the nail, what is the whitish substance?

Zn (OH) ₂

Explanation:

Zn is above Fe in the activity series, so it is more readily oxidized:

Zn (s) ⟶ Zn²⁺ (aq) + 2e⁻

The zinc ions go into solution.

The electrons travel from the Zn to the surface of the iron nail, where they reduce the water to hydrogen and hydroxide ions.

2H₂O (ℓ) + 2e⁻ ⟶ H₂ (g) + 2OH⁻ (aq)

Neither the zinc ions nor the hydroxide ions can move far through the gel.

Their concentration builds up around the hail. The ions find each other and form a precipitate.

Zn²⁺ (aq) + 2OH⁻ (aq) ⟶ Zn (OH) ₂ (s)