Which ion forms a green precipitate with sodium hydroxide?

Which ion forms a green precipitate with sodium hydroxide?

• A. Fe2+
• B. Cu2+
• C. Fe3+
• D. Ca2+

Answer: (A)

When a metal ion is treated with hydroxide ions, it can form a metal hydroxide. If that hydroxide is insoluble, it appears as a precipitate, and its color helps identify the ion. Iron(II) ions form iron(II) hydroxide, Fe(OH)2, which is pale green and shows up as a green solid when NaOH is added. Copper(II) hydroxide would be blue, iron(III) hydroxide is brown, and calcium hydroxide is only sparingly soluble and doesn’t give a distinct colored solid in this standard test. So the green precipitate points to iron(II) ions.

When a metal ion is treated with hydroxide ions, it can form a metal hydroxide. If that hydroxide is insoluble, it appears as a precipitate, and its color helps identify the ion. Iron(II) ions form iron(II) hydroxide, Fe(OH)2, which is pale green and shows up as a green solid when NaOH is added. Copper(II) hydroxide would be blue, iron(III) hydroxide is brown, and calcium hydroxide is only sparingly soluble and doesn’t give a distinct colored solid in this standard test. So the green precipitate points to iron(II) ions.