Single correct · +4 / −1
The compound K₄[Fe(CN)₆] is named:
- (a) Potassium hexacyanoferrate(II)
- (b) Potassium ferrocyanide
- (c) Hexacyanoferrate(II) potassium
- (d) Both a and b
Answer and solution
Answer (d) Both a and b
Solution
Chemistry ma’am · 4 steps
This salt answers to two names: the IUPAC name and the older common name. Both are correct.
- Find the oxidation state. Each K⁺ is +1 and each CN⁻ is -1. So 4(+1) + x + 6(-1) = 0, which gives x = +2 for iron.
- Build the IUPAC name. Name the cation first: potassium. In the complex anion, the six CN⁻ ligands are hexacyano. Because the complex is an anion, iron takes its Latin stem with "-ate": ferrate, followed by (II). That gives potassium hexacyanoferrate(II).
- The common name. In older naming, the "-o" in ferro marks the lower oxidation state of iron, +2. So the same compound is also called potassium ferrocyanide. The +3 salt K₃[Fe(CN)₆] is potassium ferricyanide.
- So. Names (a) and (b) both describe K₄[Fe(CN)₆], so the answer is (d).
The idea to keep. In a salt, always name the cation first. When the complex is an anion, the metal takes "-ate" and often its Latin stem: ferrate, cuprate, argentate. Ferro means +2 and ferri means +3.
Answer from the NTA final answer key. Solution by PrepWiser.