Problem 75 - Chemistry and Chemical Reactivity

Question

Give a systematic name or the formula for the following: (a) \(\left(\mathrm{NH}_{4}\right)_{2}\left[\mathrm{CuCl}_{4}\right]\) (b) tetraaquadichlorochromium(III) chloride (c) aquabis(ethylenediamine) thiocyanatocobalt(III) nitrate

Step-by-Step Solution

Answer

(a) Ammonium tetrachlorocuprate(II), (b) \([\mathrm{Cr(H_2O)_4Cl_2}]\mathrm{Cl}\), (c) \([\mathrm{Co(en)_2(H_2O)(SCN)]}(\mathrm{NO_3})_2\)."

Step 1: Analyzing Compound (a)

The given compound is \(\left(\mathrm{NH}_{4}\right)_{2}\left[\mathrm{CuCl}_{4}\right]\). To name this compound, recognize that it contains the ammonium ion \(\mathrm{NH}_4^+\) and a complex ion \([\mathrm{CuCl}_{4}]^{2-}\). The complex ion contains copper (Cu) and four chloride anions (Cl). Because copper can have variable oxidation states, it's important to determine the charge. Each chloride has a charge of -1, thus, for four chlorides, we have -4. Therefore, copper must be +2 to balance the overall -2 charge of the complex. The name is ammonium tetrachlorocuprate(II).

Step 2: Simplifying Compound (b) Name

Start by breaking down the name 'tetraaquadichlorochromium(III) chloride'. The prefix 'tetra' indicates four water molecules (aqua) coordinated to chromium, and 'dichloro' indicates two chloride ions directly bonded to chromium. Chromium is in oxidation state (III), as indicated in the name. Finally, there's an additional chloride ion outside the complex. The formula becomes \([\mathrm{Cr(H_2O)_4Cl_2}]\mathrm{Cl}\).

Step 3: Interpreting Compound (c)

The name 'aquabis(ethylenediamine) thiocyanatocobalt(III) nitrate' gives a complete description of the coordination compound. The term 'aqua' indicates one water ligand, and 'bis(ethylenediamine)' suggests two ethylenediamine ligands. 'Thiocyanato' refers to the SCN ligand bonded to cobalt, which has an oxidation state of +3. Nitrate is the counter ion. The formula is \([\mathrm{Co(en)_2(H_2O)(SCN)]}(\mathrm{NO_3})_2\), where \(\mathrm{en}\) is ethylenediamine.

Key Concepts

Complex Ions

Complex ions are fascinating in the world of coordination chemistry. These ions consist of a central metal atom or ion, surrounded by molecules or anions, known as ligands. The metal at the center, often a transition metal, binds to these ligands through coordinate covalent bonds. This forms a distinct structure known as a coordination complex.

For example, in \(\left(\mathrm{NH}_{4}\right)_{2}\left[\mathrm{CuCl}_{4}\right]\), copper, a transition metal, forms a complex ion with chloride ions acting as ligands. The formula inside the brackets, \[\mathrm{CuCl}_{4}\]^{2-}\, represents this complex ion. The surrounding ammonium, \(\mathrm{NH}_4^{+}\), acts as a counter ion to balance the charge.

• Central metal: Copper (\