Question 1

What is the difference between primary and secondary valency in Werner's theory?

Accepted Answer

For cobalt, primary valency is 3 in these coordination compounds. Secondary valency is the coordination number, which is 6 here because each cobalt is surrounded octahedrally by six monodentate donor atoms.

Question 2

Why is primary valency not the same as the number of free chloride ions?

Accepted Answer

Primary valency belongs to cobalt and remains 3. Changing a chloride from an outer-sphere counter-ion to a coordinated ligand changes how many free Cl- ions exist, but it does not change cobalt's primary valency.

Question 3

How many ions are produced by each Werner compound in water?

Accepted Answer

[Co(NH3)6]Cl3 gives four ions, [Co(NH3)5Cl]Cl2 gives three ions, and [Co(NH3)4Cl2]Cl gives two ions per formula unit. In each case, one intact coordination cation and the listed counter-ion chloride ions are formed.

Question 4

What is the difference between cis and trans [Co(NH3)4Cl2]+?

Accepted Answer

In the cis form, the two chloride ligands occupy adjacent octahedral positions and are separated by 90 degrees. In the trans form, they occupy opposite positions and are separated by 180 degrees.

Question 5

Which chloride ions form AgCl when AgNO3 is added?

Accepted Answer

The outer-sphere counter-ion chlorides react with Ag+ to form white AgCl. One formula unit of the three listed compositions gives 3, 2 and 1 moles of AgCl respectively; coordinated chlorides inside the brackets are not counted in that yield.

Werner's Lab: Two Valencies, One Formula

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