Question

for ionic Close the names ofthe following compounds, using the Stock system compounds and the appropriate nomenclature for molecular compounds: 8· i. CoS A cobaltImsulfide b) dicobalt trisulfide c) cobalt selenide d) cobalt (III) selenide ii. Ago silveroxide b) disilver)monoxide c) silver(I)oxide d) silver oxide

Answer 1

According to the stock system of nomenclature of an ionic compound, the oxidation state is always written in parentheses and in roman number. First a cation is written first then its oxidation state in roman number within parentheses and then anion.

For example, CuCl₂, the oxidation state of Cu is +2, thus it would be written in roman numbers in parentheses just after the name of copper

So the nomenclature of this compound would be, Copper(II) Chloride.

Thus, using the above rule, the nomenclature of your first ionic compound is:

i) Co₂S₃ , Co has +3 oxidation state and S has -2. {In case it is difficult to determine the charges over cation and anion then you just have to reverse the stoichiometry for both the elements}

Hence, it is named as Cobalt (III) Sulphide and the correct option is a.

If you check all options then only options a and d have stock notation, and out of which option d is incorrect as the anion mentioned is selenide (Se), which is actually not the case, we have sulphur in the question.

ii) In this part the chemical formula for ionic compound is Ag₂O, if you reverse the stoichiometry, you will get +1 charge on Ag and -2 charge on oxygen. { Please do remember the first symbol (Ag) here is cation which is followed by anion (oxygen), the charge over cation is always positive and on anion is negative}

Hence, the nomenclature of this compound would be silver (I) oxide.

Option 2 is incorrect as di, tri are not used in stock nomenclature,

Option 3 is incorrect as the oxidation state of Ag mentioned as II, which is incorrect and option 4 is also incorrect as no stock notation is used.

Hence, the correct option is a.

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