Question

The following list contains some common radicals. Using the charges on these ions and the idea of valence, predict the formulas for the following:_________.
1. nitrate NO3-1 phosphate PO4-3
2. sulfate SO4-2 acetate C2H3O2-1
3. ammonium NH4+ chromate CrO4-2
4. carbonate CO3-2 dichromate Cr2O7-2
5. permanganate MnO4-1 sulfide S-2
6. sodium carbonate
7. potassium permanganate

Answer 1

Answer : The formula for the compound sodium carbonate is $Na_2CO_3$

The formula for the compound potassium permanganate is $KMnO_4$

Explanation :

For formation of a neutral ionic compound, the charges on cation and anion must be balanced.

The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non-metals.

(a) Sodium carbonate

In the compound, the sodium metal forms an ionic compound with polyatomic anion (carbonate) $CO_3^{2-}$.

Here, sodium is having an oxidation state of +1 called as $Na^{1+}$ cation and carbonate $CO_3^{2-}$ is an anion with oxidation state of -2. The charges are not balanced. So, the charges are balanced by the cris-cross method. Thus, the compound formed will be, $Na_2CO_3$

Hence, the formula for the compound sodium carbonate is $Na_2CO_3$

(b) Potassium permanganate

In the compound, the potassium metal forms an ionic compound with polyatomic anion (permanganate) $MnO_4^{1-}$.

Here, potassium is having an oxidation state of +1 called as $K^{1+}$ cation and permanganate $MnO_4^{1-}$ is an anion with oxidation state of -1. The charges are balanced. Thus, the compound formed will be, $KMnO_4$

Hence, the formula for the compound potassium permanganate is $KMnO_4$