Question

1. complete the following table to find the charge on the cation in these compounds. decide if y are reasonable before you move on to step 9.

compound	charge on cation
(b) $\ce{cr_{2}o_{3}}$
(c) $\ce{pbo_{2}}$
(d) $\ce{nicl_{2}}$
(e) $\ce{crn}$
(f) $\ce{hgo}$

Explanation:

Step1: Recall anion charges

Sulfide ($\text{S}^{2-}$), oxide ($\text{O}^{2-}$), chloride ($\text{Cl}^-$), nitride ($\text{N}^{3-}$) are standard anions with fixed charges.

Step2: Neutrality rule for (a) $\text{Cu}_2\text{S}$

Total charge = 0. Let $\text{Cu}$ charge = $x$.
$$2x + (-2) = 0 \implies x = +1$$

Step3: Neutrality rule for (b) $\text{Cr}_2\text{O}_3$

Let $\text{Cr}$ charge = $x$.
$$2x + 3(-2) = 0 \implies 2x = 6 \implies x = +3$$

Step4: Neutrality rule for (c) $\text{PbO}_2$

Let $\text{Pb}$ charge = $x$.
$$x + 2(-2) = 0 \implies x = +4$$

Step5: Neutrality rule for (d) $\text{NiCl}_2$

Let $\text{Ni}$ charge = $x$.
$$x + 2(-1) = 0 \implies x = +2$$

Step6: Neutrality rule for (e) $\text{CrN}$

Let $\text{Cr}$ charge = $x$.
$$x + (-3) = 0 \implies x = +3$$

Step7: Neutrality rule for (f) $\text{HgO}$

Let $\text{Hg}$ charge = $x$.
$$x + (-2) = 0 \implies x = +2$$

Answer:

Compound	Charge on cation
(b) $\text{Cr}_2\text{O}_3$	+3
(c) $\text{PbO}_2$	+4
(d) $\text{NiCl}_2$	+2
(e) $\text{CrN}$	+3
(f) $\text{HgO}$	+2