Question

Give the names and charges of the cation and anion in each of the following compounds: (a) CuS, (b) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{Al}\left(\mathrm{ClO}_{3}\right)_{3},(\mathbf{d}) \mathrm{Co}(\mathrm{OH})_{2},(\mathbf{e}) \mathrm{PbCO}_{3}\)

Short answer

(a) CuS: Cu²⁺ (cation), S²⁻ (anion); (b) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\): Ag⁺ (cation), SO₄²⁻ (anion); (c) \(\mathrm{Al}\left(\mathrm{ClO}_{3}\right)_{3}\): Al³⁺ (cation), ClO₃⁻ (anion); (d) \(\mathrm{Co}(\mathrm{OH})_{2}\): Co²⁺ (cation), OH⁻ (anion); (e) \(\mathrm{PbCO}_{3}\): Pb²⁺ (cation), CO₃²⁻ (anion).

Step-by-step solution

(a) CuS

CuS is a compound composed of copper (Cu) and sulfur (S). In this compound, copper acts as the cation and sulfur as the anion. Copper can have multiple oxidation states, but in this case, it's in the +2 oxidation state, giving it a charge of +2 (Cu²⁺). Sulfur, as the anion, has a -2 charge (S²⁻).

(b) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\)

The compound \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) is composed of silver (Ag) cations and sulfate (SO₄) anions. Silver has only one oxidation state, +1, so the cation will have a +1 charge (Ag⁺). The sulfate anion has a -2 charge (SO₄²⁻).

(c) \(\mathrm{Al}\left(\mathrm{ClO}_{3}\right)_{3}\)

In the compound \(\mathrm{Al}\left(\mathrm{ClO}_{3}\right)_{3}\), the cation is aluminum (Al) with a +3 charge (Al³⁺) and the anion is chlorate (ClO₃) with a -1 charge (ClO₃⁻).

(d) \(\mathrm{Co}(\mathrm{OH})_{2}\)

For the compound \(\mathrm{Co}(\mathrm{OH})_{2}\), the cation is cobalt (Co) and the anion is the hydroxide ion (OH). Cobalt can have different oxidation states, but in this case, it has a +2 charge (Co²⁺). The hydroxide ion has a -1 charge (OH⁻).

(e) \(\mathrm{PbCO}_{3}\)

The compound \(\mathrm{PbCO}_{3}\) consists of lead (Pb) as the cation and the carbonate ion (CO₃) as the anion. Lead can have various oxidation states; in this instance, it has a +2 charge (Pb²⁺). The carbonate ion has a -2 charge (CO₃²⁻).

Key concepts

Cation and Anion Charges

In chemistry, ionic compounds are formed by a combination of cations and anions. Cations are positively charged ions, while anions carry a negative charge. Understanding the charges on these ions is crucial for predicting the structure and properties of ionic compounds.
For cations, the charge typically corresponds to the oxidation state of the metal. Common metal cations include copper (Cu²⁺), silver (Ag⁺), and aluminum (Al³⁺). Metals like copper and cobalt can have multiple oxidation states, so it's essential to identify the correct one based on the compound they form.
Anions, on the other hand, are generally nonmetals or polyatomic ions with a negative charge. Sulfur (S²⁻) and polyatomic ions such as sulfate (SO₄²⁻) and carbonate (CO₃²⁻) are typical examples. Recognizing the typical charge on anions helps in writing and balancing chemical formulas effectively.

Chemical Formulas

Chemical formulas represent the combination of cations and anions in a compound, displaying the proportions in which these ions come together. These formulas are crucial for understanding the composition of compounds.

• Simple Binary Compounds: These are made of two elements, such as CuS. Here, copper (Cu²⁺) combines with sulfur (S²⁻) in a 1:1 ratio.
• Compounds with Polyatomic Ions: These compounds, such as \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\), contain ions composed of more than one atom. Silver, with a charge of +1, pairs with the sulfate ion, which has a charge of -2, requiring two silver ions to balance the charge.
• Complex Formulas: Compounds like \(\mathrm{Al}\left(\mathrm{ClO}_{3}\right)_{3}\) involve aluminum (Al³⁺) and chlorate ions (ClO₃⁻), where three chlorate ions are needed to neutralize the charge of aluminum.

By understanding these formulas, you can predict how different ions combine to form electrically neutral compounds.

Oxidation States

Oxidation states, also known as oxidation numbers, are a way to keep track of the electrons in chemical reactions, particularly redox reactions. Each element in a compound is assigned a number that denotes its charge. These states help chemists understand how electrons are distributed in a compound.
Metal cations often exhibit specific oxidation states. For instance, copper can appear as Cu⁺ or Cu²⁺, depending on the compound. It's the higher oxidation state (Cu²⁺) that appears in CuS. Similarly, cobalt and lead can adopt different states; in \(\mathrm{Co}(\mathrm{OH})_{2}\) and \(\mathrm{PbCO}_{3}\), both metals exhibit a +2 oxidation state.
Understanding oxidation states not only helps in knowing the possible charges on ions but also in determining the formula of the compound through balancing these charges, ensuring overall charge neutrality.