Question

Write a chemical formula for each compound or ion, and indicate the oxidation state of the group \(5 \mathrm{~A}\) element in each formula: (a) phosphate ion, (b) arsenous acid, (c) antimony(III) sulfide, (d) calcium dihydrogen phosphate, (e) potassium phosphide, (f) gallium arsenide.

Short answer

The chemical formulas and corresponding oxidation states for the group 5A elements in each compound are as follows: (a) Phosphate ion: \(PO_4^{3-}\) (P: +5), (b) Arsenous acid: \(H_3AsO_3\) (As: +3), (c) Antimony(III) sulfide: \(Sb_2S_3\) (Sb: +3), (d) Calcium dihydrogen phosphate: \(Ca(H_2PO_4)_2\) (P: +5), (e) Potassium phosphide: \(K_3P\) (P: -3), and (f) Gallium arsenide: \(GaAs\) (As: -3).

Step-by-step solution

(a) Phosphate Ion (PO4^3-)

To find the formula for the phosphate ion, we need to know the valency and charges of the elements involved. Phosphorus (P) belongs to group 5A, so its oxidation number is typically +5. Oxygen (O) has an oxidation number of -2. To form a neutral ion, we need the charges to balance out. In this case: (+5) + 4 x (-2) = -3 Thus, the phosphate ion will have a formula of PO4^3-.

(b) Arsenous Acid (H3AsO3)

Arsenous acid contains hydrogen (H) with an oxidation number of +1, arsenic (As) from group 5A with an oxidation number of +3 (since it's arsenous), and oxygen (O) with an oxidation number of -2. We balance their charges to form a neutral compound: 3(+1) + (+3) + 3(-2) = 0 The chemical formula for arsenous acid will be H3AsO3.

(c) Antimony (III) Sulfide (Sb2S3)

Antimony (III) sulfide suggests that the antimony (Sb) has a +3 oxidation state, while sulfur (S) has an oxidation state of -2. We balance their charges to form a neutral compound: 2(+3) + 3(-2) = 0 The chemical formula for Antimony (III) sulfide is Sb2S3.

(d) Calcium Dihydrogen Phosphate (Ca(H2PO4)2)

Calcium dihydrogen phosphate involves calcium (Ca) with a +2 oxidation state, hydrogen (H) with a +1 oxidation state, and the phosphate ion (PO4^3-). We can balance their charges to form a neutral compound: (+2) + 2[(2(+1)) + (-3)] = 0 The chemical formula for calcium dihydrogen phosphate is Ca(H2PO4)2.

(e) Potassium Phosphide (K3P)

Potassium phosphide involves potassium (K) with a +1 oxidation state and phosphorus (P) from group 5A with an oxidation number of -3 (since it's a binary compound with a metal). We balance their charges to form a neutral compound: 3(+1) + (-3) = 0 The chemical formula for potassium phosphide is K3P.

(f) Gallium Arsenide (GaAs)

Gallium arsenide consists of gallium (Ga) with a +3 oxidation state and arsenic (As) from group 5A with an oxidation number of -3 (since it's in a binary compound with another metal). We balance their charges to form a neutral compound: (+3) + (-3) = 0 The chemical formula for gallium arsenide is GaAs.

Key concepts

Phosphate Ion

The phosphate ion is an important polyatomic ion with the formula \( ext{PO}_4^{3-}\). Understanding its composition helps in recognizing how oxidation states play a role in forming this ion. In the phosphate ion, phosphorus (P) is the central atom and it belongs to the group 5A elements. This means it generally takes an oxidation state of \(+5\). Meanwhile, oxygen (O) typically has a stable oxidation state of \(-2\).

In forming the phosphate ion, we need to ensure that the total charge is \(-3\). This is calculated by remembering that four oxygen atoms each contribute \(-2\), which total \(-8\), and when added to the \(+5\) from phosphorus, results in \(-3\). The phosphate ion plays a critical role in various biological and chemical processes, emphasizing its importance across science disciplines.

Chemical Formulas

Chemical formulas provide a concise method for depicting the elements and their ratios in a compound. They reveal not only the types of atoms involved but also their relative quantities. Learning to write chemical formulas, as shown in Arsenous Acid (\( ext{H}_3 ext{AsO}_3\)) and Calcium Dihydrogen Phosphate (\( ext{Ca}( ext{H}_2 ext{PO}_4)_2\)), requires an understanding of oxidation states.

The charges must balance to form a neutral compound. For example, in Arsenous Acid, arsenic (As) from group 5A has an oxidation number of \(+3\), hydrogen (H) has \(+1\), and oxygen \(-2\). By balancing these, we ensure the compound is stable. Such formulas provide essential information for calculating empirical formulas, predicting reactivity, and comprehending the structure of molecules.

Group 5A Elements

The elements within group 5A of the periodic table include nitrogen, phosphorus, arsenic, antimony, and bismuth. These elements typically have five electrons in their outermost shell, leading them to form different oxidation states, commonly \(+3\) and \(+5\). This variability in oxidation states allows them to form diverse compounds.

For instance, arsenic in Arsenous Acid (\( ext{H}_3 ext{AsO}_3\)) takes on a \(+3\) oxidation state, whereas phosphorus in the phosphate ion takes on a \(+5\) state. Learning how Group 5A elements behave and form compounds enhances understanding of chemical bonding, molecular structure, and even their role in biological processes.

Neutral Compound Balance

A fundamental rule in chemistry is that overall, compounds must be electrically neutral. This balance is achieved by having the total positive charges equal the total negative charges in a compound. In compounds like Potassium Phosphide (\( ext{K}_3 ext{P}\)) and Gallium Arsenide (\( ext{GaAs}\)), the charges must balance out.

For Potassium Phosphide, potassium (K) has a \(+1\) oxidation state, while phosphorus (P) takes on a \(-3\) state. Three potassium atoms are needed to balance the one phosphorus atom. Similarly, Gallium and Arsenic in Gallium Arsenide both have an oxidation state of \(+3\) and \(-3\) respectively, allowing them to form a stable, neutral compound. Understanding this principle is essential for writing chemical formulas correctly and predicting compound behaviors.