Question

Specify what ions are present upon dissolving each of the following substances in water: (a) \(\mathrm{MgI}_{2}\), (b) \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\), (c) \(\mathrm{HClO}_{4}\) (d) \(\mathrm{NaCH}_{3} \mathrm{COO}\).

Short answer

Upon dissolving each of the following substances in water, we obtain the following ions: (a) \( MgI_2 \rightarrow Mg^{2+} + 2 I^{-}\) (b) \( Al(NO_3)_3 \rightarrow Al^{3+} + 3 NO_3^-\) (c) \( HClO_4 \rightarrow H^+ + ClO_4^-\) (d) \( NaCH_3COO \rightarrow Na^+ + CH_3COO^-\)

Step-by-step solution

(a) Dissociation of MgI₂

When MgI₂ (magnesium iodide) is dissolved in water, it dissociates into its ions. Magnesium is in group 2 of the periodic table and has a charge of +2, while iodide is in group 17 (halogens) and has a charge of -1. Therefore, when MgI₂ dissociates, it forms the following ions: \[ MgI_2 \rightarrow Mg^{2+} + 2 I^{-}\]

(b) Dissociation of Al(NO₃)₃

When Al(NO₃)₃ (aluminum nitrate) is dissolved in water, it dissociates into its ions. Aluminum is in group 13 of the periodic table and has a charge of +3, while the nitrate ion (NO₃⁻) has a charge of -1. Therefore, when Al(NO₃)₃ dissociates, it forms the following ions: \[ Al(NO_3)_3 \rightarrow Al^{3+} + 3 NO_3^-\]

(c) Dissociation of HClO₄

When HClO₄ (perchloric acid) is dissolved in water, it dissociates into its ions. Hydrogen ion (H⁺) has a charge of +1, and the perchlorate ion (ClO₄⁻) has a charge of -1. Therefore, when HClO₄ dissociates, it forms the following ions: \[ HClO_4 \rightarrow H^+ + ClO_4^-\]

(d) Dissociation of NaCH₃COO

When NaCH₃COO (sodium acetate) is dissolved in water, it dissociates into its ions. Sodium is in group 1 of the periodic table and has a charge of +1, while the acetate ion (CH₃COO⁻) has a charge of -1. Therefore, when NaCH₃COO dissociates, it forms the following ions: \[ NaCH_3COO \rightarrow Na^+ + CH_3COO^-\]

Key concepts

Dissociation in Water

When ionic compounds are added to water, they tend to dissociate into their constituent ions. This process is important in chemistry because ions in solution can participate in various reactions.

Ions are charged particles, and when they are free in a solution, they allow the solution to conduct electricity.

• The process depends on the compound's structure and the attraction between the ions and water molecules.
• Strong ionic bonds can be overcome by the polar nature of water molecules, which can separate the ions from each other.

This is why the dissociation process is essential for many biological and chemical reactions that require ions in solution.

Magnesium Iodide (MgI₂)

Magnesium iodide is composed of magnesium ions (Mg²⁺) and iodide ions (I⁻). When magnesium iodide dissolves in water, it breaks apart into its ions.

The dissociation reaction for magnesium iodide is given by: \[ MgI_2 \rightarrow Mg^{2+} + 2 I^- \]

• Magnesium ions have a charge of +2 because magnesium is from group 2 of the periodic table.
• Iodide ions each have a charge of -1, compensating for the +2 charge of magnesium by pairing with two iodide ions.

These ions in water can participate in a range of chemical reactions.

Aluminum Nitrate (Al(NO₃)₃)

Aluminum nitrate consists of aluminum ions (Al³⁺) and nitrate ions (NO₃⁻).
When it dissolves in water, it splits into its respective ions:\[ Al(NO_3)_3 \rightarrow Al^{3+} + 3 NO_3^- \]

• Since aluminum is found in group 13 of the periodic table, it has a +3 charge.
• Nitrate ions carry a single negative charge each, so three nitrate ions are needed to balance the charge of one aluminum ion.

The dissociation of aluminum nitrate is crucial for processes involving nitrogen compounds.

Perchloric Acid (HClO₄)

Perchloric acid is an important chemical that dissociates in water to form hydrogen ions (H⁺) and perchlorate ions (ClO₄⁻).

This dissociation reaction is expressed as: \[ HClO_4 \rightarrow H^+ + ClO_4^- \]

• The hydrogen ion (H⁺) is the main contributor to the acidic nature of the solution.
• The perchlorate ion carries a single negative charge.

Perchloric acid is a strong acid, meaning it dissociates completely in water, which is essential for various industrial and research applications.

Sodium Acetate (NaCH₃COO)

Sodium acetate is composed of sodium ions (Na⁺) and acetate ions (CH₃COO⁻).
When this compound dissolves in water, it dissociates as follows:\[ NaCH_3COO \rightarrow Na^+ + CH_3COO^- \]

• Sodium is in group 1, which contributes to its +1 charge as an ion.
• The acetate ion is a common organic ion found in many biological and chemical processes.

Sodium acetate's dissociation in water is significant in buffer solutions, which are used to maintain stable pH levels in various applications.