Question

Add the physical state for each substance in the following aqueous reactions. Then write and balance a net ionic cquation for cach reaction. (a) \(\mathrm{NaCl}+\mathrm{Ag}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{AgCl}\) (b) \(\mathrm{Cu}(\mathrm{OH})_{2}+\mathrm{HCl} \longrightarrow \mathrm{CuCl}_{2}+\mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{BaCl}_{2}+\mathrm{Ag}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{BaSO}_{4}+\mathrm{AgCl}\)

Short answer

The physical states for each substance are: AgCl, Cu(OH)2, and BaSO4 are solid (s). NaCl, Ag2SO4, Na2SO4, CuCl2, BaCl2, and HCl are aqueous (aq). Water is liquid (l). The net ionic equations are: \[ \mathrm{Ag}^{+}(aq) \longrightarrow \mathrm{AgCl}(s) \], \[ \mathrm{Cu(OH)}_{2}(s) + 2\mathrm{H}^{+}(aq) \longrightarrow \mathrm{Cu}^{2+}(aq) + 2\mathrm{H}_2\mathrm{O}(l) \] and \[ \mathrm{Ba}^{2+}(aq)+\mathrm{SO}_4^{2-}(aq) \longrightarrow \mathrm{BaSO}_4(s) \]

Step-by-step solution

- Identify Physical State

Firstly, check the solubility of all substances in each reaction. For example, highlighted compounds AgCl, Cu(OH)2, and BaSO4 are insoluble and exist as solid (s) in their reactions. On the other hand, NaCl, Ag2SO4, Na2SO4, CuCl2, BaCl2, and HCl are soluble and therefore stay as aqueous (aq). For water, the physical state is liquid (l). Apply those states into each reaction: \[ \mathrm{NaCl(aq)}+\mathrm{Ag}_{2} \mathrm{SO}_{4} (aq)\longrightarrow \mathrm{Na}_{2} \mathrm{SO}_{4} (aq) + \mathrm{AgCl} (s) \] \[ \mathrm{Cu(OH)}_{2} (s) + \mathrm{HCl}(aq) \longrightarrow \mathrm{CuCl}_{2} (aq) + \mathrm{H}_{2} \mathrm{O} (l) \] \[ \mathrm{BaCl}_{2}(aq) + \mathrm{Ag}_{2} \mathrm{SO}_{4} (aq) \longrightarrow \mathrm{BaSO}_{4} (s) + \mathrm{AgCl} (s)\]

- Write Balanced Ionic Equations

Next, write total ionic equations by splitting the aqueous compounds into their ions: \[ \mathrm{Na}^+(aq)+\mathrm{Cl}^-(aq)+\mathrm{Ag}^{+}(aq)+\mathrm{SO}_4^{2-} (aq) \longrightarrow \mathrm{Na}^{+}(aq)+\mathrm{SO}_4^{2-}(aq)+\mathrm{AgCl}(s) \] \[ \mathrm{Cu(OH)}_{2}(s) + \mathrm{H}^{+}(aq)+\mathrm{Cl}^- (aq) \longrightarrow \mathrm{Cu}^{2+}(aq)+2\mathrm{Cl}^- (aq) + 2\mathrm{H}_2\mathrm{O}(l) \] \[ \mathrm{Ba}^{2+}(aq)+2\mathrm{Cl}^- (aq) + \mathrm{Ag}^{+}(aq)+\mathrm{SO}_4^{2-} (aq) \longrightarrow \mathrm{BaSO}_4(s) + \mathrm{AgCl}(s) \]

- Write Net Ionic Equations

Finally, write the net ionic equations by removing the spectator ions. These are ions that are the same on both sides of the equation. Spectator ions for these reactions include Na+, Cl-, and SO4^2- ions. Therefore, the net ionic equations can be: \[ \mathrm{Ag}^{+}(aq) \longrightarrow \mathrm{AgCl}(s) \] \[ \mathrm{Cu(OH)}_{2}(s) + 2\mathrm{H}^{+}(aq) \longrightarrow \mathrm{Cu}^{2+}(aq) + 2\mathrm{H}_2\mathrm{O}(l) \] \[ \mathrm{Ba}^{2+}(aq)+\mathrm{SO}_4^{2-}(aq) \longrightarrow \mathrm{BaSO}_4(s) \]

Key concepts

Balancing Chemical Reactions

Understanding the balancing of chemical reactions is fundamental for any student delving into the study of Chemistry. A balanced chemical equation ensures that the same number of atoms of each element is present on both the reactant side and the product side, complying with the law of conservation of mass. This means that matter cannot be created or destroyed; it only changes forms during a reaction.

For example, when you look at the reaction \(\mathrm{Cu(OH)_2} + \mathrm{HCl} \longrightarrow \mathrm{CuCl_2} + \mathrm{H_2O}\), you start by ensuring there's an equal number of each type of atom on both sides of the equation. Initially, we have one copper atom, two oxygen atoms, and two hydrogen atoms on the reactants side. To balance it, we need to ensure that we have the same amounts on the products side. Such a balancing act might require introducing stoichiometric coefficients that are number factors placed before compounds in an equation. In this case, the balanced reaction with states included becomes: \(\mathrm{Cu(OH)_2(s)} + 2\mathrm{HCl(aq)} \longrightarrow \mathrm{CuCl_2(aq)} + 2\mathrm{H_2O(l)}\).

It is through this meticulous process of balancing that we ensure the chemical equations accurately reflect the actual transformations occurring during a reaction.

Solubility in Aqueous Reactions

Solubility in aqueous reactions is a critical concept when writing net ionic equations. Compounds that are soluble in water will dissociate into ions and are represented in their ionic form, while those that are not soluble remain undissociated as solids in the equations. The solubility of substances depends on various factors, including temperature, pressure, and the nature of the solvent and solute.

In our exercise, substances like \(\mathrm{NaCl}\) and \(\mathrm{HCl}\) are soluble in water and are written as (aq), denoting their dissolved, ionic form. On the other hand, substances such as \(\mathrm{AgCl}\) and \(\mathrm{BaSO_4}\) are insoluble and thus remain solid (s) in the equation. Understanding solubility rules helps students predict whether a substance will dissolve in water, which is essential when determining the complete ionic and net ionic equations of a chemical reaction.

Spectator Ions

Spectator ions are ions in an aqueous solution that do not participate in the actual chemical reaction. They are present in the solution but do not get involved in the formation of the product; hence, it is not reflected in the net ionic equation. The role of spectator ions is crucial for students to understand because eliminating them helps simplify equations, leading to the net ionic equation that highlights the actual chemical change.

For instance, in the reaction \(\mathrm{NaCl} + \mathrm{Ag_2SO_4} \longrightarrow \mathrm{Na_2SO_4} +\mathrm{AgCl}\), the \(\mathrm{Na}^+\) and the \(\mathrm{SO_4}^{2-}\) ions are present before and after the reaction occurs. Since they don't change their oxidation state or form any new substances, they are considered as spectators. The net ionic equation only includes the ions and molecules directly involved in the reaction, such as \(\mathrm{Ag}^{+}(aq) + \mathrm{Cl}^{-}(aq) \longrightarrow \mathrm{AgCl}(s)\), representing the formation of a solid, \(\mathrm{AgCl}\), from its constituent ions. Identifying and removing spectator ions from the total ionic equation simplifies the study of chemical reactions and focuses attention on the substances that undergo a chemical change.