Question

Write balanced molecular, ionic, and net ionic equations for the reactions of the following metals with hydrochloric acid to give hydrogen plus the metal ion in solution. (a) Manganese (gives \(\mathrm{Mn}^{2+}\) ) (b) Cadmium (gives \(\mathrm{Cd}^{2+}\) ) (c) \(\operatorname{Tin}\) (gives \(\mathrm{Sn}^{2+}\) )

Short answer

For Mn: \[\text{Mn(s)} + 2\text{HCl(aq)} \rightarrow \text{MnCl}_{2}(aq) + \text{H}_{2}(g),\] Net ionic: \[\text{Mn(s)} + 2\text{H}^{+}(aq) \rightarrow \text{Mn}^{2+}(aq) + \text{H}_{2}(g).\] For Cd: \[\text{Cd(s)} + 2\text{HCl(aq)} \rightarrow \text{CdCl}_{2}(aq) + \text{H}_{2}(g),\] Net ionic: \[\text{Cd(s)} + 2\text{H}^{+}(aq) \rightarrow \text{Cd}^{2+}(aq) + \text{H}_{2}(g).\] For Sn: \[\text{Sn(s)} + 2\text{HCl(aq)} \rightarrow \text{SnCl}_{2}(aq) + \text{H}_{2}(g),\] Net ionic: \[\text{Sn(s)} + 2\text{H}^{+}(aq) \rightarrow \text{Sn}^{2+}(aq) + \text{H}_{2}(g).\]

Step-by-step solution

Writing the Balanced Molecular Equation for Manganese and Hydrochloric Acid

Write the reactants, which are manganese (Mn) and hydrochloric acid (HCl). Manganese reacts with hydrochloric acid to produce manganese(II) chloride (MnCl2) and hydrogen gas (H2). The balanced molecular equation is: \[ \text{Mn (s)} + 2\text{HCl (aq)} \rightarrow \text{MnCl}_2 \text{(aq)} + \text{H}_2 \text{(g)} \]

Writing the Ionic Equation for Manganese Reaction

Split the soluble ionic compounds into their respective ions, keeping solids, liquids, and gases intact. For this reaction, the ionic equation is: \[ \text{Mn (s)} + 2\text{H}^+ \text{(aq)} + 2\text{Cl}^- \text{(aq)} \rightarrow \text{Mn}^{2+} \text{(aq)} + 2\text{Cl}^- \text{(aq)} + \text{H}_2 \text{(g)} \]

Writing the Net Ionic Equation for Manganese Reaction

Cancel the spectator ions that appear on both sides of the ionic equation. Chloride ions are spectator ions in this reaction. The net ionic equation is: \[ \text{Mn (s)} + 2\text{H}^+ \text{(aq)} \rightarrow \text{Mn}^{2+} \text{(aq)} + \text{H}_2 \text{(g)} \]

Writing the Balanced Molecular Equation for Cadmium and Hydrochloric Acid

Write the reactants which are cadmium (Cd) and hydrochloric acid (HCl). Cadmium reacts with hydrochloric acid to produce cadmium chloride (CdCl2) and hydrogen gas (H2). The balanced molecular equation is: \[ \text{Cd (s)} + 2\text{HCl (aq)} \rightarrow \text{CdCl}_2 \text{(aq)} + \text{H}_2 \text{(g)} \]

Writing the Ionic Equation for Cadmium Reaction

Split the soluble ionic compounds into their respective ions, keeping solids, liquids, and gases intact. For this reaction, the ionic equation is: \[ \text{Cd (s)} + 2\text{H}^+ \text{(aq)} + 2\text{Cl}^- \text{(aq)} \rightarrow \text{Cd}^{2+} \text{(aq)} + 2\text{Cl}^- \text{(aq)} + \text{H}_2 \text{(g)} \]

Writing the Net Ionic Equation for Cadmium Reaction

Cancel the spectator ions that appear on both sides of the ionic equation. Chloride ions are spectator ions in this reaction. The net ionic equation is: \[ \text{Cd (s)} + 2\text{H}^+ \text{(aq)} \rightarrow \text{Cd}^{2+} \text{(aq)} + \text{H}_2 \text{(g)} \]

Writing the Balanced Molecular Equation for Tin and Hydrochloric Acid

Write the reactants which are tin (Sn) and hydrochloric acid (HCl). Tin reacts with hydrochloric acid to produce tin(II) chloride (SnCl2) and hydrogen gas (H2). The balanced molecular equation is: \[ \text{Sn (s)} + 2\text{HCl (aq)} \rightarrow \text{SnCl}_2 \text{(aq)} + \text{H}_2 \text{(g)} \]

Writing the Ionic Equation for Tin Reaction

Split the soluble ionic compounds into their respective ions, keeping solids, liquids, and gases intact. For this reaction, the ionic equation is: \[ \text{Sn (s)} + 2\text{H}^+ \text{(aq)} + 2\text{Cl}^- \text{(aq)} \rightarrow \text{Sn}^{2+} \text{(aq)} + 2\text{Cl}^- \text{(aq)} + \text{H}_2 \text{(g)} \]

Writing the Net Ionic Equation for Tin Reaction

Cancel the spectator ions that appear on both sides of the ionic equation. Chloride ions are spectator ions in this reaction. The net ionic equation is: \[ \text{Sn (s)} + 2\text{H}^+ \text{(aq)} \rightarrow \text{Sn}^{2+} \text{(aq)} + \text{H}_2 \text{(g)} \]

Key concepts

Molecular Equations

A molecular equation provides a concise way of representing a chemical reaction by displaying the compounds in their molecular form. For instance, when manganese reacts with hydrochloric acid, the molecular equation is written as:
\[ \text{Mn (s)} + 2\text{HCl (aq)} \rightarrow \text{MnCl}_2 \text{(aq)} + \text{H}_2 \text{(g)} \]
This tells us that solid manganese (Mn) reacts with hydrochloric acid in aqueous solution (HCl (aq)) to produce aqueous manganese(II) chloride (MnCl2) and hydrogen gas (H2). It's important to balance molecular equations to abide by the law of conservation of mass, ensuring that the number of atoms for each element is equal on both sides of the equation.

Ionic Equations

Ionic equations go a step further than molecular equations by breaking down soluble ionic compounds into the ions they form in solution. Here's what happens in our example with manganese and hydrochloric acid:
\[ \text{Mn (s)} + 2\text{H}^+ \text{(aq)} + 2\text{Cl}^- \text{(aq)} \rightarrow \text{Mn}^{2+} \text{(aq)} + 2\text{Cl}^- \text{(aq)} + \text{H}_2 \text{(g)} \]
This representation helps to visualize which ions are interacting in the reaction. Writing ionic equations is essential for developing a deeper understanding of the chemical changes taking place at the ionic level, especially when considering reactions in aqueous solutions.

Net Ionic Equations

Net ionic equations simplify ionic equations by eliminating the spectator ions—the ions that do not participate in the actual chemical reaction. They allow us to focus on the species that are actually changing during the reaction. For the manganese example, the net ionic equation is:
\[ \text{Mn (s)} + 2\text{H}^+ \text{(aq)} \rightarrow \text{Mn}^{2+} \text{(aq)} + \text{H}_2 \text{(g)} \]
The chloride ions (\text{Cl}^-) are omitted because they remain unchanged. Net ionic equations emphasize the essence of chemical reactions, helping students and chemists to identify the core components responsible for the chemical change.

Chemical Reactivity

Chemical reactivity refers to the tendency of a chemical substance to undergo a chemical change. The metals manganese, cadmium, and tin all react with hydrochloric acid but do so with varying reactivity levels. Reactivity is influenced by the metal's position in the reactivity series, electron configuration, and the nature of the other reactant. In this case, all three metals react to displace hydrogen from the acid, demonstrating their ability to act as reducing agents. Understanding chemical reactivity is crucial for predicting the outcome of chemical reactions and for practical applications in industry and research.

Stoichiometry

Stoichiometry is a branch of chemistry that involves the quantitative relationships between the reactants and products in a chemical reaction. In the provided examples, stoichiometry is used to balance the chemical equations, ensuring that the amount of atoms of each element is equal on both sides of the equation. It enables the calculation of reactants necessary or products formed in a chemical reaction. For educational purposes, mastering stoichiometry is fundamental for solving problems related to chemical reactions and for understanding the precise ratios of substances involved.
In all the balanced reactions presented, stoichiometry principles ensure that the ratio between manganese, cadmium, or tin and hydrochloric acid is in accordance with the stoichiometric coefficients derived from the balanced equations.