Question

Write the balanced molecular and net ionic equations for each of the following neutralization reactions: \begin{equation} \begin{array}{l}{\text { (a) Aqueous acetic acid is neutralized by aqueous barium }} \\ {\text { hydroxide. }} \\ {\text { (b) Solid chromium(II) hydroxide reacts with nitrous acid. }} \\ {\text { (c) Aqueous nitric acid and aqueous ammonia react. }}\end{array} \end{equation}

Short answer

The balanced molecular equations for each reaction are: (a) \(2CH_3COOH + Ba(OH)_2 \rightarrow Ba(CH_3COO)_2 + 2H_2O\) (b) \(Cr(OH)_2 + 2HNO_2 \rightarrow Cr(NO_2)_2 + 2H_2O\) (c) \(HNO_3 + NH_3 \rightarrow NH_4NO_3\) The net ionic equations for each reaction are: (a) \(2H^+\)(aq) + 2\(OH^-\)(aq) \(\rightarrow\) 2\(H_2O\)(l) (b) No net ionic equation (Chromium hydroxide is insoluble) (c) \(H^+\)(aq) + \(NH_3\)(aq) \(\rightarrow\) \(NH_4^+\)(aq)

Step-by-step solution

1. Balancing the molecular equation for reaction (a)

To balance the molecular equation for reaction (a), aqueous acetic acid is neutralized by aqueous barium hydroxide, we first find the chemical formulas for the reactants and possible products. Acetic acid: \(CH_3COOH\) Barium hydroxide: \(Ba(OH)_2\) A neutralization reaction occurs between an acid and a base, often producing a salt and water. In this case, the salt produced is barium acetate, and water is the other product. Barium acetate: \(Ba(CH_3COO)_2\) Water: \(H_2O\) Now, we write the unbalanced equation: \(CH_3COOH + Ba(OH)_2 \rightarrow Ba(CH_3COO)_2 + H_2O\) Balancing the equation, we get: \(2CH_3COOH + Ba(OH)_2 \rightarrow Ba(CH_3COO)_2 + 2H_2O\)

2. Balancing the molecular equation for reaction (b)

To balance the molecular equation for reaction (b), solid chromium(II) hydroxide reacts with nitrous acid, we find the chemical formulas for the reactants and possible products. Chromium(II) hydroxide: \(Cr(OH)_2\) Nitrous acid: \(HNO_2\) The products formed are chromium(II) nitrite and water. Chromium(II) nitrite: \(Cr(NO_2)_2\) Water: \(H_2O\) Now, we write the unbalanced equation: \(Cr(OH)_2 + HNO_2 \rightarrow Cr(NO_2)_2 + H_2O\) Balancing the equation, we get: \(Cr(OH)_2 + 2HNO_2 \rightarrow Cr(NO_2)_2 + 2H_2O\)

3. Balancing the molecular equation for reaction (c)

To balance the molecular equation for reaction (c), aqueous nitric acid and aqueous ammonia react, we find the chemical formulas for the reactants and possible products. Nitric acid: \(HNO_3\) Ammonia: \(NH_3\) The products will be ammonium nitrate and water. Ammonium nitrate: \(NH_4NO_3\) Now, we write the unbalanced equation: \(HNO_3 + NH_3 \rightarrow NH_4NO_3\) The equation is already balanced. Now that we have found the balanced molecular equations for each reaction, let's identify the net ionic equations.

4. Net ionic equation for reaction (a)

In reaction (a), the molecules involved in the reaction are: 2\(CH_3COOH\) (aq) + \(Ba(OH)_2\) (aq) \(\rightarrow\) \(Ba(CH_3COO)_2\)(aq) + 2\(H_2O\)(l) We can eliminate the spectator ions from this equation to get the net ionic equation. Acetate ions and barium ions are said to be spectator ions in this case. Net ionic equation: \(2H^+\)(aq) + 2\(OH^-\)(aq) \(\rightarrow\) 2\(H_2O\)(l)

5. Net ionic equation for reaction (b)

In reaction (b), the molecules involved in the reaction are: \(Cr(OH)_2\)(s) + 2\(HNO_2\)(aq) \(\rightarrow\) \(Cr(NO_2)_2\)(aq) + 2\(H_2O\)(l) This reaction doesn't have a net ionic equation since the chromium hydroxide isn't soluble in water.

6. Net ionic equation for reaction (c)

In reaction (c), the molecules involved in the reaction are: \(HNO_3\)(aq) + \(NH_3\)(aq) \(\rightarrow\) \(NH_4NO_3\)(aq) We can eliminate the spectator nitrate ion from this equation to get the net ionic equation: Net ionic equation: \(H^+\)(aq) + \(NH_3\)(aq) \(\rightarrow\) \(NH_4^+\)(aq)

Key concepts

Balancing Chemical Equations

Understanding how to balance chemical equations is fundamental in chemistry. A balanced equation has the same number of each type of atoms on both sides of the reaction. Consider a balance scale; when an equation is unbalanced, it's like having different weights on both sides—and our goal is to make these weights equal.

When balancing equations, remember to never change the subscripts of the chemical formulas, as this would alter the substances involved. Instead, we adjust the coefficients, which are the numbers placed before the compounds. An important tip is to start balancing elements that appear only once on each side, followed by more complex ones. This incremental approach simplifies the task.

For example, in the reaction of acetic acid with barium hydroxide, after writing down the unbalanced equation (\(CH_3COOH + Ba(OH)_2 \rightarrow Ba(CH_3COO)_2 + H_2O\)) we can see that the hydrogens and oxygens are not balanced. By adjusting the coefficients, we attain balance: \(2CH_3COOH + Ba(OH)_2 \rightarrow Ba(CH_3COO)_2 + 2H_2O\). Here, we focused on preserving the mass and charge balance across the equation, an essential practice in chemistry.

Net Ionic Equations

Net ionic equations represent the essence of a chemical reaction by highlighting the species that actively participate in the reaction—known as the net ionic compounds—while omitting the spectator ions, which do not change during the course of the reaction.

To write a net ionic equation, one must first write a complete ionic equation where all strong electrolytes (substances that dissociate completely in solution) are represented as their constituents ions. Then, remove the ions that appear on both sides of the equation, as these are the spectators. The remaining ions constitute the net ionic equation, which depicts the actual chemical change.

An exemplary net ionic equation for the neutralization of acetic acid and barium hydroxide can be expressed as \(2H^+\)(aq) + \(2OH^-\)(aq) \(\rightarrow\) \(2H_2O\)(l), illustrating that the protons from the acid and the hydroxide ions from the base combine to form water, which is the driving force behind this acid-base reaction.

Acid-Base Reactions

Acid-base reactions, also known as neutralization reactions, are processes where an acid reacts with a base to produce water and usually a salt. The acids donate protons (\(H^+\)), and the bases provide hydroxide ions (\(OH^-\)), which combine to form water (\(H_2O\)). If there is a formation of a salt, it comprises the remaining ions from the acid and base.

These reactions are exothermic, releasing heat as they form new bonds in the products. The general form of a neutralization reaction can be represented as: \(acid + base \rightarrow salt + water\). Each acid-base pair in the reaction would need to be balanced to reflect the law of conservation of mass.

Often in a classroom, students are asked to predict the products of acid-base reactions, write balanced molecular equations, and then distill these down to their net ionic forms. Through practice, students become adept at understanding the underlying patterns in these reactions, such as how to identify the conjugate acid-base pairs and the resulting neutralization reaction, enhancing their comprehension of chemical reactivity and stoichiometry.