5.3: Acid-Base Reactions

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Page ID: 541908

Muhammad Arif Malik
Fresno City College

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Learning Objectives

Understand common acid-base reactions.

We have previously learned about some common acids and bases. Now let's examine some acid-base reactions in more detail.

Acids Reacting with Hydroxide Bases

Acids release proton (H⁺) and Arrhenius bases release hydroxide ions (OH^-) in solution. When an acid mix with the Arrhenius base, H⁺ and OH^- ions react with each other and produce water molecules. The generic word equation and the specific chemical equation for the reaction of hydrochloric acid and sodium hydroxide are shown below.

Generic Equation:

\[Acid + Base \rightarrow Salt(an~ionic~compound) + Water\]

Reaction:

\[Hydrochloric~Acid + Sodium~Hydroxide \rightarrow Sodium~Chloride + Water\]

Chemical Equation:

\[\mathrm{HCl}(\mathrm{aq})+\mathrm{NaOH}(a q) \rightarrow \mathrm{NaCl}(a q)+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})\nonumber\]

Example \(\PageIndex{2}\)

Write a balanced chemical equation of a reaction between HCl and Ca(OH)₂?

Solution

Step 1) Write the formula of acid and base in the reactants and salt and water in the products. All the strong electrolytes dissolve in water, so use (aq) to represent their state.

\[\mathrm{HCl}(\mathrm{aq})+\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow \text { Salt(aq) }+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})\nonumber\]

Step 2) Balance the H⁺ in the acid with the OH^- in the base.

\[2 \mathrm{HCl}(\mathrm{aq})+\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow \mathrm{Salt}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})\nonumber\]

Step 3) Balance the H₂O with the H⁺ in the acid, or with the OH^- in the base.

\[2 \mathrm{HCl}(\mathrm{aq})+\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow \text { Salt }(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\nonumber\]

Step 4) Write the salt by combing the cations from the base and the anions from the acid. Make sure the charges are balanced in the salt to make it a neutral substance.

\[2 \mathrm{HCl}(\mathrm{aq})+\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\]

Example \(\PageIndex{3}\)

Write a balanced chemical equation of a reaction between H₂SO₄ and Ba(OH)₂?

Solution

Step 1) Write the formula of acid and base in the reactants and salt and water in the products. All the strong electrolytes dissolve in water, so use (aq) to represent their state.

\[\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{Ba}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow \mathrm{Salt}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})\nonumber\]

Step 2) Balance the H⁺ in the acid with the OH^- in the base. They are already balanced in the above equation.

Step 3) Balance the H₂O with the H⁺ in the acid, or with the OH^- in the base.

\[\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{Ba}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow \mathrm{Salt}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\nonumber\]

Step 4) Write the salt by combing the cations from the base and the anions from the acid. Make sure the charges are balanced in the salt to make it a neutral substance.

\[\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{Ba}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow \mathrm{BaSO}_{4}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\nonumber\]

Acids Reacting with Carbonate Bases

When carbonates react with acids, a new acid (Carbonic acid, H₂CO₃) is briefly formed. This acid then immediately breaks down into carbon dioxide (CO₂) and water (H₂O). Carbon dioxide is a gas, so it bubbles out of the solution as shown below.

Figure \(\PageIndex{2}\): The reaction of sodium carbonate with HCl. Before and after HCl addition. Carbon dioxide bubbles out after HCl addition. Source: NCSSM, 05/18/20, https://youtu.be/TJYOxGHNTzg, CC BY 3.0

The equation for this reaction is shown below.

Generic Equation:

\[Acid + Carbonate~Base \rightarrow Salt(an~ionic~compound) + Carbon~Dioxide + Water\]

Reaction:

\[Hydrochloric~Acid + Sodium~Carbonate \rightarrow Sodium~Chloride + Carbon~Dioxide + Water\]

Chemical Equation:

\[\mathrm{2HCl}(\mathrm{aq})+\mathrm{Na}_{2}\mathrm{CO}_{3}(a q) \rightarrow \mathrm{2NaCl}(aq)+\mathrm{CO}_{2}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \nonumber\]

Similarly, calcium carbonate found in limestone reacts with acids. For example, sulfuric acid is one of the components in acid rain that reacts with calcium carbonate and damages sculptures made of stone.

\[\mathrm{CaCO}_{3}(\mathrm{s})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \rightarrow \mathrm{CaSO}_{4}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \nonumber\]

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Example \(\PageIndex{2}\)

Example \(\PageIndex{3}\)