Reactions of Acids and Bases: Equations and Applications

Chapter 14: Acids and Bases

14.7 Reactions of Acids and Bases

This section explores the chemical reactions of acids with metals, carbonates, bicarbonates, and bases. Understanding these reactions is essential for predicting products and writing balanced chemical equations in introductory chemistry.

Acids with Metals

Acids commonly react with certain metals to produce hydrogen gas and a metal salt. This is a type of single replacement reaction where the metal displaces hydrogen from the acid.

• Reactive metals: Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Aluminum (Al), Zinc (Zn), Iron (Fe), and Tin (Sn).

• General reaction: Acid + Metal → Hydrogen gas + Metal salt

• Example: Magnesium reacts rapidly with hydrochloric acid to form hydrogen gas and magnesium chloride.

Sample Equations:

• $2HCl(aq) + Mg(s) \rightarrow H_2(g) + MgCl_2(aq)$

• $2HNO_3(aq) + Zn(s) \rightarrow H_2(g) + Zn(NO_3)_2(aq)$

Acids React with Carbonates and Bicarbonates

Acids react with carbonates and hydrogen carbonates (bicarbonates) to produce carbon dioxide gas, water, and a salt. This reaction is commonly observed in everyday life, such as when baking soda (sodium bicarbonate) reacts with vinegar (acetic acid).

• General reaction: Acid + Carbonate/Bicarbonate → Carbon dioxide + Water + Salt

• Example: Sodium carbonate reacts with hydrochloric acid:

• $2HCl(aq) + Na_2CO_3(aq) \rightarrow CO_2(g) + H_2O(l) + 2NaCl(aq)$

• $HBr(aq) + NaHCO_3(aq) \rightarrow CO_2(g) + H_2O(l) + NaBr(aq)$

• $HC_2H_3O_2(aq) + NaHCO_3(s) \rightarrow CO_2(g) + NaC_2H_3O_2(aq) + H_2O(l)$

Application Example: The reaction between baking soda and vinegar produces fizzing due to the release of carbon dioxide gas.

Acids React with Hydroxides (Neutralization)

Neutralization is the reaction between an acid and a base (usually a hydroxide) to produce water and a salt. This is a fundamental concept in acid-base chemistry.

• General reaction: Acid + Base → Water + Salt

• Example: Sodium hydroxide reacts with hydrochloric acid:

• $NaOH(aq) + HCl(aq) \rightarrow H_2O(l) + NaCl(aq)$

The H+ ion from the acid combines with the OH- ion from the base to form water:

• $H^+(aq) + OH^-(aq) \rightarrow H_2O(l)$

Other ions (spectator ions) remain in solution and form the salt.

Balancing Neutralization Reactions

In neutralization reactions, it is important to balance the number of H+ ions from the acid with the number of OH- ions from the base. Coefficients may be needed to ensure the equation is balanced.

• One H+ always reacts with one OH-.

• Balance the equation by adjusting coefficients as needed.

Sample Problem: Balancing Equations for Acids

Problem: Write the balanced equation for the neutralization of HCl(aq) and Ba(OH)2(s).

1. Step 1: Write the reactants and products. $HCl(aq) + Ba(OH)_2(s) \rightarrow H_2O(l) + \text{salt}$

2. Step 2: Balance the H in the acid with the OH in the base. $2HCl(aq) + Ba(OH)_2(s) \rightarrow H_2O(l) + \text{salt}$

3. Step 3: Balance the H2O with the H+ and the OH-. $2HCl(aq) + Ba(OH)_2(s) \rightarrow 2H_2O(l) + \text{salt}$

4. Step 4: Write the formula of the salt from the remaining ions. $2HCl(aq) + Ba(OH)_2(s) \rightarrow 2H_2O(l) + BaCl_2(aq)$

Review Table: Summary of Acid Reactions

Type of Reaction	General Equation	Products	Example
Acid + Metal	Acid + Metal → H2 + Salt	Hydrogen gas, Salt	$2HCl(aq) + Mg(s) \rightarrow H_2(g) + MgCl_2(aq)$
Acid + Carbonate/Bicarbonate	Acid + (Bi)carbonate → CO2 + H2O + Salt	Carbon dioxide, Water, Salt	$2HCl(aq) + Na_2CO_3(aq) \rightarrow CO_2(g) + H_2O(l) + 2NaCl(aq)$
Acid + Base (Neutralization)	Acid + Base → H2O + Salt	Water, Salt	$NaOH(aq) + HCl(aq) \rightarrow H_2O(l) + NaCl(aq)$

Key Points

• An acid reacts with a metal to produce hydrogen gas and a salt.

• The reaction of an acid with a carbonate or bicarbonate produces carbon dioxide, water, and a salt.

• In neutralization, an acid reacts with a base to produce water and a salt.

Additional info: These reactions are foundational for understanding chemical changes, laboratory techniques, and real-world applications such as antacid function, cleaning agents, and industrial processes.