Question

Write a balanced equation to describe any acid-base neutralization reaction that might occur when the following substances are mived. (a) \(\mathrm{H}_{2} \mathrm{~S}(a q)\) and \(\mathrm{Cu}(\mathrm{OH})_{2}(s)\) (b) \(\mathrm{CH}_{4}(g)\) and \(\mathrm{NaOH}(a q)\) (c) \(\mathrm{KHSO}_{4}(a q)\) and \(\mathrm{KOH}(a q)\)

Short answer

The balanced neutralization reactions are: (a) \(\mathrm{H}_{2}\mathrm{S} (aq) + Cu(OH)_2 (s) -> CuS + 2H_2O\). (b) No reaction occurs, as CH4 is not an acid or a base. (c) \(\mathrm{KHSO}_{4}(a q) + \mathrm{KOH}(a q) -> \mathrm{K}_{2}\mathrm{SO}_{4}(a q) + H_2O.l\)

Step-by-step solution

Identifying the Reactants

In each part of the problem, two substances are presented. For example in problem (a), the reactants are \(\mathrm{H}_{2} \mathrm{S}(a q)\) and \(\mathrm{Cu}(\mathrm{OH})_{2}(s)\). The reactants must first be identified accurately by their chemical formulas. \(\mathrm{H}_{2} \mathrm{S}(a q)\) is an acid and \(\mathrm{Cu}(\mathrm{OH})_{2}(s)\) is a base.

Identifying the products

In a typical acid-base neutralization reaction, the products are a salt and water. Therefore, in problem (a), the products would be water (H2O) and the salt \(\mathrm{CuS}\).

Writing the unbalanced chemical equation

Having identified the reactants and products, an unbalanced chemical equation is then written. For part (a), this unbalanced equation would be: \(\mathrm{H}_{2}\mathrm{S} (aq) + Cu(OH)_2 (s) -> CuS + H_2O\).

Balancing the chemical equation

The unbalanced chemical equation is then balanced by adjusting the stoichiometric coefficients of the reactants and products until the number of atoms of each element is the same on both sides. For part (a), the reaction is balanced as: \(\mathrm{H}_{2}\mathrm{S} (aq) + Cu(OH)_2 (s) -> CuS + 2H_2O\)

Repeating for other scenarios

The same process of identification, writing and balancing is then repeated for parts (b) and (c) to obtain their respective balanced chemical equations.

Key concepts

Chemical Equation Balancing

The balancing of chemical equations is a fundamental process in chemistry that ensures the law of conservation of mass is obeyed during a chemical reaction. Essentially, what goes into a reaction must come out, meaning the number of atoms for each element must be the same on both sides of the reaction.

When faced with an unbalanced equation like \(H_2S (aq) + Cu(OH)_2 (s) -> CuS + H_2O\), we can see that the number of oxygen atoms doesn't match on both sides. To balance it, we must add coefficients—a simple numerical factor—to the chemical species in the equation. In our example, placing a '2' before \(H_2O\) balances the hydrogen and oxygen atoms, resulting in the balanced equation \(H_2S (aq) + Cu(OH)_2 (s) -> CuS + 2H_2O\).

This process is similar to a mathematical equation where both sides must be equal. Patience and attention to detail are necessary because sometimes multiple iterations are needed to find the correct balance. Moreover, start by balancing elements that appear in only one reactant and one product, and leave hydrogen and oxygen for last as they often appear in multiple compounds.

Reactants and Products Identification

Understanding the reactants and products in a chemical reaction is an essential step in solving chemistry problems. In an acid-base neutralization reaction, as seen in the provided exercise, the reactants usually consist of an acid and a base.

For instance, in part (a) of the exercise, \(H_2S (aq)\) is the acid, and \(Cu(OH)_2 (s)\) is the base. Recognizing the states of matter, which are aqueous (aq) and solid (s) in this case, is also crucial as they provide clues about how the substances will interact. The typical products of an acid-base reaction are water and a salt. After the reactants are clearly identified, we can deduce the likely products—water (\(H_2O\)) and a salt formed from the remaining ions (in our case, \(CuS\)).

In summary, effective identification of reactants and products is a skill that involves recognizing the characteristics of acids and bases, paying attention to their states, and predicting the most probable outcomes of their interaction.

Stoichiometry

Stoichiometry is akin to the recipe for a chemical reaction. It involves calculations based on the balanced chemical equation to understand the quantitative relationships between the amount of reactants used and the amount of products formed.

Through stoichiometry, we determine how much of a reactant is needed to react completely with another, as seen in our exercise with \(H_2S\) and \(Cu(OH)_2\). The balanced equation allows us to see that one mole of hydrogen sulfide reacts with one mole of copper(II) hydroxide to produce one mole of copper(II) sulfide and two moles of water. The coefficients in the balanced equation provide the mole ratio, which is crucial for converting between masses of substances and determining yields. In practical applications, stoichiometry can be utilized to calculate the amount of reactants required for a desired product amount, or to find out how much product can be formed from given reactants.

Mastery of stoichiometry is vital for anyone engaging in chemical experiments and can be useful in real-life scenarios, such as cooking, where ingredient proportions are crucial for the final outcome.