Problem 22 - Chemistry: Atoms First

Question

Complete and balance the following acid-base equations: (a) A solution of \(\mathrm{HClO}_{4}\) is added to a solution of LiOH. (b) Aqueous \(\mathrm{H}_{2} \mathrm{SO}_{4}\) reacts with \(\mathrm{NaOH}\) (c) \(\mathrm{Ba}(\mathrm{OH})_{2}\) reacts with HF gas.

Step-by-Step Solution

Answer

\(\mathrm{HClO}_4 + \mathrm{LiOH} \rightarrow \mathrm{LiClO}_4 + H_2O\), \(\mathrm{H}_2\mathrm{SO}_4 + 2\mathrm{NaOH} \rightarrow \mathrm{Na}_2\mathrm{SO}_4 + 2H_2O\), \(\mathrm{Ba}(\text{OH})_2 + 2\mathrm{HF} \rightarrow \mathrm{BaF}_2 + 2H_2O\)

Step 1: Identifying the Reaction Type

All the given reactions are acid-base neutralization reactions where an acid reacts with a base to produce a salt and water.

Step 2: Balancing Equation (a)

First, write the formula for the reaction: \(\mathrm{HClO}_4(aq) + \mathrm{LiOH}(aq) \rightarrow \mathrm{LiClO}_4(aq) + H_2O(l)\). There is one chlorine atom on both sides, one lithium atom on both sides, and four oxygen atoms on both sides. The hydrogens balance with one hydrogen from the perchloric acid and one hydrogen from the lithium hydroxide forming one water molecule. Thus, the reaction is already balanced as written.

Step 3: Balancing Equation (b)

Write the formula for the reaction: \(\mathrm{H}_2\mathrm{SO}_4(aq) + \mathrm{NaOH}(aq) \rightarrow \mathrm{Na}_2\mathrm{SO}_4(aq) + H_2O(l)\). Since there are two sodium atoms in the sodium sulfate product, you'll need two moles of NaOH to balance the equation: \(\mathrm{H}_2\mathrm{SO}_4(aq) + 2\mathrm{NaOH}(aq) \rightarrow \mathrm{Na}_2\mathrm{SO}_4(aq) + 2H_2O(l)\). Now each element is balanced with 2 sodiums, 1 sulfur, 4 oxygens from the sulfate, and an additional 2 oxygens and 2 hydrogens from the two water molecules.

Step 4: Balancing Equation (c)

Write the formula for the reaction: \(\mathrm{Ba}(\text{OH})_2(s) + \mathrm{HF}(g) \rightarrow \mathrm{BaF}_2(s) + H_2O(l)\). Barium hydroxide has two hydroxides, so it will react with two moles of HF to neutralize: \(\mathrm{Ba}(\text{OH})_2(s) + 2\mathrm{HF}(g) \rightarrow \mathrm{BaF}_2(s) + 2H_2O(l)\). This balances the barium, fluorine, and the water molecules.

Key Concepts

Chemical Equation Balancing

Understanding how to balance chemical equations is a foundational skill in chemistry. Balancing chemical equations ensures that the same number of atoms for each element is present on both the reactant and product sides of the equation, aligning with the Law of Conservation of Matter. This means that matter is neither created nor destroyed during a chemical reaction.

Let's look at a concrete example from the exercise where hydrochloric acid (\tHClO_4) reacts with lithium hydroxide (LiOH) to form lithium perchlorate (LiClO_4) and water (H2O). The balanced chemical equation is already provided in the solution:\[\tHClO_4(aq) + \tLiOH(aq) \rightarrow \tLiClO_4(aq) + H_2O(l)\].In this case, the reaction involves a one-to-one ratio of acid to base, which simplifies balancing. If you're new to chemical equation balancing, try a systematic approach:

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• Write down the number of atoms of each element in the reactants and products.
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• Adjust coefficients (the numbers in front of compounds) to get the same number of each atom on both sides.
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• Double-check to make sure the charge is balanced, important for ionic substances.
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• Ensure that any states of matter (solid, liquid, gas, aqueous) are correctly denoted.

It's important to practice with a variety of equations, as the difficulty can range from simple to complex, like the reaction between sulfuric acid and sodium hydroxide where coefficients play a crucial role for balance.

Stoichiometry

Stoichiometry is the section of chemistry that deals with the quantities of substances that react and are produced in chemical reactions. It's a quantitative study relying heavily on mole ratios derived from a balanced chemical equation. To comprehend stoichiometry, one must understand the concept of the 'mole', which is a unit of measure in chemistry representing Avogadro's number (6.022 x 10^23) of particles, atoms, ions, or molecules.

In one of the problems, \[\tH_2\tSO_4(aq) + 2\tNaOH(aq) \rightarrow \tNa_2\tSO_4(aq) + 2H_2O(l)\],stoichiometry tells us that one mole of sulfuric acid reacts with two moles of sodium hydroxide to produce one mole of sodium sulfate and two moles of water. Recognizing these relationships is crucial for solving problems involving reaction yields, reactant amounts, and to also determine if you have a limiting reactant in a reaction. A balanced equation provides the molar ratios needed to perform these calculations. Hence, the stoichiometry bridges the gap between micro-level particles and real-world, measurable quantities in the lab.

Acid-Base Reaction

Acid-base reactions, often referred to as neutralization reactions, are essential concepts within chemistry, where an acid and a base react to form water and a salt. Acids typically have a pH less than 7 and contain a higher concentration of hydrogen ions (H+), while bases, with a pH greater than 7, contain a higher concentration of hydroxide ions (OH-).

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• Acid: Proton donor capable of releasing hydrogen ions (H+).
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• Base: Proton acceptor that can release hydroxide ions (OH-) in solution.

For instance, the reaction between barium hydroxide and hydrofluoric acid:\[\tBa(OH)_2(s) + 2\tHF(g) \rightarrow \tBaF_2(s) + 2H_2O(l)\],illustrates the neutralization process. Barium hydroxide, a solid base, reacts with gaseous hydrofluoric acid to produce barium fluoride, a solid salt, and liquid water. The 1:2 ratio of Ba(OH)2 to HF calls attention to the necessity of balancing not just the atoms but also the charges. Understanding acid-base reactions is pivotal as they are ubiquitous, ranging from biological systems to industrial processes. Their study resonates with understanding pH, buffer solutions, and more in-depth chemical principles.