Problem 100 - Chemistry The Science in Context

Question

What overall reaction consists of the following elementary steps? (1) \(\quad \mathrm{ClO}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{HClO}(a q)+\mathrm{OH}^{-}(a q)\) (2) \(\quad \mathrm{I}^{-}(a q)+\mathrm{HClO}(a q) \rightarrow \mathrm{HIO}(a q)+\mathrm{Cl}^{-}(a q)\) (3) \(\quad \mathrm{OH}^{-}(a q)+\mathrm{HIO}(a q) \rightarrow \mathrm{H}_{2} \mathrm{O}(\ell)+1 \mathrm{O}^{-}(a q)^{-}\)

Step-by-Step Solution

Answer

Answer: The overall reaction is $\mathrm{ClO}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(\ell) + \mathrm{I}^{-}(a q) \rightarrow \mathrm{Cl}^{-}(a q) + \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{IO}^{-}(a q)$.

Step 1: Write down the given elementary steps

First, let's write down all the elementary steps given. (1) $\quad \mathrm{ClO}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{HClO}(a q)+\mathrm{OH}^{-}(a q)$ (2) $\quad \mathrm{I}^{-}(a q)+\mathrm{HClO}(a q) \rightarrow \mathrm{HIO}(a q)+\mathrm{Cl}^{-}(a q)$ (3) $\quad \mathrm{OH}^{-}(a q)+\mathrm{HIO}(a q) \rightarrow \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{IO}^{-}(a q)$

Step 2: Add all elementary steps together

Now let's add all the equations together in order to get the overall equation: \(\quad \mathrm{ClO}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(\ell) + \mathrm{I}^{-}(a q)+\mathrm{HClO}(a q) + \mathrm{OH}^{-}(a q)+\mathrm{HIO}(a q) \rightarrow \mathrm{HClO}(a q)+\mathrm{OH}^{-}(a q) + \mathrm{HIO}(a q)+\mathrm{Cl}^{-}(a q) + \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{IO}^{-}(a q)\)

Step 3: Cancel out species on both sides of the equation

Now we can cancel out any species that appear on both sides of the equation: - \(\mathrm{HClO}(a q)\) appears on both sides, so we can cancel it out - \(\mathrm{OH}^{-}(a q)\) appears on both sides, so we can cancel it out - \(\mathrm{HIO}(a q)\) appears on both sides, so we can cancel it out After cancelling, we get: \(\quad \mathrm{ClO}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(\ell) + \mathrm{I}^{-}(a q) \rightarrow \mathrm{Cl}^{-}(a q) + \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{IO}^{-}(a q)\)

Step 4: Write the final overall reaction

Now we have our overall balanced reaction: \(\quad \mathrm{ClO}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(\ell) + \mathrm{I}^{-}(a q) \rightarrow \mathrm{Cl}^{-}(a q) + \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{IO}^{-}(a q)\)

Key Concepts

Chemical Reaction Steps

Understanding the steps of a chemical reaction is fundamental in the study of chemistry. An elementary reaction is a single, indivisible process that represents one step in a series of reactions leading to the overall chemical change. A good analogy for an elementary step is a single move in a dance routine. Each step must be performed correctly to achieve the desired overall performance. Similarly, to understand the full chemical equation, one must account for all the elementary steps involved.

For example, in the provided exercise, you can see three elementary steps that are part of a larger reaction. We start by writing out each step, observing the reactants and the products. As students practice, they develop an eye for details, such as the physical states of the reactants and products, denoted by symbols like (aq) for aqueous solutions and (l) for liquids. This is critical, as the physical state can affect how different species will interact.

Recognizing Intermediates and Catalysts

Intermediate species can appear in an overall reaction but not in the net equation, as they are formed and then used up during the process. Catalysts, on the other hand, may appear initially but are regenerated by the end of the reaction sequence. The ability to identify these helps in deciphering the complete mechanism of the reaction.

Balancing Chemical Equations

The art of balancing chemical equations is just like solving a puzzle; each side of the equation must tally to respect the law of conservation of mass. Students often find this part challenging, but it is crucial for understanding chemical reactions. When balancing equations, one matches the number of atoms of each element on the reactant side with the product side.

In the exercise, once the elementary steps are laid out, the next step is to combine them to form a tentative overall equation. Students should then scrutinize every atom on each side. It’s important to remember that the coefficients of compounds or elements must be whole numbers, and proper technique involves starting with elements that appear only in one reactant and one product and moving towards those in multiple substances.

Working with Complex Reactions

Complex reactions that proceed in steps, like the one in our exercise, require particular attention since one must both combine steps and ensure that intermediates do not appear in the final balanced equation. This hones the pinpoint accuracy and systematic approach necessary for solving any chemical balancing puzzle.

Aqueous Reactions

Aqueous reactions are the playground where soluble substances interact in water. Understanding these reactions is essential as they are omnipresent in both laboratory settings and our daily life. They involve ions and molecules in a water solution, indicated by the (aq) symbol. The behavior of substances in an aqueous solution depends on their solubility and the possibility of ion interaction.

When we look at the equations in our exercise, we notice reactants such as \(\mathrm{ClO}^{-}(aq)\) and products like \(\mathrm{OH}^{-}(aq)\), indicating that the reaction takes place in an aqueous environment. The solubility rules help predict what species will remain dissolved in water and which ones will precipitate or react further. This knowledge is vitally important when predicting the products of a reaction.

Identifying Spectator Ions

Moreover, during such reactions, some ions do not participate and are called spectator ions. They remain in the solution unchanged. Spotting them is key as they are not included in the net ionic equation. Mastering aqueous reactions means understanding solubility, recognizing spectator ions, and being able to predict the outcome when substances are mixed in water, which is a skill essential for practical applications in chemistry.