Video: Selecting the Classification for the Production of Silver Chloride from Solution

Which classification best describes the reaction represented by the equation below? Ag⁺(aq) + Cl⁻(aq) ⟶ AgCl(s) [A] Oxidation [B] Decomposition [C] Precipitation [D] Acid-base [E] Reduction

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Video Transcript

Which classification best describes the reaction represented by the equation below? Ag⁺ aqueous plus Cl⁻ aqueous react to form AgCl solid. A) Oxidation, B) decomposition, C) precipitation, D) acid-base, or E) reduction.

Ag⁺ is the symbol for the silver(I) ion. Cl⁻ is the symbol for the chloride ion. These react together to form silver chloride. In this ionic equation, both ions are given the aqueous state symbol, indicating they’re in solution. AgCl, silver chloride, has the S state symbol, indicating that it’s solid. Now that we’ve looked at the reaction equation and worked out what it’s describing, let’s have a look at the five classifications to see which one best applies.

In an oxidation reaction, an agent will lose electrons or increase its oxidation number. The oxidation state of Ag⁺ is plus one. And the oxidation state of Cl⁻ is minus one. When these ions combine, they form the ionic solid, silver chloride, where they preserve their charges. So their oxidation numbers remain the same. None of the oxidation states change because of the reaction. So the reaction cannot be classified as an oxidation. We can jump directly to looking at reduction, which is the opposite of oxidation. Reduction is the gaining of electrons or the decrease in an oxidation number. We can dismiss this possible answer because there’s no change in the oxidation state, neither positive nor negative. So the reaction is neither an oxidation or a reduction.

A decomposition reaction usually involves a single component breaking down into multiple components. For example, calcium carbonate, under exposure to heat, can decay into calcium oxide and carbon dioxide. Instead, in this reaction, we’re seeing two separate dissolved species coming together to form a single solid. So this reaction is not a decomposition reaction.

Next, a precipitation reaction involves the formation of a solid from solution. In our reaction, we can see two ions coming together, both dissolved in solution, forming a solid. This reaction produces a white precipitate of silver chloride. This reaction is a vital part of the tests performed on solutions that might contain halides, where silver nitrate is introduced. So our reaction is definitely a precipitation. Let’s see whether it’s the best description by looking at acid-base. While there are many types of acid-base reaction, the most common involves H⁺ ions reacting with something else. For example, hydrochloric acid, HCL, will react with sodium hydroxide to produce sodium chloride and water. There is no H⁺ present in our reaction. There is water present. But it’s not participating in the reaction.

So the reaction is definitely not acid-base, meaning that the best classification for this reaction is precipitation.

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