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Chapter 8: Problem 140

Simple soaps, like sodium laurate, \(\mathrm{NaC}_{12} \mathrm{H}_{22} \mathrm{O}_{2}\) are ionic compounds with small cations and large covalent anions. These soaps are somewhat soluble in water but form a soap scum if the water is "hard," which means it contains calcium ions \(\mathrm{Ca}^{2+}\) or magnesium ions, \(\mathrm{Mg}^{2+}\). Write a net ionic equation for the formation of soap scum. Also classify the reaction type or types.

Short Answer

Expert verified
The net ionic equations for the formation of soap scum are: Calcium ions reaction: \(\mathrm{Ca}^{2+}\) + 2 \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{2}^{-}\) \(->\) \(\mathrm{Ca(C}_{12} \mathrm{H}_{22} \mathrm{O}_{2})_2\) Magnesium ions reaction: \(\mathrm{Mg}^{2+}\) + 2 \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{2}^{-}\) \(->\) \(\mathrm{Mg(C}_{12} \mathrm{H}_{22} \mathrm{O}_{2})_2\) These reactions are classified as precipitation reactions.

Step by step solution

01

Write down the given formulae and ions

Sodium laurate: \(\mathrm{NaC}_{12} \mathrm{H}_{22} \mathrm{O}_{2}\) Calcium ions: \(\mathrm{Ca}^{2+}\) Magnesium ions: \(\mathrm{Mg}^{2+}\)
02

Predict the products

When sodium laurate reacts with calcium or magnesium ions, the sodium ions will be replaced by calcium or magnesium ions, forming calcium or magnesium laurate, which is the soap scum. Calcium laurate: \(\mathrm{Ca(C}_{12} \mathrm{H}_{22} \mathrm{O}_{2})_2\) Magnesium laurate: \(\mathrm{Mg(C}_{12} \mathrm{H}_{22} \mathrm{O}_{2})_2\)
03

Write the balanced chemical equation

Let's consider the reaction between sodium laurate and calcium ions: 2 \(\mathrm{NaC}_{12} \mathrm{H}_{22} \mathrm{O}_{2}\) \(+\) \(\mathrm{Ca}^{2+}\) \(->\) \(\mathrm{Ca(C}_{12} \mathrm{H}_{22}\mathrm{O}_{2})_2\) \(+\) 2 \(\mathrm{Na}^+\) And the reaction between sodium laurate and magnesium ions: 2 \(\mathrm{NaC}_{12} \mathrm{H}_{22} \mathrm{O}_{2}\) \(+\) \(\mathrm{Mg}^{2+}\) \(->\) \(\mathrm{Mg(C}_{12} \mathrm{H}_{22} \mathrm{O}_{2})_2\) \(+\) 2 \(\mathrm{Na}^+\)
04

Determine the net ionic equation

Removing the spectator ions (sodium ions) from each reaction, we obtain the following net ionic equations: Calcium ions reaction: \(\mathrm{Ca}^{2+}\) + 2 \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{2}^{-}\) \(->\) \(\mathrm{Ca(C}_{12} \mathrm{H}_{22} \mathrm{O}_{2})_2\) Magnesium ions reaction: \(\mathrm{Mg}^{2+}\) + 2 \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{2}^{-}\) \(->\) \(\mathrm{Mg(C}_{12} \mathrm{H}_{22} \mathrm{O}_{2})_2\)
05

Classify the reaction type

These reactions are examples of precipitation reactions, where an insoluble solid (the soap scum) is formed from the reaction between soluble reactants (the soap and the ions in hard water).

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Most popular questions from this chapter

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