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Chapter 1: Problem 29

Which compound, \(\mathrm{CaCl}_{2}\) or \(\mathrm{CaO}\) , would you expect to have a high melting point? Why? (A) \(\mathrm{CaCl}_{2}\) because there are more ions per lattice unit (B) \(\mathrm{CaCl}_{2}\) because a chlorine ion is smaller than an oxygen ion (C) Cao, because the charge of oxygen ion exceeds that of chlorine ion (D) CaO, because the common charges of calcium and oxygen ions are identical in magnitude

Short Answer

Expert verified
The compound with a higher melting point is CaO, because the charge of oxygen ion exceeds that of chlorine ion.

Step by step solution

01

List the properties of the ionic compounds

The calcium chloride (\(\mathrm{CaCl}_{2}\)) is formed by calcium (Ca) and chlorine (Cl), whereby each calcium ion is surrounded by two chloride ions. The calcium oxide (\(\mathrm{CaO}\)) is formed by calcium (Ca) and oxygen (O), each calcium ion is surrounded by one oxide ion.
02

Recap the relation of lattice energy and melting point

The lattice energy of an ionic compound is the energy required to separate one mole of a compound into its gaseous ions. Higher lattice energy suggests higher melting points because it takes more energy to break the bonds between the ions.
03

Compare the charge on ions

From the compounds, Calcium in both has a charge of +2. Chlorine ion in \(\mathrm{CaCl}_{2}\) has a charge of -1 and Oxygen ion in \(\mathrm{CaO}\) has a charge of -2. Lattice energy increases with the increase in charge of the ions. So, the compound with Oxygen ion, \(\mathrm{CaO}\), will have higher lattice energy.
04

Compare the size of ions

Even though Chloride ion is larger than the Oxygen ion and larger ions typically have lower lattice energies because the ions aren't as closely packed. Despite this, the combined effect of charge and size of the ion make \(\mathrm{CaO}\) have higher lattice energy.
05

Select the correct option

Considering the above facts, the correct answer is (C) \(\mathrm{CaO}\), because the charge of oxygen ion exceeds that of chlorine ion.

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Most popular questions from this chapter

The following reaction is found to be at equilibrium at 25°C: \(2 \mathrm{SO}_{3}(g) \leftrightarrow \mathrm{O}_{2}(g)+2 \mathrm{SO}_{2}(g) \quad \Delta H=-198 \mathrm{kJ} / \mathrm{mol}\) Which of the following would cause a reduction in the value for the equilibrium constant? (A) Increasing the amount of \(\mathrm{SO}_{3}\) (B) Reducing the amount of \(\mathrm{O}_{2}\) (C) Raising the temperature (D) Lowering the temperature

\(\mathrm{PCl}_{3}(g)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{PCl}_{5}(g) \Delta H=-92.5 \mathrm{kJ} / \mathrm{mol}\) In which of the following ways could the reaction above be manipulated to create more product? (A) Decreasing the concentration of \(\mathrm{PCl}_{3}\) (B) Increasing the pressure (C) Increasing the temperature (D) None of the above

Use the following information to answer questions 29-31. Pennies are made primarily of zinc, which is coated with a thin layer of copper through electroplating, using a setup like the one above. The solution in the beaker is a strong acid (which produces H' ions), and the cell is wired so that the copper electrode is the anode and zinc penny is the cathode. Use the following reduction potentials to answer questions \(29-31 .\) $$\begin{array}{|l|l|}\hline \text { Half-Reaction } & {\text { Standard Reduction Potential }} \\ \hline \mathrm{Cu}^{2++2 e^{-} \rightarrow \mathrm{Cu}(s)} & {+0.34 \mathrm{V}} \\ \hline 2 \mathrm{H}^{++2 e^{-} \rightarrow \mathrm{H}_{2}(g)} & {0.00 \mathrm{V}} \\ \hline \mathrm{Ni}^{2++2 e^{-} \rightarrow \mathrm{Ni}(s)} & {-0.25 \mathrm{V}} \\\ \hline \mathrm{Zn}^{2++2 e^{-} \rightarrow \mathrm{Zn}(s)} & {-0.76 \mathrm{V}} \\ \hline\end{array}$$ What is the required voltage to make this cell function? (A) 0.34 V (B) 0.42 V (C) 0.76 V (D) 1.10 V

\(\mathrm{Cu}^{2+}+2 e^{-} \rightarrow \mathrm{Cu} \quad E^{\circ}=+0.3 \mathrm{V}\) \(\mathrm{Fe}^{2+}+2 e^{-} \rightarrow \mathrm{Fe} \quad E^{\circ}=-0.4 \mathrm{V}\) Based on the reduction potentials given above, what is the reaction potential for the following reaction? \(\mathrm{Fe}^{2+}+\mathrm{Cu} \rightarrow \mathrm{Fe}+\mathrm{Cu}^{2+}\) (A) \(-0.7 \mathrm{V}\) (B) \(-0.1 \mathrm{V}\) (C) \(+0.1 \mathrm{V}\) (D) \(+0.7 \mathrm{V}\)

Which gas exerts the greatest pressure? (A) He (B) Ne (C) NO (D) All gases exert the same amount of pressure.
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