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Chapter 8: Problem 104

Potassium peroxide is composed of \(70.96 \% \mathrm{~K}\) and $29.04 \% \mathrm{O}\(. Each peroxide ion has a net charge of \)2^{-}$. (a) Given the molecular weight of the compound is 110.19 , determine the chemical formula of potassium peroxide. \((\mathbf{b})\) What is the number of valance electron pairs in the peroxide ion? (c) Draw the Lewis structure of the peroxide ion. (d) Compare the \(\mathrm{O}-\mathrm{O}\) bond distance in oxygen molecule and potassium peroxide.

Short Answer

Expert verified
The chemical formula of potassium peroxide is \(K_2O_2\). The peroxide ion has 6 valence electron pairs. The Lewis structure of the peroxide ion is O-O with a '-' sign on both O. The O=O bond in an oxygen molecule is shorter and stronger than the O-O bond in potassium peroxide due to the double bond in the oxygen molecule.

Step by step solution

01

1. Calculate the moles of K and O in the compound

Since we know the percentage composition of potassium (K) and oxygen (O) in potassium peroxide, we can assume we have 100 grams of the compound. With this assumption, we can calculate the moles of K and O present in 100 grams of potassium peroxide: Moles of \(K = \dfrac{70.96 g}{39.1 g/mol} = 1.815\text{ moles}\) (using the molar mass of K = 39.1 g/mol) Moles of \(O = \dfrac{29.04 g}{16.0 g/mol} = 1.815\text{ moles}\) (using the molar mass of O = 16.0 g/mol)
02

2. Determine the chemical formula

Using the moles of K and O calculated in step 1, the chemical formula of the compound can be determined by dividing the moles of each element by the lowest moles value and then multiplying the ratios by the net charge of the peroxide ion (2^-): Moles ratio of K : O = 1.815 moles : 1.815 moles = 1 : 1 Thus, the chemical formula of potassium peroxide is \(K_2O_2\).
03

3. Count the valance electron pairs in the peroxide ion

In the peroxide ion, the two oxygen atoms are bonded together. Since oxygen has 6 valence electrons, and there are two oxygen atoms, there are a total of 12 valence electrons for the peroxide ion. As each bond requires 2 electrons, there are a total of 6 valence electron pairs in the peroxide ion.
04

4. Draw the Lewis structure of the peroxide ion

To draw the Lewis structure of the peroxide ion (O2^2-), follow these steps: i. Arrange the O atoms to form an O-O bond ii. Allocate the remaining valence electrons to form O=O with 4 valence electrons already used iii. Add the extra 2 electrons to fulfill the octet rule iv. Add the charge specification as 2^- The resulting Lewis structure is shown below: O-O with a '-' sign on both O.
05

5. Compare the O-O bond distance in oxygen molecule and potassium peroxide

The O=O bond in an oxygen molecule is shorter and stronger than the O-O bond in potassium peroxide because the oxygen molecule has a double bond (O=O) while the potassium peroxide has a single bond (O-O). The double bond in the oxygen molecule requires more overlap of atomic orbitals, which brings the O atoms closer together and results in a shorter bond distance.

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Most popular questions from this chapter

In the following pairs of binary compounds, determine which one is a molecular substance and which one is an ionic substance. Use the appropriate naming convention (for ionic or molecular substances) to assign a name to each compound: (a) \(\mathrm{SiF}_{4}\) and \(\mathrm{LaF}_{3}\), (b) \(\mathrm{FeCl}_{2}\) and \(\mathrm{ReCl}_{6}\), (c) \(\mathrm{PbCl}_{4}\) and RbCl.

Draw the Lewis structure for \(\mathrm{NO}^{+}\). Is the nitrogen-oxygen bond in \(\mathrm{NO}^{+}\) longer, shorter, or the same length as the nitrogen-oxygen bond in NO? Explain.

Using Lewis symbols and Lewis structures, make a sketch of the formation of \(\mathrm{NCl}_{3}\) from \(\mathrm{N}\) and \(\mathrm{Cl}\) atoms, showing valence- shell electrons. (a) How many valence electrons does N have initially? (b) How many bonds Cl has to make in order to achieve an octet? (c) How many valence electrons surround the \(\mathrm{N}\) in the \(\mathrm{NCl}_{3}\) molecule? (d) How many valence electrons surround each Cl in the \(\mathrm{NCl}_{3}\) molecule? (e) How many lone pairs of electrons are in the \(\mathrm{NCl}_{3}\) molecule?

Draw the dominant Lewis structures for these chlorineoxygen molecules/ions: $\mathrm{ClO}, \mathrm{ClO}^{-}, \mathrm{ClO}_{2}^{-}, \mathrm{ClO}_{3}^{-}, \mathrm{ClO}_{4}^{-}$. Which of these do not obey the octet rule?

A new compound is made that has a \(\mathrm{C}-\mathrm{N}\) bond length of $118 \mathrm{pm}$. Is this bond likely to be a single, double, or triple C-N bond?
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