Problem 2 - Chemistry in 30 days

Question

The species that does not contain peroxide ions is (b) \(\mathrm{H}_{2} \mathrm{O}_{2}\) (c) \(\mathrm{SrO}_{2}\) (d) \(\mathrm{BaO}_{2}\) (a) \(\mathrm{PbO}_{2}\)

Step-by-Step Solution

Answer

(a) \(\mathrm{PbO}_2\) does not contain peroxide ions.

Step 1: Understanding Peroxides

Peroxides are compounds that contain the peroxide ion, which is \( ext{O}_2^{2-}\). It is important to identify which compounds contain this ion.

Step 2: Analyze Each Option

We need to check each chemical formula to see if it contains the \( ext{O}_2^{2-}\) ion. Check each option one by one: (a) \( ext{PbO}_2\) (b) \( ext{H}_2 ext{O}_2\) (c) \( ext{SrO}_2\) (d) \( ext{BaO}_2\).

Step 3: Identify Peroxide Ions

- \( ext{H}_2 ext{O}_2\) is hydrogen peroxide, and it contains the \( ext{O}_2^{2-}\) ion. - \( ext{SrO}_2\) contains \( ext{O}_2^{2-}\) because it is a metal oxide known to form peroxides. - \( ext{BaO}_2\) also contains \( ext{O}_2^{2-}\) because it forms a peroxide with barium.

Step 4: Identify the Non-Peroxide Compound

From the analysis, \( ext{PbO}_2\) does not contain the \( ext{O}_2^{2-}\) ion. It is lead dioxide and does not typically form peroxides. Therefore, \( ext{PbO}_2\) is not a peroxide.

Key Concepts

Chemical Formulas

Chemical formulas are essential to understanding how elements combine to form compounds. They provide information about the types and numbers of atoms in a molecule, represented by their chemical symbols and subscripts. For example, in the compound \( \mathrm{H}_{2}\mathrm{O}_{2} \), the formula shows that there are two hydrogen atoms (\( H \)) and two oxygen atoms (\( O \)) in each molecule.

• Subscripts indicate the number of each type of atom present.
• A subscript of 1 is typically implied and not written.

For instance, in \( \mathrm{PbO}_2 \), the formula tells us there is one lead (\( \text{Pb} \)) atom and two oxygen atoms. Thus, chemical formulas are like the language researchers use to describe the composition of substances in a precise way.

Oxygen Ions

Oxygen ions are crucial when discussing peroxides and other related compounds. An oxygen ion can exist in various forms based on its number of electrons compared to protons. The most common oxygen ion is the oxide ion \( \text{O}^{2-} \), which occurs when an oxygen atom gains two electrons, giving it a negative charge.
In peroxides, such as hydrogen peroxide \( \mathrm{H}_{2}\mathrm{O}_{2} \), the peroxide ion \( \text{O}_2^{2-} \) plays a central role. Unlike the simple oxide ion, the peroxide ion consists of two oxygen atoms bonded together with a total charge of \( 2- \).

• The \( \text{O}_2^{2-} \) ion indicates two oxygen atoms sharing this charge.
• Peroxide ions are less stable than individual oxide ions due to their unique oxygen-oxygen bond.

Understanding these ions helps distinguish between substances like metal oxides and peroxides based on their oxygen content.

Metal Oxides Peroxides

Metal oxides and peroxides are both compounds involving metals and oxygen but differ in their structure and properties. Metal oxides, such as lead dioxide \( \mathrm{PbO}_2 \), contain oxygen ions bonded with a metal. In contrast, peroxides contain the peroxide ion \( \text{O}_2^{2-} \), which pairs with metals to form compounds like \( \mathrm{SrO}_2 \) and \( \mathrm{BaO}_2 \).
Peroxides are distinct because they feature a pair of oxygen atoms with a shared charge, making them unique in composition and reactivity.

• Metal oxides typically include simple \( \text{O}^{2-} \) ions.
• Metal peroxides have \( \text{O}_2^{2-} \) ions.

Identifying these differences is crucial for understanding chemical behaviors, predicting reactivity, and identifying materials in various applications.