Problem 76 - Chemistry Matter and Change

Question

When mercury oxide is heated, it decomposes into mercury and oxygen. If 28.4 g of mercury oxide decomposes, producing 2.0 g of oxygen, what is the percent by mass of mercury in mercury oxide?

Step-by-Step Solution

Answer

The percent by mass of mercury in the given 28.4 g of mercury oxide sample is 92.96%.

Step 1: Understand the Given Information and Variables

In this problem, we have a sample of mercury oxide that decomposes into mercury and oxygen with a total mass of 28.4g. We are given the mass of oxygen produced, which is 2g.

Step 2: Calculate the Mass of Mercury Produced

To find the mass of mercury in the given mercury oxide sample, we need to subtract the mass of oxygen from the total mass of mercury oxide sample. Let's denote the mass of mercury as 'm_Hg': m_Hg = mass of mercury oxide - mass of oxygen m_Hg = 28.4g - 2g = 26.4g

Step 3: Calculate the Mass Percentage of Mercury

Now that we have the mass of mercury (26.4g), we can calculate the mass percentage of mercury in the mercury oxide sample. We'll use the following formula for mass percentage: mass percentage = (mass of element / total mass) * 100 mass percentage of mercury = (m_Hg / mass of mercury oxide) * 100 mass percentage of mercury = (26.4 g / 28.4 g) * 100 mass percentage of mercury = 0.9296 * 100 = 92.96%

Step 4: Provide the Final Answer

The percent by mass of mercury in the given mercury oxide sample is 92.96%.

Key Concepts

Mercury Oxide

Mercury oxide is a compound consisting of mercury and oxygen, represented by the chemical formula HgO. In its natural state, mercury oxide appears as a bright red or orange solid, though it can also appear yellow in a powdery form. This compound is significant because it readily decomposes into its elemental components upon heating.

• Chemical Formula: HgO
• Appearance: Red/orange solid or yellow powder
• Key Property: Decomposes into mercury (Hg) and oxygen (O₂) when heated

Understanding mercury oxide is crucial for studying chemical decomposition reactions. This specific decomposition unlocks fundamental concepts in chemistry, such as stoichiometry and gas evolution.

Mass Percentage Calculation

Mass percentage is a way of expressing a concentration by describing how much of a specific substance is present in a mixture relative to the total volume or mass. In terms of the decomposition of mercury oxide, calculating mass percentage helps in determining how much of the original compound contributed to the formation of mercury.

• Formula: \( \text{Mass percentage} = \left( \frac{\text{mass of the component}}{\text{total mass}} \right) \times 100 \)
• Purpose: Allows for the understanding of composition and concentration of elements in a compound

For instance, in the problem, we determine the percent by mass of mercury in mercury oxide. This involves finding the mass of mercury produced versus the total mass of the original mercury oxide sample. Such calculations are fundamental in analytical chemistry, helping quantify the composition of compounds efficiently.

Chemical Decomposition

Chemical decomposition is a type of chemical reaction where one compound breaks down into two or more simpler substances. In the case of mercury oxide, heating triggers the decomposition process, resulting in the production of mercury and oxygen gas.

• Type of Reaction: Decomposition reaction
• Example: \( 2 \text{HgO} \rightarrow 2 \text{Hg} + \text{O}_2 \)
• Characteristic: Often requires energy input, such as heat

Understanding chemical decomposition reactions is essential as it helps in learning how larger compounds are broken down under various conditions. It also plays a critical role in numerous industrial processes and in the study of chemical kinetics.

Oxygen Production

Oxygen production during the decomposition of mercury oxide not only aids in understanding the chemical process but also highlights the practical implications. When mercury oxide decomposes, it releases oxygen gas, which can be observed as a by-product.

• Output: Oxygen gas (O₂)
• Significance: Demonstrates a common method of oxygen generation in laboratory settings
• Challenges: Controlled conditions required to prevent contamination

Producing oxygen from mercury oxide demonstrates how essential reactions can be harnessed in controlled environments to produce gases needed for various scientific and medical applications. It underscores the practical relevance of mastering chemical reactions and decomposition in real-world settings.