Problem 43 - Chemistry The Molecular Science

Question

A black powder is placed in a long glass tube. Hydrogen gas is passed into the tube so that the hydrogen sweeps out all other gases. The powder is then heated with a Bunsen burner. The powder turns red-orange, and water vapor can be seen condensing at the unheated far end of the tube. The red-orange color remains after the tube cools. (a) Was the original black substance an element? Explain briefly. (b) Is the new red-orange substance an element? Explain briefly.

Step-by-Step Solution

Answer

(a) No, it's not an element; it reacts with hydrogen. (b) Uncertain; could be an element or stable compound.

Step 1: Identify Evidence

Examine the evidence provided in the experiment: The black powder changes color, and water vapor condenses at the end of the tube after the hydrogen gas has been passed through and the powder is heated.

Step 2: Analyze Reaction Outcomes for Part (a)

The black powder, upon heating in the presence of hydrogen, changes its color and produces water vapor. This suggests a reaction has occurred. Since elements do not change their basic identity under conditions such as heating, the black substance must not be an element, as it reacts and forms new compounds.

Step 3: Drawing Conclusion for Part (a)

Based on the reaction evidence, the black powder cannot be considered an element because it reacts with hydrogen, indicating it was a compound comprising at least two elements.

Step 4: Assessing the New Substance for Part (b)

The resulting substance is red-orange and remains unchanged after cooling. The absence of further reaction when cooled suggests stability akin to elements, but one piece of evidence you have is insufficient alone to conclude its elemental nature without additional testing.

Step 5: Drawing Conclusion for Part (b)

The new red-orange substance could be either an element or a stable compound. More information would be needed to definitively categorically label it as an element because its stability alone doesn't prove its elemental nature.

Key Concepts

Element Identification

In the world of chemistry, identifying whether a substance is a simple element or a more complex compound is crucial. Elements are substances that consist of only one type of atom. They are the building blocks of all matter and cannot be broken down into simpler substances by ordinary chemical reactions.
Contrastively, when a substance undergoes a change, like a color change or the production of new substances (like water vapor), it suggests that it may not be a simple element, as elements do not transform into other substances under normal conditions. Instead, these changes may indicate the formation or breaking apart of compounds. Whenever you encounter a chemical change during an experiment, ask the following questions:

• Did the substance change appearance or state?
• Did it produce a gas, liquid, or any other new substance?

Answering yes to these may indicate you are dealing with a compound rather than a pure element.

Compound Formation

Compounds result from the chemical combination of two or more elements. They have unique properties that are different from the individual elements that constitute them. In our experiment, the black powder changed upon heating, suggesting it interacted with hydrogen to form a different substance.
When compounds form, the atoms of the different elements rearrange to create a new substance with new properties. This process often results in visible changes, such as a shift in color or the formation of new materials like gases or solids. For example, when the black powder was heated, it reacted with hydrogen and formed water vapor, signifying that new, stable compounds were formed.
Recognizing a compound involves observing these changes and understanding that the original substances have undergone a transformation at the molecular level - a departure from their original elemental form.

Experimental Procedure

In chemical experimentation, following a precise procedure is vital to obtaining accurate results. The described experiment involves placing a black powder in a glass tube, displacing other gases with hydrogen, and heating the powder with a Bunsen burner.
Each step is crucial for a controlled reaction:

• Displacing air with hydrogen ensures the black powder reacts with hydrogen, not oxygen or other gases.
• Heating induces a reaction, providing the necessary energy to break bonds in the initial compound and allow new products to form.
• Observing changes, such as the powder turning red-orange and water vapor forming, are signs of successful interaction.

Following these steps ensures that the changes observed are due to the intended chemical reaction without interference from outside variables.

Chemical Change

Chemical change is a process where substances are transformed into new substances with different properties. This change is often irreversible under the conditions of the reaction.
In the context of the experiment, heating the black powder in the presence of hydrogen causes such a chemical change. The original black powder reacts, resulting in a color change to red-orange and the production of water vapor. These transformations illustrate that a chemical reaction has taken place, not merely a physical change.
Chemical changes can be identified by:

• Color change
• Gas production
• Formation of a precipitate
• Change in temperature

These indicators help determine whether a new compound has been formed from the original substances.