Question

Solutions containing copper(II) ions are bright blue in color. When sodium hydroxide is added to such a solution, a solid material forms that is colored a much paler shade of blue than the original solution of copper(II) ions. The fact that a solution containing copper(II) ions is bright blue is a ___ property.

Short answer

The fact that a solution containing copper(II) ions is bright blue is a **physical property**.

Step-by-step solution

Understand the given information

We are given a solution containing copper(II) ions with a bright blue color. When sodium hydroxide is added to the solution, a pale blue solid material forms.

Analyze the property

The property in question is the bright blue color of the solution containing copper(II) ions. We need to determine whether this property is related to a chemical reaction, or can be observed without altering the chemical composition of the substance.

Physical or Chemical property?

In this case, the bright blue color of the solution is something that can be observed without changing the chemical composition of the solution, as no chemical reaction is necessary to observe the color. Therefore, it is a physical property. The fact that a solution containing copper(II) ions is bright blue is a physical property.

Key concepts

Copper(II) Ions

Copper(II) ions, also known as cupric ions, are a common form of copper found in various chemical compounds. They are denoted by the chemical formula \( \text{Cu}^{2+} \). These ions are widely studied for their characteristic properties and their role in various chemical reactions. When dissolved in water, these ions interact with the water molecules around them to produce solutions with notable properties.
One of the most distinctive features of copper(II) ions is their ability to form brightly colored solutions. This is because the cupric ions can absorb certain wavelengths of light due to their electron configurations. The absorbed wavelengths make the ions appear blue to the human eye, which is a unique characteristic among metal ions.
Understanding copper(II) ions is crucial for comprehending the behavior of copper in different environments. It's also important in fields like electrochemistry, where the movement of ions is essential to the functioning of batteries and electroplating.

Chemical vs Physical Properties

Chemical and physical properties define how substances interact in a variety of situations. Physical properties are characteristics that can be observed without changing the substance's identity, such as color, melting point, or density. In contrast, chemical properties describe the potential of a substance to undergo a chemical change, transforming it into one or more different substances.
For example:

• Color: A copper(II) ion solution is blue, a color visible without altering its chemical makeup.
• Reactivity with acids: If copper reacts with an acid to produce a new substance, that behavior is a chemical property.

To determine whether a property is chemical or physical, consider whether observing it changes the substance's composition. If it does not, it's a physical property.
Understanding the distinction between these properties helps in predicting how substances will behave under various conditions, which is especially useful in experimental chemistry.

Color of Solutions

The color of a solution is a noticeable physical property. It depends on the specific ions or molecules dissolved in the liquid. In chemistry, the color can give clues about the identity of the ions or molecules present. For instance, solutions containing copper(II) ions are renowned for their bright blue hue.
Color arises due to the interaction of light with the particles in the solution. The ions absorb certain wavelengths from white light while reflecting others, causing the solution to appear colored. For copper(II) ions, the absorbed wavelengths do not include blue, which is why the solution seems blue to our eyes.
It's also important to note that color can shift when other substances are added. In the case of copper(II) solutions, adding sodium hydroxide results in a pale blue solid because a chemical reaction takes place, forming a new compound with different light absorption properties. This highlights the intricate relationship between the physical properties of a solution and its chemical composition.