Problem 89 - Chemistry Matter and Change

Question

Iced Tea Is a mixture of tea and ice homogeneous or heterogeneous? Does that change as the ice melts?

Step-by-Step Solution

Answer

Iced tea is initially heterogeneous but becomes homogeneous after the ice melts.

Step 1: Understand the Definitions

Define that a "homogeneous mixture" is one in which the composition is uniform throughout, and a "heterogeneous mixture" is one where the components can be distinguished and are not uniform throughout.

Step 2: Analyze the Components of Iced Tea

Identify the components of iced tea: tea (a liquid solution) and ice (solid water). Initially, you can see both the tea and the pieces of ice.

Step 3: Determine Initial Mixture Type

Since iced tea shows distinct separate phases where both tea and ice are visible and can easily be separated, it is a heterogeneous mixture initially.

Step 4: Consider Changes as Ice Melts

As the ice melts, it converts into water and mixes with the tea, leading to a uniform solution where the different components are no longer visible separately.

Step 5: Determine Mixture Type After Melting

Once the ice has completely melted and mixed with the tea, the mixture becomes homogeneous as the composition is uniform throughout.

Key Concepts

Homogeneous Mixture

A homogeneous mixture is one where the composition is consistent throughout. This means that no matter how you sample the mixture, the components remain evenly distributed.
This is often seen in solutions where substances are dissolved completely into one another. A great example is saltwater where salt dissolves uniformly in water.

• Characteristics include uniform appearance and composition.
• The substances involved are indistinguishable from one another.

Homogeneity ensures that every sample taken has the same properties and composition.

Heterogeneous Mixture

A heterogeneous mixture has components that are not uniformly mixed. This results in an uneven distribution, where different parts of the mixture may have different compositions.
An easy example is a salad, where you can find distinct ingredients like lettuce, tomatoes, and cucumbers.

• Each component is usually easily distinguishable.
• These mixtures have visibly different phases or parts.

Heterogeneous mixtures can be separated physically, such as picking out ingredients with your hands.

Phase Change

A phase change refers to the transformation of a substance from one state of matter to another, such as solid to liquid or liquid to gas. This process does not affect the chemical structure of a substance.
For instance, melting ice involves a phase change from solid to liquid without altering the water itself.

• Common phase changes include melting, freezing, condensation, and evaporation.
• During a phase change, the energy levels of the particles change, though the substance remains the same chemically.

Phase changes are usually reversible, allowing substances to switch states under different conditions.

Solution

A solution is a specific type of homogeneous mixture where one substance, the solute, is dissolved in another, the solvent.
The solute particles are evenly distributed at a molecular level within the solvent, resulting in a uniform mixture.

• Solutions are often transparent, as with sugar dissolved in water.
• They can exist in different states of matter, such as gases dissolving in liquids.

The properties of a solution are uniform, meaning any sample taken from it will have the same ratio of solute to solvent.