Question

Classify each mixture as homogeneous or heterogeneous. (a) coffee (b) chocolate sundae (c) apple juice (d) gasoline

Short answer

Homogeneous mixtures: coffee (assuming no grounds), apple juice (if filtered), and gasoline. Heterogeneous mixture: chocolate sundae, and apple juice if unfiltered with pulp.

Step-by-step solution

Definition of Homogeneous and Heterogeneous Mixtures

Before classifying, it's important to understand the definitions. A homogeneous mixture has a uniform composition throughout, with only one phase of matter visible. A heterogeneous mixture contains visibly different parts or phases.

Classify coffee

Assuming the coffee is well-mixed and no individual parts can be seen (no coffee grounds, for example), it can be classified as a homogeneous mixture, as it looks the same throughout.

Classify chocolate sundae

A chocolate sundae typically has different layers and chunks of ingredients like chocolate syrup, ice cream, and sprinkles. These parts are visible and do not blend uniformly, classifying it as a heterogeneous mixture.

Classify apple juice

Apple juice, when filtered, appears uniform throughout and with no distinguishable parts, making it a homogeneous mixture. If the juice is unfiltered and contains pulp, it would be considered heterogeneous.

Classify gasoline

Gasoline is a mixture of different hydrocarbons but appears uniform and consistent throughout to the naked eye. It is a homogeneous mixture.

Key concepts

Chemistry Mixtures

In chemistry, a mixture is a combination of two or more substances in which each substance retains its individual chemical properties. The importance of mixtures cannot be understated, as they are the basis for many products we use daily. Understanding how these substances combine and interact with one another is essential for many applications in industries such as pharmaceuticals, food technology, and materials engineering.

An essential skill for students is distinguishing between the different types of mixtures. This is crucial as the properties of a mixture directly influence its use and the methods for its separation. For example, understanding that air is a homogeneous mixture of gases is key when discussing our atmosphere, or knowing that salad dressing is a heterogeneous mixture has implications in culinary arts.

Classification of Mixtures

Mixtures can be largely categorized into two types: homogeneous and heterogeneous. The straightforward classification is based on the uniformity of ingredients and their distribution.

A homogeneous mixture exhibits a consistent composition and a single phase throughout, no matter how closely you look. On a molecular level, the different components are mixed uniformly. Common methods for separating components in homogeneous mixtures involve taking advantage of different physical properties, like boiling points, using techniques such as distillation.

Conversely, a heterogeneous mixture is easy to identify because you can often see the different ingredients or parts, as they aren't uniformly distributed. For example, sand in water or a plate of nachos exhibits heterogeneous properties. The separation techniques might include filtration, decantation, or handpicking.

Homogeneous Mixtures Examples

Homogeneous mixtures are all around us and in products we use daily. Here are a few examples:

• Air: A mix of gases primarily made up of nitrogen and oxygen, well mixed to appear as a single phase.
• Vinegar: Acetic acid uniformly distributed in water.
• Brass: A solid solution of copper and zinc that presents a uniform composition throughout the material.

When we look at coffee, assuming it is filtered without any coffee grounds, it's homogeneous because it's the same throughout. The same applies to filtered apple juice and gasoline, which are consistent and single-phased.

Heterogeneous Mixtures Examples

In contrast to homogeneous mixtures, heterogeneous mixtures have components that are easily distinguished. Examples include:

• Salad: Various ingredients such as lettuce, tomatoes, cucumbers, and dressing, each retaining their individual properties.
• Granite: An amalgamation of different minerals such as quartz, feldspar, and mica, which can be seen clearly.
• Concrete: A mixture of cement, water, sand, and gravel, with the distinction between the components visible to the naked eye.

A chocolate sundae is another excellent example that showcases layers of ice cream, syrup, and toppings, making it a classic heterogeneous mixture. When looking at apple juice with pulp, each piece of pulp is distinguishable, thus fitting the criteria for a heterogeneous mixture.