Question

Determine whether each of the following is a pure substance or a mixture: (a) dirt (b) salad dressing (c) tungsten (d) dinitrogen monoxide (e) brass (f) egg

Short answer

(a) Mixture, (b) Mixture, (c) Pure Substance, (d) Pure Substance, (e) Mixture, (f) Mixture

Step-by-step solution

- Understand Pure Substances

A pure substance consists of only one type of element or compound. It has a fixed or constant structure. Examples include elements like gold or compounds like water.

- Understand Mixtures

A mixture is composed of two or more different substances that are not chemically united but physically mixed together. Examples include air and salad.

- Determine Dirt

Dirt is a combination of various substances such as minerals, organic matter, gases, and liquids. Therefore, dirt is a mixture.

- Determine Salad Dressing

Salad dressing consists of multiple ingredients like oil, vinegar, and spices. Therefore, salad dressing is a mixture.

- Determine Tungsten

Tungsten is an element with the atomic number 74 in the periodic table. It has a fixed atomic structure. Therefore, tungsten is a pure substance.

- Determine Dinitrogen Monoxide

Dinitrogen monoxide (N₂O) is a chemical compound consisting of nitrogen and oxygen. As a compound with a fixed composition, dinitrogen monoxide is a pure substance.

- Determine Brass

Brass is an alloy made of copper and zinc. Since it is composed of multiple metals but not chemically combined, brass is a mixture.

- Determine Egg

An egg is composed of multiple substances, including proteins, fats, and water. Therefore, an egg is a mixture.

Key concepts

Elements

Elements are the simplest form of pure substances. They consist of only one type of atom and cannot be broken down into any simpler substances. Each element is unique and has its own distinct properties. For example, tungsten is an element with the atomic number 74. It has a fixed atomic structure, meaning every atom of tungsten is the same. Elements are often displayed on the periodic table, which organizes them based on properties like atomic number and reactivity.

Key characteristics of elements include:

• Made of one type of atom
• Cannot be broken down by chemical means
• Have unique properties
• Represented by chemical symbols (e.g., W for tungsten)

Elements are the building blocks for all other substances on Earth, and by combining them, we can create compounds and mixtures.

Compounds

Compounds are pure substances formed from two or more elements that are chemically bonded together. They have a fixed composition and always contain the same elements in the same proportions. For example, dinitrogen monoxide (N₂O) is a compound made from nitrogen and oxygen. These elements are chemically combined in a specific ratio (2:1).

Compounds have distinct properties that are different from the individual elements that make them up. For instance, N₂O is a gas with unique properties that are not found in either nitrogen or oxygen alone.

Features of compounds include:

• Made of two or more elements chemically combined
• Have a fixed, definite composition
• Display unique properties
• Can only be separated into their elements by chemical means

Compounds are everywhere around us. Water (H₂O) is another common compound, made of hydrogen and oxygen. Each molecule of water is always composed of two hydrogen atoms and one oxygen atom.

Mixtures

Mixtures are made from two or more substances that are not chemically bonded. The components in a mixture can vary in proportion and can be separated by physical means. Examples include dirt, salad dressing, and brass.

There are two main types of mixtures: homogeneous and heterogeneous. Homogeneous mixtures have a uniform composition throughout, like saltwater. Heterogeneous mixtures have a non-uniform composition, meaning you can see the different parts, like in a salad.

Key points about mixtures:

• Contain multiple substances not chemically combined
• Can be homo- or heterogeneous
• Components retain their individual properties
• Can be separated by physical means (e.g., filtration, distillation)

For instance, dirt is a mixture composed of organic matter, minerals, gases, and liquids. Salad dressing, another mixture, consists of ingredients like oil and vinegar, which do not chemically combine but are simply mixed together. Lastly, brass is an alloy made mostly of copper and zinc, showcasing the diverse nature of mixtures.