Question

Determine whether each of the following is a pure substance or a mixture: (a) hot tea (b) beach sand (c) carbon dioxide (d) cement (e) zinc (f) vinegar

Short answer

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

Step-by-step solution

- Understand Pure Substances

A pure substance has a uniform and definite composition. It can either be an element or a compound. Examples include pure water (H₂O), oxygen gas (O₂), and gold (Au). Pure substances have consistent properties throughout the sample.

- Understand Mixtures

Mixtures contain two or more different substances that are physically combined. Mixtures can be homogeneous (uniform composition) or heterogeneous (non-uniform composition). Examples include seawater, air, and salad.

- Analyze Hot Tea

Hot tea is a mixture because it contains water, tea compounds, and often other substances like sugar or milk. These components are physically combined and can vary in proportion.

- Analyze Beach Sand

Beach sand is a mixture. It contains different particles like silica, shell fragments, and organic matter that are physically combined and non-uniform.

- Analyze Carbon Dioxide

Carbon dioxide (CO₂) is a pure substance. It is a compound with a definite chemical composition and specific properties.

- Analyze Cement

Cement is a mixture. It is made up of various ingredients such as limestone, clay, and gypsum that are combined together.

- Analyze Zinc

Zinc (Zn) is a pure substance. It is an element with a uniform composition and consistent properties.

- Analyze Vinegar

Vinegar is a mixture. It mainly consists of water and acetic acid along with other components. These substances are physically combined.

Key concepts

pure substances

Pure substances are materials that have a uniform and definite composition. They can be classified into two main categories: elements and compounds.
Elements are substances that cannot be broken down into simpler substances by chemical means. Examples include carbon (C), oxygen (O₂), and gold (Au).
Compounds are substances formed when two or more elements are chemically combined in a fixed ratio, like water (H₂O) and carbon dioxide (CO₂).
Pure substances have consistent properties throughout the sample, which means their behavior and characteristics do not change, regardless of the sample size or source. Understanding this is crucial when distinguishing between pure substances and mixtures.

mixtures

A mixture is a combination of two or more different substances where each substance retains its own chemical identity and properties. A mixture can be either homogeneous or heterogeneous.
Homogeneous mixtures, also known as solutions, have a uniform composition throughout. An example is saltwater, where the salt is evenly distributed in the water.
Heterogeneous mixtures have a non-uniform composition, like a salad or a chocolate chip cookie, where different parts of the mixture can be easily seen and separated.
Mixtures can be separated into their individual components by physical means such as filtration, distillation, or evaporation.

homogeneous mixtures

Homogeneous mixtures are mixtures that have a uniform composition and appearance throughout. This means that the different components are not visible and are evenly distributed.
Examples include:

• Tea or coffee, where the solutes (like sugar) are completely dissolved in the solvent (water)
• Air, which is a mixture of gases like nitrogen, oxygen, and other trace gases
• Vinegar, which is primarily a mixture of acetic acid and water.

Homogeneous mixtures cannot be separated easily by simple mechanical means because their components are thoroughly mixed at a molecular level.

heterogeneous mixtures

Heterogeneous mixtures are mixtures where the different components can be visibly distinguished and are not evenly distributed. The substances in a heterogeneous mixture can often be separated through physical means because they retain their individual properties.
Examples include:

• Beach sand, which contains various particles like silica, shells, and organic matter
• Concrete, a composite material made of cement, water, sand, and gravel
• Salads, where you can see and separate ingredients like lettuce, tomatoes, and cucumbers.

In these mixtures, the individual substances are physically combined rather than chemically bonded.

chemical compounds

A chemical compound is a pure substance that is composed of two or more elements that are chemically combined in fixed proportions. Unlike mixtures, the components in a compound do not retain their individual properties but form a new substance with new properties.
Examples of chemical compounds include:

• Water (H₂O), formed from hydrogen and oxygen
• Carbon dioxide (CO₂), created by the combination of carbon and oxygen
• Sodium chloride (NaCl), which is table salt created by the chemical bonding of sodium and chlorine.

The formation of a compound involves a chemical reaction, and the compound has a definite chemical structure.

elements

Elements are fundamental substances that consist of only one type of atom and cannot be broken down into simpler substances by chemical means. These are the building blocks of all matter and are listed in the periodic table.
Examples of elements include:

• Oxygen (O), essential for respiration
• Gold (Au), valued for its use in jewelry and electronics
• Zinc (Zn), used in various alloys and as a protective coating for other metals.

Each element has unique properties and a specific atomic structure, which determine its reactivity and role in forming compounds.