Element Compound Mixture Worksheet Answer Key

Element, Compound, and Mixture Worksheet: A Comprehensive Guide with Answers

Understanding the fundamental differences between elements, compounds, and mixtures is crucial for grasping basic chemistry concepts. This worksheet will delve into the characteristics of each, providing examples and clarifying the distinctions through practice problems and their detailed solutions. This guide serves as an answer key and a learning resource, reinforcing your understanding of matter's fundamental building blocks.

What are Elements?

Elements are pure substances that cannot be broken down into simpler substances by chemical means. They are the basic building blocks of all matter. Each element is defined by the number of protons in its atoms, also known as its atomic number. Elements are represented by chemical symbols, usually one or two letters, derived from their English or Latin names.

Examples of Elements:

• Oxygen (O): A vital gas necessary for respiration.
• Hydrogen (H): The lightest element, a component of water.
• Carbon (C): The foundation of organic molecules, essential for life.
• Iron (Fe): A transition metal used in construction and numerous industrial applications.
• Gold (Au): A precious metal known for its conductivity and resistance to corrosion.

What are Compounds?

Compounds are pure substances formed when two or more elements chemically combine in a fixed ratio. This chemical combination results in a new substance with properties different from the original elements. Compounds can only be broken down into their constituent elements through chemical reactions. Their composition is represented by chemical formulas, showing the types and numbers of atoms present.

Examples of Compounds:

• Water (H₂O): Composed of two hydrogen atoms and one oxygen atom. Its properties are vastly different from hydrogen and oxygen gases.
• Sodium Chloride (NaCl): Common table salt, formed from the reaction of sodium (a highly reactive metal) and chlorine (a toxic gas).
• Carbon Dioxide (CO₂): A gas produced during respiration and combustion, crucial in the carbon cycle.
• Glucose (C₆H₁₂O₆): A simple sugar, a primary source of energy for living organisms.
• Sulfuric Acid (H₂SO₄): A strong acid used extensively in industrial processes.

What are Mixtures?

Mixtures are combinations of two or more substances that are not chemically bonded. Unlike compounds, mixtures retain the individual properties of their components. The components of a mixture can be separated by physical methods, such as filtration, distillation, or evaporation. Mixtures can be homogeneous or heterogeneous.

Types of Mixtures:

• Homogeneous Mixtures: The components are evenly distributed throughout the mixture, appearing uniform in composition. Examples include saltwater, air, and sugar dissolved in water.
• Heterogeneous Mixtures: The components are not evenly distributed, and different parts of the mixture have different compositions. Examples include sand and water, oil and water, and a salad.

Worksheet Questions and Answers

Let's test your understanding with the following questions. Remember to justify your answers based on the definitions provided above.

Question 1: Identify each of the following as an element, compound, or mixture:

a) Air b) Iron (Fe) c) Water (H₂O) d) Saltwater e) Sugar (C₁₂H₂₂O₁₁) f) Soil g) Gold (Au) h) Carbon Dioxide (CO₂) i) Milk j) Oxygen (O₂)

Answers:

a) Air: Mixture (a homogeneous mixture of gases like nitrogen, oxygen, and others). b) Iron (Fe): Element (a pure substance with a specific atomic number). c) Water (H₂O): Compound (two hydrogen atoms chemically bonded to one oxygen atom). d) Saltwater: Mixture (a homogeneous mixture of salt dissolved in water). e) Sugar (C₁₂H₂₂O₁₁): Compound (a complex organic compound with a fixed ratio of carbon, hydrogen, and oxygen). f) Soil: Mixture (a heterogeneous mixture of minerals, organic matter, water, and air). g) Gold (Au): Element (a pure substance with a specific atomic number). h) Carbon Dioxide (CO₂): Compound (one carbon atom chemically bonded to two oxygen atoms). i) Milk: Mixture (a heterogeneous mixture of water, fats, proteins, and sugars). j) Oxygen (O₂): Element (although it exists as a diatomic molecule, it's still the same element).

Question 2: Explain the difference between a homogeneous and a heterogeneous mixture, giving an example of each.

Answer:

A homogeneous mixture has a uniform composition throughout. The different components are evenly distributed and not easily distinguishable. An example is saltwater, where the salt is dissolved completely in the water. A heterogeneous mixture has a non-uniform composition. Different parts of the mixture have different properties, and the components are easily distinguishable. An example is sand and water, where the sand particles are clearly visible and separated from the water.

Question 3: Can a compound be separated into its constituent elements by physical means? Explain your answer.

Answer:

No, a compound cannot be separated into its constituent elements by physical means. Compounds are formed by chemical bonds, which require chemical reactions to break. Physical methods like filtration or distillation only separate mixtures, not compounds. To separate the elements in a compound, you need chemical processes such as electrolysis or chemical decomposition.

Question 4: Classify each of the following changes as a physical or chemical change:

a) Dissolving sugar in water b) Burning wood c) Melting ice d) Rusting of iron e) Boiling water

Answers:

a) Dissolving sugar in water: Physical change (the sugar is still sugar; it's just dispersed in the water). b) Burning wood: Chemical change (wood undergoes a chemical reaction with oxygen, producing ash, gases, and heat). c) Melting ice: Physical change (water changes from solid to liquid state but remains chemically the same). d) Rusting of iron: Chemical change (iron reacts with oxygen and water to form iron oxide, a new compound). e) Boiling water: Physical change (water changes from liquid to gas state but remains chemically the same).

Question 5: Describe a method to separate a mixture of sand and iron filings.

Answer:

A mixture of sand and iron filings can be separated using a magnet. Since iron is a magnetic substance, a magnet can be used to attract and separate the iron filings from the non-magnetic sand.

Question 6: Explain why the properties of a compound are different from the properties of the elements that compose it.

Answer:

The properties of a compound differ from the properties of its constituent elements because the elements are chemically bonded together. This chemical bonding involves a rearrangement of electrons, creating a new substance with unique physical and chemical properties. For instance, sodium is a highly reactive metal, and chlorine is a toxic gas. When they react to form sodium chloride (table salt), they form a crystalline, non-toxic compound with completely different properties.

Question 7: Provide three examples of elements that are gases at room temperature.

Answer:

Three examples of elements that are gases at room temperature are: Oxygen (O₂), Hydrogen (H₂), and Nitrogen (N₂).

Question 8: What is the difference between an atom and a molecule?

Answer:

An atom is the smallest unit of an element that retains the chemical properties of that element. A molecule is a group of two or more atoms chemically bonded together. A molecule can be composed of atoms of the same element (like O₂) or different elements (like H₂O).

Question 9: Explain how you would separate a mixture of salt and water.

Answer:

A mixture of salt and water can be separated using the process of evaporation. Heating the solution causes the water to evaporate, leaving behind the salt crystals.

Question 10: Give an example of a homogeneous mixture that is a liquid and a heterogeneous mixture that is a solid.

Answer:

A homogeneous mixture that is a liquid is saltwater. A heterogeneous mixture that is a solid is granite (a mixture of different minerals).

This comprehensive worksheet and answer key provide a robust foundation for understanding elements, compounds, and mixtures. Remember to practice identifying these types of matter in different contexts to further solidify your understanding. The key to mastering these concepts lies in actively engaging with examples and applying the definitions to real-world scenarios.