Pure substances vs mixtures: Definition, examples, and key differences

📚 Quick Study Guide

• ⚛️ Pure substances are composed of only one type of atom or molecule.
• 💧 Examples of pure substances include elements like gold (Au) and compounds like water ($H_2O$).
• ⚗️ Mixtures are combinations of two or more substances that are physically combined.
• 🍦 Mixtures can be homogeneous (uniform composition, like saltwater) or heterogeneous (non-uniform composition, like a salad).
• 🌡️ The composition of a mixture can vary, while a pure substance has a fixed composition.
• Separating mixtures involves physical methods like filtration, evaporation, or distillation.
• 🧪 Pure substances have definite melting and boiling points, while mixtures typically have a range of melting and boiling points.

Practice Quiz

1. What is a defining characteristic of a pure substance?
   1. It can be separated by physical means.
   2. It has a variable composition.
   3. It consists of only one type of atom or molecule.
   4. It appears transparent.
2. Which of the following is an example of a homogeneous mixture?
   1. Sand and water
   2. Oil and water
   3. Saltwater
   4. Pizza
3. Which method is most suitable for separating a mixture of iron filings and sand?
   1. Distillation
   2. Filtration
   3. Magnetism
   4. Evaporation
4. What distinguishes a compound from an element?
   1. A compound cannot be broken down further.
   2. A compound consists of multiple elements chemically bonded.
   3. An element can be separated physically.
   4. An element always exists as a gas.
5. Which of the following is a heterogeneous mixture?
   1. Air
   2. Vinegar
   3. Granite
   4. Sugar dissolved in water
6. What happens to the boiling point of water when salt is dissolved in it?
   1. It decreases.
   2. It remains the same.
   3. It increases.
   4. It fluctuates randomly.
7. Which of the following is NOT a physical method for separating mixtures?
   1. Filtration
   2. Distillation
   3. Chromatography
   4. Electrolysis