Question

(a) Is the concentration of a solution an intensive or an extensive property? (b) What is the difference between 0.50 mol HCl and 0.50\(M \mathrm{HCl}\) ?

Short answer

(a) The concentration of a solution is an intensive property, as it does not depend on the amount of substance present and remains constant even when the solution is divided into smaller parts. (b) The difference between 0.50 mol HCl and 0.50\(M \mathrm{ HCl }\) is that 0.50 mol HCl represents the quantity of HCl molecules present in a system, which is an extensive property, while 0.50\(M \mathrm{ HCl }\) represents the concentration of HCl in a solution, which is an intensive property, describing the ratio of moles of HCl to the volume of the solution in liters.

Step-by-step solution

(a) Intensive or Extensive Property?

To determine if the concentration of a solution is an intensive or extensive property, it is important to understand the difference between them. Intensive properties do not depend on the amount of substance present, whereas extensive properties do depend on the amount of substance present. Examples of intensive properties are boiling point and color, while examples of extensive properties are mass and volume. Concentration is defined as the amount of solute per unit volume of the solution. Thus, concentration is unaffected by the total volume of the solution or the amount of solute present, and it remains constant even when the solution is divided into smaller parts. Therefore, the concentration is an intensive property.

(b) Difference between 0.50 mol HCl and 0.50\(M \mathrm{ HCl }\)

0.50 mol HCl refers to the actual amount of HCl molecules present in a system. This amount is an extensive property, as it depends on the total quantity of HCl molecules. 0.50\(M \mathrm{ HCl }\) (0.50 molar HCl) describes the concentration of HCl in a solution. This is the ratio of moles of HCl (the solute) to the volume of the solution, expressed in liters. The concentration is an intensive property and represents how much HCl is present in a specific volume of the solution. In this case, there are 0.50 moles of HCl in every 1 liter of the solution. In conclusion, 0.50 mol HCl represents the quantity of HCl molecules, while 0.50\(M \mathrm{ HCl }\) represents the concentration of HCl in a solution.

Key concepts

Intensive vs Extensive Properties

Understanding the difference between intensive and extensive properties is crucial in many areas of science, particularly in chemistry. Intensive properties are characteristic of the material itself and do not change with the amount present. They include boiling point, density, color, and temperature. On the other hand, extensive properties change when the size of the sample changes and are dependent on the quantity of the substance. Examples include mass, volume, and energy.

For instance, if you have a cup of water, the temperature (an intensive property) will be the same as if you had a swimming pool full of water, assuming uniform conditions. However, the volume (an extensive property) is quite different between the two. Concentration, which is a measure of the amount of solute per unit volume of solution, is also an intensive property. It remains constant regardless of the amount of solution you have, making it a useful parameter for standardizing solutions.

Molar Concentration

The molar concentration of a solution, often expressed in molarity (M), is a measure of how many moles of a solute are present in a given volume of solvent. It can be calculated using the formula: \[ M = \frac{\text{moles of solute}}{\text{liters of solution}} \].

This concept allows chemists to prepare solutions with precise chemical compositions, which is essential for reactions and experiments. For example, a 1 M solution of sodium chloride means there is 1 mole of sodium chloride dissolved in 1 liter of water. Molar concentration is a convenient way to communicate the strength of a solution, and because it's an intensive property, it allows for reproducibility in different labs around the world.

Properties of Solutions

Properties of solutions refer to the various attributes that a solution can exhibit based on the intermolecular interactions between the solute and the solvent. These properties can be chemical, such as reactivity and stability, or physical, such as boiling point elevation and freezing point depression.

Solubility, the maximum amount of solute that can be dissolved in a solvent, is another important property, and it varies with temperature and pressure. Understanding these properties is essential for practical applications like creating antifreeze solutions or saltwater aquariums that mimic ocean conditions. Solutions also exhibit colligative properties, which depend only on the ratio of the number of solute particles to solvent particles, not the identity of the solute molecules.

Mole Concept in Chemistry

The mole concept is a fundamental principle in chemistry that provides a bridge between the microscopic world of atoms and molecules and the macroscopic world we can measure. One mole is defined as the amount of a substance that contains the same number of units (atoms, molecules, ions, or other particles) as there are atoms in 12 grams of pure carbon-12. This number is known as Avogadro's number and is approximately \(6.022 \times 10^{23}\) units.

The concept allows chemists to count particles by weighing, as measuring individual particles directly is impractical. It also enables calculations involving the chemical reactions where reactants convert to products, as the reactions occur in fixed ratios of moles. In essence, the mole concept is central to comprehending and calculating chemical compositions, reactions, and the outcomes.