Question

In which mode of expression, the concentration of a solution remains independent of temperature? a. Formality b. Molality c. Molarity d. Normality

Short answer

Molality remains independent of temperature.

Step-by-step solution

Understanding the Question

We need to identify which mode of expression for concentration of a solution remains unaffected by changes in temperature. The options given are formality, molality, molarity, and normality.

Analyzing the Options

Let's consider each option: - Molarity, normality, and formality are based on volume, which can change with temperature. - Molality is based on mass, which does not change with temperature. Thus, molality remains constant irrespective of temperature changes.

Conclusion

Since molality is based on mass rather than volume, it remains constant when temperature changes. Therefore, molality is the mode of expression where concentration remains independent of temperature.

Key concepts

Molality

Molality is a term used to describe the concentration of a solution. It is typically expressed as the number of moles of solute per kilogram of solvent. This might sound a bit complicated, but it's quite straightforward once you break it down.

In a molal solution, you're measuring the amount of solute using its weight, or mass, within the solvent. Hence, the mathematical definition is given by:\[\text{Molality (m)} = \frac{\text{moles of solute}}{\text{mass of solvent in kg}}.\]

The use of kilograms for the solvent is essential, as it differentiates molality from other methods of expressing concentration. The flexibility of molality comes from its reliance on mass, which doesn't change with physical conditions like temperature. This characteristic makes it incredibly useful in various chemical calculations.

Temperature Independence

One of the most significant advantages of using molality is its temperature independence. But what does that mean for the solution? Let's break it down.

• Volume-based measures, such as molarity, can change as the liquid expands or contracts with temperature.
• Molality, however, relies on mass, which remains the same regardless of temperature changes.

This lack of temperature dependence means that calculations using molality can be more reliable when working in environments where temperatures may vary. It's especially significant in

• scientific experiments,
• industrial applications, and
• situations where precise calculations are necessary

across different environmental temperatures.

Mass vs. Volume Concentration

When discussing solution concentrations, understanding mass versus volume-based concentrations is crucial.

Concentrations like molarity depend on volume and are calculated in

• liters or milliliters of a solution.

Volume can shift with temperature.

• This affects the concentration, making it less stable for certain calculations.

On the other hand, molality is focused entirely on the mass:

• the constant weight of the solvent.

Mass remains constant regardless of the temperature changes. This difference makes molality a preferred concentration measure for temperature-influencing scenarios. Using mass-based measurements helps ensure that the concentration is accurate and consistent, which is essential for precise scientific experiments and industrial processes.