Problem 147 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following concentration factor is affected by change in temperature? (a) molarity (b) molality (c) mole fraction (d) weight fraction

Step-by-Step Solution

Answer

Molarity is affected by temperature changes.

Step 1: Define Concentration Factors

Concentration factors refer to different ways to express the composition of a solution. Important factors include molarity, molality, mole fraction, and weight fraction, and each is influenced differently by various conditions.

Step 2: Understand Temperature Impact on Volume

Know that temperature changes can affect the volume of a solution. Typically, as temperature increases, the volume of the solution expands.

Step 3: Analyze Molarity

Molarity ( M ) is defined as moles of solute per liter of solution. Since it's volume-based, it is affected by temperature changes as the solution's volume can expand or contract with temperature.

Step 4: Analyze Molality

Molality (\(m\)) is defined as moles of solute per kilogram of solvent. It depends on the mass, not the volume of the solution, and hence, it remains unaffected by temperature changes.

Step 5: Analyze Mole Fraction

Mole fraction, represented by \(X\), is defined as the ratio of the number of moles of one component to the total number of moles in the solution. It is a ratio of amounts and hence remains unaffected by temperature changes.

Step 6: Analyze Weight Fraction

Weight fraction is the ratio of the mass of a component to the total mass of the mixture. Since it is mass-based, weight fraction is unaffected by changes in temperature.

Step 7: Conclusion

Only molarity is affected by changes in temperature because it is based on the volume of the solution, which changes with temperature.

Key Concepts

Molarity

Molarity is a key concept in chemistry that allows us to express the concentration of a solution. It is calculated as the number of moles of solute divided by the volume of the solution in liters. One of the unique aspects of molarity is its dependency on volume. This means that any change in volume will directly affect molarity. For example, if you have a solution of salt in water, and you measure the amount of salt per liter, that is molarity. If you increase the water temperature, the water can expand, changing the volume and thus changing how many moles of solute there are per liter. These changes make molarity a convenient, but temperature-sensitive, way to measure concentration.
Understanding molarity is important when preparing solutions in labs, as improper calculation can lead to incorrect results. Always remember that since molarity is volume-based, checking the temperature is necessary to ensure precision.

Temperature Effect on Concentration

Temperature plays a significant role in altering the concentration of solutions, particularly when it comes to volume-based measures like molarity. Generally, as the temperature of a solution increases, the solvent's molecules move apart. This expansion leads to an increase in the solution's volume.

• When volume increases, molarity decreases because the same amount of solute is now distributed in a larger volume.
• Chemical reactions in solutions are often temperature-dependent, so changes in concentration can impact reaction rates and dynamics.

It's crucial for scientists and students alike to understand these relationships. Consider measuring solution concentration at a constant temperature, or adjusting for temperature changes, to maintain accurate results. Always remember, molality, mole fraction, and weight fraction are not affected by temperature due to their mass dependence, unlike molarity.

Solution Volume Change

Volume changes in solutions, an important phenomenon in chemistry, occur primarily due to temperature fluctuations. When temperature increases, most solutions expand, and when it decreases, they contract. This is because molecules move faster and further apart at higher temperatures.

• While the mass of solute and solvent remains constant, the volume change alters concentration measurements like molarity.
• This can be crucial in experiments and industrial applications where precision is needed.

To manage these changes, scientists may hold solution temperatures constant or use concentration measurements not affected by volume, such as molality. Understanding the interplay between temperature and solution volume helps in making accurate assessments of how substances will behave in various conditions.