Difficulty: Easy
Correct Answer: increase
Explanation:
Introduction:
Molarity is a common concentration unit used in material balances and reactor calculations. Understanding how molarity responds to evaporation is crucial in evaporation, crystallization, and syrup concentration operations in the food and biotech industries.
Given Data / Assumptions:
Concept / Approach:
Molarity M is defined as moles of solute per liter of solution. During evaporation, the number of moles of sugar remains constant while the volume of solution decreases as water is removed. Therefore, the ratio moles/volume increases. This remains true for any starting concentration as long as only solvent is removed and temperature-induced volume changes are negligible compared with solvent loss.
Step-by-Step Solution:
Let initial moles of sugar = n_s (constant during evaporation).Initial volume V1 → final volume V2, where V2 < V1 after evaporating water.M1 = n_s / V1; M2 = n_s / V2.Because V2 < V1, M2 > M1 ⇒ molarity increases.
Verification / Alternative check:
Mass balance on solute confirms constant solute moles. A quick numerical example (e.g., halving the volume doubles molarity) provides an intuitive check.
Why Other Options Are Wrong:
Common Pitfalls:
Confusing molarity with molality. Molality increases even more directly since solvent mass decreases; molarity depends on solution volume.
Final Answer:
increase
Discussion & Comments