Definition check: Molality (m) is defined as the number of gram-moles of solute per what quantity of solvent?

Introduction / Context:
Concentration units appear throughout reaction engineering and separation processes. Molality is particularly useful because it is independent of temperature and pressure, unlike molarity which depends on solution volume.

Given Data / Assumptions:

• Molality symbol m.
• We are using standard chemical engineering definitions.

Concept / Approach:
Molality is defined as m = (moles of solute) / (kilograms of solvent). The denominator is the mass of the solvent only, not the total solution mass, and not the volume, which makes molality insensitive to thermal expansion or contraction.

Step-by-Step Solution:

Verification / Alternative check:
Compare with molarity: M = moles solute per litre of solution; this varies with temperature through density changes, unlike molality.

Why Other Options Are Wrong:

• Litre: Volume-based—this is molarity, not molality.
• gm mole: Dimensionally incorrect as a denominator.
• gm: If used, must be converted to kg; the canonical unit is kg.

Common Pitfalls:
Confusing solvent mass with solution mass; molality excludes the solute in the denominator.

Final Answer:
kg