# Which of the following is temperature independent?

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Which of the following is temperature independent?
1. Molality
2. Molarity
3. Normality
4. All of these

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Correct Answer - Option 1 : Molality

Concept:

Molality:

• It is defined as the number of moles of solute per kilogram of solvent.
• Unit of Molality is the mole. Kg-1.

${\rm{Molality}} = \frac{{{\rm{Moles\;of\;Solute}}}}{{{\rm{Kilogram\;of\;solvent}}}}$

Molarity:

• It is defined as the moles of a solute per liters of a solution.
• It is also known as the molar concentration of a solution.
• The unit of Molarity is the mole. lit-1.
• It is given by:

$\rm \frac{{Number\;of\;moles\;of\;solute}}{{Mass\;of\;solvent\left( {in\;g} \right)}} \times 1000$

• Normality:
• It is defined as the number of grams equivalent per liter of solution.
• Also known as equivalent concentration.

${\rm{Normality}} = \frac{{{\rm{Gram\;equivalents}}}}{{{\rm{volume\;of\;solution\;in\;liter}}}}$

Explanation:

• Volume is dependent on temperature. When we increase the temperature, a liquid expands and its volume increases.
• When we decrease the temperature, keeping the pressure constant, the volume of a liquid decreases.
• Thus we can say that volume is directly proportional to temperature.
• So, the concentration terms having volume terms in them will also be dependent on temperature.
• We see that Molarity and Normality are the terms that are dependent on volume.
• Molarity and Normality are both inversely proportional to the volume and are temperature dependent.
• On the other hand, we know that mass does not depend on temperature, so Molality which is the number of moles per kg of a solvent is independent of temperature.

Hence, Molality is temperature independent.