Calculate Molecular Weight From Boiling Point Elevation

Molecular Weight Formula:

\[ M = \frac{w}{\left( \frac{\Delta T_b}{i K_b} \right) W} \]

Mass of Solute (w):

Boiling Point Elevation (ΔT_b):

°C

Van't Hoff Factor (i):

Constant (K_b):

°C kg/mol

Solvent Mass (W):

Molecular Weight (M):

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1. What is Molecular Weight Calculation?

Molecular weight calculation from boiling point elevation is a colligative property method that determines the molar mass of a solute based on the increase in boiling point when the solute is dissolved in a solvent.

2. How Does the Calculator Work?

The calculator uses the molecular weight formula:

\[ M = \frac{w}{\left( \frac{\Delta T_b}{i K_b} \right) W} \]

Where:

\( M \) — Molecular weight (g/mol)
\( w \) — Mass of solute (g)
\( \Delta T_b \) — Boiling point elevation (°C)
\( i \) — Van't Hoff factor (dimensionless)
\( K_b \) — Ebullioscopic constant (°C kg/mol)
\( W \) — Mass of solvent (kg)

Explanation: The formula calculates molecular weight based on the colligative property of boiling point elevation, which depends on the number of solute particles in the solution.

3. Importance of Molecular Weight Determination

Details: Accurate molecular weight determination is crucial for identifying unknown compounds, quality control in chemical synthesis, and understanding the physical properties of substances.

4. Using the Calculator

Tips: Enter all values with appropriate units. Ensure mass of solute and solvent are in grams and kilograms respectively. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the van't Hoff factor?
A: The van't Hoff factor (i) represents the number of particles a solute dissociates into in solution. For non-electrolytes, i = 1; for electrolytes, it depends on the degree of dissociation.

Q2: What are typical values for K_b?
A: Common ebullioscopic constants: Water (0.512 °C kg/mol), Benzene (2.53 °C kg/mol), Ethanol (1.22 °C kg/mol), Acetic acid (3.07 °C kg/mol).

Q3: When is this method most accurate?
A: This method works best for non-volatile solutes in dilute solutions where the concentration is low and ideal solution behavior can be assumed.

Q4: What are the limitations of this method?
A: The method may be less accurate for high concentrations, volatile solutes, or when association occurs between solute molecules.

Q5: Can this method be used for polymers?
A: While possible, boiling point elevation is less commonly used for polymers due to small ΔT_b values; other methods like osmometry are preferred.