Derive equation for molar mass of solute from freezing point depression

Table of Contents • • • What is Depression in Freezing Point The temperature at which a liquid turns into solid or liquid particles takes the physical structure of a solid is called the melting point. When you add solutes to a solution, you lower the freezing point of the solutes in the solution. This is one of the cumulative properties of a solution. It varies according to the softness of the solute in the solution. According to Raoult’s law, the vapor pressure of a pure solvent decreases when the solute dissolves in the solution, which is the reason for the lowering of the melting point. We know that a non-volatile solvent has zero vapor pressure. As a result, the total vapor pressure of the solution is lower than the vapor pressure of the pure solvent. For example, the melting point of water is 0 °C. The vapor pressure of a solution containing non-volatile solute is less than that of a solvent with a decrease of vapor pressure, and the freezing point of the solvent decreases. There is a dynamic equilibrium between the solid and liquid phases and this is possible when the vapor pressure of both phases is the same. Thus, the Freezing point is the temperature at which the vapor pressure of the liquid phase (solvent) is equal to its vapor pressure in a solid phase. Let T f is the freezing point of the solution and T° f be the freezing point of the solvent then the difference between T fand T° f is known as depression in freezing point (∆Tf). Formulas and Derivations of Depr...

Determining Molar Mass Determining Molar Mass We can use a measurement of any one of the following properties to determine the molar mass (molecular weight) of an unknown that is the solute in a solution: • • • From Boiling Point Elevation • Determine the change in boiling point from the observed boiling point of the solution and the boiling point of the pure solvent. • Determine the molal concentration, m, from the change in boiling point and the boiling point elevation constant. • Determine the moles of unknown (the solute) from the molality of the solution and the mass of solvent (in kilograms) used to make the solution. • Determine the molar mass from the mass of the unknown and the number of moles of unknown. From Freezing Point Depression • Determine the change in freezing point from the observed freezing point of the solution and the freezing point of the pure solvent. (This will be a negative number.) • Determine the molal concentration, m, from the change in freezing point and the freezing point depression constant. • Determine the moles of unknown (the solute) from the molality of the solution and the mass of solvent (in kilograms) used to make the solution. • Determine the molar mass from the mass of the unknown and the number of moles of unknown. From Osmotic Pressure • Determine the molar concentration of the unknown in the solution from the observed osmotic pressure. • Determine the moles of unknown (the solute) from the molarity of the solution and the volum...

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Calculate Molecular Masses Using Boiling and Freezing Points of Solvents - dummies A solid understanding of molality helps you to calculate changes in boiling and freezing points. In the same way, a solid understanding of boiling point elevation and freezing point depression can help you determine the molecular mass of a mystery compound that's being added to a known quantity of solvent. refers to the tendency of a solvent's freezing point to decrease when an impurity is added. Calculate the molecular mass When you're asked to solve problems of this type, you'll always be given the mass of the mystery solute, the mass of solvent, and either the change in the freezing or boiling point or the new freezing or boiling point itself. From this information, you then follow a set of simple steps to determine the molecular mass: • Find the boiling point elevation or freezing point depression. If you've been given the boiling point, calculate the • Calculate the number of moles of solute in the solution by multiplying the molality calculated in Step 3 by the given number of kilograms of solvent. • Divide the given mass of solute by the number of moles calculated in Step 4. This is your molecular mass, or number of grams per mole, from which you can often guess the identity of the mystery compound. Common K b Values Solvent K b in Degrees C/m Boiling Point in Degrees C Acetic acid 3.07 118.1 Benzene 2.53 80.1 Camphor 5.95 204.0 Carbon tetrachloride 4.95 76.7 Cyclohexane 2.79 80.7 Et...

This problem has been solved! You'll get a detailed solution from a subject matter expert that helps you learn core concepts. See Answer See Answer See Answer done loading Question:Q1) Derive a formula for the molar mass of the solute in terms of the freezing point depression, DeltaT, the freezing-point depression constant, Kf, and the masses of solvent, msolvent, and solute, msolute, used in an experiment like this one. Show your work, and include all units in your final formula. Q2 Define enthalpy of fusion, and explain why the Q1) Derive a formula for the molar mass of the solute in terms of the freezing point depression, DeltaT, the freezing-point depression constant, Kf, and the masses of solvent, msolvent, and solute, msolute, used in an experiment like this one. Show your work, and include all units in your final formula. Q2 Define enthalpy of fusion, and explain why the cooling curve flattens out while a pure solvent is freezing. Q3 Explain why the cooling curves of solutions are more steeply sloping during the freezing process than the curve for same pure solvent

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