Une solution obtenue en dissolvant 10,0 g de glucose (C6 H12 O6) dans 500 mL d'eau commence à

step 1 Good day. The topic is about colligative properties. When solute is dissolved in solvent, the pr

Une solution obtenue en dissolvant 10,0 g de glucose (C6...

Key Concepts

van't Hoff Factor

The van't Hoff factor represents the number of particles into which a solute dissociates in solution. For non-electrolytes, which do not dissociate into ions, the van't Hoff factor is typically one. This factor directly influences the degree of colligative properties by determining the effective number of solute particles in the solution.

Molar Mass

Molar mass is the mass of one mole of a substance and is used to convert between the mass of a solute and the number of moles present. In solution chemistry, knowing the molar mass of a solute is essential for calculating its molality, which in turn is used in evaluating colligative effects such as freezing point depression.

Colligative Properties

Colligative properties are characteristics of solutions that depend on the number of solute particles rather than their identity. These include phenomena such as freezing point depression, boiling point elevation, and osmotic pressure, and are crucial in understanding how solutes affect the physical properties of solvents.

Freezing Point Depression

Freezing point depression refers to the lowering of the freezing temperature of a solvent when a solute is dissolved in it. This occurs because the addition of solute particles interferes with the formation of the solid phase, requiring a lower temperature to achieve freezing. The magnitude of the depression is directly related to the concentration of solute particles in the solution.

Molality

Molality is a concentration unit defined as the number of moles of solute per kilogram of solvent. It is particularly useful in calculating colligative properties because it does not change with temperature. In the context of freezing point depression, the molality of the solution determines the extent to which the freezing point is lowered.

Transcript

00:02 Good day.

00:03 The topic is about colligative properties.

00:06 When solute is dissolved in solvent, the properties of the solution that is formed are different from the properties of the pure solvent.

00:13 In particular, the solution freezes at a lower temperature than that of the pure solvent.

00:19 When a non -electroletic solute, that is a solute that doesn't dissolve into ion, at the same time, a non -volatile solute that is a solute that doesn't evaporate, is dissolved in solvent, then the solution that is formed freezes according to the following equation.

00:38 Tf of the solution is equal to tf of the solvent minus kf times m, where kf is the freezing point constant and which value depends on the solvent that is used, and m is the molality of the solution.

00:50 Now let us consider a solution that is formed using a certain mass of sucrose dissolved in 725 kilograms.

01:05 Grams or rather grams of water we don't know the mass of the sucrose in fact it's the one that we're looking for and the mass of water is given to be 725 water here stands as the solvent it was found out that the solution formed from these freezes at a temperature of negative 1 .85 degrees celsius now we wish to find the mass of the sucrose that is added so we will start by first finding the molality of the solution.

01:45 So using the formula above, we have tf solution, tf solvent minus kf times m.

01:55 We note the tf of the solution is given to be negative 1 .85.

02:05 And that of the solvent, which is water, is zero.

02:10 Since we know water freezes at zero degree celsius under normal atmospheric condition, we will be able to solve for kf, or rather, m, but of course we note that kf for water is 1 .86.

02:26 We can search this up from several sources.

02:30 So we have negative 1 .85 equals 0 minus 1 .86 times m.

02:38 And this gives us negative 1 .85 over negative 1 .86 or this is equal to 1 .1...

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