Colligative property, examples

Before doing this, however, it is informative to compare the sensitivity of the four colligative properties in the determination of molecular weight. In the following example this is done by making the appropriate numerical calculations. 

Vapor pressure lowering is a true colligative property that is, it is independent of the nature of the solute but directly proportional to its concentration. For example, the vapor pressure of water above a 0.10 M solution of either glucose or sucrose at 0°C is the same, about 0.008 mm Hg less than that of pure water. In 0.30 M solution, the vapor pressure lowering is almost exactly three times as great, 0.025 mm Hg. 

Colligative properties, particularly freezing point depression, can be used to determine molar masses of a wide variety of nonelectrolytes. The approach used is illustrated in Example 10.9. 

Molar masses can also be determined using other colligative properties. Osmotic pressure measurements are often used, particularly for solutes of high molar mass, where the concentration is likely to be quite low. The advantage of using osmotic pressure is that the effect is relatively large. Consider, for example, a 0.0010 M aqueous solution, for which... 

Freezing point lowering (or other colligative properties) can be used to determine the extent of dissociation of a weak electrolyte in water. The procedure followed is illustrated in Example 10.11. 

Colligative properties can be sources of insight into not only the properties of solutions, but also the properties of the solute. For example, acetic acid, CH.COOH, behaves differently in two different solvents, (a) The freezing point of a 5.00% by mass aqueous acetic acid solution is — l.72°C. What is the molar mass of the solute Explain any discrepancy between the experimental and the expected molar mass, (b) The freezing-point depression associated with a 5.00% by mass solution of acetic acid in benzene is 2.32°C. Whar is the experimental molar mass of the solute in benzene What can you conclude about the nature of acetic acid in benzene ... 

C12-0027. Define and give an example of each of the following (a) alloy (b) amalgam (c) aerosol (d) colligative property and (e) surfactant. 

The depression of the freezing point of a solvent due to the presence of a dissolved solute is an example of a colligative property, that is, a property of a dilute solution that depends on the number of dissolved particles and not on the identity of the particles. Water has a freezing point depression constant, Kf, of 1.86 K kg mol-1. In other words, for every mole of nonvolatile solute dissolved in a kilogram of water, the freezing point of water is lowered by 1.86°C. The change in freezing point, A T, can be calculated from the equation... 

The depression of a melting point is one of the simplest manifestations of a colligative property. Other everyday examples include pressure, osmotic pressure, vapour pressure and elevation of boiling point. 

Let s examine a few examples of how to approach colligative property problems. We will begin with a Raoult s law example. 

In the next example, we will examine the colligative property of osmotic pressure. This will require us to use the relationship 1r = i(nRT/V). 

When the activity of the solvent is determined from a colligative property, then g can be calculated with Equation (19.44). If we use osmotic pressure as an example, we can combine Equation (15.33) and Equation (16.1) to obtain the expression... 

Anyone who has ever made ice cream knows that the addition of rock salt to ice causes it to melt and produce a liquid-ice solution below 0°C. This is just one example of how the physical properties of a solution differ from those of a pure solvent. Properties that depend on the amount of solute present in a solution are termed colligative properties. Colligative means collective properties. These properties are termed colligative, because the properties depend on the collective number of particles present in solution rather than the types of particles. The major colligative properties and how they affect solutions compared to their pure solvents are summarized in Table 11.4. 

Cohesion intermolecular attractive force between particles within a substance Colligative Property a property dependent on the number of particles in solution and not on the type of particles, for example, boiling point elevation and freezing point depression... 

This procedure and the / V I Hall-Heroult process discussed below are examples of commercial uses of a colligative property (freezing point depression) to enable electrolytic reactions to be carried out more economically. 

The up to now most frequently used techniques as, for example, vapour pressure osmometry (VPO) or freezing point depression (with its limitation regarding the solvent dependent measuring temperature) are based upon the colligative properties of the system the classical absolute light-scattering and ultracentrifugation techniques are only occasionally and approximately applicable with respect to the determination of CMC values. Evaluation of critical micelle concentrations which are based on these latter methods suffer considerably from the insensitivity of these techniques if measurements below the CMC, i.e., below about 10-3 mol dm-3, are carried out. More sensitive methods will be discussed below. 

Of all of the colligative properties, osmotic pressure shows the most dramatic effect. For example, a 1.0 M solution of glucose exerts an osmotic pressure of 24.5 atm at 25°C. A pressure of 24.5 atm is equivalent to 360 psi ... 

Certain properties of solutions depend only on the number of solute particles dissolved in a given amount of solvent and not on the nature of these particles. Such properties are called colligative properties. For example, one such property is the freezing point depression. One mole of any solute dissolved in 1000 g of water lowers the freezing point of the water by 1.86°C. We call this value, 1.86 degree/mole/1000 g water, the freezing point depression constant of water, Kf. Each solvent has a characteristic freezing point depression constant that is related to its heat of fusion. The nature of the solute does not matter. 

The lowering of the vapour pressure of a pure liquid A by the addition of B (as above) is one example of a colligative property (defined in Frame 51) where such properties are further discussed and include ... 

Various salts can cause freezing point depressions. These depressions are the results of the ions colligative properties within solution. A significant freezing point depression is created not by any particular type of material, but rather by the number of particles you have in solution. The effects can be enhanced by achieving a supersaturation of material. For example, if you mix ice with a salt such as NaCl, you will end up with two particles within solution (Na+ + Cl ) (the temperature of ice water supersaturated with sodium chloride (23% by weight) is -20.67°C). If you place a salt such as CaCl2- H20 into ice, you will end up with three particles within the solution (Ca+ + 20 ) [the temperature of ice water... 

Real colligative properties are only found in ideal gases and ideal solutions. Examples are osmotic pressure, vapour pressure reduction, boiling-point elevation, freezing-point depression, in other words the osmotic properties. 

Tfp) the freezing point of a solution is always lower than the freezing point of the pure solvent. The freezing point depression is roughly proportional to the molality of solute particles in the solution. Freezing point depression is an example of a colligative property of a solution. 

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