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Understanding Colligative Properties
Understanding behind why we have to add salt in ice cream and why does pure water boils faster than saltwater gives an overview to every learner of what colligative properties is all about. For the information of everybody, colligative properties are properties of a solution that depend only on the number and not on the identity of the solute particles. The colligative properties are very useful for characterizing the nature of a solute after it is dissolved in a solvent and for determining the molar masses of substances. For you to understand more, click this link to redirect you to how does molality affects colligative properties.
Boiling-point elevation
Boiling - point elevation on the other hand describes the phenomenon that the boiling point of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent. This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water. To get the boiling point elevation of the solution,
Freezing point depression
Lastly, we also have a freezing point depression. This is defined as the decrease of the freezing point of a solvent on the addition of a non-volatile solute. Examples include salt in water, alcohol in water, or the mixing of two solids such as impurities into a finely powdered drug. Freezing Point Depression has a formula of Where m is the molality Kf is the molal freezing –point-depression constant usually given in the problem. It has a unit of °C/m ΔTf is the change in the temperature in freezing. It has a unit of °C The freezing point of a solution is the temperature at which the first crystals of pure solvent begin to form in equilibrium with the solution. To get the freezing point of the solution, Sample Problem Freezing Point Depression What is the freezing point of a solution prepared by adding 140 g trichothecin (C 19 H 24 O 5 ) to 0.746 kg of benzene? The freezing point of pure benzene is 5.5 °C. The freezing point constant for benzene is 5.12 °C/m. Solution: First, we have to understand the freezing point depression formula. The solvent in the problem is benzene. We have to get ΔTf in order for us to determine the freezing point of the solution. Looking back at the formula,
Vapor Pressure Lowering
Vapor Pressure Lowering Vapor pressure or equilibrium vapor pressure is defined as the pressure exerted by a vapor. The vapor pressure of a liquid is determined by how easily its molecules can escape the surface of the liquid and enter the gaseous phase. The vapor pressure of the solution is lowered because the solute particles at the liquid/vapor boundary block the solvent particle from jumping into the vapor state. NOTE: As the atmospheric pressure equals to vapor pressure, normal boiling happens. The lower the vapor pressure, the higher the boiling point. Increasing the vapor pressure lowers the boiling point Link: https://www.youtube.com/watch?v=aiwynTBdln8&feature=emb_rel_pause
Osmosis & Osmotic Pressure
Osmosis - The movement of solvent molecules through a semipermeable membrane from a region of low solute concentration to a region of high solute concentration. Osmotic pressure can be defined as the minimum pressure that must be applied to a solution to stop the flow of solvent molecules through a semipermeable membrane (osmosis). It is a colligative property (Links to an external site.) and is dependent on the concentration of solute particles in the solution.
The chambers are filled to equal heights, one side with pure water and the other with the solution of interest. As water molecules cross the membrane, the liquid level rises on the right. As the height differential increases, the column of liquid on the right pushes back against the membrane. When the push of water molecules on the membrane due to water’s higher concentration on the left is exactly balanced by the push of gravity from the higher column of liquid on the right, equilibrium is reached. Thus the height of the column of liquid on the right indicates the osmotic pressure of the solution. Counter pressure exerted on the side with more solute molecules will reduce or halt the net movement of water through the semi- permeable membrane. Even higher pressure can be exerted to force solvent from the side with more solute to the side with less solute, a process called reverse osmosis. Note: For reverse osmosis, from a region of high solute concentration to a region of low solute concentration. To understand more, please click the link below. Link: https://www.youtube.com/watch?v=gcrmhtarYmk
