Glucose solutions of about 0. The concentration of an isotonic sodium chloride NaCl solution is only half that of an isotonic glucose C 6 H 12 O 6 solution because NaCl produces two ions when a formula unit dissolves, while molecular C 6 H 12 O 6 produces only one particle when a formula unit dissolves.
The osmolarities are therefore the same even though the concentrations of the two solutions are different. Osmotic pressure explains why you should not drink seawater if you are abandoned in a life raft in the middle of the ocean. Its osmolarity is about three times higher than most bodily fluids. You would actually become thirstier as water from your cells was drawn out to dilute the salty ocean water you ingested.
Our bodies do a better job coping with hypotonic solutions than with hypertonic ones. The excess water is collected by our kidneys and excreted. Osmotic pressure effects are used in the food industry to make pickles from cucumbers and other vegetables and in brining meat to make corned beef.
It is also a factor in the mechanism of getting water from the roots to the tops of trees! The use of perfusionists has grown rapidly since the advent of open-heart surgery in Most perfusionists work in operating rooms, where their main responsibility is to operate heart-lung machines.
During many heart surgeries, the heart itself must be stopped. In these situations, a heart-lung machine keeps the patient alive by aerating the blood with oxygen and removing carbon dioxide. The perfusionist monitors both the machine and the status of the blood, notifying the surgeon and the anesthetist of any concerns and taking corrective action if the status of the blood becomes abnormal.
Despite the narrow parameters of their specialty, perfusionists must be highly trained. Certified perfusion education programs require a student to learn anatomy, physiology, pathology, chemistry, pharmacology, math, and physics.
A college degree is usually required. Some perfusionists work with other external artificial organs, such as hemodialysis machines and artificial livers. Explain how the following properties of solutions differ from those of the pure solvent: vapor pressure, boiling point, freezing point, and osmotic pressure.
Colligative properties are characteristics that a solution has that depend on the number, not the identity, of solute particles. In solutions, the vapor pressure is lower, the boiling point is higher, the freezing point is lower, and the osmotic pressure is higher.
Estimate the boiling point of each aqueous solution. The boiling point of pure water is Estimate the freezing point of each aqueous solution. The freezing point of pure water is 0. Explain why salt NaCl is spread on roads and sidewalks to inhibit ice formation in cold weather. Salt NaCl and calcium chloride CaCl 2 are used widely in some areas to minimize the formation of ice on sidewalks and roads. One of these ionic compounds is better, mole for mole, at inhibiting ice formation.
Which is that likely to be? What can you conclude about the salt? Determine the osmolarity of each solution and the direction of solvent flow, if any, across the membrane. NaCl lowers the freezing point of water, so it needs to be colder for the water to freeze. There will be no net difference in the solvent flow. Learning Objectives To describe how the properties of solutions differ from those of pure solvents. Colligative Properties Solutes affect some properties of solutions that depend only on the concentration of the dissolved particles.
Vapor Pressure Depression All liquids evaporate. The presence of solute particles blocks some of the ability for liquid particles to evaporate.
Thus, solutions of solid solutes typically have a lower vapor pressure than the pure solvent. Boiling Point and Freezing Point Effects A related property of solutions is that their boiling points are higher than the boiling point of the pure solvent.
Solution Colligative properties depend on the number of dissolved particles, so the solution with the greater number of particles in solution will show the greatest deviation.
Boiling point elevation can be explained in terms of vapor pressure. Vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature.
A liquid boils when its vapor pressure is equal to the air pressure. This happens because of the displacement of solvent molecules by the solute. This means that some of the of solvent molecules at the surface of the liquid are replaced by the solute; it can occur in both electrolytic and non-electrolytic solutions.
The lower number of solvent molecules at the surface means that fewer will evaporate, and thus the vapor pressure is lowered. For the vapor pressure to equal the atmospheric pressure, a higher temperature is required, and a higher boiling point is observed. The extent of the boiling point elevation can be calculated. It is directly proportional to the molal concentration of the solution.
The amount the boiling point is elevated is determined using the equation:. The pressure on the surface is holding them in. Once you reach the boiling point temperature, the vapor pressure is then equal to the external pressure and the molecules can escape. Note that you really have to exceed the boiling point temperature to fully evaporate the liquid. Now back to colligative properties Well, we now understand that solute molecules taking up positions at the surface of the liquid will depress the vapor pressure.
We also know that we have to raise the vapor pressure of the liquid in order to reach the boiling point so this must mean we will have to input more energy to reach the same vapor pressure. Input of more energy equates to the input of heat in this type of system, so the boiling point temperature must be higher to obtain the same vapor pressure. Adding a non-volatile solute to a solution therefore raises the boiling point of that solution.
When a solute is dissolved in a solvent, the boiling point of the solution is raised according to the equation:. Want to practice some calculations using this equation? Click here.
Let's start this discussion the same way we started the others, by defining the normal freezing point. The normal freezing point of a liquid is is the temperature at which a liquid becomes a solid at 1 atm. A more specific definition of freezing point is the temperature at which solid and liquid phases coexist in equilibrium.
Let's see if we can figure out why the freezing point is lowered when we add solutes to a solution. We already know that in order to freeze a liquid, we have to lower the temperature. As the temperature lowers, the solution becomes more ordered as it moves toward the solid phase. This is an effect that works against the second law of thermodynamics.
In short, entropy disorder likes to increase not decrease in the natural scheme of things. So if we have to lower the temperature to a certain point to freeze a pure solvent, when we add a solute we add to the entropy of the system, right?
0コメント