13.3.4 Osmosis

Question 1

Osmosis

Answer 1

• Osmotic pressure is related to concentration by = M·R·T.
• The osmotic pressure at the membrane is equal to density times gravity times height (d·g·h), thus
= M·R·T = d·g·h.
• Osmotic pressure is the most sensitive colligative property.
• The osmotic pressure generated by the sugar solution in a maple tree is able to raise sap to a height of about 25 meters

Question 2

note

Answer 2

• Osmotic pressure is related to concentration by = M · R · T.
• A semi permeable membrane allows passage of some molecules but not others. In this case the solvent is able to cross the membrane, but the solute is not. In the illustration, the solvent will try to move across the semipermeable membrane until the concentration of solute is equal on both sides. The osmotic pressure (P) can be measured if the solution is held in a rigid container as in the illustration.
• The osmotic pressure is related to the product of the
  concentration of the solution (M), the temperature of the solution in kelvins (T) and the gas constant (R).
• A more convenient way to measure osmotic pressure in the lab is by measuring the height of a column of solution as illustrated.
• The osmotic pressure at the membrane is equal to d·g·h (density times gravity times height), thus = MRT = dgh.
• Osmotic pressure is the most sensitive colligative property.
• The example illustrates the ease of measuring osmotic pressure (as the height of the solution) compared to the measures for the other colligative properties of the solution.

Question 3

note 2

Answer 3

• An application of the osmotic pressure relations allows the determination of the height to which a maple tree is able to raise sap.
• The concentration of the sap solution is used to calculate the osmotic pressure ( ). Using the osmotic pressure and the density of the sap (converting atmospheres to pascals) allows the calculation of the height of the column of sap.
• The osmotic pressure generated by the sugar solution in a maple tree is able to raise sap to a height of about 25 meters.

Question 4

Osmosis is the process where ____ are able to pass through a semipermeable membrane, but ___ are blocked.

Answer 4

• solvent particles, solute particles
• small molecules, hydrated ions
• solvent molecules, large molecules

Question 5

How does increasing the temperature of a solution change the osmotic pressure?

Answer 5

The osmotic pressure will increase

Question 6

Sucrose (C12H22O11 ) was added to water in a volumetric flask. After the sucrose had dissolved, water was added to make the solution 1.0 L. The resulting solution had an osmotic pressure of 15 atm at 22°C. How many grams of sucrose were added?

Answer 6

212 g

Question 7

Two solutions are prepared. In Solution A, 5.0 g of a substance of molecular weight 50 is dissolved in 100 mL of pure water. In Solution B, 5.0 g of a substance with molecular weight of 75 is dissolved in 100 mL of pure water. The solute is non volatile and non ionic. Which solution will have the higher osmotic pressure?

Answer 7

Solution A

Question 8

Which of the following does not create osmotic pressure?

Answer 8

The system is trying to minimize the disorder of the system.

Question 9

A tree has a height of 25 m. What concentration of sugars in the tree’s sap will provide sufficient osmotic pressure to raise the sap to the top of the tree? Assume the sap has a density of 1.0 g / mL, the water around the roots is pure water, and the temperature is 25°C.

Answer 9

0.099 mol / L

Question 10

1.0 g of bovine insulin (a protein) is dissolved in 1.0 L of water. The solution is measured to have an osmotic pressure of 3.1 mm Hg at 25°C. What is the molecular weight of bovine insulin?

Answer 10

6.0 × 10^3 g / mol

Question 11

If the same solute is dissolved in two different solvents to the same concentration and the same temperature, the osmotic pressure ____

Answer 11

will be the same for both

Question 12

Suppose you needed to determine the molecular weight of an unknown substance. The substance will dissolve in water. Which colligative property would be the best one to use to make this determination?

Answer 12

Osmotic pressure

Question 13

How will increasing the concentration of the solute change the osmotic pressure of the solution?

Answer 13

The addition of a solute will increase osmotic pressure.