Chapter 21

Molar Mass Calculations

Colligative Properties:

Osmotic Pressure

10.4g of solute is dissolved in 164g of phenol. The freezing point of the solution is 36.3°C.

What is the molecular mass?

102 g/mol

10.4g of solute is dissolved in 164g of phenol. The freezing point of the solution is 36.3°C.

What is the molecular mass?

102 g/mol

2.53g of solute is dissolved in 63.5g of nitrobenzene. The freezing point of the solution is 3.40°C.

Calculate the molecular mass?

116 g/mol

Semi-permeable Membrane• a partition that allows solvent particles to pass

through but not solute particles

Osmosis

• Osmosis: the net movement of a solvent through a semipermeable membrane toward the solution with greater solute concentration.

Other everyday examples of osmosis:

• A cucumber placed in brine solution loses water and becomes a pickle.

• A wilting flower placed in water will perk up because water enters by osmosis.

• Eating large quantities of salty food can cause edema (swelling in the body caused by the accumulation of abnormally large amounts of fluid in the spaces between the body's cells or in the circulatory system).

Osmosis Examples

Can You Drink Too Much Water?

“Hold Your Wee for a Wii”

• SACRAMENTO, Calif. - The coroner’s office has ruled that a woman who competed in a radio station’s contest to see how much water she could drink without going to the bathroom died of water intoxication.

• Jennifer Strange, 28, was found dead Friday in her suburban Rancho Cordova home hours after taking part in the “Hold Your Wee for a Wii” contest in which KDND 107.9 promised a Nintendo Wii video game system for the winner.

• “She said to one of our supervisors that she was on her way home and her head was hurting her real bad,” said Laura Rios, one of Strange’s co-workers at Radiological Associates of Sacramento. “She was crying and that was the last that anyone had heard from her.” Initially, contestants were handed eight-ounce bottles of water to drink every 15 minutes.

• “They were small little half-pint bottles, so we thought it was going to be easy,” said fellow contestant James Ybarra of Woodland. “They told us if you don’t feel like you can do this, don’t put your health at risk.”

• Ybarra said he quit after drinking five bottles. “My bladder couldn’t handle it anymore,” he added.

• After he quit, he said, the remaining contestants, including Strange, were given even bigger bottles to drink.

• “I was talking to her and she was a nice lady,” Ybarra said. “She was telling me about her family and her three kids and how she was doing it for kids.”

Water Intoxication

• When too much water enters the body's cells, the tissues swell with the excess fluid.

• Your cells try to maintain a specific osmotic pressure, so they try to regain the electrolyte balance by allowing water outside the cells to rush into the cells via osmosis.

• Theoretically the cells could swell to the point of bursting.• From the cell's point of view, water intoxication produces the

same effects as would result from drowning in fresh water. • Electrolyte imbalance and tissue swelling can cause an

irregular heartbeat, allow fluid to enter the lungs, and may cause fluttering eyelids. Swelling puts pressure on the brain and nerves, which can cause behaviors resembling alcohol intoxication. Swelling of brain tissues can cause seizures, coma and ultimately death.

Osmotic Pressure• Osmotic Pressure (π) – the pressure required to prevent

osmosis from occurring.

Reverse Osmosis

Osmotic Pressure Osmotic Pressure ((ππ))

ππ = MRT = MRT

R valuesR valuesa

75.9g of solute (gfm = 3722 g/mol) is dissolved to make a 1.10L solution at 25°C.

What is the osmotic pressure?

45.8kPa

12.7g of C12H22O11 is dissolved to make 150mL of solution at 30°C. What is the osmotic pressure?

624kPa

Homework

• Worksheet: Molecular Mass and Osmosis