Reported by:Mr. Joey C. Ajera

MAT – Gen Sci

Objectives:

1.) to explain and understand the process of Osmosis;2.) to differentiate hypertonic, hypotonic and isotonicsolutions;3.) enumerate some important applications of Osmosis;

MENU (Topics to be discussed)

• What is Osmosis?• Osmosis vs. Diffusion• Terms used in Osmosis• Applications of Osmosis• Osmotic Pressure

What is Osmosis?

It is the spontaneous net movement of a solventlike water, across a semipermeable membrane from aless concentrated solution into a more concentratedone, thus equalizing the concentrations on each side ofthe membrane.

Both are processes that equalize the concentration oftwo solutions but both differ in their nature and process.

Diffusion involves solvent and solute particles to moveto equalize concentrations from lower to higherconcentrations. But no semi-permeable membrane is involved.It mainly occurs in gaseous state or within gas molecules andliquid molecules and usually does not need water formovement.

How does osmosis differ from diffusion?

Example of diffusion may involve the following:(a) Perfume or Air Freshener where the gas molecules diffuseinto the air spreading the aroma, and (b) diffusion of dye inwater

On the other hand, in osmosis, only solvent particlesmove. Solute particles tend not to move and the movement isthrough the semi-permeable membrane. It may require liquidsfor movement and a semi-permeable membrane.

Terms used in Osmosis

1.) Hypertonic used to refer to the solution with higherconcentration or more solute.

2.) Hypotonic used to refer to the solution with lowerconcentration or less solute.

3.) Isotonic If both solutions have equal concentrations,they are said to be isotonic.

Applications of Osmosis

So where can we usually use osmosis? How can human and other living organisms benefit from the concept of osmosis?1. It assists plants in receiving water.2. It helps in the preservation of fruit and meat.3. It is used in kidney dialysis.4. It can be reversed to remove salt and other impurities from

water.5. Osmotic generation of power.

Osmotic PressureIt is basically the pressure that would have to be applied to a puresolvent to prevent it from passing into a given solution by osmosis,often used to express the concentration of the solution. The osmoticpressure of a dilute solution is found to obey a relationship of the sameform as the ideal gas law:

where:

π = osmotic pressureM is the molar concentration of dissolved species (units of mol/L).R is the ideal gas constant (0.08206 L atm mol-1 K-1, or other values depending on the pressure units).T is the temperature on the Kelvin scale.

Problem 1:

What is the osmotic pressure of a solution

prepared by adding 13.65 g of sucrose

(C12H22O11) to enough water to make 250 mL of

solution at 25 °C?

Step 1: Find the molar concentration of sucrose

C = 12g/mol

H=1 g/mol

O = 16 g/mol

Step 2: Solve for the molecular masses

molar mass of sucrose = 12(12) + 22(1) + 11(16)

molar mass of sucrose = 144 + 22 + 176

molar mass of sucrose = 342g

nsucrose = 13.65 g x 1 mol/342 g

nsucrose = 0.04 mol

Step 3:solve for the molarity and temperature.

Msucrose = nsucrose/Volume solution

Msucrose = 0.04 mol/(250 mL x 1 L/1000 mL)

Msucrose = 0.04 mol/0.25 L

Msucrose = 0.16 mol/L

T = °C + 273

T = 25 + 273

T = 298 K

Step 4: - Find osmotic pressure

Π = MRT

Π = 0.16 mol/L x 0.08206 L·atm/mol·K x 298 K

Π = 3.9 atm

Answer:

The osmotic pressure of the sucrose solution is

3.9 atm.

Problem 2A salt solution having an osmotic pressure of 5.6 atm was

prepared by adding 10 g of sodium chloride (NaCl) in a

200mL solution. Find the temperature of the solution.

Step 1: Solve for the molar concentration.

Na = 23 g/mol

Cl = 35 g/mol

Step 2: Solve for the molecular masses

molar mass of salt = 1(23) + 1(35)

molar mass of salt = 23 + 35 = 58

molar mass of salt = 58 g

nsalt= 10 g x 1 mol/58 g

nsalt = 0.172 mol

Step 3:Solve for the molarity

Msalt = nsalt/Volume solution

Msalt = 0.172 mol/(200 mL x 1 L/1000 mL)

Msalt = 0.172 mol/0.2 L

Msalt = 0.86 mol/L

Step 4: - Solving for the temperature

Π = MRT

T = Π / MR

T = 5.6 atm / (0.86 mol/L)(0.08206 L·atm/mol·K)

T = 79.35 K

Answer: The temperature of the salt solution is 79.35 K.

TRY IT YOURSELF:1.) Calculate the concentration of non-electrolyte

solutes in the human body if the osmotic pressure of

human blood is 7.53 atm at body temperature 37°C.

Solution:

Π = MRT

M = Π/RT

T = 37 °C + 273 = 310 K

M = 7.53 atm / (0.08206 L·atm/mol·K)(310 K)

M= 7.53 / 25.439 L/mol

M= 0.296 mol / L

TRY IT YOURSELF:2.) Sea water contains dissolved salts at a total ionic

concentration of about 1.13 mol/L at 25°C. What

pressure must be applied to prevent osmotic flow of pure

water into sea water through a membrane permeable

only to water molecules?

Solution:

Π = MRT

T = 25 °C + 273 = 298 K

Π = (1.13 mol/L)(0.08206 L·atm/mol·K)(298K)

Π = 27.63 atm

bn bnnn bb b bv cnm vc