Colligative nature
1.
Colligative nature
Colligative
nature is the physical properties of a solution that depends only on the
concentration of solute particles, but not on the type. The electrolyte
solution has a greater colligative property than the non-electrolyte solution
having the same concentration because the electrolyte solution has a larger
number of solute particles.
A.
Kemolalan (m)
The
molecularity or molality indicates the number of moles (n) of solute in 1 kg (=
1,000 g) solvent. Therefore, the kemolalan is expressed in mol kg-1.
M
= n / p
M
= concentration of solution
N
= number of moles of solute
P
= mass of solvent (in kg)
Example:
What
is the solubility of the solution made by mixing 3 grams of urea with 200 grams
of water?
Answer:
a solution of 3 grams of urea in 200 grams of water.
Mol
urea = 3/60 g mol-1 = 0.05 mol
The
solvent mass = 200 grams = 0.2 kg
M
= n / p = 0.05 mol = 0.25 mol kg-1
0.2
kg
B.
Mole fraction (X)
The
mole fraction (x) represents the ratio of the number of moles of solute or
solvent to the number of moles of the solution. If the number of moles of
solvent is nA, and the number of moles of solute is nB, then the mole fraction
of the solvent and solute is:
The amount of solvent mole fraction with solute is 1
XA + XB = 1
Example:
Calculate the mole fraction of urea in a 20% urea solution (Mr. urea = 60)
Answer:
In 100 grams of 20% urea solution there are 20 grams and 80 grams of water.
Water mol = 80 g / 18 g mol-1 = 4.44 mol
Mol urea = 20 g / 60 g mol-1 = 0.33 mol
X urea = XB = 0.33 mol / (4.44 + 0.33) mol = 0.069
C. Solvent Pressure
The vapor pressure of a substance is the pressure generated by the saturated vapor of the substance. The higher the temperature, the greater the vapor pressure. If the solute does not evaporate then the vapor pressure of the solution becomes lower than the vapor pressure of the solvent. The difference between purified solvent vapor (P0) and the vapor pressure of the solution (P) is called the decrease in the vapor pressure of the solution (ΔP).
D. Raise the Boiling Point
The solution has a higher boiling point and a freezing point lower than the solvent. The difference between the boiling point of the solution and the boiling point of the solvent is called the boiling point increase (ΔTb). Formula: ΔTb = Kb x m
Where: m = molality of solution
Kb = the increase in boiling point
E. Decrease of Freezing Point
Increase the boiling point and decrease of freezing point is proportional to the solubility of the solution: ΔTb = m x Kb and ΔTf = m x Kf. The difference between the freezing point of the solvent and the freezing point of the solution is called the freezing point drop (ΔTf). The boiling point increase and the decrease in freezing point of the solution can be explained by the phase diagram
F. Osmotic Pressure
• Osmosis is solvent molecular seepage from solvent into solution, or from a dilute solution to a more concentrated solution, via a semipermiable membrane.
• The osmotic pressure is the pressure that must be applied to the surface of the solution to prevent osmosis from pure solvent.
• Formula: л = M. R .T
• Solutions having the same osmotic pressure are called isotonic
Why Po it more bigger from P in solvent pressure
BalasHapusIn a solution, the solute particles block the solvent molecular motion from changing the liquid form to the vapor form so that the saturated vapor pressure of the solution is lower than the saturated vapor pressure of the pure solution.
HapusWhat distinguishes molality from molarity?
BalasHapusMolarity expresses the number of moles of solute in every one liter of solution. Molarity is denoted by the M notation and the unit is mol / liters The molality or molal concentration (m) denotes the number of moles of solute in 1000 grams of solvent
HapusCan you explain about how the solution can be called isotonic?
BalasHapusIsotonic = a solution having the same solute concentration as the other (non-moving) solution
HapusThe osmotic pressure of a 0.01 M KI solution at 25 ° C is 0.465 atm. Calculate van't Hoff factor for KI at this concentration.?
BalasHapusTekanan osmotik larutan KI 0,01 M pada suhu 25 ° C adalah 0,465 atm. Hitung van't Hoff
HapusPhi = n RT
0,465 = 0,01 × 0,082 × 298xi
I = 1,90
I = 1 + alfa (n-1)
1,90 = 1 + alfa (2-1)
0,90 = alfa
Alfa = 0,90 / 90%