solvent is the liquid in which the solute is dissolved
an aqueous solution has water as solvent
A saturated solution is one where the concentration is at a maximum - no more solute is able to dissolve.
A saturated solution represents an equilibrium: the rate of dissolving is equal to the rate of crystallization. The salt continues to dissolve, but crystallizes at the same rate so that there “appears” to be nothing happening.
If 0.435 g of KMnO 4 is dissolved in enough water to give 250. mL of solution, what is the molarity of KMnO 4 ?
Now that the number of moles of substance is known, this can be combined with the volume of solution — which must be in liters — to give the molarity. Because 250. mL is equivalent to 0.250 L . As is almost always the case, the first step is to convert the mass of material to moles. 0.435 g KMnO 4 • 1 mol KMnO 4 = 0.00275 mol KMnO 4 158.0 g KMnO 4 Molarity KMnO 4 = 0.00275 mol KMnO 4 = 0.0110 M 0.250 L solution
When a solution is diluted, solvent is added to lower its concentration.
The amount of solute remains constant before and after the dilution:
moles BEFORE = moles AFTER
C 1 V 1 = C 2 V 2
Dilution A bottle of 0.500 M standard sucrose stock solution is in the lab. Give precise instructions to your assistant on how to use the stock solution to prepare 250.0 mL of a 0.348 M sucrose solution. Suppose you have 0.500 M sucrose stock solution. How do you prepare 250 mL of 0.348 M sucrose solution ? Concentration 0.500 M Sucrose 250 mL of 0.348 M sucrose
Factors Affecting Solubility 1. Nature of Solute / Solvent . - Like dissolves like (IMF) 2. Temperature - i) Solids/Liquids- Solubility increases with Temperature Increase K.E. increases motion and collision between solute / solvent. ii) gas - Solubility decreases with Temperature Increase K.E. result in gas escaping to atmosphere. 3. Pressure Factor - i) Solids/Liquids - Very little effect Solids and Liquids are already close together, extra pressure will not increase solubility. ii) gas - Solubility increases with Pressure. Increase pressure squeezes gas solute into solvent.
Solubilities of several ionic solid as a function of temperature. MOST salts have greater solubility in hot water.
A few salts have negative heat of solution, (exothermic process) and they become less soluble with increasing temperature.
Temperature & the Solubility of Gases The solubility of gases DECREASES at higher temperatures
Henry’s Law The effect of partial pressure on solubility of gases
At pressure of few atmosphere or less, solubility of gas solute follows Henry Law which states that the amount of solute gas dissolved in solution is directly proportional to the amount of pressure above the solution.
Use the concept of vapor pressure lowering to explain this phenomenon.
Raoult’s Law Describes vapor pressure lowering mathematically.
The lowering of the vapour pressure when a non-volatile solute is dissolved in a volatile solvent (A) can be described by Raoult’s Law:
P A = A P° A
P A = vapour pressure of solvent A above the solution
c A = mole fraction of the solvent A in the solution
P° A = vapour pressure of pure solvent A
only the solvent (A) contributes to the vapour pressure of the solution
What is the vapor pressure of water above a sucrose (MW=342.3 g/mol) solution prepared by dissolving 158.0 g of sucrose in 641.6 g of water at 25 ºC? The vapor pressure of pure water at 25 ºC is 23.76 mmHg . mol sucrose = (158.0 g)/(342.3 g/mol) = 0.462 mol mol water = (641.6 g)/(18 g/mol) = 35.6 mol P sol’n = X water P water = (0.987)(23.76 mm Hg) = 23.5 mm Hg
Mixtures of Volatile Liquids Both liquids evaporate & contribute to the vapor pressure
Some Boiling Point Elevation and Freezing Point Depression Constants Normal bp (°C) K b Normal fp (°C) K f Solvent pure solvent (°C/m) pure solvent (°C/m) Water 100.00 +0.5121 0.0 1.86 Benzene 80.10 +2.53 5.50 4.90 Camphor 207 +5.611 179.75 39.7 Chloroform 61.70 +3.63 - 63.5 4.70 (CH 3 Cl)
FP is depressed when solute inhibits solvent from crystallizing.
When solution freezes the solid form is almost always pure. Solute particles does not fit into the crystal lattice of the solvent because of the differences in size. The solute essentially remains in solution and blocks other solvent from fitting into the crystal lattice during the freezing process.
Phase Diagram and the lowering of the freezing point.
T f = i ·m ·k f Where, T f = FP depression i = van’t Hoff Factor m = molality , k f = FP Constant Generally freezing point depression is used to determine the molar mass of an unknown substance . Derive an equation to find molar mass from the equation above.
Osmosis is the spontaneous movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration
Osmotic Pressure - The Pressure that must be applied to stop osmosis
= i CRT where P = osmotic pressure i = van’t Hoff factor C = molarity R = ideal gas constant T = Kelvin temperature
Osmosis and Blood Cells (a) A cell placed in an isotonic solution. The net movement of water in and out of the cell is zero because the concentration of solutes inside and outside the cell is the same. (b) In a hypertonic solution, the concentration of solutes outside the cell is greater than that inside. There is a net flow of water out of the cell, causing the cell to dehydrate, shrink, and perhaps die. (c) In a hypotonic solution, the concentration of solutes outside of the cell is less than that inside. There is a net flow of water into the cell, causing the cell to swell and perhaps to burst.