solutions. 12.1 a solution is a homogenous mixture of 2 or more substances the solute is(are) the...
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Solutions
12.1
A solution is a homogenous mixture of 2 or more substances
The solute is(are) the substance(s) present in the smaller amount(s)
The solvent is the substance present in the larger amount
Solutions
Solvent: greater quantity (water)
Solute: smaller quantity (sugar)
Immiscible: two liquids do not mix
miscible: two liquids can mix alcohol in water (in any quantities)
Parts of a Solution
Solute Solvent Example
solid solid
solid liquid
gas solid
liquid liquid
gas liquid
gas gas
A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.
An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.
A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.
Sodium acetate crystals rapidly form when a seed crystal isadded to a supersaturated solution of sodium acetate.
12.1
12.2
Three types of interactions in the solution process:• solvent-solvent interaction• solute-solute interaction• solvent-solute interaction
Hsoln = H1 + H2 + H3
“like dissolves like”
Two substances with similar intermolecular forces are likely to be soluble in each other.
• non-polar molecules are soluble in non-polar solvents
CCl4 in C6H6
• polar molecules are soluble in polar solvents
C2H5OH in H2O
• ionic compounds are more soluble in polar solvents
NaCl in H2O or NH3 (l)
12.2
Concentration Units
M =moles of solute
liters of solution
Molarity (M)
Molality (m)
m =moles of solute
mass of solvent (kg)
12.3
Temperature and Solubility
Solid solubility and temperature
solubility increases with increasing temperature
solubility decreases with increasing temperature
12.4
Temperature and Solubility
Gas solubility and temperature
solubility usually decreases with
increasing temperature
12.4
Pressure and Solutions
P Solubility (gas in liquid)Henry’s law
Pressure and Solubility of Gases
12.5
The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law).
c = kP
c is the concentration (M) of the dissolved gas
P is the pressure of the gas over the solution
k is a constant (mol/L•atm) that depends onlyon temperature
low P
low c
high P
high c
Calculating the solubilityIf we want to make an accurate prediction about whether something will dissolve in water or not, we need to know four key factors:
•1 the type of solute 3 the volume of solvent
•2 the mass of solute 4 the temperature
•We can say, for example, that the solubility of salt in water at 20 °C is 35 grams per 100 cm3 of water.
•This means that at 20 °C you can completely dissolve 35g of salt in 100cm3 of water.
•In general: Solubility = mass of solute / volume of solvent
How Much Will Dissolve?
• The table shows how much potassium nitrate (a type of fertiliser) and potassium chloride (the main ingredient in ‘Lo-Salt’) dissolve in water at different temperatures. The numbers tell you how many grams of solute dissolve in 100 cm3 water.
Temperature (°C) Solubility of potassium nitrate
Solubility of potassium chloride
10 20 32
20 30 35
30 44 36
40 60 38
50 78 40
60 100 42
Graph showing the solubility of potassium nitrate and potassium chloride.
0
15
30
45
60
75
90
105
10 20 30 40 50 60
Temperature C
So
lub
ility
PotassiumNitrate
PotassiumChloride
Questions1. How does the solubility of the substances change as the
temperature changes?
2. Which substance is the most soluble at 10°C?
3. Which substance is the most soluble at 40°C?
4. Copy and complete this sentence: ‘As the temperature rises, the solubility …’
5. Which of the two solids dissolves best a at 10 °C b at 40 °C?
6. Use your graph to estimate the solubility of potassium chloride at 55 °C
A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance.
Colloid versus solution
• collodial particles are much larger than solute molecules
• collodial suspension is not as homogeneous as a solution
12.8
Suspensions
• These are mixed, but not dissolved in each other
• Will settle over time
• Particles are small
Mayo