Investigating Solutions
Jan 29, 2016
Investigating Solutions
Components of a Solution
Homogeneous mixture at least 2 substances proportions of the substances are not fixed
(variable composition) one phase
2 componentsa) Solvent - the substance that does the dissolving
- present in the largest amountb) Solute - the substance that dissolves in the solvent (can be solid, liquid, gas)
SOLUTION = SOLVENT + SOLUTE
Types of SolutionsState of solute Solvent Examples
Gas Gas Air
Gas Liquid Carbonated drinks
Liquid Liquid Alcohol in water
Solid Liquid Salt Water
Solid Solid Alloys (copper-nickel alloy)
Concentrated solution vs Dilute solution
Concentrated• Higher
percentage of solute
• Dissolved ions are close together
Dilute• Low percentage
of solute• Ions are farther
apart
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Solubility• maximum amount of that substance
which will dissolve in a fixed quantity of the solvent at a specified temperature
• Example: mass of solute that dissolves in 1 kg of solvent at a given temp.
Factors That Affect Rate of dissolving
1. For most solids, the rate of dissolving is greater at higher temperatures.
2. Agitating a mixture by stirring or by shaking the container increases the rate of dissolving
3. Decreasing the size of particles increases the rate of dissolving
More Factors
Solubility and attraction - When forces of attraction between different particles are stronger than the forces of attraction between like particles in the mixture, a solution forms.
Polar and Non-polar substances
1. Polar substances dissolve in polar solvents (sugar in water)
2. Non-polar compounds dissolve in non-polar solvents (iodine in benzene)
Solubility and Intermolecular Forces
Dipole-Dipole Attractions
• Attraction between charges on two different polar molecules
• Weak forces of attraction
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Ion-dipole attractions• Attractive forces between
an ion and a polar molecule• Negative ends of water
attract cation (+ve)• Positive end of water
attracts the anion (-ve) Generally an ionic
compound will dissolve in a polar solvent
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Solubility of Covalent Compounds
• Covalent compounds do not have negative and positive charges to attract water molecules
• Generally they are not soluble in water
Predicting solubility
In general1. Ionic solutes and polar covalent
solutes both dissolve in polar solvents.
2. Non-polar solutes dissolve in non-polar solvents.
Factors that Affect Solubility
1. Small molecules are often more soluble that larger molecules
2. Temperature and solubility– Solubility of most solids increases
with temperature– Solubility of most liquids is not
greatly affected by temperature– Solubility of gases decreases with
higher temperature
3. Pressure and solubility– changes in pressure have hardly
any effect on solid and liquid solutions
– Solubility of the gas is directly proportional to the pressure of the gas above the liquid
Solubility Curves
• solubility of a solute changes with temperature
• solubility of each compound is different at different temperatures
• solubility of each compound changes in a different way as temperature changes
UNSATURATED, SATURATED AND SUPERSATURATED SOLUTIONS
1. UNSATURATED SOLUTION• more solute can be dissolved while the temperature remains
constant• *any point in the region under the solute’s solubility curve2. SATURATED SOLUTION• no more solute can be dissolved into the solution at a fixed • temperature• * any point ON the solubility curve3. SUPERSATURATED SOLUTION• solution containing more dissolved solute than normal at a
particular temperature• unstable• may suddenly form solid crystals leaving only a saturated
solution behind• * any point ABOVE the solubility curve
Solubility curve for KClO3
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90Temperature (*C)
10 g
/ 10
0 g
Calculations using solubility curvesCalculations using solubility curvesUsing The Graph On the Previous Slide1. Is the solution saturated, unsaturated or supersaturated if there are
20g of KClO3 at 30°C
2. Is the solution saturated, unsaturated or supersaturated if there are 5g of KClO3 at 50°C
3. Is the solution saturated, unsaturated or supersaturated if there are 20g of KClO3 at 50°C
4. 100 g H2O is saturated with KClO3 at 100°C. How much KClO3
will come out of solution if the temperature is decreased to 48°C?
57 g-18 g = 39 g
Saturated
Unsaturated
Supersaturated