Solutions www.brainybetty.com
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• Solution – a homogeneous mixture
• Solute – substance being dissolved
• Solvent – the component present in the greatest amount
• Aqueous Solution – Solution which has water for the solvent www.brainybetty.com
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Solute
(Salt)
Solvent
(Water) www.brainybetty.com
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• Listed as solute-solvent [Page 238]
– Gas/Gas: Air
– Gas/Liquid: Carbonated drinks
– Gas/Solid: Hydrogen in platinum
– Liquid/Gas: Water vapor in air
– Liquid/Liquid: Alcohol in water
– Liquid/Solid: Mercury in Silver
– Solid/Gas: Mothballs in the air
– Solid/Liquid: Sugar in water
– Solid/Solid: Alloys www.brainybetty.com
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• Concentrated Solution – higher proportion of solute to solvent than a dilute solution
• Diluted Solution – has a lower proportion of solute to solvent than a concentrated solution www.brainybetty.com
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• Solvation – the process of dissolving
( the process in which an ion or molecule is surrounded by solvent molecules arranged in a specific manner )
1. Solvent-solvent interactions
2. Solute-solute interactions
3. Solvent-solute interactions
NOT A CHEMICAL REACTION!!!
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• Consider NaCl (solute) dissolving in water (solvent).
• Water molecules orient themselves on the
NaCl crystals.
• H-bonds between the water molecules have to be broken.
• NaCl dissociates into Na+ and Cl-.
• Ion-dipole forces form between the Na+ and the negative end of the water dipole.
• Similar ion-dipole interactions form between the Cl- and the positive end of the water dipole.
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• Degree of polarity is very important when dealing with aqueous solutions.
• Ex. Water
– The OH bonds in water are polar
– The O is slightly negative and will therefore cluster around positively charged molecules
– The H is slightly positive and will cluster around negatively charged molecules www.brainybetty.com
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• A non-polar solute dissolves in a non-polar solvent
• A polar solute dissolves in a polar solvent
• A polar solute will not dissolve in a non-polar solvent
• A non-polar solute will not dissolve in a polar solvent www.brainybetty.com
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• Soap/Detergent
– polar “head” with long nonpolar “tail”
– dissolves non-polar grease in polar water www.brainybetty.com
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• An electrolyte is a substance that, when dissolved in water, gives a solution that can conduct electricity
• A non-electrolyte does not conduct electricity when dissolved in water.
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- +
Non-
Electrolyte
Not ionized in water sugar
- + Weak
Electrolyte
Incompletely ionized in water acetic acid
+
Strong
Electrolyte salt www.brainybetty.com
Completely ionized in water
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• The amount of solute that can be dissolved in a given amount of a saturated solution at a fixed temperature is the solubility of the solute in the solvent.
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UNSATURATED
SOLUTION more solute dissolves
SATURATED
SOLUTION no more solute dissolves at a certain temp
SUPERSATURATED
SOLUTION becomes unstable, crystals form concentration www.brainybetty.com
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• Solubility
– maximum grams of solute that will dissolve in 100 g of solvent at a given temperature
– varies with temperature
– based on a saturated solution www.brainybetty.com
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• Solubility
Curve shows the dependence of solubility on temperature
X-axis : temperature
Y-axis : grams solute per 100mL water www.brainybetty.com
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• Anything that falls below the line is UNSATURATED
• Anything above the line is
SUPERSATURATED www.brainybetty.com
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• Solids are more soluble at...
– high temperatures.
• Gases are more soluble at...
low temperatures & high pressures.
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Solute-Solvent Interactions – the greater the attractions between solute and solvent molecules, the greater the solubility. If two substances have similar attractive intermolecular forces are likely to be soluble. “Like dissolves like.”
Pressure – relates mostly to the solubility of gases in liquids.
The solubility of the gas increases in direct proportion to its partial pressure above the solution.
Temperature – solubility of most solid solutes in water increases as the temperature of the solution increases. Gases decrease in solubility in water as temperature increases.
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• Two liquids are said to be miscible if they are completely soluble in each other in all portions
– Ex. ethanol and water
• In contrast, immiscible liquids do not mix significantly.
- Ex. gasoline and water www.brainybetty.com
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