Notes Solutions and Properties of Water Definitions • A solution is a homogeneous mixture • A solute is dissolved in a solvent. • solute is the substance being dissolved • 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 supersaturated 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. Definitions • Solutions can be classified as saturated or unsaturated. • A saturated solution contains the maximum quantity of solute that dissolves at that temperature. • An unsaturated solution contains less than the maximum amount of solute that can dissolve at a particular temperature
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Notes Solutions and Properties of Water
Definitions• A solution is a homogeneous mixture
• A solute is dissolved in a solvent.
• solute is the substance being dissolved
• 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 supersaturated 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.
Definitions• Solutions can be classified as saturated or unsaturated.
• A saturated solution contains the maximum quantity of solute that dissolves at that temperature.
• An unsaturated solution contains less than the maximum amount of solute that can dissolve at a particular temperature
Notes Solutions and Properties of Water
Factors that affect solubility
• The nature of the solute or solvent ionic vs. covalent, polar vs. non polar – a way to remember is "like dissolves like"
• Temperature heat vs room temperature• Agitation of the solvent like stirring• Surface area of the solute particle size• Pressure solubility of gases
pg. 474
Notes Solutions and Properties of Water
Dissolution of Solid Solute
• What are the driving forces which cause solutes to dissolve to form solutions?
• 1. Covalent solutes dissolve by Hbonding to water
• 2. Ionic solutes dissolve by dissociation into their ions.
Notes Solutions and Properties of Water
Water is a “Universal” Solvent• A liquid that is a completely homogeneous mixture of two or more substances is called a solution.
• A sugar cube in a glass of water will eventually dissolve to form a uniform mixture of sugar and water.
• The dissolving agent is the solvent and the substance that is dissolved is the solute.
• In our example, water is the solvent and sugar the solute.
• In an aqueous solution, water is the solvent.
• Water is not really a universal solvent, but it is very versatile because of the polarity of water molecules.
DefinitionsSUPERSATURATED SOLUTIONS
contain more solute than is possible to be dissolved
Supersaturated solutions are unstable.
The supersaturation is only temporary, and usually accomplished in one of two ways:
Warm the solvent so that it will dissolve more, then cool the solution
Evaporate some of the solvent carefully so that the solute does not solidify and come out of solution.
Notes Solutions and Properties of Water
Quick Review• Nonpolar covalent compound: a compound in which e shared equally.
• Polar covalent compound: uneven distribution of e, unequal sharing…electrons in the compound are more attracted to electronegative atom.
In this case water is a POLAR MOLECULE!
Polar molecule: one in which there are oppositely charged ends.
• Water consists of an oxygen atom bound to two hydrogen atoms by two single covalent bonds.
• Oxygen has unpaired & paired electrons which gives it a slightly negative charge while Hydrogen has no unpaired electrons and shares all others with Oxygen
• Leaves molecule with positively and negative charged ends
Water is a Polar Molecule
has oppositely charged ends
Notes Solutions and Properties of Water
slightly positive charge
slightly negative charge
hydrogen bond between (+) and () areas of different water molecules
Water molecules form Hydrogen bonds
General Rule: “Like dissolves like”• Means that a polar solute dissolves
only in a polar solvent
• Water is a solvent for many, but not all substances
• Some substances will not dissolve in water, non polar
Notes Solutions and Properties of Water
• Water is an effective solvent as it can form hydrogen bonds.
• Water clings to polar molecules causing them to be soluble in water.
• Hydrophilic attracted to water
• Water tends to exclude nonpolar molecules.
• Hydrophobic repelled by water
IONIC SOLUTIONS• An ionic compound dissolves in
water because the + ions and the – ions are surrounded by & pulled into solution by water’s + and – poles
Notes Solutions and Properties of Water
• Metal alloys, solution of two or more metals
• The metal in greatest abundance is the solvent and the other metal(s) are the solutes.
Not all solvents are liquids
Hydrations and Hydrates • This process with water as the
solvent is called hydration
• Compounds that have water chemically attached are called hydrates
• Like copper (II) sulfate pentahydrate
• CuSO4● 5H2O
Notes Solutions and Properties of Water
Calculate the percent of water by mass • CaCl2●2H2O