1 Solution Chemistry Unit 8 General Chemistry Spring ’13 Objectives (Ch. 15) Understand and describe the basic properties of water and ice and how they effect the world around you. Explain the high surface tension and low vapor pressure of water in terms of the structure of the water molecule and hydrogen bonding (15.1.1) Distinguish between solvent and solute (15.2.1) Describe what happens in the solution process (15.2.2) Explain why all ionic compounds are electrolytes (15.2.3) Distinguish between suspension and solution (15.3.2) Identify the distinguishing characteristic of a colloid (15.3.2) WATER AND ITS PROPERTIES 15.1 Simply Water Ice has a low density. (Does ice float?) It’s a polar molecule Slightly positive (+) on one end Slightly negative (-) on another Look what it does to salt! It also easily bonds to itself and easily pulls compounds apart Polar vs. Non-polar? It’s like a tug of war… Even pulling of electrons means it’s non-polar Uneven pulling means it’s polar Water’s Hydrogen Bond Water molecules are not connected by full covalent bonds, but they’re pretty strong The formation between the hydrogen atoms on one molecule and a highly electronegative atom on another is called a hydrogen bond. Atoms that can do this are hydrogen, oxygen, fluorine, and nitrogen Keep reading…
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Solution ChemistryUnit 8
General ChemistrySpring ’13
Objectives (Ch. 15)
� Understand and describe the basic properties of water and ice and how they effect the world around you.
� Explain the high surface tension and low vapor pressure of water in terms of the structure of the water molecule and hydrogen bonding (15.1.1)
� Distinguish between solvent and solute (15.2.1)
� Describe what happens in the solution process (15.2.2)
� Explain why all ionic compounds are electrolytes (15.2.3)
� Distinguish between suspension and solution (15.3.2)
� Identify the distinguishing characteristic of a colloid (15.3.2)
WATER AND ITS PROPERTIES
15.1
Simply Water
� Ice has a low density. (Does ice float?)
� It’s a polar molecule
� Slightly positive (+) on one end
� Slightly negative (-) on another
� Look what it does to salt!
� It also easily bonds to itself and easily pulls compounds apart
Polar vs. Non-polar?
� It’s like a tug of war…
� Even pulling of
electrons means it’s
non-polar
� Uneven pulling means it’s polar
Water’s Hydrogen Bond
� Water molecules are not connected
by full covalent bonds, but they’re pretty strong
� The formation between the hydrogen
atoms on one molecule and a highly
electronegative atom on another is called a hydrogen bond.
� Atoms that can do this are hydrogen,
oxygen, fluorine, and nitrogen
� Keep reading…
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Hydrogen Bonds cont.
� Any molecule with O-H bonds has the potential to form hydrogen bonds.
� Alcohols (molecules with O-H bonds) also form hydrogen bonds.
� Have similar properties to water
� Proteins, nucleic acids, and carbohydrates also can form hydrogen bonds.
� How they form and shape determines how they’re used biologically
Basic Properties of Water
� Boils at 100oC
� Freezes at 0oC
� Expands due to hydrogen bonding
� Solid state is highly organized
� One drop = ~2x1021 molecules
Surface Tension
� Surface tension: the inward force, or pull, that tends to minimize the surface area of a liquid� Causes drop to pull together
� All liquids have a surface tension� Mercury has high surface tension
� Surfactants� Interfere with H-bonding and reduce
surface tension
� Soaps and detergents
Surface Tension at work
Vapor Pressure of Water
� Results from the molecules escaping from the surface of the liquid and
entering the vapor phase.
� In water, H-bonds hold on to water
molecules tightly
� Tendency for molecules to escape is low
� Evaporation of water is low
� What would happen if it was fast?!
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Specific Heat of water
� Specific heat: measures the amount of heat, in joules, needed to raise the temperature of 1g of
substance by 1oC.
� For water it’s 4.18, pretty high.
� Why it takes so long to boil water
� It takes a long time to absorb or release more heat
for its temperature to change 1oC than a lot of other
substances.
� Think of a pool in the summer time.
Specific Heat
Substance Specificheat
Water 4.18
Chloroform 0.96
Aluminum 0.90
Mercury 0.14
Water in the Solid State
� The structure of ice is a regular open framework of water molecules arranged like a honeycomb.
� Add energy and the
framework collapses
� The molecules are closer
together making water more dense than ice
� Implications on aquatic life?
HOMOGENEOUS AQUEOUS SYSTEMS
15.2
Water: The Universal Solvent(Homogeneous Aqueous Systems)
� Almost always found in solution
� A very good solvent due to its polar abilities
� Examples of aqueous solutions
� Milk
� Soda pop
� Coffee and tea
� Tap water
� Look at the ingredient list of a liquidy beverage. Water is probably there.
Solutions
� When one substance dissolves into another, that is called a SOLUTION
� Example: sugar water, Kool-Aid
� There are two main parts of a solution:� SOLUTE= the dissolved material
� Example: sugar, salt, oxygen (air)
� SOLVENT= the substance that is doing the dissolving (usually a liquid)� Usually present in the highest amount
� Example: Water, nitrogen (air)
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The Solution Process
� Water, a polar molecule, is capable of dissolving a range of compounds
� As individual solute ions break away from the crystal, the negative and positive ions become
surrounded by solvent molecules and the ionic crystal dissolves
The Solution Process Cont.
� Ionic solids are composed of positive and negative ions.
� Water has a positive and negative end (it’s polar)
� Opposites attract and the ionic compounds
separate into ions.
� The process by which charged particles in an
ionic solid separate from one another is solvation
“Like Dissolves Like”
� This means that dissolving occurs when similarities exist between the solvent and the solute.
� Sugar is a polar molecule, so is water, and water tends to dissolve substances that are polar or that form hydrogen bonds.
� Oil and water don’t mix.� Oil is nonpolar
� But different oils are “like” enough to mix and stay mixed.
� Oil and gasoline.
Electrolytes vs. Nonelectrolytes
� Electrolyte
� A compound that conducts an electric current when it is in an aqueous solution
� All ionic compounds are electrolytes because they dissociate into ions
� Nonelectrolyte� A compound that does not conduct an
electric current in aqueous solution
� Many covalents are this because they are not composed of ions
The electric pickle
HETEROGENEOUS AQUEOUS SYSTEMS
15.3
5
Suspensions
� A (heterogeneous) mixture from which particles settle out upon standing
� A suspension differs from a solution because the particles are much larger
and do not stay suspended indefinitely
� Cornstarch mixed with water thickens
sauces
Suspensions
� At least two substances are clearly identified
� Think of a glass of water with sand or mud in it.
� Typically easy to separate
Colloids
� A heterogeneous mixture containing particles that range in size from 1nm to 1000nm
� Particles spread throughout the dispersion medium (s, l, g)� Glues
� Gelatin
� Paint
� Aerosol sprays
� Smoke
� Difficult to sep. due to the tiny size of particles