SBI4U: Biochemistry Lesson 4 - Polarity and Hydrophobic & Hydrophilic Molecules
Learning Goals:
I will be able to describe the properties of water that make it a good solvent for polar
compounds
I will explain the process of how soap works by using the terms hydrophobic and
hydrophilic
I will be able to describe what acids and bases are and how they compare to water
What are we talking about?
RECAP:
Draw the shape of a water molecule above, and show the polar ends.
How might 2 or more water molecules interact with each other?
Solubility: How easily a substance dissolves
• The general rule is "like dissolves like"
• Polar substances dissolve polar substances
• Non-polar substances dissolve non-polar substances
• HYDROPHOBIC:
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HYDROPHILIC:
*Often, the subscript “(aq)” is visible - means that aqueous substances are soluble in water.
H-Bonding Is Responsible for Density of Ice Being Less than Water
• H-bonds lock into lattice structure in the solid state
•
Ice - Solid water is __________________ than liquid water, allowing it to float
Water is the universal solvent
• Water can dissolve many hydrophilic (water loving) substances
Ionic compounds
Other polar compounds
• Any substance that dissolves in water is called a ____________.
• Water, then, is a ____________.
• Hydration is the process of water molecules surrounding ions to make “spheres of
hydration”
Q1: Can water dissolve non-polar oil? Why or why not?
Q2: Can water pass freely through the cell membrane?
• Some substances do not dissolve readily in water because they are ___________ solutes
• Oil (fats or lipids) is an example of a hydrophobic – “water-fearing” - substance
• Application: How does soap work to clean grease/oil from our dishes?
How soap works: micelles
• Soap can suspend oil/dirt in such a way that it can be removed.
• Soap is an excellent cleanser
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Grease and oil are __________ and ____________ in HOH.
When soap is added to oil-containing solution, the non-polar hydrocarbon portion of
the soap attaches to the non-polar oil molecules.
A ___________ then forms—with nonpolar solutes (grease/oil) in the
centre.
The outside of the micelle is polar (water soluble) and now the grease
and oil can be washed away.
•
Isn’t our cell membrane made of fat? What happens when soap comes in
contact with our cell membrane?
Acids & Bases:
• When 2 water molecules interact, one molecule gains a hydrogen (to become H3O+,
hydronium ion) while the other loses a hydrogen (and becomes OH-, hydroxide ion).
•
________ are defined as substances that increase the concentration of H+ (or
H3O+) ions in solution.
•
________ are defined as substances that increase the concentration of OH- ions in
solution.
•
•
When an acid is mixed with a base, the result is a _________________________.
Neutralization reactions produce water and a salt.
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A solution with a pH of 7 is considered _________(equal amounts of H3O+ and OH-).
Solutions whose pH is less than 7 are ___________ (more H3O+).
Solutions whose pH is greater than 7 are ___________ (more OH-).
H.W. Read pgs. 16-23, Do Q’s #7, 8, 13, 14, 15, 16 and questions on the back.