Chemistry Review & Water Chapters 2 & 3

YOU MUST KNOW The 3 subatomic particles and their significance The types of chemical bonds and how they form The importance of hydrogen bonding to the properties of water Four unique properties of water and how each contributes to life on Earth How to interpret the pH scale How changes in pH can alter biological systems The importance of buffers in biological systems

Bonding Review Covalent Bonds Atoms share electrons Can have single, double, triple bonds Relatively strong bonds Many different types for specific kinds of molecules (ex. peptide, glycosidic, phosphodiester) Can be polar or non-polar (are electrons shared equally?)

Bonding Review Ionic Bonds Atoms gain/lose electrons, resulting in charges which attract them to each other Generally the strongest bonds

Bonding Review Van der Waals Interactions (hydrophobic interactions) Weak connections, break and reform, as a result of asymmetrical distribution of electrons (since electrons are always moving) aka intermolecular forces

Water Polarity: Uneven distribution of charges around a molecule Hydrogen side of water molecule is slightly positive while oxygen side is slightly negative Attraction between positive side of one water molecule and negative side of next = Hydrogen bond

Water 1. Cohesion & Adhesion Cohesion - Water molecules are attracted to other water molecules

Cohesion - Water molecules are attracted to other water molecules Water forms into droplets (which join together when close)

Cohesion - Water molecules are attracted to other water molecules Water forms into droplets (which join together when close) Water has strong surface tension (remember penny lab?)

Cohesion - Water molecules are attracted to other water molecules Water forms into droplets (which join together when close) Water has strong surface tension (remember penny lab?) Water can move as a column in plants Go to 1:55

Water Adhesion - Attraction between water molecules and other types of molecules Also at play in movement of water in vascular plants (capillary action) - Once water moves into the vascular tissue, adhesion keeps it from dropping back down

Water High Specific Heat The amount of heat required to raise or lower the temperature of a substance by 1degree C Makes temperature of Earth stable (ocean temps stable) Helps plants and animals maintain temperatures Evaporative cooling

Less dense in solid form Water Less dense in solid form Ice floats – insulates large bodies of water to keep them from freezing entirely (life can survive the winter) Forms habitat for some species

Water 4. Solvent Capable of dissolving an abundance of other molecules Makes it extremely valuable in transporting molecules in your body Water being transported by cohesion and adhesion in plants is carrying dissolved substances everywhere it goes Blood is composed mainly of water – carries dissolved substances around your body (glucose, ions, amino acids) Also makes it an excellent medium for metabolic reactions *Remember Solvent = substance doing the dissolving Solute = substance that gets dissolved Together they make a solution

Water Hydrophilic molecules – molecules that dissolve in water Generally polar (like likes like) Ex. glucose and other carbohydrates, ions such as sodium (Na+, Ca++, Cl-) Hydrophobic molecules – don’t dissolve in water Generally non-polar Ex. Lipids, methane https://www.youtube.com/watch?v=Oe3St1GgoHQ

pH

pH Buffers Weak acids/bases that minimize changes in pH Ex. Carbonic acid (H2CO3) – in living systems Moderates pH changes in blood plasma https://www.youtube.com/watch?v=NJyAme5GVF8

Molarity (M) Number of moles (6.022 x1023 molecules) per liter of solution (***Note that it is L of solution, NOT solvent!) How we quantify the concentration of a solution

Molarity Sample Problem: How many grams of sucrose (C12H22O11) would you add to water to make 0.75L of a 0.6M aqueous solution?

Molarity Step 1: Determine the molecular mass of sucrose. C12H22O11 - (12 atoms of carbon x 12) + (22 atoms of hydrogen x 1) + (11 atoms of oxygen x 16) = (144) + (22) + (176) = 342g/mol

Molarity Step 2: Solve for number of moles in the solution Molarity (M) = m (moles)/V (volume in liters) 0.6M = m/0.75L m = 0.45 moles

Molarity Step 3: Determine g in 0.45 moles 342 g/mol = X/0.45 mol X = 154g