Biology : Water, acids, and bases

Hydrogen bonding in water

Hydrogen bonding in water

• hydrogen bond
• oxygen is more electronegative(electron-greedy) than hydrogen
• that gives the oxygen end of the water molecule a partial negative charge
• hydrogen has a partial positive charge
• water is classified as a polar molecule
• is attracted to other polar molecules and to ions

Solvent properties of water

• solvent+solute=solution
• water is good at dissolving ions and polar molecules
• poor at dissolving nonpolar molecules
• water can form electrostatic interactions(charge-based attractions) with other polar molecules and ions
• hydration shell
• it allow particles to be dispersed(spread out) evenly in water
• into the water, NaCl to dissociate(break apart) into Na+ and Cl- ions
• hydration shell is formed around each ions which would be dispersed

Cohesion and adhesion

• cohesion: the attraction of molecules for other molecules of the same kind
• water's cohesive force: thanks to their ability to form hydrogen bonds with one another
• cohesive force: are responsible for surface tension
• adhesion: the attraction of molecules for other molecules of a different kind
• ex. capillary action: the upward motion of water molecules in a thin tube
• capillary action = water&glass(adhesion) + water&water(cohesion)
• meniscus that water shows, bc glass molecules are even more polar than water molecules(glass's O(with Si) is stronger negative charged than water's O(with H))
• thus, water's H is going to be attracted to the glass even harder than each other

Temperature and state changes in water

• liquid water: hydrogen bonds are being formed and broken by the energy of motion(kinetic energy, vibration)
• gas: the higher kinetic energy caused the hydrogen bonds to break completely, allow water molecules to escape into the air
• solid: too little heat energy left to break the hydrogen bonds
• density of ice: the water molecules are pushed farther apart than they are in liquid form
• specific heat capacity: the amount of heat(to break hydrogen bonds) needed to raise the temp of 1g of a substance by 1 degree celsius(for water, calorie)
• heat of vaporization: the amount of energy needed to change 1g of a liquid substance to a gas(at constant temp), 540 cal/g at 100'c
• evaporative cooling: the molecules with the highest energy escape away from other molecules

Acids, bases, and pH

Autoionization of water

• autoionization of water: H20 <-> H+(aq)hydrogen ion+OH-(aq)hydroxide ion
• this H+ transfer to a neighboring water molecule, form H3O+, hydronium ion
• the concentration of hydrogen ions produced by autoionization is: 1*10^-7M

Acids and bases

• an acidic solution: high concentration of hydrogen ion than pure water
• a basic solution: low concentration of hydrogen ion than pure water
• pH=-log₁₀[H⁺]
• neutral pH=pure water's=7
• generate H+, it goes to acidic
• release OH-(it absorb H+), it goes to basic(alkaline)
• an acidic solution: high concentration of hydrogen ion than pure water
• a basic solution: low concentration of hydrogen ion than pure water

Buffers

• carbonic acid: a basic form of carbon dioxide enters the bloodstream
• HCO₃^-bicarbonate ion <too low H+<<>>too many H+> H₂CO₃carbonic acid
• too many H+: bicarbonate ion absorbs H+ >> turn into carbonic acid
• too low H+: carbonic acid release H+ >> turn into bicarbonate ion