Chapter 3: Water Flashcards
What are the properties of molecules based on?
Composition
Covalent Structure
Bonding and Molecular Geometry
What is electronegativity?
The ability of an atom within a molecule to draw electrons towards itself
Which atom in water is partially negative? why?
Oxygen because it has a larger electronegative pull than the Hydrogens so the electrons reside slightly closer to the oxygen
Are Hydrogen Bonds polar or nonpolar?
Hydrogen Bonds are Polar.
In water, are the hydrogen bonds static or are they broken and reformed?
Hydrogen Bonds break and reform constantly and typically only last mere moments
What kind of molecules is water a good solvent for?
Water is a good solvent for polar/charged molecules, but it is a poor solvent for nonpolar molecules.
How does water dissolve crystalline salts?
Water does this by hydrating their component ions and breaking up ionic interactions. The water molecules cluster around the ions with positive ions having the oxygen facing them and negative ions having the hydrogens face towards it.
What are the types of Noncovalent Interactions?
Ionic (Coulombic) interactions
Dipole interactions
Van der Waals interactions
Hydrophobic Effect
What are Ionic (Coulombic) interactions?
electrostatic interactions between permanently charged species, or between the ion and a permanent dipole
What are Dipole Interactions?
electrostatic interactions between uncharged but polar molecules
What are Van der Waals interactions?
- weak interactions between all atoms, regardless of polarity
- attractive (dispersion) and repulsive (steric) component
What is the Hydrophobic Effect?
complex phenomenon associated with the ordering of water molecules around nonpolar substances
Does water surrounding nonpolar solutes have low or high entropy?
It has low entropy and therefore is thermodynamically unfavorable.
Know the Functional Groups
Can’t upload pictures :(
What do amines act as?
They act as bases
Which functional group can act as either a base or an acid?
Imidazole
How do you find pH from the concentration of protons?
pH = -log[H+]
What is the definition of an acid?
An Acid is a substance that contains hydrogen and dissociates in water to yield H+
Examples: HCl, HNO3, HCOOH
What is the definition of a base?
A Base is a substance that contains a hydroxyl group (OH-) that dissociates in water to yield OH-
Examples: NaOH, KOH, Ba(OH)2
What is the difference between a weak and a strong acid?
Strong acids dissociate from their proton to completion while weak acids reach an equilibrium with their conjugated base.
Explain why water has a dipole moment while methane or carbon dioxide does not.
Water has a dipole moment due to the electronegative differences between O and H causing the electrons to move more towards the oxygen molecule and causing it to be partially negative. Methane does not have a large enough difference in electronegativity to cause a dipole moment, and carbon dioxide is in a linear geometry which means that the pulls of the Oxygens are against each other and do not cause a dipole moment.
What is an organic acid?
An organic acid is an acid with at least one carboxylic group
What is an oxoacid?
An acid where the number of Oxygens equals or exceeds by one the number of Hydrogens. Examples: HNO2 and H3PO4
How do you calculate Ka?
ka = ([H+]eq[A-]eq)/[HA]eq
If an acid’s Ka is higher, does that mean it is a stronger or weaker acid?
It means it is a stronger acid because more of the acid dissociates and forms its conjugate base.
What is pKa relative to ka?
pKa = -logka
If an acid’s pKa is higher does that mean it is a stronger or weaker acid?
It means that it is a weaker acid
What is the Henderson-Hasselbach Equation?
pH = pKa + log([H+]/[HA])
When is buffering capacity greatest?
It is greatest when pH = pKa (This means there are equivalent amount of acid and conjugate base in solution)
In vivo, what are buffer systems based on?
- Phosphate, concentration in millimolar ranges
- bicarbonate, important for blood plasma
- histidine, efficient buffer at neutral pH
Do hydrogen bonds only occur between separate molecules? Explain
Hydrogen bonds can occur within the same molecule if there is a large enough molecule with multiple areas capable of forming hydrogen bonds.
Explain the differences between covalent bonds and hydrogen bonds.
Covalent bonds are actual chemical bonds in which electrons are shared and are quite strong. Hydrogen bonds are electrostatic interactions that are individually weak.
