Module 1 Flashcards
What is meant by the conservation of mass?
Matter can’t be created or destroyed
What happens when the limiting reactant gets used up?
The reaction will stop
What is solubility of substances in aqueous biological solutions crucial for?
Transport of gases, transport of inorganic materials and application and transport of drugs
What are the bonds present in water?
Two O-H bonds
Explain the electronegativity of O-H bonds in water
The oxygen atom is more electronegative than the hydrogen atom so the electron pair spends more of the time surrounding the oxygen atom
What has a partial negative charge in O-H bonds?
Oxygen
What has a partial positive charge in O-H bonds?
Hydrogen
What is the shape of a water molecule?
Bent
How are water molecules attracted to each other?
By electrostatic interactions between the partial charges (dipole-dipole interaction)
What are the dipole-dipole interactions between water molecules called?
Hydrogen bonding because they are usually strong
What states does water undergo hydrogen bonding in?
Solid and liquid
What is soluble in water?
Polar molecules and ionic solids
What are the melting and boiling points of water and why?
They are both high (melting=0 and boiling=100) because of the extensive hydrogen bonding which is strong
Why does water become more dense as it melts?
In liquid water, the molecules move closely together, continuously making and breaking hydrogen bonds. In solid water, the molecules are held rigidly in a structure which is more open than in liquid and therefore less dense
What happens to the freezing point of water as pressure increases?
It decreases
Water has a large…
Surface tension and heat capacity
What is the concentration of water?
55 mol/L
What is water a good solvent for?
Electrolytes (substances which give ions when dissolved)
Dissolution of electrolytes in water occurs…
spontaneously, despite the electrostatic forces holding the electrolyte together being strong
What does solvation do to ions?
Helps to stabilise them as they are high energy species
What causes all of the ions in water to be surrounded by water molecules?
Interactions of the charged ions with the dipoles of the water molecules
What is it called when water is the solvent?
Hydration
The water molecules surrounding the ions…
continuously change
What polar molecules may water be a good solvent for?
Alcohols, amines, carboxylic acids and amino acids
What is the solubility of non-polar molecules?
They aren’t very soluble in water but their solubility isn’t zero
Why isn’t the solubility of non-polar molecules 0?
Because the permanent dipole in water can induce an instantaneous dipole in a non-polar molecule.
What does the size of the instantaneous dipole depend on?
The number of electrons and shape of the molecule (polarisability)
What non-polar gas is soluble in water and why?
Ammonia because it can hydrogen bond
What is the dissociation of strong electrolytes?
Complete meaning everything is ions
What is the dissociation of weak electrolytes?
Incomplete meaning mostly molecules but also some ions are present in solution
What is the dissolution of strong electrolytes?
Tiny
What is the dissolution of weak electrolytes?
Enormous
What is the reaction quotient, Q used for?
To determine whether the reaction has gone to completion or not by quantifying the amounts of reactants and products present in the reaction mixture over time
What is Q?
The ration of products over reactants
What happens when Q stops increasing?
Dynamic Equilibrium has been reached but the reaction hasn’t gone to completion as there is still product and reactant molecules present
What is meant by dynamic equilibrium?
The rate at which the product molecules are being formed is equal to the rate at which the reactant molecules are being used
What doesn’t appear in an equilibrium constant?
Pure solids and liquids because their concentration is constant
What happens when Q is less than K?
The reactants are converted into products until equilibrium is reached
What happens when Q is more than K?
The products are converted back into reactants until equilibrium is reached
What does K depend on?
Temperature and not the starting concentrations
Where is the equilibrium when K is large?
It lies to the right
Where is the equilibrium when K is small?
It lies to the left
What is le chatelier’s principle?
If a system at equilibrium is disturbed, it will move in such a way to counteract the disturbance and restore equilibrium
What happens if a reactant is added to a system at equilibrium?
The equilibrium will move to the right to use up the added reactant and form products
How can pressure in a system be changed?
By changing volume or adding an inert gas
What happens when the pressure is increases?
There is less space for molecules so the reaction will move to favour the side with less gaseous moles
What happens when pressure is decreased?
There is more space for molecules so the reaction will move to favour the side with more gaseous moles
What is solubility?
A measure of how much solute will dissolve in a given volume of solvent
When is a saturated solution formed?
at equilibrium when the maximum amount of solute is dissolved in a particular volume of solvent and no more will dissolve
What does solubility depend on?
Chemical nature of solute and solvent (polarity and bonding), temperature and pressure (for gaseous solutes)
How can we know if a precipitate will form?
By comparing Qsp and Ksp
What happens when Qsp is greater than Ksp?
Precipitation will occur
What happens when Qsp is less than Ksp?
No precipitate will form
What is a common ion?
An ion which is common to the equilibrium
What does the presence of a common ion do?
Decrease the solubility of an ionic solid
What are the three types of chemical reactions?
Electron transfer: X+Y»>X++Y-
Precipitation: X++Y-»_space;> XY
Acid-base: Acid + Base»_space;> Products
What is a lewis acid?
An electron pair acceptor
What is a Lewis base?
An electron pair donor
What is an acid?
A proton (H+) donor
What is a base?
A proton (H+) acceptor
What are things which act as an acid or base?
Amphriotic
Forward and reverse reactions are both…
Acid-base reactions
What are conjugate acid-base pairs?
Things which differ by one proton (the conjugate acid will have the most protons)
What is Kw?
The auto-ionisation constant of water = 1x10^-14
What is the pH scale used for?
Measuring the concentration of H3O+ in aqueous solution
If pH is less than 7 does it mean something is acidic?
Not necessarily, the concentration of H3O+ and OH- may be equal and the pH may be less than 7 but this is still a neutral solution
What are majority of acids?
Weak acids
What is the equilibrium like for weak acids?
Lies almost completely to the left because they don’t dissociate much
What is Ka a measure of?
Acid strength
What is indicated by a large Ka value?
Extensive dissociation and the better the weak acid
What is Kb a measure of?
Base strength
What is indicated by a large Kb value?
Extensive dissociation and the better the weak base
The better the acid, …
The poorer the conjugate base
The conjugate acid of a strong base is…
very weak
The conjugate bas of a strong acid is…
very weak
How is the strength of the conjugate pair found in weak acids and bases?
By comparing the Ka values
How are transition metal complexes (ligand and transition metal cations) formed?
When transition metals form bonds with ligands
What can transition metal complexes do when water is the ligand?
Act as a weak base
How can a transition metal complex act as a weak base when water is the ligand?
Interaction between the cation and oxygen of the bound water molecules weakens the O-H bonds. Therefore a proton (H+) can easily be lost to a free water molecule
What is a buffer solution?
A solution of a weak acid and its conjugate base (or a weak base and its conjugate acid) both at reasonable concentration which will maintain a reasonably constant pH on addition of significant amounts of H3O+ or OH- ions.
Where must the conjugate base come from in a buffer solution?
Somewhere other than equilibrium as this would would mean there is only a small amount
What happens to the pH of a buffer when diluted?
It is unaffected when it is a reasonable dilution
What is meant by buffer capacity?
Acid or base can’t continually be added to a buffer without the pH changing. It will eventually get to the point where the weak acid or the conjugate base is all used up and the pH will change significantly
What happens when the pH of a buffer changes?
The buffer capacity has been exhausted
What is a polar molecule?
One which forms favourable interactions with water molecules. Has polar bonds or charged regions
What are polar molecules also called?
Hydrophilic molecules
What are non polar molecules?
A molecule which doesn’t have any polar bonds or charged parts so will not dissolve in water but will dissolve in other non-polar solvents
What are non-polar molecules also called?
Hydrophobic molecules
What is the ionisation status of molecules influenced by?
pH of the aqueous environment and the tendency of particular ionisable functional groups to ionise- the pKa (how far to the right a reaction will go)
When does pH=pKa?
When 50% of the functional groups of the molecule are ionised
When is amino group protonated?
When it is charged positive
When is a carboxyl acid group protonated?
When charged negative
What do side chains of some amino acids contain?
Ionisable functional groups so their ionisation state depends on the pH of the solution
When may small changes in amino acids occur?
When the pKa of the molecule is close to the pH
What remains constant in a biological system and what does this mean?
pH so anything added to the system will have to change its ionization state to match the pH
What does net charge on proteins rely on?
The ionisable side chain groups and the N- and C- termini at the end of the chain because most of the amino and carbonyl groups on amino acids are involved in bonding and not available for ionisation
What do non-polar regions of macromolecules do?
Hide away from the aqueous environment
What do water molecules do to non-polar molecules?
Attempt to hydrate then in an aqueous environment by forming a constrained hydration shell around the molecule
What is a titration?
An experimental technique that allows the determination of the concentration of a solution of some compound A through a reaction with a known concentration of a second compound B
What is the initial pH of a strong base, weak acid titration?
The pH of the acid in the flask
What is present before the half equivalence point in a strong base, weak acid titration?
More acid than the conjugate base
What is present at the half equivalence point in a strong base, weak acid titration?
equal amounts of acid and conjugate base so the solution is a buffer and pH=pKa
What is present after the half equivalence point in a strong base, weak acid titration?
More conjugate base than acid
What is present at the equivalence point in a strong base, weak acid titration?
All the acid has reacted and the buffer has been exhausted
What happens in a strong acid/strong base titration curve?
Because a strong acid is used there is no effective conjugate base and therefore a buffer can’t be formed. The pH would also be affected upon reasonable dilution which is not characteristic of a buffer
What are diuretic acids?
Acids which have two protons which it can donator and on a titration curve it shows each proton being donated separately
What is attached to an amino acid?
A weak acid, a weak base, a proton and an R group
What are zwitterions?
Neutral amino acids which contain a positive and negative charge but are neutral overall
How do zwitterions form?
By internal protonation from the COOH to NH2 to form COO- and NH3+
How do zwitterions behave?
Like inic salts so have high melting points, are water soluble and are insoluble in non polar solvents
What happens to zwitterions in very acidic conditions?
The COOH and NH3+ will be protonated
What happens to zwitterions in very basic conditions?
Both the COO- and NH2 groups will be deprotonated
How do amino acids act in a titration curve?
Like diuretic acids
What is present at the initial pH of an amino acid titration?
The cationic form of the amino acid
What is present before the 1st halfway point of an amino acid titration?
More of the cationic form but also some of the zwitterion form
What is present at the 1st halfway point of an amino acid titration?
Equal amounts of cationic form and the zwitterion (buffer)
What is present after the 1st halfway point of an amino acid titration?
More zwitterion than cationic form
What is present at the first equivalence point of an amino acid titration?
Only zwitterion which has a net charge of zero and this is called the isoelectronic point which is only associated with amino acids
What is present before the 2nd halfway point of an amino acid titration?
More zwitterion than anionic form
What is present at the 2nd halfway point of an amino acid titration?
Equal amounts of zwitterion and anionic form (buffer)
What is present after the 2nd halfway point of an amino acid titration?
More anionic form than zwitterion
What is present at the final equivalence point of an amino acid titration?
Only anionic form
