Nutrition and erosion Flashcards
Describe the physical structure of water
It is a tetrahedral structure with intermolecular hydrogen bonds between + hydrogens and - oxygens
What do neutron and x ray scatter suggest about oxygen in water?
Suggests there’s a high possibility of finding oxygen jatos 2.8A apart from each other
How far apart in nm are oxygen atoms from each other in water
0.28NM
What determines the structure of liquid ice?
Hydrogen bonds
What is the 0.28nm distance between oxygens in water dependent on?
Weakly dependent on temperature
Name soem intermolecular forces
- Hydrogen bonding
- Dipole Dipole
- Van der Waals
What happens when a solvent eg LiCl is added to water?
The soft breaks apart and the Li+ ion attracts the oxygen causing the oxygen of water to arrange in a tetrahedral war around Li+
What effect do polar molecules have on water?
They have a disordering effect on liquid water structure
Why is water important?
It constitutes about 70% of mass of most living things
Is water polar or on polar?
Polar
Describe the ionisation of water and what it yields
Water can undergo REVERSIBLE ionisation to yield H+ and OH-
How is the degree of ionisation of water at equilibrium represented?
KeQ=
[H+][OH-]/
[H2O]
Describe the relationship between the total concentration of H+ and OH-?
The total concentration of H+ and OH- is constant, an increase in one ion concentration is
compensated by a decrease in the concentration of the other ion
What does table salt dissolve into in water?
NaCl-> Na+ +Cl-
Equilibrium favours which reaction in the dissolution of table salt?
Favours the forward reaction (In favour of dissolution)
What would happen if we put a tooth in water?
It would dissolve in a reversible reaction:
Ca(PO4)6OH2 -> 10Ca2+ + 6PO4 3- + 2OH-
What happens to weak acids in water?
They partially ionise (dissociate) in water
When is equilibrium reached?
When the forward and reverse reaction of a chemical equation are equal
What does the Ka tell us?
Tells us the degree of dissolution
What is the equilibrium constant (acid dislocation constant Ka) GIVEN by for acetic acid ?
Ka= [H+][CH3COO-]/
[CH3COOH]
What is the equilibrium constant (acid dislocation constant Ka) GIVEN by for HCL?
Ka= [H+][Cl-]/
HCL
Describe the general relationship between pKa and acid strength?
pKa is smaller for stronger acids and larger for weaker acids
What is the relationship between pH and hydrogen ion concentration?
pH= -log[H+]
What is the relationship between pKa and Ka?
pKa= -logKa
What effects the erosive potential of a drink or food?
- ph
- Titratable acidity (major factor)
- Presence of chelators
- Frequency, flow rate of how a drink is drug
- Bottle design ie if you are drinking from a cap or straw
- Saliva flow
- Cohesion of the drink to the enamel surface
What happens when you eat carbohydrates
They are fermented to produce acid
What happens to the acid produced by the bacterial fermentation of carbohydrates on the mouth?
Initially H+ is buffered in the plaque and saliva.
But as pH reduces the fluid medium is depleted of OH- and PO4 3- and these react with H+ to form H2O and PO4 2-
State the value of the critical pH of the oral cavity?
5.5
State Le Chatelier’s principle
If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure then the equilibrium shifts to counteract the imposed change and a new equilibriumis established
How does chemical erosion occur?
Can occur by the hydrogen ion derived from acids as they disassociate in water
How does H+ cause damage?
The H+ can attack the mineral by directly dissolving and combining with phosphate
Go through the mechanism of dissolution of enamel by cheating agents
- Ca10(PO4)6(OH)2 -> 10Ca+ +6PO4 3- + 2OH-
- 6PO4 3- + 6H+ -> 6HPO4 2-
- 6PO4 2- + 6H+ -> 6H2PO4-
- 6H2PO4- + 6H+ -> 6H3PO4 (strong acid)
What happens to all acids in aqueous solutions
All acids ionise in aqueous solutions to give:
HA -> A- + H+
Give the KA for a general acid HA
Ka = [A-][H+]/[HA]
What does a small pKa mean?
It means the acid has a large Ka so theres a large amount of A- and H+
If an acid has a small pKa describe its Ka and is it a weak or strong acid?
It has a large Ka and so is a strong acid
What does a large pKa mean?
It means the acid has a small Ka so theres a small amount of A- and H+
If an acid has a small pKa describe its Ka and is it a weak or strong acid?
It has a small Ka and so is a weak acid
State the Henderson Hasselbach Equation
pH = pKa + log ([A-] /[HA])
What is special about the half was point of acid titration
It is the point where pH=pKa
What is the stabile constant?
It is represented as K
It is used to measure the strength of interactions
What do high values of logK indicate?
A stronger bond
What happens as the pH of a drink increases?
Its acid erosion potential decreases and its chelation potential increases
Go through the steps of demineralisation and demineralisation
- Acid attack drops the oral pH from 7 to 4.5
- Calcium and phosphate dissolve increasing local concentration
- Salivary buffering takes pH back to 7
- Solution is again supersaturated and minerals can form on the crystal surface
- If fluoride is preset fluoroapatite can form
which is less soluble than hydroxyapatite or enamel.
What can we add to acidic drinks to reduce erosive attack?
We can add calcium and phosphate
What happens when you aadd calcium to a drink
The drink moves towards supersaturation and the calcium also neutralises the chelating effect by binding to citrate
What happens to a tooth as soon as it erupts?
A salivary pellicle forms on the surface
What are the benefits of having salivary pellicles?
They form a diffucito barrier and protect the outer surface of the tooth from direct acid attacks thus slowing down erosion
