Biominerals

Question 1

Dispersion forces strength

Answer 1

• increases in strength as the number of electrons in a molecule increases
• there is greater opportunity for instantaneous dipole to arise

ie. BP and MP increase as length of carbon chain increases

Question 2

How to dipole-dipole interactions arise

Answer 2

• arise between polar molecules because of the electrostatic interactions between dipoles

Question 3

Advantage of high specific heat of water

Answer 3

Allows it to maintain temperature within narrow ranges even though external temperatures may fluctuate

Question 4

Density of water and its advantages

Answer 4

polar region aquatic life are critically dependent upon ice having lower density than water

Question 5

What are the 2 common mineral forms of CaCO3?

Answer 5

Calcite
• low pressure
• less dense

Aragonite
• high pressure form
• more dense

Question 6

What is the composition of apatites?

Answer 6

Ca5(PO4)3X
X=F gives fluoro-apatite
X=OH gives hydroxy-apatite

Question 7

Where are hydroxy-apatites found in humans?

Answer 7

Bones and teeth

Question 8

Shells composition

Answer 8

99% CaCO3 and 1% protein
• disc-like microcrystal slabs of aragonite grown between membrane like protein sheets
• contains outer layer oc calcite

Question 9

What does the protein determine in shells?

Answer 9

• whether calcite or aragonite is grown

* shape and size of the crystals and their crystallographic orientation

Question 10

What causes the dizziness in vertigo?

Answer 10

Calcium carbonate crystal (otoconia) has moved out position in the canals in the inner ear

Question 11

Describe the apatite structure in bones

Answer 11

• mainly consist of hydroxy-apatite
• in a matrix of protein collagen
• apatite crystals are largely flat plates
• lightweight, strong but not brittle

Question 12

Describe the apatite structure in teeth

Answer 12

• approximately twice the mineral content of bone - 95% volume is mineral
• hydroxy-apatite is present in the form of needle like fibres with small amounts of protein in between

Question 13

fluoridation in tooth enamel

Answer 13

• food acids dissolve enamel bc strong bases like OH i enamel
• F- in diets replace OH- giving fluoro-apatite
• produces a tougher structure, less susceptible to attack by acids

Question 14

Describe the different levels of solubility of ionic solids

Answer 14

Insoluble
• ores (PbS, ZnS, Fe2O3)

Limited Solubility
• CaCO3 - hydroxyapatite

Soluble
• drugs - LiCO3
• electrolytes, flavourings (salt, etc)

Question 15

Effect of temperature on solubility

Answer 15

• gases decrease in solubility as you raise the temperature

* solubility of solids increase with increased temperature, most of the time

Question 16

What is the common ion effect on solubility?

Answer 16

• solubility of a sparingly soluble ion is reduced in the presence of a common ion
• e.g. BaSO4
BaSO4 Ba2+ + SO42-
• BaSO4 is very insoluble

Question 17

How is Barium used in radiology and why is it used?

Answer 17

• heavy metal Ba is a strong absorber of X-rays
• Barium ‘meal’ is used in radiology - BaSO4 is made up as a slurry in Na2SO4 - this reduces the solubility of toxic Ba2+ ion due to present of common ion (SO42-)