The Oceans Notes

HideShow resource information
  • Created by: Teresa
  • Created on: 18-04-13 18:36
Preview of The Oceans Notes

First 345 words of the document:

The Oceans- Notes
Storing Carbon Dioxide
o The solubility of gases decreases as temperature increases; this is illustrated in the following graph
which shows the solubility of carbon dioxide in water:
o There is also a relationship between pressure and the solubility of gas; the higher the pressure, the
greater the volume of gas dissolves in the solution.
o Carbon dioxide is put into drinks under considerable pressure in order to make them fizzy.
o Therefore a high pressure and low temperature will help keep your can of coke fizzy.
o These conditions also favour carbon dioxide dissolving in the oceans, thus removing it from the
atmosphere, helping to maintain a constant environment on Earth.
o The exchange of CO2 between the atmosphere and the ocean takes place rapidly; much faster than
if water was left to rest in a glass.
o The uptake of CO2 by the oceans is made much more efficient by the effects of marine life; for
example, CO2 is taken up by phytoplankton (for photosynthesis), the phytoplankton is then eaten
and metabolised by animals which release CO2 into the water.
o Carbon dioxide is much more polar than O2 and N2; this is related to the fact that it has polar bonds
which can interact with the dipolar water molecules.
o At the surface of the oceans, the following equilibrium is taking place:
CO2 (g) CO2 (aq)
o Some of the carbon dioxide then reacts with water:
CO2(aq) + H2O(l) H+(aq) + HCO3-(aq)
HCO3-(aq) H+(aq) + CO32-(aq)
o This removes some of the aqueous carbon dioxide from the water, and thus shifts the position of
equilibrium (in the reaction of CO2dissolving in water) to the right.
o Much of the carbon dioxide we pump into the atmosphere is absorbed by the oceans in this way
(probably around 35-50% is removed in this way).
1

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

The Oceans- Notes
o The aborption of CO2 into the oceans is a continual process; the surface water that is rich in
CO2 sinks to the deeps of the oceans, where it is stored for hundreds of years.
Dissolving calcium carbonate
The overall equations listed previously can be combined into one equation:
CO2(aq) + H2O(l) 2H+(aq) + CO32- (aq)
o According to Le Chatelier's principle, removing the H+ ions will result in more CO2 dissolving into the
ocean.…read more

Page 3

Preview of page 3

Here's a taster:

The Oceans- Notes
o There are no shells on the ocean floor; they have all dissolved by the time they reach the low
temperatures and high pressures.
o This means that the calcium carbonate cliffs must have formed in shallow seas; it is likely that the
water was also warm and tropical.
Ions in Solution
o There are two important factors in deciding how ions behave in solution and how they behave in
ion-exchange; the size of the ion and the charge on the ion.…read more

Page 4

Preview of page 4

Here's a taster:

The Oceans- Notes
o For example, in Group I, the atomic radii of the atoms increases down the group as more electrons
are added:
o Moving across a period, the atomic radii decreases even though extra electrons are being added.
o This is because the number of protons increases along the period.…read more

Page 5

Preview of page 5

Here's a taster:

The Oceans- Notes
o Removing an electron results in an ion that is smaller than the atom. Removing more than one
electron has an even greater effect.
o The general rule is:
r2+ < r+ < r(atom) < r- < r2-
o This effect of charge can be illustrated in the following examples:
Hydration
o The above situation works for ions in the solid, liquid and gaseous phases; however, when an ionic
substance is dissolved in water, the situation is different.…read more

Page 6

Preview of page 6

Here's a taster:

The Oceans- Notes
o Hydration makes small, strongly attractive ions behave as if they are larger and less attracting.
Solubility Products
o Nothing is insoluble; there will always be some substance dissolved in solution, no matter how
small.
o The increase in entropy associated with dissolving ensures that this is so.
o Thus, even on a beach, rain water will leach out the silicon dioxide and transport it to the sea.…read more

Page 7

Preview of page 7

Here's a taster:

The Oceans- Notes
o As the solution is saturated, adding more solid will not push the position of equilibrium any further
to the right; therefore the solid can be neglected from the expression for the equilibrium constant;
this gives the following equilibrium constant:
Ksp = [Ca2+(aq)] [CO32-(aq)]
o This is known as the solubility product.…read more

Page 8

Preview of page 8

Here's a taster:

The Oceans- Notes
o The Ksp value can also be used to determine the how other ions in the solution can affect the
solubility of a sparingly soluble compound, for example, how adding extra Cl- or Ag+ ions will effect
the concentrations.
o Imagine that we added some silver chloride to a 0.1 mol dm-3 solution of sodium chloride; the
concentration of dissolved silver ions at equilibrium can be worked out.…read more

Page 9

Preview of page 9

Here's a taster:

The Oceans- Notes
o Forming a lattice from gaseous ions is always an exothermic process, and so Hle is always
negative.
o In order for an ionic substance to dissolve in water, the ions in the lattice must be separated; this
requires energy to overcome the electrical attraction between the ions.
o The strength of the ionic attractions in the lattice is measured using the lattice energy.…read more

Page 10

Preview of page 10

Here's a taster:

The Oceans- Notes
o The smaller the ion and the higher its charge, the more water molecules it attracts.
o The strength of the attractions between the ions and the water molecules is measured by the
enthalpy of hydration ( Hhyd).
o The enthalpy change of hydration is defined as the enthalpy change for the production of a
solution of ions from one mole of gaseous ions.
o For example:
o Enthalpies of hydration depend upon the concentration of the solution produced.…read more

Comments

Aisha


do you have any for medicine by design 

thank you for the notes what did u get for chemistry ?

Suhel Haque

Medicine by Design? 

Similar Chemistry resources:

See all Chemistry resources »See all resources »