O The Oceans

 

 

The story of the oceans: their role in regulating the climate, in forming rocks and in supporting life. Main topics:

• oceans and climate;

• the special properties of water;

• solids from the oceans: salt and calcium carbonate;

• dissolving and precipitation;

• acid-base processes in the oceans;
• oceans and the history of life.

 

 

 

O2 Learning outcomes

 

Candidates should be able to:

(a)   describe the factors determining the relative solubility of a solute in aqueous and non­aqueous solvents;

 

(b)   explain and use the terms: enthalpy change of solution, lattice enthalpy, enthalpy of solvatio (hydration);

 

(c)    describe the solution of an ionic solid in terms of an enthalpy cycle involving enthalpy change of solution, lattice enthalpy and enthalpies of solvation (hydration) of ions;

 

(d)   use enthalpy cycles to perform calculations involving enthalpy change of solution, lattice

       enthalpy  and enthalpy of solvation (hydration);

 

(e)

explain the factors determining the radii of anions and cations, including atomic number,

 

charge and hydration, and relate ionic size to properties;

(f)

 construct and use a Born-Haber cycle for a simple ionic compound;

(g)

discuss entropy changes in a qualitative manner, interpreting entropy as a measure of       the number of ways that molecules and their associated energy quanta can be arranged.

(h)

discuss qualitatively the process of dissolving in terms of energy and entropy factors;

 

(i)

interpret the tendency of a process to occur in terms of entropy changes in the system

 

(∆Ssys) and surroundings (∆Ssurr), and the requirement that the total entropy change (∆Stotal) should be positive.

(j)

calculate entropy changes using the expression: ∆Stotal = ∆Ssys + ∆Ssurr ;

 

(k)

 

calculate the entropy change for a reaction given the entropies of the reactants and products;

(l)

compare the following properties of water to those of other liquids, and other hydrides of

 

Group 6 elements, and relate them to molecular structure:

 

(i)

specific heating capacity,

 

(ii)

enthalpy change of vaporisation,

(m)

account for the influence of oceans on climate in terms of the characteristic properties of

 

water;

(n)

explain and use the following terms: strong acid and strong base, pH;

(o)

explain the significance of the ionic product of water, Kw ;

(p)

use given data to calculate the pH of solutions of strong acids and strong bases;

 

(q)

explain and use the following terms: weak acid, acidity constant Ka , pKa;

 

(r)

use given data to calculate the pH of solutions of weak acids;

 

(s)

explain the action of buffer solutions;

 

(t)

describe applications of buffer solutions;

 

(u)

use given data to calculate the pH of a buffer solution;

 

(v)

explain and use the term solubility product for simple ionic compounds of formula

 

 X n+Y n-

(w)

use solubility products quantitatively to perform calculations concerning dissolving and

 

precipitation processes;

 

(x)

 

interpret acid-base and precipitation processes in the oceans in terms of Ka and Ksp;

 

 

(y)

 

discuss the global influence of the processes occurring when carbon dioxide dissolves in

 

water.