E-chem Exam

aW+bX->cY+dZ

K=[Y]^c[Z]^d/[W]^a[X]^b

• Equilibrium-constant equations
• Mass-balance equations
• –Relate
• equilibrium concentrations of species with the analytical concentration of
• solutes

• Charge-balance equations
• –Based
• on idea that electrolyte solutions have to be electrically neutral

• # moles positive charge/L = # mols negative charge/L

•  Remember that the # mol gets multiplied by charge to give the moles of charge, e.g., for 0.20 mol Mg2+, there are 0.40 mol of positive charge.

• 1)Write balanced chemical equations for all
• relevant equilibria
• 2)State in terms of equilibrium conc. the
• variable being sought
• 3)Write equilibrium constant expressions
• for all the equilibria and find the appropriate K values
• 4)Write mass balance expressions
• 5)Write any available charge-balance
• expressions
• 6)Make sure # of unknowns equals # of
• equations.  If not, try to approximate
• concentrations of some of the unknowns
• 7)Approximate as possible to simplify the algebra
• 8)Solve the equations
• 9)Check validity of approximations

• HA + H2O = H3O+ + A-  

• Na+ + A- + H2O=OH- + HA + Na+          

[H₃O⁺][A^-]/[HA]

[OH^-][HA]/[A^-]

• 1.if Ka or Kb
• is >10-3 (strong acid or base)

• 2. if the molar concentrations of HA or A- are very small so that the assumptions
• that we can ignore [OH-]
• and/or [H3O+]
• no longer hold.

comes from charge balance.  

# negatively charged species = # positively charged species

• Kolinite
• illite
• chlorite
• montmorillonite

product of intense tropical and desert weathering. Most found in equatorial sediments. Note lack of exchangeable cations…

• polar sources
• physical weathering 
• lots of exchangeable ions

• one of the most common clays.
• High in potassium
• Land-derived, in oceans highest in concentration in midlatitudes in the northern hemisphere (which has more land)

• expanding clay
• weathering in poor drainage areas
• in situ weathering product of volcanic ash

potassium or sodium salt of a fatty acid

acts to reduce interfacial or surface tension

X=P_CO2/P_total

life such as plants that use photosynthesis to creat organic carbons form the atmosphere

oceans take up 2.2Gt/yr of carbon due to solubiliy

K_sp=[X]^a[Y]^b= XY in molarity

–Building blocks for life/energy source for heterotrophs

–Global C cycle

–O2 balance

–Climate

• –Affects
• contaminant transport

• –Affects
• nutrient transport

• –Affects
• light penetration

Dissolved organic matter

Particulate organic matter

-leftovers of biologically-produced material

-Heterogeneous

-Biologically refractory

-Involved in photochemical reactions

-Form complexes with metals

-Involved in hydrophobic interactions with anthropogenic organic compounds

-Form disinfection by-products during drinking water treatment

-Affect soil fertility, also weathering processes

• soluble in alkaline solutions, insoluble
• below pH 1 (I have also seen pH 2 used as criterion)

• alkaline extractable, soluble over whole
• pH range

Insoluble in acid or base

• - have aromatic character, phenolic OH
• groups, carboxylic groups, aliphatic OH groups
• -yellow or brown color

H⁺=A^- as long as the dissosciation of HA is the main source of H⁺ ion and not water

K_w=[H⁺][OH^-]

=K_a(C_HA/C_NaA)