Water and SoilWater and SoilE7 + E12

Glossary!Glossary!

Soil pollution◦Any sort of chemicals or harmful gases that

pollute the soil◦Industrial waste from tankers and used engine

oil◦Pesticides and fertilizers disrupt food chains

and affect soil

Soil degradation◦Soil quality is lowered due to acid soils,

contamination, erosion, dry soil and sea water. ◦Also by human activities such as logging,

industry waste and grazing◦Results in reduced crop production

Salinization◦Caused by excess irrigation (supplying land

with water or wastewater)◦When water evaporates, salt is accumulated◦Roots of plants can’t take root on salty soil◦High level of salt is also toxic to plants

Nutrient Depletion◦Plants take out nutrients out of soil◦Nutrient level in soil reduces◦Levels should be replenished so crops can grow

healthily◦Done by adding manure or planting clovers and

legumes

Soil Organic Matter (SOM)Soil Organic Matter (SOM)

Organic chemicals in the soil◦Such as plant and material waste

Decomposition of these waste material creates high molecular mass molecules and smaller molecular mass molecules, these are called Humus (IMPORTANTE!)

Functions of HumusFunctions of Humus

Organic Soil PollutantsOrganic Soil Pollutants

Organic Soil Pollutants Source

Hydro Carbons Transport, solvents

VOCS, SVOCS (semi/volatile organic compounds)

Transport, solvents

Agrichemicals Pesticides, fungicides, herbicides

Polyaromatic hydrocarbons Incomplete combustion

Polychlorinated biphenyls (PCBs) Fridges, capacitors, transformers

Organotin compounds Bactericides, fungicides

Removal by chemical PrecipitationRemoval by chemical Precipitation

Removing heavy metals ions, phosphates and nitrates from water/sewage can be done by chemical precipitation◦Hg (aq)

2+ + S(aq) 2- = HgS (S)

◦Cu (aq) 2+ + OH (aq) 2- = Cu(OH) 2(S)

CalculationsCalculations

Solubility product Ksp is measure of solubility

Ksp=[A][B]◦E.g. find Ksp of PbS (S)

◦Pb (aq) 2+ + S(aq) 2- = PbS (S) 

◦Ksp = [Pb (aq) 2+][ S(aq) 2-]

Solubility Product KSolubility Product Kspsp

Ksp is temperature dependent.Precipitation will only form when the

product of the ions exceeds the numerical value of Ksp at that temperature◦[A][B] > Ksp

◦E.g. [Pb (aq) 2+][ S(aq) 2-] > Ksp

How to solve problems of How to solve problems of solubilitysolubility

Three types of questions for solubility1. Determine Molar Solubility2. Determining if precipitate is formed3. Find minimum concentration of one ion

Molar Solubility1. Write out ionic equation of problem2. Substitute Ksp value

3. Calculate molar solubility by square root of Ksp

Determining if precipitate forms1. Write out ionic equation of problem2. Determine if forms precipitate by finding product

of concentration of ions3. If products of concentration of ions greater than

Ksp then precipitate formsDetermine minimum concentration of one ion

1. Write out ionic equation of problem2. Substitute concentration of one ion, and Ksp 3. Figure other concentration

A Problem to solveA Problem to solve

a) Calcium ions in water are precipitated by adding sulfate ions

b) Given Ksp = 3.0 x 10 -5 mol2 dm-6 at 25˚C, calculate its molar solubility at 25˚ C

c) Determine if a precipitate will form when the concentrations are as follows [Ca (aq)

2+] = 1.0 x 10-3 mol dm-3 and [ S04(aq) 2-] = 1.0 x 10-2 mol dm-3

d) Calculate the minimum concentration of sulfate to precipitate the Ca (aq)

2+ ions, when [ S04(aq) 2-] = 1.0 x 10-3 mol dm-3

AnswerAnswer

a) Ca (aq) 2+ + S04(aq) 2- = CaS04(aq)

b) [Ca (aq) 2+] [ S04(aq) 2-] = 3.0 x 10 -5

Molar solubility = √(3.0 x 10 -5) = 5.5 x 10 -3 mol dm-3

c) 1.0 x 10-3 x1.0 x 10-2 =1.0 x 10-5 mol dm-3

1.0 x 10-5 mol dm-3 < 3.0 x 10 -5, therefore no precipitate

d) [Ca (aq) 2+] x 1.0 x 10-3 = 3.0 x 10 -5

[Ca (aq) 2+] = 3.0 x 10 -5/1.0 x 10-3 = 3 x 10 -2

mol dm-3

Cation-exchange capacityCation-exchange capacity

Plants swap H+ ions on the root hairs with negatively charged soil organic matter and clay particles

The more the soil can hold positive ions, the higher the CEC

The more acidic the soil, the higher the % of acidic cations, therefore pH of soil affects the CEC◦More acidic soil = lower CEC