solutions

Question 1

water molecule characteristics

Answer 1

Charge Distribution: No charge; net negative on oxygen, positive on hydrogen.
Properties: Forms weak hydrogen bonds; 3D structure.
Hydrogen Bonds: Weaker than ionic, covalent; continuous break and reform.

Question 2

polaraisation and solvation

Answer 2

Solvation Example: Na+ cation in water; Cl- anion surrounded by water molecules.
Effect: Solvation prevents interaction between solvated ions, inhibiting solid precipitation.

Question 3

water and ethanol interaction

Answer 3

Water Polar Molecule: Oxygen negative, hydrogen positive.
Ethanol Interaction: Weak bonds with water; OH group attachment.
Result: Weak bonds prevent ethanol rotation, causing volume shrinkage in mixture.

Question 4

Concentration Representation

Answer 4

Molality: Moles of solute per kg of solution; accurate representation.
Molarity: Moles per liter; common in field measurements, corrected for temperature.

Question 5

pH and activity in solution

Answer 5

pH: Minus log to the base 10 of hydrogen ion activity.
Activity: Effective concentration of a species in a solution.
Activity Coefficient: denoted as ‘γ’, modifies concentration to effective activity.

Question 6

ionic strength and Debye Huckle equation

Answer 6

Ionic Strength: Measure of solute dissolved in solvent.
Debye Huckel Equation: Base 10 log of activity coefficient (‘γ’) expression.
Components: Constants (‘A’ and ‘B’), total ionic strength (‘I’), ion charge (‘z’), and ionic radius (‘a’).

Question 7

equilibrium conditions

Answer 7

Definition: Balance in a reaction where the rates of the forward and reverse reactions are equal.
Example: Carbonic acid dissociating into protons and bicarbonate.
Equilibrium Constant (K):
Describes relative ratios of products and reactants.
Computed using activities, raised to stoichiometry powers.
Determined experimentally for specific conditions.

Question 8

equilibrium constant rules

Answer 8

Rule 1: Each species activity raised to its stoichiometry power.
Rule 2: Activities of water and pure solid phases are considered 1.
Simplification: Equations can be simplified based on phase characteristics.

Question 9

element distribution

Answer 9

Example: Distribution of La between Olivine and Clinopyroxene.
Expression: Ratio of La concentration between minerals.
Application: Helps reconstruct pressure and temperature during mineral formation.

Question 10

Solubility Product (Ksp)

Answer 10

Concept: Extension of the equilibrium constant for dissolution.
Example: NaCl dissolving in water.
Expression: Ksp = product activities multiplied.
Usefulness: Determines saturation state; oversaturation leads to precipitation, undersaturation may cause dissolution.
Caution: Thermodynamics predicts equilibrium, not reaction speed.

Question 11

Barite (BaSO4) solubility

Answer 11

Example: Ksp for barite (BaSO4) determined by experiments.
Application: Measure Ba2+ and SO42- concentrations; calculate activity product.
Result Interpretation: If greater than Ksp, oversaturated; precipitation expected. If less, undersaturated; dissolution possible.
Omega Value: Measures oversaturation or undersaturation; omega > 1 (oversaturation), omega < 1 (undersaturation).

Question 12

complex formation

Answer 12

Equation: Dissolved uranium reacts with organic matter and water to form uraninite and carbonic acid.
Degrees of Interaction:
Solvation shell contact.
Shared solvation shell.
Formation of dissolved complex.
Impact of Concentration:
Weak dipole bonds between water and ions.
Increasing concentration leads to complex formation.
Complex Strength:
Depends on ion charge and temperature.
Higher ion charge favors complex formation.
Cation Interactions:
Form electrostatic bonds with anions.
Weaker than ionic and covalent bonds.
Ligand Types:
Bidentate ligand illustrated with oxalate anion.
Examples: Cu2+ complexed by glycine, Enterobactin complexing Fe3+.

Question 13

Equilibrium constants for complrx formation

Answer 13

Term: Equilibrium constants for complex formation are stability constants.
Control Over Solubility:
Hydroxide ligands from water dissociation.
Least soluble salts of many metals.
Example Reaction:
Solid Al(OH)3 (gibbsite) reacting with protons.
Dissolved Al3+ complexing with increasing hydroxide ligands.
Solubility Product Type:
Incorporates solid’s activity as 1.
Free Ion:
Ion not associated with any ligands.
Al-Hydroxide Complexes:
Different complexes based on the number of OH ions.
Stability constants determined by experiments.

Question 14

solubility of Gibbsite

Answer 14

Solubility Product: 10 to the power of 8.1 under standard conditions.
pH Impact: Higher pH lowers dissolved Al3+ activity.
Prediction: If Al3+ activity exceeds 0.126 M/kg, gibbsite precipitates.
Calculation: Calculate Al-hydroxide complexes’ activities based on Al3+ activity at a particular pH.
pH Influence: Lower pH allows higher dissolved Al3+ activity.
Application: Predicts gibbsite precipitation or dissolution based on pH and Al3+ activity.