Mod 5 Solubility Equilibria Flashcards
Describe the processes involved in the dissolution of ionic compounds in water
It is only when the solution is saturated, that the dissolution reaction is equilibrium.
Water is a polar molecule, where it is slightly positive at the hydrogen ends and slightly negative on the oxygen end. These charged ends of the molecule will attract the opposite charge in the ionic compound.
However, not all ionic compounds are soluble in water or are partially soluble in water. This is because the ion dipole forces between ions and the polar molecule is not strong enough to break the ionic bonds that holds the ions together in the lattice
What is a saturated solution?
A solution in which the maximum amount of solvent has been dissolved. Any more solute added will sit as crystals on the bottom of the container.
What is the solubility of a substance?
Max amount of solute that dissolves in a specific amount of solvent at a particular temp.
What is a solute?
Substance that is dissolved in a solvent, forming a solution
What is a solvent?
Something that dissolves
What is the difference between molar solubility and solubility?
Solubility is typically the mass of solute/volume of saturated solution, molar solubility is typically number of moles/ volume (L)
What is density(p)?
Mass of substance (m)/ volume of substance (v)
How to calculat parts per million?
mass of substance (in mg)/ volume of substance ( in kg)
How to calculatee parts per billion?
Mass of substance (in micrograms)/ volume of substance (in kg)
How to calculate percentage by mass?
g/100g = %w/w
How to calculat percentage by volume
mL/100mL = %v/v
What is the formula of solubility product constant (ksp)?
It is the equilibrium constant for the dissolution process of an ionic solid that dissociates completely in solution
What is the geeneral equation for ksp?
AaBb (s) ⇌ aA x+ (aq)+ bB y- (aq)
What is the formula for Ksp?
[A^x+]^a [b^y-]^b
What happens if value of Ksp is small?
Indicates a highly insoluble solution, as there are less dissociated ions than there are solids.
What happens if value of Ksp is big?
Indicates a highly soluble solution, as there are more dissociated ions than there are solids.
What is Qsp?
Essentially same as Ksp but does not have to be in equilibrium
What happens if Qsp > Ksp
Therefore, system attempts to reach equilbrium through favouring the reaction which reduces aqueous ions –> favouring reverse reaction –> formation of precipitate
What happens if Qsp < Ksp?
Therefore, system attempts to reach equilbrium through favouring the reaction which increases aqueous ions –> favouring forward reaction –> less precipitate, more aqueous ions –> no formation of precipitate
How does adding water (dilution) affect the Ksp? According to LCP
LCP: Equilibrium will shift to minimise the disturbance. When we add water, concentration of ions decrease, disturbing equilibrium and to counteract this change, the equilibrium will shift to favour the forward reaction to increase conc of aqueous ions –> more of solid precipitate will dissolve
How does adding water (dilution) affect the Ksp? According to Qsp and Ksp?
Compare valus of Qsp and Ksp to predict direction of change and new equilibrium. When water is added, there is dilution of concentration of aq ions, this indicates decreased Qsp, as Qsp increases to reach Ksp, therefore the concentrations of the products have to increase –> favouring the forward reaction
How does adding water (dilution) affect the Ksp? According to collision theory
When water is added, conc of ions decrease, disturbing the equilibrium. As concentrations of ions decrease, frequency of collisions for reverse reactions will decrease, thus equilibrium shifts in the right as the forward reaction is left unchanged, thus equilibrium shifts right (more precipitate dissolving)=
What are th steps in calculating solubility from Ksp?
- Write an equation for the dissolution and the corresponding Ksp expression
- Determine the ion concentrations from thee moles of the solute using the mole ratios (
- Substitute the concentrations into the equilibrium expression to solve for x
How to calculate solubility from Ksp using ICE table?
- Write equation for the dissolution and Ksp expression
- Make an ICE table in units of M to set out working for calculations
- Determine thee ion concentrations using the ICE tables, noting that reactants will have a ‘+x’
- Sub concentrations into equilibrium expression to solve for x
How to calculate Ksp from solubility?
- Write an equation for the dissolution and the corresponding Ksp expression
- Calculate the ion concentration from the moles of the solute using the mole ratio
- Substitute the concentrations into the Ksp expression and solve for Ksp
CHECK TABLES IN BOOK LEARANABLES
DO IT
What are common ions?
In an aqueous solution, a solute dissolves and dissociates to produce ions, this means in solution, ions of the same species are indistinguishable . Thus, when another compound is dissolved in a solution with a common ion, it is called the common ion
What is the common ion effect?
A solution containing a mixture of salts with a common ion will produce a solution a combined total of moles (and concentration) of the common ion
How to calculate solubility under common ion effect?
- Chemical equation and Ksp
- Construct ICE table
- Calculate equilibrium concentrations using ICE tables
- Solve for K using eq concentrations (and HAVE TO MENTION THAT X IS SO SMALL THAT IT IS NEGLIGBILE - COMMON ION EFFECT MAKES X NEGLIGIBLE)
What Ksp value is considered slightly soluble?
Salts with Ksp >= 10^-6
What Ksp value is considered insoluble?
Salts with Ksp < 10^-6
What is detoxification?
Process of removing toxins (which are poisonous substances produced by organisms such as plants)
What methods are commonly used to detoxify foods?
Heating
Fermentation
Leaching
What is heating as a form of detoxification?
When food items are heated, heat causes the decomposition of toxins
What is fermentation as a form of detoxification?
During fermentation, food items are stored for several months to years. In this, the various biological processes break down the toxins. Toxins can then be digested by micro organisms or broken down by plant’s natural enzymes which accelerate transformation of toxins into other substances
What is leeching?
Process of removing a soluble solute (toxin) from host substancce using a solvent
What are cycads?
Cycads are palm like plants that produces seeds in cones. However, they contain highly toxic chemicals which can cause liver damage, cancer and loss of muscle control, neurodegenerative diseases
What are the two main toxins in cycads?
Cycasin and β - methylamino - L - alaine (BMAA)
What are the steps required to detoxify cycads?
- Heating ; seeds are placed in an oven or fire
- Grinding; The seeds are cut open or ground up
- Leaching; Seeds are leached in water. They are placed in mesh bays or wooven baskets and submerged i running water for pprox a week
What is the detoxification technique for moreton bay chestnuts?
Same as cycads
State the solubility rules regarding substances which are SOLUBLE
Eight
All Nitrates
All Acetates
All Sulfates (except calcium, barium, lead, mercury and silver)
All Chlorides, bromides, iodides (Group 7)(except lead, mercury and silver)
All ammonium compounds
Group 1 metals
What are the exceptions to sulfates and chlorides, bromides, iodides being soluble?
Sulfates - Calcium, lead, mercury, silver, barium
Chloride, bromides, iodides - Lead, Mercury, Silver
State the solubility rules regarding substances which are INSOLUBLE
5
All carbonates (except sodium, potassium, ammonium)
All oxides and hydroxides (except sodium, potassium, calcium, magnesium and barium)
All sulfides (except sodium, potassium, magnesium, calcium, barium and ammonium)
All phosphates (except sodium, potassium and ammonium)
What is required for solubility (in terms of bonds)
if the ion dipole forces between ions and the polar molecule are strong enough to break the ionic bonds
Why are some ionic compounds dissolving in water at higher temps but still in lattice forms at cooler temperatures?
Because the heat energy at higher temperatures provide energy that is stronger than the ion dipole force as well as the ionic bonds that hold the lattice together
