chemistry

CH3COO-

Ethanoate

No3-

Nitrate

Ionic product formula? What is it used for?

- Determines whether the solution is saturated or not (whether ppt will form). To calculate the product of the conc of the ions, raised to the same powers as in the Ks expression, is called the ionic product. Eg PbOH2 I.P = [Pb2+] [OH-]^2 - When 2 solutions are mixed calculate diluted ion conc. dont forget to account for V In saturated solution I.P=S.P, the dissolved ions are in equilibrium w/ the undissolved solid, the I.p then = to the solubility product. no more can dissolve I.P < Ks not saturated, conc can be inc by dissolving more solid I.P > Ks Supersaturated, PPt usually occurs, ions come out of solution to form solid to reduce the high ion conc.

The common ion effect on solubility

- When ions are shared between 2 different compounds they can-t be used as a measure of the solubility - when ionic solid dissolves in a solution which has an ion in common with the solid its solubility is reduced - The solubility of the solid is measured by the conc of the ion which is not in common

PH scale formula for ph calculation dissociation of water

-The acidity of a solution is determined by its hydronium ion concentration (H+/H3O+) -Ph is a measure of the hydrogen ion concentration -Ph= -log[H+] -(1 times 10^-14)

calculating phs of 1) strong acids 2)strong bases 3)weak acids 4)weak bases 5)ionic salts that dont hydrolyse 6)ionic salts where cation hydrolyses 7)ionic salts where anion hydrolyses

1) strong acids -dissociates completely, none of original acid in solution and the anion wont hydrolyse with water bc reforming the acid will cause it to dissociate completely again -Small amounts of H3O+ and OH- present from dissociation of water but assume the amount of H3O+ is negligible in comparison to the H3O+ formed from acid dissociation so [H3O+]=Acid Ion conc [H3O+]=[ClO4-]>>[OH-] 2)strong bases -dissociates completely, none of original base left in solution, the cation wont hydrolyse with water bc it will reform the base and cause it to dissociate completely again -small amounts of OH- and H3O+ present from dissociation of water but assume it is a negligible amount of OH- compared to the OH- formed from dissociation of the base so [OH]-=Base's ion conc [Na+]=[OH-]>>[H3O+] 3)weak acids -very little of the weak acid reacts with water so undissociated acid molecules are present in the highest concentration. -For each molecule of acid that reacts, equal amounts of separated ions are formed. Extremely small amounts of H3O+ and OH- are present due to the dissociation of water. [CH3COOH]>[H3O+]≈[CH3COO-]>>[OH-] weak conductor as it is a weak acid and there arent a lot of freely moving hydrated ions in solution 4)weak bases -very little of the weak base reacts with water so undissociated base are present in the highest conc -for each molecule of base that reacts, equal amounts of separated ions are formed extremely small amounts of h3O+ and OH- are present due to the dissociation of water [NH3]>[OH-]≈[NH4+]>>[H3O+] weak conductor as it is a weak base so there arent a lot of freely moving hydrated ions in solution 5)ionic salts that dont hydrolyse -dissociation of the salt molecule results in a neutral ph because species originate from strong acids and strong bases, none of original salt left in the solution -Extremely small amounts of H3O+ and OH- are present due to the dissociation of water. Equal amounts are also formed so the solution is neutral. [Cl-]>[Mg2+]>>[H3O+]=[OH-] salts formed from a strong acid and strong base are good conductors of electricity due to the high concentration of ions. 6)ionic salts where cation hydrolyses weak base/strong acid. dissociates completely, no original salt left in solution Extremely small amounts of H3O+ and OH- are present due to the dissociation of water. the ions react further with water and changes the conc of the species present equilibrium shifts [Cl-]≈[NH4+]>[H3O+]≈[NH3]>>[OH-] As there are many ions in solution, the salt is a good conductor of electricity as there are many ions to carry the current. 7)ionic salts where anion hydrolyses strong base/weak acid. dissociates completely no original salt left in solution Extremely small amounts of H3O+ and OH- are present due to the dissociation of water. ions react further with water and changes the conc of the species present equilibrium shifts [Na+]≈[CN-]>[OH-]≈[HCN]>>[H3O+] As there are many ions in solution, NaCN is a good conductor of electricity as there are many ions to carry the current.

Types of solutions 1)Strong acids and bases 2)Weak acids 3)Weak bases 4)Ionic solids 5)Molecular substances

1)Strong acids and bases -dissociate completely in H2O, forming H3O+ and OH-, and conjugate acid and base ions -solutions of these will be good conductors because of the presence of ions - high ph or low ph unless diluted 2) weak acids -dont react completely with water(and their conjugate weak bases)both the acid(usually a molecule) and its conjugate base (usually ion) will be present -conduct better than water but less than strong acids/bases due to fewer ions present in solution ph 3-6 3) weak bases -similar conductivity to weak acids ph 8-11 4)ionic solids -dissociate completely into separate aqueous ions -very good conductors, presence of freely moving aqueous ions -ph is determined on whether the ions react further with h20 (hydrolyse) 5) molecular substances -separate into aqueous molecules -unless the molecules hydrolyse the conductivity wont be better than water (poor conductor) -neutral ph of 7

factors that affect solubility

A sparingly soluble ion solid may dissolve completely if able to form a soluble complex ion, mostly transitions metal ions form complex ions then dissolve.

NH4+

Ammonium

Properties of Aqueous Solutions

Aqueous solutions are formed when a solute dissolves in water - the solution will conduct electricity if aqueous ions are present conductivity inc with the numver of ions in solution - [H+]> 1times10^-7 solution is acidic and ph<7 more H+ than OH- -[H+]<1times10^-7 solution is basic and ph>7 more OH- than H+

simple ionic substance

Atoms that gain or loose electrons to form cations or anions

sparingly soluble compounds

BaSO4 Ca(OH)2 Ag2S

CO3 2-

Carbonate

Equilibrium

Chemical equilibria are dynamic= not visible to eye but microscopically changes happen chemical equilibrium is -a closed system -macroscopic properties remain constant -changes continue at molecular level -rates of forward and reverse reactions are equal

CrO4 2-

Chromate

Cr2O7 2-

Dichromate

-Calculation of Ph for strong acid - strong acids -assumptions with phrase

For strong monoprotic acids, the hydronium ion = the conc of the acid because the acid molecule completely dissociates into hydronium ions and conjugate base ions Monoprotic= The acid molecule is able to donate one proton (H+) -HCl Hydrochloric acid HNO3 Nitric acid HClO4 Perchloric H2SO4 Sulfuric Assumptions made when the phrase [H3O+]=conc of strong acid by definition a strong acid will dissociate completely, this means no original acid should be left in solution at equilibrium for every molecule of HCl that reacts with water 1Cl- and 1H3O+ ion will be formed so H3O+=Cl- PROVIDED THAT WE ASSUME that the amount of H3O+ ions contributed by the dissociation of H2O (2H20equilibrium arrow H3O+(aq) + OH-(aq) is negligible, this is valid because the conc is significantly bigger than Kw (1 times 10^-14).

Polyatoic Ionic substance

Groups of atoms that are covalently bonded together and have an overall charge

measuring acidity or alkalinity Water

H2o + H20 -> H3O+ + OH- Acids produce hydrogen ions (hydronium ions in water Bases produce Hydroxide ions in water Acids are proton donors (H+) and bases are proton acceptors Water is Amphiprotic: can act as an acid or a base/ can either donate or accept protons HCO3- is also Amphiprotic HCO3- as acid HCO3-(aq) + OH-(aq) -> CO3^2-(aq) + H2O(aq) HCO3- as base HCO3-(aq) + H3O+(aq) -> H2CO3(aq) + H2O(aq)

HSO3-

Hydrogen Sulfite

HSO4-

Hydrogen sulfate

Hydrolysis of Salt solutions ph definition

Hydrolysis is an acid base reaction between ions of a salt, and water (involves splitting h20) Salts are an ionic compound made up of a cation and an anion the ph of a salt may be neutral (NaCl) acidic (NH4Cl, NaHSO4) or basic (CH3COONa, Na2CO3) some anions are conjugate bases of weak acids. The anions split h2o molecules by taking H+ from them, as a result OH- is formed Anions that are conjugate bases of strong acids don't hydrolyse (Cl-, NO3-,ClO4-) So4^2- hydrolyses very slightly So4^2-(aq) + H2O(L) equilibrium arrow HSO4(aq) + OH-(aq)

ionic solids dissolving

Individual ions break away from their fixed lattice positions and are surrounded by H20 molecules to form aqueous ions

-Acid equilibria -conc of water? -Ka for general acid HB

Ka is equilibrium constant for weak acids Weak acids partially dissociatte with the other present dissociated ions existing in equilibrium The H ion conc is related to - the conc of the acid -The acid dissociation equilibrium constant K=Products multipled/reactants multiplied -conc of water=55mol.L-l and is always constant -Ka for general acid HB is (B- being the conjugate base) HB(aq) + H2O(l) equilibrium arrow B-(aq) + H30+(aq) Ka for Hb= [B-][H3O+]/[HB] Ka varies with temp

base equilibria

Kb is the equilibrium constant for weak base Molecule partially dissociates, with the dissociated ions existing in equilibrium with the base molecule of OH- relating to both - the conc of base - base dissociation equilibrium constant K=Products multipled/reactants multiplied in water a weak base dissociates partially to form NH4+, OH- Kb=[NH4][OH-]/[NH3][H20] Kb[H20]=[NH4][OH-]/[NH3] and sub in water=55mol.L-1 Kb varies with temp

common ion effect

Le Chatelier's principle: If change is imposed on a system at equilibrium then the position of the equilibrium will shift to lessen the amount of change.

MnO4 2-

Manganate

Solubility

Maximum amount of a substance which dissolves per litre of solution (measured in m.L-1 / g.L-1). temp must be given

No2-

Nitride

Limitations of the Solubility product principle

Only sparingly soluble salts have been discussed when talking about solubility product, this is because the solubility product principle is valid for solutions where total C of ions is low, 0.01 mol.L-1 or less

PO4 3-

Phosphate

PKa defined and calculated

Pka=-logKa has no units a way of measuring Ka values without writing powers of 10

relationship between Ka and Kb

Related to Kw(dissociation of water constant) Kw=[H3O+][OH-]=1times10^-14 Ka for HB =[B-][H3O+]/[HB] Kb for B-=[HB][OH-]/[B-] (Ka times Kb)= Kw The stronger a base the weaker its conjugate acid because Kw=ka times kb and kw is a constant value

Soluble or insoluble

Soluble = 10g or more dissolves in 1L of solvent Insoluble = less than 0.001g dissolves in 1L sparingly soluble = between 0.001 and 10g

Hydrolysis of Cations

Some cations are conjugate acids of weak bases. These cations donate H+ to water molecules eg. [Al(H2O)6]3+(aq) + H2O(l) equilibrium arrow [Al(H2O)5OH]2+(aq) + H3O+(aq) In this example one of the H2o molecules bonded to the Al ion Has been split and donates an H+ to a non bonded H20 molecule in solution -small metal ions w/ high charges such as Al3+ or Fe3+ hydrolyse strongly -metal ions such as Zn2+, Cu2+ only slightly hydrolyse

conc of saturated solution

Stays the same because no more solid will dissolve in the given amount of solution Conc of ions and cations are dependent on ration of ions in the formula of the substance

- Calculation of pH in strong bases. - different strong bases

Strong bases dissociate completely into its ions For strong bases such as NaOh and KOH the OH- ions conc is the same as the conc of the base. Ph= -log[OH-] Kw=[H3O+][OH-]= 1 timesed 10^-14 Kw/conc=H3O+ Ph=-log[H3O+] -NaOH Sodium hydroxide, KOH Potassium hydroxide Mg(OH)2 Magnesium hydroxide Ca(OH)2 Calcium Hydroxide

Relationship between acid strength and Ka or Pka values

Strongest acids : - give solutions with highest [H3O+] and lowest ph - highest Ka values and lowest Pka

SO4 2-

Sulfate

SO3 2-

Sulfite

Solubility product expression

When a saturated solution forms theres a relationship between the conc of the ions in solution and the undissolved solid (PPT) as an equilibrium is established AB(s) (equilibrium arrow) A+(aq) + B-(aq) Ks=s^2 Solids have a constant value for conc, so its expression for its constant is Ks=[A+(aq)] [B-(aq)]= solubility product When AB2 then Ks=4s^3 Because: AB2 (s) (equilibrium arrow) A2+(aq) + 2B-(aq) Ks= [A2+] [B-]^2

Complex ions

consist of a metal ion and one or more ligand ligand= an ion or molecule which is bonded to the metal ion by coordinate bonding e.g H2O, NH3, CO, CN-, Cl-, OH-

equilibrium constant size of equilibrium constant and what that means

determines whether products or reactants are favoured Kc= equilibrium constant and this is the relationship between products and reactants at equilibrium at a given specific temp [products]/[reactants] The size indicates the position of equilibrium. Shows the extent to which a reaction favours the reactants or products. Large Kc Values: Kc>1 (25C) then there is a greater conc of products than reactants hence products are favoured Small Kc values: KC<1 (25C) then greater conc of reactants than products. Reactants are favoured

Effect of Ph on solubility

eg of CaOH2 (Equilibrium arrow) Ca2+ (aq) + 2OH-(aq) Ks= [Ca2+][OH-]^2 A PH>7 has higher [OH-] so [Ca2+] decreases to keep the Ks value constant- less Ca(OH)2 (s) dissolves A PH<7 has less [OH-] so [Ca2+] inc to keep Ks value constant so more Ca(OH)2 (s) dissolves. -Reaction with acid or base affects solubility of the solute with eg of CaCO3 it is sparingly soluble in water but in low PH(acidic) solutions it will readily dissolve. this is due to the basic carbonate ion, CO3-, reacts with H+ ions CaCo3(s) + 2H+ (aq) -> Ca2+(aq) + H2O(l) + CO2(g)

ph calculation for weak acids

equation, ka expression, assumptions (eg H3O+ is formed in equal molar amounts to a conjugate base), ka substitution

Conc of dissolved species

for any ionic solid where the amount of dissolved solid = smolL-1 and neither of the ions reacts further with water the conc of the ions in solution will be as follows Conc A ion Conc B ion AB s s A2B 2s s AB2 s 2s

How to calculate ph of salt solutions

helps to know the ph of salt solutions to identify ph changes and then identify equivalence points w/ anions: Calculate the pH of a 0.300 mol L-1 solution of potassium cyanide KCN.Ka (HCN) = 6.03 × 10-10 and Kw = 1.0 × 10-14. KCN(s)H2O→K+(aq) + CN-(aq) The K+ doesn't react with H2o because it comes from strong base of KOH (strong bases dissociate completely) The CN- ion is the conjugate base of the weak acid HCN, so will react(Hydrolyse) as shown H2O(l) + CN-(aq) equilibrium arrow HCN(aq) + OH-(aq) Assumptions: For this reaction, make two assumptions to simplify the calculation: [CN-] = 0.300 mol L-1 (Because cyanide is a weak base, assume the amount y that reacts with H2O is negligible compared to 0.300.) [HCN] = [OH-]. In the equation above, for each molecule of CN that reacts, one HCN ion and one OH- ion are formed. Ignore OH- ions contributed by the dissociation of water. Kb for CN-=[OH-]^2 0.300 Cations: same but [H3O+]^2=Ka Assumptions: ignore H3O+ contributed by dissociation of water

HCO3-

hydrogen carbonate

HPO4 2-

hydrogen phosphate

OH-

hydroxide

equilibrium in saturated solution

no more solid that is added will dissolve in the given V of solvent (at fixed temp) There must be undissolved solid present for you to determine if its saturated eg undissolved salt crystals

MnO4-

permanganate ion

Conjugate acid and conjugate base

when a proton is removed from an acid its conjugate base is formed in turn each base will have a conjugate acid H3O+(aq) is the conjugate acid of H2O(l) (accepts H+ so base) NH3(aq) + H2O(l) equilibrium arrow NH4+(aq) + OH-(aq)