CHEM12 - solubility equilibrium - unit 3

electrolyte def

• ex

• how to show these

substance that dissolves to create a conductive solution

• ionic compounds + acids

-show using dissociation/ionization eq (these form ions in solutions ∴ ionic solutions)

• start as SOLID then into multi AQ (with charges)

dissocation/ionization eq

always start w/ SOLID then form ions in solutions (AQ w/ charges)

-showing electrolyte

all ionic compounds are ____ before they are ______

are ionic compounds are SOLID before they are dissolved

what state are acids

acids can be solid, liquid, gas, it depends on the acid

• eg. HCl (g), CH₃COOH (l), H₂C₂O₄ (s)

non-electrolyte def

• eg

• how show

substance that dissolves to create a non-conductive solution

• eg. covalent compounds → except acids

-composed of molecules and DO NOT form ions ∴ molecular solution + no dissociation eq

-dissolves but no bonds break, change state

• eg. C₆H₁₂O₆ (s) → C₆H₁₂O₆ (aq)

saturated solution def

dissolved substance is in equilibrium with undissolved substance

molar solubility def

• units

equilibrium [ ] of the dissolved substance

→ the compound as a whole, NOT individual ions

• Molarity (mols/L)

equilibrium eq vs dissociation/ionization eq

both are solids decomposed into its AQ state w/ charges

• equilibrium eq has forward + reserve (two-way arrow)

• dissociation/ionization only is NOT reversible (one way arrow)

equilibrium eq

-represents what

-only for what compounds

-always start with SOLID, then AQ with charges

-two-way arrow

-forward rxn represents dissolving process

-reverse rxn represents crystallization/precipitation process

• (think abt becoming a solid)

-ONLY FOR FULLY SOLUBLE (not saturated) → check solubility table

how to determine concentration of ions given Molarity of one compound

• eg. Mg(NO₃)₂ has 4.2M

fully soluble = not saturated ∴ not eqb ∴ dissociation/ionization eq:

Mg(NO₃)₂ (s) → Mg ²⁺ (aq) + 2 NO₃^- (aq)

4.2M 4.2M 8.4M

following mol ratio:

[NO3 -] = 8.4M

[Mg 2+] = 4.2M

CHARGES MUST STAY INSIDE OF CONCENTRATION BRACKET

(think that we’re measuring the concentration of the ion)

how to determine which type of arrow to use for finding ion concentrations (will decompose into ions)

either..

• dissociation/ionization (one-way)

• equilibrium (two-way arrow)

check solubility table

a. if soluble = not saturated = not eqb = one-way arrow

b. if not soluble = saturated = eqb = two-way arrow

how to find concentration of ions if has two compounds (each w Molarity)

1. dilution calculation

2. dissociation eq of each diluted compound

3. if there’s a common ion, need to ADD tgt to get final ion concentration

soluble compounds def

compounds that can dissolve to produce a solution thats 0.1M or greater

low soluble/insoluble def

compounds that can dissolve but their concentration will always be less than 0.1M

• ie. very little dissolves + most stay undissolved

-will form a precipitate (solid)

compounds containing these will ALWAYS be soluble

• what state

• H+

• NH4 + (ammonium)

• Alkali Metals ions (group 1)

• NO3 -

aq state

precipitate reactions def

a double replacement reaction that produces a precipitate

difference between:

-formula/balanced eq

-total ionic eq

-net ionic eq

-formula/balanced eq

• just regular

-total ionic eq

• breaking the compounds into their ions

• CAREFUL OF THE COEFFICIENTS (consider past coefficients and subscripts)

• keep solid as a compound bc totally bonded

-net ionic eq

• only the ions needed to make precipitate

what happened when double replacement but both aq

no solid ∴ no evidence of chemical reaction ∴ no reaction

qualitative analysis

using knowledge of solubility to determine what ions are present in an unknown solution

what to do to if we know solution has mixture of ions but need to confirm

• eg of wording

we can add various ions in a specific order to precipitate out one ion at a time

1. set up a table with possible cations and all 5 groups of anions

2. determine where a precipitate will form (set up table)

3. determine in which order to add in (only one at a time)

4. write a procedure describing how to carry this out (using amounts and compounds)

• add 1M NaCl + filter off PbCl₂ (s)

Ksp expression def

• eg. for CaCO3

• eg. for Fe(OH)2

a special case of Keq for salts in a saturated solution

-since solids aren’t part of Keqs, will only be the aq ions

• Ksp = [Ca 2+] [CO3 2-]

• value from data booklet

-note that multiple ions are shown by putting it as an exponent

• Ksp = [Fe 2+] [OH-]²

Ksp is proportional to _____

-greater Ksp means

-smaller Ksp means

Ksp proportional to [ions] → bc solids aren’t counted

-greater Ksp means more soluble salt

-smaller Ksp means less soluble salt

when will a DR produce a compound w/ low solubility then a ppt form

only if there are enough ions to saturate the solution w the insoluble compound

-compare Q (trial Ksp) to Ksp

if Q<Ksp, ppt will not form (not enough ions - solution is not saturated)

if Q>Ksp, ppt will form (more than enough ions - sol. is saturated)

if Q=Ksp, ppt just starts to form (just enough ions - sol. is AT saturation point)

how to compare Q (trial Ksp) with Ksp to determine if ppt will form

• what arrow to use

1. find the solid in DR

2. Ksp value by data booklet

3. dilution eq

   a. show [ion] is same as given [compound] bc 1:1 ratio

4. put tgt to find Q

5. compare then state

• DR is one way arrow

• two way arrow after bc its going to be Ksp (which is eqb)

what to keep in mind when stating that an ion has a concentration of x bc its equal to a given compound with that same ion

when showing the proof that the ion has concentration of x bc given compound has that ion too… (think 1:1 ratio and same ion)

the proof eq will be a one-way arrow bc not part of calc Ksp

what to consider when saying how much mass needed to add in

-reference steps

when calculating the concentration needed of that ion,

can’t just add that ion, needs to be within a compound!