CHEM12 - unit 4 - acid and base part 2

try do more Hebden

what happen when mix strong acid and strong base

• eg

neutralize one another

• HCl + NaOH → NaCl + H2O

• H + OH → H2O

-goes to completion

what arrow used in neutralization reaction

one-way arrow

because goes to completion

when will adding of acid and base be neutral?

• eg. HCl + NaOH

when not? how come?

-how to find this pH?

if acid and base react in stoichiometric amounts

• # mol HCl = # mol NaOH

not neutral when NOT in stoichiometric amounts..

-pH of result will be dictated by the excess

1. need to find out what is the excess

2. by how much excess

whats the pH of a solution made by mixing 50.0mL of 0.250M NaOH and 50.0mL of 0.350M HCl ?

• what type of thing is this

• steps

find pH when mix strong acid and base

• steps

1. dilution to determine [OH-] and [H3O+]

2. determine which in excess and by how much

   1. whichever one has higher concentration

   2. subtract from other

3. determine pH or pOH by -log[amount of excess]

4. use pKw = pH + pOH

what value of pKw

14.000

how to determine how much [OH-] needed when have initial [H3O+] and final pH?

or vice versa

needed [ ] = [ ]final - [ ] initial

• in terms of [OH-] and [H3O+]

hydrolysis of salt

-result? + how to determine this

-step

reaction between a salt (ionic compound) and water

-resulting solution may be acidic, basic, or neutral

-need to consider how the ions that make up salt behave in water

• spectators ions don’t react in water

  • will cross out!

• weak acid and weak base forms H3O+/OH

-steps

1. dissociation eq

2. discard any spectator ions

3. determine if remaining ION acts acid or base or amphiprotic

4. write hydrolysis eq (rxn w/ water)

   a. if amphiprotic.. do 2 hydrolysis (one as acid, one as base)

5. state if result is acidic, basic, or neutral..

   a. test by putting result ion in water to see if forms OH- or H3O+ or neither

   b. amphiprotic: see if Ka or Kb is bigger

spectators ions behave in water?

• what are these

-spectator ions do not react with water

• spectator ion = conjugates of strong acid + bases; group 1 and group 2 metals

how to find Kb

• products/reactants

• kW/ka_{conjugate acid}

what does larger Ka or Kb mean

Ka > Kb = solution is acid = [H3O+] > [OH-] = amphiprotic ion is a stronger weak acid than as a weak base

Kb > Ka = solution is basic = [OH-] > [H3O+] = amphiprotic ion is a stronger weak base than as a weak acid

how much do weak acids/base ionize in water

• what does this mean in terms of [ ] of acid/base

• what arrow + steps

-less than 100% ionization

• [acid] ≠ [H3O+]

• [base] ≠ [OH-]

-arrow is eqb arrow since not fully ionize

-use ICE table

• steps

1. ICE table → values are molarity

2. reactants are subtract change / products add change

3. use Ka or Kb depending on if product has [H3O+] or [OH]

   a. use products/reactants and replace w/ eqb/final values

4. state value of x (depends on what question wants)

5. do assumption if needed

6. state ans

what assumption we will make in this unit

• what do we have to make sure to do

• we dont use quadratic formula

• in denominator of (# - x) = #

  • but not x = # bc theres other places of x

acid:

• make sure facts are still right ( [acid] not equal to [H3O+] )

• [H3O+]eqb is less than 5% of [HA]initial

  • divide eqb by initial x100%

base

• make sure facts are still right - [base] not equal to [OH-]

• [OH-]eqb is less than 5% of [Base-]initial

  • divide eqb by initial x 100%

kW value

1.00 × 10^^-14

kB calcs.

will need to switch back and forth from Kb = Kw/Ka and Kb = products/reactants when products may be answer needed

finding [H3O+] or [OH-] formula

10^{-(pH or pOH or pKa)}

point of titration

acid + base → water + salt

using known concentration to find unknown concentration

-until equivalence / stoichiometric point

if titration trials, how to tell what volume to use?

• rule

• how to find volume used

-volume should agree within 0.1mL or 0.02 mL

-average the acceptable trials

-final volume mark - initial volume mark

-do titration using stoich

how to determine how much proton a polyprotic acid donates

-compare the mol of acid and base

• L x (mol/L) = mol

-ration of bigger over smaller

• show the ratio fraction + include the units! its marked

-write balanced eqn with correct amount of proton donated

percent purity question

• determining formula

• [actual] / [expected]

-find [actual] by titration

• using stoich

-find [expected] by sample grams

• g x (1mol/periodic table g) x (1/inital vol.)

molar mass problem

1. titration to find mol of acid

2. find g/mol by sample and initial volume

indicator def

• weak organic acid or base with its conjugate

-change pH

-change colour

indicator endpoint means…

[HIn] = [In-]

Ka = [H3O+]

pKa = pH

pH of indicator is the “range” which indicator is at endpt

standard solution def

solution with accurately known concentration that can be used to titrate another sol. with unknown conc.

primary standard def

pure and stable

-doesnt absorb H2O or CO2

strong acid + strong base

• solution is acidic, basic, or neutral

salt dissociated = spectators

• so neutral

• pH = 7

weak acid + strong base

salt dissociated = basic

• weak base (since conjugate of strong base) so.. pH is 8-10

weak base + strong acid

salt dissociated = acid

• weak acid (since conjugate of strong acid) so.. pH 4-6

buffers def

-if diluted

• resist large changes in pH when small amounts of acid or base are added

• made up of: weak (acid/base) + conjugate (acid/base)

• if diluted equally.. no change in pH

• buffers have limited capacity.. once enough neutralize x will remain unneutralized and pH change

acidosis def

when blood pH too low <7.2

alkalosis def

when blood pH too high >7.5

-optimal blood pH

-what buffers regulates blood pH

-two relevent egs

• 7.35

• CO2/HCO3-

• 1. hyperventilating: low CO2 bc breathe out

  - H2O + CO2 ⇌ H2CO3

  - H2CO3 + H2O ⇌ HCO3- + H3O+

  low CO2 ∴ low H2CO3 bc shift
  low H3O+ bc shift ∴ low pH
  = acidosis

• 2. hypoventilating: too much CO2

  - H2O + CO2 ⇌ H2CO3

  - H2CO3 + H2O ⇌ HCO3- + H3O+

  high CO2 ∴ high H2CO3

  high H3O+ bc shift ∴ high pH

  = alkalosis
  

metal oxides vs non-metal oxides

metal oxides = basic (some exceptions, see table) AKA basic anhydrides

nonmetal oxides = acidic AKA acid anhydrides

acid rain

-why have

-what makes bad

-rain already acidic since CO2 in atmosphere w/ water forms carbonic acid

-combustion so more CO2 but also..

• sulfur

  • H2SO3

  • H2SO4

• nitrogen

  • HNO2 + HNO3

containing oxides which contributes to acid rain and make more acids :(