DO NOW – place your acid & base samples in an order relative to the other items on the table

pHObjectives:

Connect pH numbers to what they represent.Practice converting pH values.

Evaluate strengths of acids & bases.

What is the chemical equation for this beaker of distilled water?

H2O + H2 ↔ H3O+ + OH- or

H2O ↔ H+ + OH-

DEMONSTRATIONForm water moleculesMove around roomDissociate & ressociate randomly

Equilibrium is a dynamic stateIt is rare for a hydrogen atom to leave the

stability of the water moleculeMore likely to happen if water is

heated or Influenced by other chemicals

Chemical EquilibriumIs the concentration of water the same as the

total concentration of H+ and OH-?No

What does it mean to be at equilibrium?The reaction is still flowing back and forth,

however, there is no net gain in either products or reactants

H2O ↔ H+ + OH-

Chemical EquilibriumCan an equation tend to one direction or the

other?Yes (usually in the direction of the products)

Which is in higher concentration in the beaker?

H2O or [H+ + OH- ]?H2O

pH ConcentrationHow do you write the concentration of pH value

3?H+ = 1 x 10-3

How do you write pH 3 as a decimal?0.001

How do you write pH 3 as a fraction?1/1,000

What does this mean?If you reach into the beaker you would find only one

dissociated H+ ion for every intact H2O molecules.

Calculate the ratio of dissociated to intact water molecules in a beaker of distilled water of pH 7 at 25CpH 7, concentration of hydrogen [H+] = 1 x

10-7

Which is [H+] = 1/10,000,000Which is one dissociated molecule of H2O for

every 10 million intact H2O molecules

What is the difference in hydrogen concentration between pH 5 and pH 2?

How are the concentrations of [H+] and [OH-] related?

What is the concentration of [OH-] if the pH is 3?

What is the concentration of [OH-] if the pH is 13?

Which of these two examples is more basic/alkaline?

Electronegativity & pHElectronegativity can reveal the strengths of

acids and basesIf a hydrogen atom is in a molecule with other

atoms that have a very strong ability to dominate the electrons, the the molecule will be polarized with hydrogen being stripped of its electron (think HCl)

If the hydrogen does not have much association with its electron, then it leaves the molecule to become an ion and the solution is said to be more acidic

QUESTIONSWhat is the difference between a strong

acid/base and a weak acid/base?A strong acid/base dissociates readily

Difference in electronegativity greaterA weak acid/base dissociates less readily

Minimal difference in electronegativity

Which acids/bases are weaker and which are stronger – HCl, NH3, H2CO3, NaOH?Strong – HCl and NaOHWeak –NH3 and H2CO3