ACIDS AND BASES: Strong and Weak

OUTCOME QUESTION(S): C12-5-07 ACID/BASE AND pH Outline acid/base theories and write acid/base equations. Include: Arrhenius, Bronsted-Lowry, Lewis. Distinguish between strong and weak acids and bases. Include: electrolytes and non-electrolytes Formulate an operational definition of pH and solve problems. Vocabulary & Concepts  polyprotic

This means the compound must dissociate or ionize in solution For a solution to conduct an electric current, charged particles (ions) must be present. C6H12O6 C6H12O6 This means the compound must dissociate or ionize in solution

as do highly polar molecules Electrolytes: conduct an electric current when in aqueous solution or in a molten (melted) state. All ionic compounds act as electrolytes Most molecular compounds are non-electrolytes. electrolytes as do highly polar molecules non-electrolytes NaCl (s) Na+(aq) + Cl–(aq) C6H12O6 (s) C6H12O6 (aq)

A (s) B+(aq) + C–(aq) A (s) B+(aq) + C–(aq) Electrolytes are classified as strong OR weak: Strong: produces many ions in solution. dissociates 100% in water (NaCl) A (s) B+(aq) + C–(aq) Equilibrium can favour the forward or reverse reaction – this determines how many electrolytes are in solution Weak: partially dissociates (<<100%) in solution. usually weak polar molecules (vinegar) A (s) B+(aq) + C–(aq)

polar ionic You should be able to identify polar and ionic compounds from the formula ionic polar

HCl (l) + H2O H+(aq) + Cl–(aq) Strong acids are strong electrolytes easily donate protons completely dissociate or ionize [acid] initially will equal [H+] at equilibrium (think of an ICE table) HCl (l) + H2O H+(aq) + Cl–(aq) Indicate complete dissociation using single arrow and simplifying the equation by ignoring water Common Strong Acids Formula perchloric acid HClO4 hydrochloric acid HCl sulfuric acid H2SO4 nitric acid HNO3 hydroiodic acid HI hydrobromic acid HBr

HC2H3O2 + H2O H3O+ + C2H3O2- Weak acids are weak electrolytes poorly donate protons incompletely dissociate or ionize equilibrium favors reverse reaction – ions regroup quickly HC2H3O2 + H2O H3O+ + C2H3O2- Indicate incomplete dissociation and equilibrium reached by using reversible arrow and including water Common weak Acids Formula carbonic acid H2CO3 hydrofluoric acid HF acetic acid CH3COOH phosphoric acid H3PO4 There are many weak acids and they are listed on your acid strength chart

Relative Strength of Acids Strongest Why would the strong acids have Ka without measurable values? Weakest

An acid that contains more than one ionizable hydrogen is called polyprotic. Two – diprotic Only one – monoprotic Phosphoric acid H O s p H O s Each hydrogen ion has a unique affinity for ionizing which creates unique equilibrium values Cl H Sulfuric acid

Strong bases create hydroxide (OH1-) or oxide (O2-) ions Strong bases are strong electrolytes easily accept protons completely dissociate or ionize [base] initially will equal [OH-] at equilibrium NaOH (s) Na+(aq) + OH–(aq) Common Strong Bases Formula barium hydroxide Ba(OH)2 strontium hydroxide Sr(OH)2 lithium hydroxide LiOH potassium hydroxide KOH Strong bases create hydroxide (OH1-) or oxide (O2-) ions Basically, any Alkali (I) or Alkali Earth (II) metal hydroxide would be a strong base

Weak bases are typically related to strong acids… Weak bases are weak electrolytes poorly accept protons incompletely dissociate or ionize equilibrium favors reverse reaction – ions regroup quickly NH3(g) + H2O (l) NH4+(aq) + OH-(aq) Indicate incomplete dissociation and equilibrium reached by using reversible arrow and including water Common weak Bases Formula carbonate ion CO32- alanine C3H5O2NH2 pyridine C5H5N methylamine CH3NH2 Weak bases are typically related to strong acids…

Common weak bases are usually conjugate bases of strong acids. HA + H2O H3O+ + A- Con. acid Con. base acid base Logic: for a strong acid - the forward reaction is favoured because it is a poor base in the reverse reaction The stronger the A/B, the weaker its conjugate. The weaker the A/B, the stronger its conjugate.

This side contains the conjugate bases of the acids Strongest Weakest This side contains the conjugate bases of the acids Note: these are all still “weak” bases as there are no strong metal hydroxides here BASES Stronger Weakest

forward reaction is favoured The equilibrium reaction favours the strongest acid: HSO4- + HTe- H2Te + SO42- acid base Con. acid Con. base Use the acid strength table to evaluate the two acids of the equation – the acid with the larger Ka value is the stronger acid and will dominate the reaction forward reaction is favoured HSO4– is the stronger acid

Reverse reaction is favoured Which direction is favoured at equilibrium? HCO3- + PO43- CO32- + HPO42- acid base Con. acid Con. base Hydrogen carbonate ion is higher than hydrogen carbonate ion Reverse reaction is favoured HCO31- is the stronger acid

CAN YOU / HAVE YOU? C12-5-07 ACID/BASE AND pH Outline acid/base theories and write acid/base equations. Include: Arrhenius, Bronsted-Lowry, Lewis. Distinguish between strong and weak acids and bases. Include: electrolytes and non-electrolytes Formulate an operational definition of pH and solve problems. Vocabulary & Concepts  polyprotic