6.5- The Strength of Acids and Bases

Strong acids

A strong acid is an acid that reacts almost completely ( >99%) with water to form hydronium ions

HCl(aq) +H2O(l) >99% H3 O+ + Cl-

(aq) Most common strong acids are HCl(aq) ,

H2SO4(aq) , and H2 NO3(aq) Strong acids have a low pH level, the higher

the pH level the weaker the acid

Strong acids

Good conductors of electricityFast reaction with waterAlmost complete reaction with waterpH<<7

Weak Acids

Most acids are weak acidsLess than 50% reacts with water to produce

hydronium ionsCH3 COOH(aq) +H2 O(l) <50% H3 O+

(aq)

+CH3COO(aq) pH<7 low conductivity slow reaction rate partially reacts with water to form H3O+

(aq)

Strong Bases

completely to form OH- (aq)

NaOH(aq) Na+(aq) + OH-

(aq)

high conductivity

Fast reaction rateVery high pH (pH>>7)

Weak Bases

Partially reacts with water to form OH-(aq)

NH3(aq) + H2 O(l) <50% OH-(aq) +NH4 (aq)

Slow reaction rateLow conductivityMedium pH ( pH>7)

Polyprotic Substances

Monoprotic acids are acids that can react only once with water ( like HCl(aq) )

Polyprotic acids are able to react more than once with water

Ex) H3 PO4(aq) +H2O(l)<50% H2 PO4

- (aq) +H3O+

(aq)

H2 PO4- +H2O(l)

<1% HPO42-

(aq) +H3O+(aq)

HPO42-

(aq) +H2O(l) 0% PO4

3- (aq) +H3O+

(aq)

With polyprotic acids, their reaction with water decreases with every step.

Typically polyprotic acids are weaker than monotropic acids

The same idea works with polyprotic bases, they react more than once with water

CO32-

(aq) + H2 O(l)<50% OH- (aq) + HCO3 –

(aq) HCO3 –

(aq) + H2 O(l)<1% OH- (aq) +H2 CO3 (aq)

The reaction with water decreases with every step

assignment

Read page 255-259Do pg 256 #1,2,4 pg 257#7,9 pg 259 #1,3,5,7,12