Strong Acid (SA)• an acid that dissociates completely into ions in water Ex. All molecules of HCl(aq) dissociate into H+ and Cl- ions ▫ H+ ions that are formed bond with H2O to form H3O+ HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)
Dissociation (Strong Acid)100% of hydrogen chloride molecules dissociate
Weak Acid (WA)• an acid that dissociates very slightly into ions in water Ex. not all molecules of CH3COOH(aq) break apart, some remain intact • only about 1% of acetic acid molecules dissociate
Dissociation (Weak Acid)1% of acetic acid molecules dissociate. In solutionthere are mostly acetic acid molecules and only someions.
Concentration• the concentration of H3O+(aq) ions, [H3O+], in a dilute solution of a SA is equal to the concentration of the acid, [acid] [H3O+] = [strong acid]• Ex. In a sample of 1.0 mol/L HCl(aq) [H3O+] = 1.0 mol/L Recall: C = n square bracket V Molar Concentration
Concentration• the concentration of H3O+(aq) ions, [H3O+], in a dilute solution of a WA is much less than the concentration of the acid, [acid] • Ex. In a sample of 1.0 mol/L CH3COOH (aq) [H3O+] <<< 1.0 mol/L • That is, [H3O+] < [weak acid]
Strong Base (SB)• a base that dissociates completely into ions in water Ex. all molecules of NaOH(aq) dissociate into Na+ and OH- ions • other SB’s are… KOH Ca(OH)2 Ba(OH)2
Weak Base (WB)• most bases are weak• WB dissociates very slightly into ions in water ▫ Ex. Ammonia [OH1-] < [weak base]
Concentration• the concentration of OH1-(aq) ions, [OH1-], in a dilute solution of a SB is equal to the conc. of the base, [base] [OH1-] = [strong base] Ex. In a sample of 1.0 mol/L NaOH(aq) [OH1-] = 1.0 mol/L
Measuring Strength – pH Scale• In pure water, [H3O+] = [OH-] = 1.0 x 10-7 mol/L• In acidic solution, [H3O+] > [OH-]• In basic solution, [H3O+] < [OH-]
19 pH and acidityThe pH values of severalcommon substances areshown at the right.Many common foods areweak acidsSome medicines and manyhousehold cleaners arebases.
Indicators• An acid-base indicator is a substance that changes colour in acid and base solutions. It is used to determine if neutralization is complete.• ex. litmus phenolphthalein (phth) bromothymol blue (BTB) universal indicator
pH Scale Review• Now that we know when an acid or base is dissolved in water it will produce either: ▫ OH- ▫ H+• pH measures the concentration (how many) of H+ in the solution• When pH is 7 that means the concentration of OH- is equal to H+• When pH is less than 7 we have a higher concentration of H+• When pH is bigger that 7 we have a higher concentration of OH-
Neutralization• Adding a base to an acid neutralizes the acid’s acidic properties.• This is called a neutralization reaction. ▫ Ex. for an upset stomach, use an ANTACID
Neutralization• In general: ACID + BASE SALT + WATER H2SO4(aq) + Ca(OH)2(aq) CaSO4(aq) + 2H2O(l)
Example1. In an experiment, 15.85 mL of HCl(aq) completely neutralizes 25.00 mL of 0.125 mol/L KOH(aq). Calculate the concentration of this acid.
Example 22. What volume of 0.185 mol/L H2SO4(aq) will react completely with 25.00 mL of 0.225 mol/L KOH(aq)?
Learning Check3. What mass of aluminum hydroxide will react completely with 27.50 mL of 0.255 mol/L H2SO4(aq)?
Learning Check 24. What is the molar concentration of phosphoric acid if 17.50 mL of this acid reacted with 3.22 g of magnesium hydroxide?
Titration• lab procedure involving neutralization, used to determine an unknown concentration• progressive addition of a solution (called titrant) from a graduated tube (called burette) to a known volume or mass of a second solution, until the endpoint ▫ endpoint is indicated by a colour change of an added indicator• at equivalence point, nH+ = nOH- ▫ given the concentration of one sol’n, you can calculate the concentration of the other sol’n
Titration• Read p468 - 469 to review procedure