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Titration Wrap-Up. Strong vs. Weak Acids and Bases Titration Curves. Naming Acids and Bases. Strong acids. Acids can be strong or weak. Strong acids dissociate fully into solution, so that all their H + ions are released into the mixture. +. HA. H +. A –. - PowerPoint PPT Presentation
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Titration Wrap-Up
Strong vs. Weak Acids and BasesTitration Curves
Naming Acids and Bases
Strong acidsAcids can be strong or weak.
Strong acids dissociate fully into solution, so that all their H+ ions are released into the mixture.
Hydrochloric acid is a typical strong acid, so the dissociation reaction is complete:
HCl H+ + Cl–
HA H+ + A–
The dissociation of a weak acid in water is a reversible reaction:
Weak acids
Weak acids do not dissociate fully, some of their H+ ions stay attached to the acid molecule.
Ethanoic acid is a typical weak acid, with its ions in dynamic equilibrium with the un-dissociated acid. The reaction is moving both directions at the same rate.
HA ⇌ H+ + A–
CH3COOH ⇌ H+ + CH3COO–
Properties of strong and weak acids
Strong or weak?
pH of strong and weak acids
have lower pH values
are better conductors of electricity
react more quickly.
pH is a measure of the number of H+ ions in solution, with a lower pH meaning more H+ ions.
Because strong acids dissociate fully in solution, they contain more H+ ions per molecule of acid, producing a lower pH.
Compared to weak acids of the same concentration, strong acids:
high H+ low H+
Strong Acids
• HI• HBr• HCl• HNO3
• H2SO4
• HClO4
• HClO3
Properties of strong and weak basesBases can be classified as strong and weak in the same way as acids. A strong base, such as sodium hydroxide, fully dissociates in solution.
A weak base, such as ammonia, does not fully dissociate, and some of the OH– ions are not released into solution.
NH3 + H2O ⇌ NH4+ + OH–
NaOH Na+ + OH–
Comparable levels of ion dissociation mean that strong and weak bases have similar properties to strong and weak acids.
Properties of strong and weak alkalis
Strong Bases
• NaOH• KOH• LiOH• RbOH• CsOH• Ca(OH)2
• Ba(OH)2
• Sr(OH)2
Strong and weak acids and bases
Titration Curves
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Titration & Titration Curves• Titration: the adding of one solution of an known
concentration into another solution– standard solution: a solution with a known concentration
• Titration curve: a graph showing pH vs volume of acid or base added – The pH shows a sudden change near the equivalence point– The Equivalence point (a.k.a. stoichiometric point) is the
point at which the moles of OH- are equal to the moles of H3O+
• End point- Point at which titration is complete; indicator color change
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Strong acid-strong base Titration Curve
• At equivalence point, Veq:
Moles of H3O+ = Moles of OH-
• There is a sharp rise in the pH as one approaches the equivalence point
• With a strong acid and a strong base, the equivalence point is at pH =7
15_327
01.0
Vol NaOH added (mL)
50.0
7.0
13.0
pH
100.0
Equivalencepoint
pH
mL base added
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Weak acid-strong base Titration Curve
• The increase in pH is more gradual as one approaches the equivalence point
• With a weak acid and a strong base, the equivalence point is higher than pH = 7
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Indicators