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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 –.
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Titration Wrap-Up Strong vs. Weak Acids and Bases Titration Curves
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– Hydrochloric acid is a typical strong acid, so the dissociation reaction is complete: + HCl H+ Cl–
Weak acids Weak acids do not dissociate fully, some of their H+ ions stay attached to the acid molecule. The dissociation of a weak acid in water is a reversible reaction: ⇌ + HA H+ A– Ethanoic acid is a typical weak acid, with its ions in dynamicequilibrium with the un-dissociated acid. The reaction is moving both directions at the same rate. ⇌ + CH3COOH H+ CH3COO–
pH of strong and weak acids 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: • have lower pH values • are better conductors of electricity • react more quickly. high H+ low H+
Strong Acids • HI • HBr • HCl • HNO3 • H2SO4 • HClO4 • HClO3
Properties of strong and weak bases Bases can be classified as strong and weak in the same way as acids. A strong base, such as sodium hydroxide, fully dissociates in solution. + NaOH Na+ OH– 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– Comparable levels of ion dissociation mean that strong and weak bases have similar properties to strong and weak acids.
Strong Bases • NaOH • KOH • LiOH • RbOH • CsOH • Ca(OH)2 • Ba(OH)2 • Sr(OH)2
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
pH mL base added 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
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