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Strong Acids & Bases

Strong Acids & Bases. Strong acids & bases dissociate completely in water. Strong acids completely ionize (100%) in aqueous solutions . HCl + H 2 O  H 3 O + + Cl - (100 % ions ) Strong bases completely (100%) dissociate into ions in aqueous solutions.

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Strong Acids & Bases

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  1. Strong Acids & Bases Strong acids & bases dissociate completely in water. Strong acids completely ionize (100%) in aqueous solutions. HCl + H2O  H3O+ + Cl- (100 % ions) Strong bases completely (100%) dissociate into ions in aqueous solutions. NaOH Na+ (aq) + OH-(aq) (100 % ions)

  2. Strong acids: HCl, HNO3 ,H2SO4 Most other acids are weak. Strong bases: NaOH, KOH, and Ca(OH)2 Most other bases are weak.

  3. Dissociation vs. Ionization • Ionization and dissociation indicate ions form • Dissociation: ions form when a chemical comes apart. E.g. NaCl melts to form Na+, Cl– • Ionization: ions form when two chemicals react. E.g. HCl(aq) + H2O  H3O+(aq) + Cl–(aq)

  4. Ka- chemical equilibrium for an acid • Generally Ka tells you about acid strength • Strong acids have high Kavalues • A “strong” acid is an acid that completely ionizes. E.g. HCl + H2O  H3O+ + Cl– • A “weak” acid is an acid that doesn’t ionize completely. E.g. HF + H2O  H3O+ + F– • Note: don’t get confused between strength and concentration. • In general: Ka < 10–3 Weak acid 10–3 < Ka < 1 Moderate acid Ka > 1 Strong acid

  5. Kb – the last K (I promise) • Kb is similar to Ka except b stands for base • The general reaction involving a base can be written as B(aq) + H2O  BH+(aq) + OH–(aq) Thus Kb = [BH+] [OH–] / [B]

  6. Sample Problems – strong acids & bases 1. Find the [H3O+] & pH of a 0.0065 M solution of NaOH. (strong base)

  7. 2. If 0.456 g of pure HCl is added to enough water to make 0.75 L of acid solution, find a) [H3O+] b) pH

  8. Find the pH of a 0.024 M solution of the strong base, Ba(OH)2. • Calculate the [H3O+]& [OH-] if 10.0 mL of 0.40 M HCl is added to 90.0 mL of H2O. Also find pH.

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