I don't understand how the volume of 0.200 M NaOH needed to neutralize 250.0 mL of 0.010 M HCl (0.0125 mL) is the same volume of 0.200 M NH3 that would be needed to neutralize 250.0 mL of 0.010 M HCl.

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    $\begingroup$ Well, depends what you mean by neutralize. Solution of NH4Cl is still weakly acidic. $\endgroup$ – Mithoron Feb 4 '18 at 20:56
  • $\begingroup$ Related: chemistry.stackexchange.com/questions/60407/… $\endgroup$ – Ivan Neretin Feb 4 '18 at 21:06
  • $\begingroup$ @IvanNeretin Thanks for providing that link. Can you tell me if I understand the concept correctly?: So from what I understand, since the HCl ionizes completely there is an abundance of H+ ions that can neutralize the small amount of OH- ions that are ionizing from the weak base. As a OH- ion is neutralized the equilibrium shifts to replace the neutralized OH- ion which again gets neutralized by the H+ ion present in solution. This cycle continues until the strong acid is completely neutralized by the weak base. In terms of the strong base NaOH, since it ionizes completely, there are alrea- $\endgroup$ – Sam Feb 4 '18 at 21:16
  • $\begingroup$ dy the needed amount of OH- ions present in solution to neutralize the H+ ions in solution. Is this all I need to understand for a Chemistry 12 course for this concept? $\endgroup$ – Sam Feb 4 '18 at 21:19

Well it's because the strength of an acid or base is a measure of it's dissociation in water. But for the the reaction of an acid with a base the equilibrium lies completely to the right as the products (salt and water) are much more stable than the acid and base.

You're trying to compare the dissociation of a species in water with the equilibrium constant of an actual reaction. I understand why, but think of them as two different situations.

  • $\begingroup$ Thanks for the answer. So while the weak base ionizes only slightly, because the products are more stable than the acid and base, the weak base will continue to neutralize the H+ ions and continue to ionize until the products have been formed or in other words until the HCl is neutralized completely? $\endgroup$ – Sam Feb 4 '18 at 21:23
  • $\begingroup$ Yes, the weak base will ionize only slightly. The extent of that determines the stability of the forward reaction. A slight ionization means the forward reaction is not preferred/ 'products' not as stable. $\endgroup$ – 124c41 Feb 4 '18 at 22:04
  • $\begingroup$ Yes, that's the idea. For dissociation: Yes, the weak base (ammonia) will ionize only slightly in water. Water is already a stable molecule to start, so to break the O-H bonds in water and form ions requires a good deal of energy. For neutralization: All reactions are a measure of enthalpy (more important) and entropy (less important). If we use this and compare the energy level of the acid and base molecules versus the energy of the salt and water formed, we see that the products are at a lower energy and thus preferred. $\endgroup$ – 124c41 Feb 4 '18 at 22:13

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