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### Course: AP®︎/College Chemistry>Unit 8

Lesson 5: Acid–base reactions

# Strong acid–strong base reactions

When a strong acid and a strong base are mixed, they react according to the following net-ionic equation: H₃O⁺(aq) + OH⁻(aq) → 2H₂O(l). If either the acid or the base is in excess, the pH of the resulting solution can be determined from the concentration of excess reactant. If the acid and base are equimolar, the pH of the solution is 7.00 at 25°C. Created by Jay.

## Want to join the conversation?

• At why is it 2H2O instead of 1H2O?
(1 vote)
• At , why is it 2H2O?
Surely if H3O+ and H+ are interchangeable, then we could have written the equation as H+ + OH- --> H2O
But this would have resulted in half as many H2O molecules.

Can someone explain?
(1 vote)
• If you take a hydronium ion, H3O^(+), and you deprotonate (remove an H^(+)) that you get a water molecule, H2O. If you take a hydroxide ion, OH^(-), and you protonate (add an H^(+)) that you get another water molecule. Both of these steps happen together so you receive 2 water molecules in total for a single proton exchange.

The reaction where two water molecules are produced is more accurate to what is happening, while the reaction where only a single water is produced is the net ionic equation which simplifies the reaction to the most important chemical species.

Molecular equation: H3O^(+) + OH^(-) → 2H2O
Complete ionic equation: H^(+) + H2O + OH^(-) → H2O + H2O
So we see that there is at least one water molecule on both sides of the reaction, so we can cancel one of the waters like it’s a spectator ion.
Net Ionic equation: H^(+) + OH^(-) → H2O

We use this simplification since it makes the amount of symbols and calculations more concise, but we should keep in mind that it’s only a simplification and not what is actually happening. Especially when we do equilibrium and ICE tables, the amount of water is irrelevant so we can use either equation and get the same answers (so might as well use the simpler one).

Another reason we use the net ionic equation of and acid-base reaction is that the solvation of hydronium (the surrounding of hydronium by water molecules) which actually happens in aqueous solutions creates a variety of interesting and complicated ions. The three main structures (which all form) are the Eigen, Zundel, and Stoyanov ions. The Eigen is a tetrahydrate ion, H3O^(+)(H2O)3. The Zundel cation is a symmetric dehydrate ion, H^(+)(H2O)2. The Stoyanov cation is an expanded Zundel cation which is a hexahydrate: H^(+)(H2O)2(H2O)4. Given the variety and complexity of hydronium ions, we can use the net ionic equation to again make the work much simpler.

Hope that helps.
• At , why doesn't he use the net ionic equation as he does in ?
(1 vote)
• It just shows that can you use either the molecular equation or the net ionic equation to do ICE tables.
• at why is it if we have 1 mole of each (1 mol of hcl and 1 mol of naoh) that means the total moles would be 2 (in terms of weight) but the yield was only 1 mol (which is 1 nacl
(1 vote)
• so if the strong acid and the strong base have the same number of moles, will the ph always be 7?
(1 vote)
• If we assume that are both are indeed strong and dissociate 100%, then yes.

Hope that helps.
(1 vote)
• Previously, when we did ICE tables, we used the Molar concentrations of each molecule or ion in the equation. In this video I noticed that he used actual mole amounts rather than Molar concentrations for the ICF table. Is there any reason for this change, or is it up to us to choose whether we use molar concentrations or mole amounts on our ICF and ICE tables?
(1 vote)
• ICE tables where you want to use the results for equilibrium equation need to have molarities since equilibrium equations utilize molarity. Here we're essentially seeing how much base and acid react with each other in a neutralization reaction and want to know what remains.

Hope that helps.
(1 vote)
• When doing the example that had 300 ml of 1 M HCl and 100 mL of 1 M NaOH, why is it that you solved for mols instead of using the M concentration that you were given??
(1 vote)
• Jay used an ICF table which uses moles instead of an ICE table which uses molarity. Jay explained this at . He’s using an ICF table because he’s reacting strong acids and strong bases which do not have a significant equilibrium and don’t proceed in the reverse direction to any appreciably amount.

Hope that helps.
(1 vote)
• isn't the net ionic equation basically the autoionization of water reversed? why would it be a double arrow in that case but not in this case
(1 vote)