Acid-Base Reactions Monday, 4/21/14

Acid + Base  Water + Salt Acid-Base Reactions When an acid and a base are placed together, they react to neutralize the acid and base properties, producing a salt and water. The H+ cation of the acid combines with the OH- anion of the base to form water. The compound formed by the remaining ions is called a salt. Acid + Base  Water + Salt Ex: HCl + NaOH  H2O + NaCl

H2SO4 + Ca(OH)2 → ??? Predicting Products What are the most likely products of the following acid-base reaction? H2SO4 + Ca(OH)2 → ???

Check: Do the charges on the salt =0 (remember criss-cross)? Predicting Products What are the most likely products of the following acid-base reaction? H2SO4 + Ca(OH)2 → H2O + CaSO4 Check: Do the charges on the salt =0 (remember criss-cross)?

Neutralization vs. Buffers

Types of Acids and Bases Strong Acids: completely dissociate (break apart) in solution to form H+ ions. Strong Bases: completely dissociate in solution to form OH- ions. Weak Acids: Only partially dissociate; some H+ ions stay bonded to the rest of the acid molecule. Weak Bases: Only partially dissociate; some OH- ions stay bonded to the rest of the base molecule.

Strong Acids and Strong Bases Both fully ionize (break apart) The reaction leads to a pH=7 solution, with only the water and salt remaining.

Weak Acids and Weak Bases These do not fully break apart There is more than just water and salt remaining! Weak Acid: HA, H+, A- Example: HCN leads to HCN, H+, and CN- Weak Base: BOH, OH-, B+ Example: NH4OH leads to NH4OH, NH4+, and OH-

Buffer Reactions Having the extra weak acid and weak base present means that the solution can still neutralize additional acids or bases. This allows the solution to RESIST a change in pH. Left over weak acid and base neutralizes whatever else is added in! This is called a “buffer.”

If I were to add a base to this kind of solution, there is still acid left to “buffer” a potential change in pH. It will resist a change in “equilibrium.”

Your Job Complete the Neutralization and Buffer Practice for tomorrow! We will begin our unit project on Wednesday. (It will be partner/small group)