Acid-Base Reactions

Neutralization Reactions Type of acid-base reaction Strong Acid + Strong Base----all OH- ions combine with H+ ions to give water molecules Produce water and a SALT, MX. A salt is an ionic compound. HX + MOH  MX + H2O ACID + BASE  SALT + WATER Antacid analogy….chewing TUMS to help with acid reflex. The basicity of TUMS neutralizes stomach acid. Neutralization Reactions “neutralize” the acid and base in the reaction.

NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l) Example 1: NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l) What are the spectator ions? What is the net ionic equation?

NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l) Example 1: continued NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l) Na+(aq)+ OH-(aq) + H+(aq)+ Cl-(aq)  Na+(aq)+ Cl-(aq)+ H2O(l) What are the spectator ions? Na+ and Cl- What is the net ionic equation? OH-(aq) + H+(aq)  H2O(liq)----always with strong acids and bases

Salts Ionic compounds Formed using cation from base and anion of acid Can have acidic or basic properties if one acid/base component is strong and the other is weak. Examples: NaCl, Na2SO4, MgCl2 Antacid analogy….chewing TUMS to help with acid reflex. The basicity of TUMS neutralizes stomach acid. Neutralization Reactions “neutralize” the acid and base in the reaction. Give example:

Example 2: Predict the products from the acid-base reaction between H2CO3 + Sr(OH)2 Write the complete, balanced equation as well as the net-ionic equation. Complete equation: H2CO3 + Sr(OH)2  SrCO3 + 2H2O Net-ionit equation: H+ + OH- --- H2O

Practice! Complete and balance the following acid-base reactions. Write the net-ionic equation as well: HClO4 + NaOH  2) HBr + Ba(OH)2  3) HNO3 + KOH  4) Ca(OH)2 + HNO3  5) Mg(OH)2 + HCl 

What are acid-base indicators? Contains a weak acid and its conjugate base Weak acid—one color Conjugate base—different color Changes color based on what solution (acidic or basic) it is placed in. Change color over a specific pH range –transition interval Used when specific pH measurements not needed, seen a lot with titrations

Common Indicators Phenolphthalein Litmus indicator Broad pH range Dye originating from lichens pH < 4.5 (red), pH > 8.3 (blue)

Buffers A mixture composed of a weak acid and its conjugate base OR weak base and its conjugate acid buffers” or reduces the affect of a change in the pH of a solution Absorbs slight changes in pH resulting from the addition of small acid/base amounts to water. Buffer capacity— indicates how much strong acid/base can be tolerated in a buffer solution before pH changes Trait of buffer Mixture allows both a weak acid and weak base to be present in solution—maintains pH -so if strong acid added, the acid reacts with the weak conjugate base in an acidic buffer -if a strong base added, the base reacts with the weak acid in an acidic buffer –keeps H+ and OH- ions from increasing to a point (only small amounts) -concentrations of weak acid and CB > amt. of base or acid added to maintain pH

Types of buffers Acidic Buffers Basic Buffers Formed from mixing a weak acid and its conjugate base pH < 7 Basic Buffers Formed from mixing a weak base and its conjugate acid pH > 7

Why are buffers important to us? Buffers present in our body keep fluids within a certain pH range. Blood has a pH range of approximately 7.3-7.4. A buffer involving H2CO3/HCO3- maintains the blood pH This pair is carbonic acid/hydrogen carbonate ion Buffers help keep fluids in our body at a certain pH range—buffers present in our body -Increase blood pH—alkalosis (base) -Decrease blood pH--acidosis

Homework: Additional pH calculations worksheet