Acid & Base Solutions

Properties of Acids  What we know about acids:  Sour taste  pH 0 – 7  Turns blue litmus to red  Turns methyl orange to red  Indicator: a chemical compound that changes color in the presence of H + ions  Ionic chemical formula starts with “H”  Are electrolytes  Electrolytes – substances that conduct electricity while dissolved in water

Physical Properties of Acids Acids will react with:  … some metals to produce a salt and H 2 gas Mg + 2HCl → MgCl 2 + H 2  … metal oxides to produce a salt and H 2 O. Li 2 O + 2HCl → 2LiCl + H 2 O  … metal carbonates to produce a salt, H 2 O, and CO 2. Na 2 CO 3 + 2HCl → 2NaCl + H 2 O + CO 2  … bases to produce a salt and H 2 O. Ca(OH) 2 + 2HCl → CaCl 2 + 2H 2 O

Naming Acids o Common strong acids: o HCl - hydrochloric acid o HBr - hydrobromic acid o HNO 3 - nitric acid o HClO 3 - chloric acid o H 2 SO 4 - sulfuric acid o Common weak acids o HC 2 H 3 O 2 - Acetic acid o HF - Hydrofluoric acid *Note: These all start with H and are ionic!

Properties of Bases Coffee is acidic, but caffeine is alkaline (basic), and contributes to the bitter taste  What we know about bases:  bitter taste  Slippery to touch  Fats on skin get turned into soap  pH 7 – 14  Turns red litmus to blue  Turns phenolphthalein to pink  Ionic chemical formula ends with “OH”  Are also electrolytes  Reacts with acids to produce a salt & water HCl + NaOH  NaCl + H 2 O

Naming Bases o Like strong acids, strong bases ionize completely. o Strong bases = soluble hydroxides o LiOH - lithium hydroxide o NaOH - sodium hydroxide o KOH - potassium hydroxide o Ca(OH) 2 - calcium hydroxide o Sr(OH) 2 - strontium hydroxide o Ba(OH) 2 - barium hydroxide o Weak Bases o NH 3 - ammonia o Insoluble bases

Acid & Base Definition  There are 3 common definitions of acids and bases.  Arrhenius definition – acids increase H + concentration, bases increase OH - concentration  Brønsted-Lowry definition – acids are proton donors, bases proton acceptors  Lewis definition – acids accept a pair of electrons  Arrhenius acid- a substance that produces an H + (or H 3 O + ) cation in solution.  Acids dissociate like salts because of water’s strong polarity  HCl(aq) → Cl - (aq) + H + (aq)  can also be written as:  HCl(aq) + H 2 O(l) → Cl - (aq) + H 3 O + (aq)  H 3 O + is called hydronium

Acid & Base Definition + +  Hydrochloric acid dissociates because it is ionic +

Acid & Base Definition +  Arrhenius Base- a substance that produces an OH - anion in solution.  NaOH(s) → Na + (aq) + OH - (aq)  Neutralization Reaction + +

Review pH Scale Traditionally Can have pH 14. pH < 7  Acidic solution. pH > 7  Basic solution. pH = 7  Neutral solution.

pH Scale AcidicBasic

The pH Concept  Water is extremely polar  Auto-ionizes by itself  H 2 O(l) ↔ H + (aq) + OH - (aq) 1mol 1mol 1mol  Double-arrow means reaction goes in both directions  Called “self-ionization”  In solution, the H + and OH - concentrations are equal.  A solution where [H + ] = [OH - ] is called neutral  Not all solutions are neutral  Solutions with acids increase the concentration of H +  Called acidic  Solutions with bases increase the concentration of OH -  Called basic

pH Concept  pH system developed by Danish chemist Søren Sørensen  pH = - log [H + ] (page 3 NC Chemistry Ref. Tables)  “the power of the Hydrogen ion”  Based on the concentration of hydrogen ions in solution  [H + ] = the concentration of the H + ion in solution  Monoprotic acids (“one proton”)-concentration of the acid is equal to the concentration of the H + produced  Ex: HCl → H + + Cl -  one mole of HCl produces one mole of hydrogen ions and one mole of chloride ions  Diprotic acids produces twice as many H+ ions  Ex: H 2 SO 4 → 2H + + SO 4 2-

pH Concept  pH and concentration formula  pH = -log [H + ]  [H + ] = Molar concentration of H + ion  Example: What is the pH of a M HCl solution?  Note: the concentration of H + is the same as HCl, because there is only one H + is produced  pH = - log [0.0045M]  pH = 2.35  ** double check- is this pH good for an acid?  What is the pH of a solution with a concentration of acetic acid(HC 2 H 3 O 2 ) at 3.98x10 -6 M?  pH = - log [3.98x10 -6 ]  pH = 5.40

pH and pOH  pOH is the “power of hydroxide”  Formula: pOH = - log [OH - ]  Example: What is the pOH of a 3.41 x M NaOH solution?  pOH= -log[OH - ]  = -log[3.41 x M]  = 3.47

pH and pOH  Bases have pH values too  Earlier, we stated that in pure water, [H + ] and [OH - ] are equal. Therefore:  pH + pOH = 14 (Page 3 of NC Ref. Tables)  What is the pH of the base in the previous example?  pH + pOH = 14  pH = 14  pH = ** is this a good pH for a base?

Hydrogen and Hydronium Ions H HH HH HH H Acid H Hydrogen ion (proton) Hydronium ion, H 3 O +1 H H H H H H H H H H H H H H H H H H H H

Hydroxide Ions H Base H + Hydroxide ion, OH -1 H H H H H H H H H H H H H H H H H H H H H H H H H H H H HH H H H H