Acids and Bases Topic 8 General Properties Definitions pH Scale

Naming Acids Binary Acids Only 2 elements Use “hydro-” prefix Change element ending to “-ic” Add acid HCl – hydrochloric acid Oxyacids 3 or more elements Use polyatomic name Change ending – ate  “-ic” – ite  “-ous” Add acid For S and P re-add element ending – Sulfuric acid

Characteristics Acids – Sour taste – Change color of indicators – React with metals to release H 2 gas – React with base to produce salt and water – Conduct electric current – React with carbonates to from CO 2 Bases – Taste bitter – Change color of indicators – Dilute solutions feel slippery – React with base to produce salt and water – Conduct electric current

Arrhenius Acids – Produce H + (H 3 O + ) – Compounds usually start with H HNO 3  H + + NO 3 - Bases – Produce OH - – Compounds must contain OH NaOH  Na + + OH -

Bronsted-Lowry Acid – Donates protons (H + ) Base – Accepts protons (H + ) HClO + H 2 O  H 3 O + + ClO - acid base acid base The proton moves from HCl (donate) to H 2 O (accept). HClO/ClO - would be an acid-base conjugate pair. Acid-Base conjugate pairs differ by only a H +.

Lewis Acid/Base Acid: electron pair acceptor Base: electron pair donator Formation of a new covalent bond in which both electrons are provided by one substance (dative covalent bonds). Formation of complexes and complex ions are usually Lewis acid-base reactions

Lewis Examples The Lewis definition is the broadest of the three acid definitions. Generally the Lewis base has a lone pair of electrons for donating (H 2 O, NH 3, CN -, OH - are all common examples. A bare proton (hydrogen ion) is a Lewis acid H + (aq) + :NH 3 (aq)  H:NH 3 + (aq) or NH 4 + (aq) The silver ion can be a Lewis acid Ag + (aq) + 2 :NH 3 (aq)  [H 3 N:Ag:NH 3 ] + (aq) or [Ag(NH 3 ) 2 ] +

Strong Acids and Bases Memorize Acids (7) – HCl – HBr – HI – HClO 3 – HClO 4 – HNO 3 – H 2 SO 4 Bases (7) – NaOH – KOH – RbOH – CsOH – Ca(OH) 2 – Sr(OH) 2 – Ba(OH) 2

Strong (acid/base) The term strong relates to electrolytes. Strong acids and bases are strong electrolytes: they conduct electricity. Strong just means that they dissociate or ionize 100%

Neutraliztion Reactions The products are generally a salt (ionic substance) and water. Double replacement, hydrogen and the metal from the base switch anions. Charge balance the salt then balance the reaction. H 2 SO 4 + Al(OH) 3  Al 2 (SO 4 ) 3 + H 2 O 3H 2 SO 4 + 2Al(OH) 3  Al 2 (SO 4 ) 3 + 6H 2 O

pH Scale pH is a measure of H + or H 3 O + pH from 0-7 acidic pH from 7-14 basic pH = 7 neutral Each unit change in pH represents a change of 10x for hydronium ion concentration. Brackets indicate concentration in moles per liter (M): [X] concentration of X.

Ions of Interest Hydronium H 3 O + Also just H + Produced by acids Hydroxide OH - Produced by bases [H 3 O + ] x [OH - ] = 1 x This allows you to determine the concentration of hydroxide or hydronium ion given one of the two. They are inversely related via a constant.

pX = - log [X] pH = - log [H + ] pH = - log [H 3 O + ] pOH = - log [OH - ] pH + pOH = 14 (always) This allows you to determine the pH or pOH given one of the two. The sum always equal 14.

‘Strehl Square’

Strong acid/base pH ‘Strong’ substances dissociate completely Write out the dissociation of the acid or base. The concentration will be based upon the starting concentration and the coefficient. For monoprotic and monohydroxides the coefficient is 1.

Strong Example 2.5M HCl – HCl  H + + Cl - – 2.5M HCl  2.5M H + 0.5M Ca(OH) 2 – Ca(OH) 2  Ca OH - – 0.5M Ca(OH) 2  1.0M OH -

Titration Determination of an unknown concentration by careful quantitative addition of a known solution (with a buret). An indicator is used that will change color near the equivalence point where moles of H + are equal to moles of OH -. It is important to write the balanced neutralization reaction before any calculations.

Titration Calculations At the end of the titration the moles of hydronium and hydroxide are equal. Molarity (M) = moles/volume We can find the moles of know by taking the M known x volume known to get moles. We can then use the balanced reaction to convert to moles of unknown. Finally by dividing by the volume of the unknown we determine the concentration of the unknown.

Titration Example 15.00mL of Sr(OH) 2 were neutralized via titration with 13.5mL of 2.00M HNO 3. What is the concentration of Sr(OH) 2 Sr(OH) 2 + 2HNO 3  Sr(NO 3 ) 2 + 2H 2 O 13.5mL = L; L x 2.00M = moles HNO moles HNO 3 x 1Sr(OH) 2 /2HNO 3 = mole Sr(OH) 2 M = mole/0.015L = 0.90M Sr(OH) 2