Acids and Bases

Acids & Bases ● 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. ● HCl (aq) → Cl - (aq) + H + (aq) ● Acids dissolved in water create hydronium ions ● H + + H 2 O → H 3 O + ● Arrhenius Base- a substance that produces an OH - anion in solution. ● NaOH(s) → Na + (aq) + OH - (aq)

Physical Properties of Acids Have a sour taste.

Physical Properties of Acids Turns blue litmus to red. Turns methyl orange to red. Indicator - a chemical compound that change color when the acidity of the solution changes.

Physical Properties of Acids Will react with: some metals to produce a salt and H 2 gas metal oxides to produce a salt and H 2 O. metal carbonates to produce a salt, H 2 O, and CO 2. bases to produce a salt and H 2 O. Mg + 2HCl  MgCl 2 + H 2 MgO + 2HCl  MgCl 2 + H 2 O MgCO 3 + 2HCl  MgCl 2 + H 2 O + CO 2 Mg(OH) 2 + 2HCl  MgCl 2 + 2H 2 O

Acids Are electrolytes. electrolytes are substances that conduct an electric current when dissolved.

Strong Acids Common strong acids: hydrochloric acid, HCl hydrobromic acid, HBr nitric acid, HNO 3 chloric acid, HClO 3 sulfuric acid, H 2 SO 4 Common weak acids Acetic acid, HC 2 H 3 O 2 Hydrofluoric acid, HF

Physical Properties of Bases Have a bitter taste. Coffee itself is acidic, but it contains an alkaline compound – caffeine – which contributes to its bitter taste.

Physical Properties of Bases Feel slimy or slippery to the touch.

Physical Properties of Bases Turns red litmus to blue. Turns methyl orange to yellow. Turns phenolphthalein to pink. Litmus pH scale.

Physical Properties of Bases React with acids to produce salt and H 2 O. HCl + NaOH  NaCl + H 2 O

Physical Properties of Bases Are also electrolytes.

Strong Bases Like strong acids, strong bases ionize completely. Strong bases = soluble hydroxides lithium hydroxide, LiOH sodium hydroxide, NaOH potassium hydroxide, KOH calcium hydroxide, Ca(OH) 2 strontium hydroxide, Sr(OH) 2 barium hydroxide, Ba(OH) 2 All other bases, including NH 3, are weak.

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

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

pH Scale AcidicBasic

pH and Concentration pH = the “power” of hydrogen – it is the strength of the H + ion – Concentration is measured using Molarity However, brackets are used to indicate concentration [H + ] = the concentration of the H + ion in solution 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?

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 Water itself is an acid and a base [H + ] and [OH - ] are equal H 2 O → H + + OH - Therefore: pH + pOH = 14 - Page 3 of NC Ref. Tables · What is the pH of the base in the previous example ? Formula: pH + pOH = 14 - Page 3 of NC Ref. Tables pH = 14 pH = ** is this a good pH for a base?