UNIT 4 ACID BASE EQUILIBRIUM. Bronsted Lowery Acids and Bases

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1 UNIT 4 ACID BASE EQUILIBRIUM Bronsted Lowery Acids and Bases

2 Acids ate & ide to ic ite to ous Binary Oxy Pure Aqueous Pure Aqueous HCl (g) HCl (aq) H 2 SO 4(l) H 2 SO 4(aq) hydrogen chloride hydrochloric acid hydrogen sulphate sulphuric acid HF (g) HF (aq) H 2 CO 3(l) H 2 CO 3(aq) hydrogen fluoride hydrofluoric acid hydrogen carbonate carbonic acid H 2 S (g) H 2 S (aq) H 2 SO 3(l) H 2 SO 3(aq) Hydrogen sulphide hydrosulphuric acid hydrogen sulphite sulphurous acid

3 Acids ate & ide to ic ite to ous Binary Oxy Pure Aqueous Pure Aqueous HI (g) HI (aq) H 2 Cr 2 O 7(l) H 2 Cr 2 O 7(aq) hydrogen iodide hydroiodic acid hydrogen chromate dichromic acid HBr (g) HBr (aq) CH 3 COOH (l) CH 3 COOH (aq) hydrogen bromide hydrobromic acid hydrogen acetate acetic acid

4 Properties of Acids & Bases Acids (from Latin acidus meaning sour) taste sour feel like water good electrolytes turn blue litmus paper pink ph less than 7 at 25 C

5 Properties of Acids & Bases Bases (from Old English meaning to bring low ) taste bitter feel slippery good electrolytes turn pink litmus paper blue ph greater than 7 at 25 C

6 ARRHENIUS THEORY(1887) 1 Electrolytes conduct electricity by releasing charged particles or ions. 2 Acids are substances which ionize in water to produce hydrogen ions (H + or free protons) HCl (g) H + (aq) + Cl- (aq)

7 More Arrhenius 3. Bases are substances which ionize in water to produce hydroxide ions (OH - ) NaOH (cr) Na + (aq) + OH- (aq)

8 Problems With the Arrhenius Theory The Arrhenius definition says that acids and bases can only occur in water solutions. There are many substances which are acidic or basic but do not have a hydrogen ion or a hydroxide ion. For example, sodium bicarbonate (NaHCO 3 ) in water turns litmus blue, but has no apparent hydroxide ion. Also, it doesn t make much sense that a proton (H+) would just stay free-floating in a solution!

9 The H + in Water

10 BRØNSTED-LOWRY THEORY (1923) In a chemical reaction, acids & bases are found together. Acid is a hydrogen ion donor, (it gives up a H + ) Base is a hydrogen ion acceptor, (it takes a H + )

11 Bronsted Acid in Water A proton (H + ) donor H + HCl + H 2 O H 3 O + + Cl - Bronsted Base in Water A proton (H + ) acceptor NH 3 + H 2 O H + NH OH -

12 At the Molecular Level

13 Write a Bronsted reaction for the weak base HCO - 3 H + HCO H H 2 CO 3 + OH - 2 O base acid

14 Conjugate Acid Base Pairs

15 Conjugate Acid Base Pairs

16 Write a Bronsted reaction for the weak base HCO - 3 H + H + HCO H H 2 CO 3 + OH - 2 O base acid acid base HCO 3 - and H 2 CO 3 H 2 O and OH - Conjugate acid base pairs differ by one proton H +

17 Conjugate Acid Conjugate Base One more H + 1 less H + C 6 H 5 OH C 6 H 5 O - H 2 CO 3 H 2 O HPO 4 2- H 2 PO 4 - HCO - 3 OH - PO 3-4 HPO 2-4 Look In Data Book C 6 H 5 COOH C 6 H 5 COO - NH 4 + NH 3 Fe(H 2 O) 6 3+ Fe(H 2 O) 5 (OH) 2+

18 Mixing Acids and Bases

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20 Amphiprotic Substances

21 Amphiprotic Chemical Species Amphiprotic chemical species can act as acids and donate protons or bases and accept protons. They are listed both on the left side of the table as an acid and the right side as a base. Acid, Base, or Amphiprotic PO 4 3-

22 Amphiprotic Chemical Species Amphiprotic chemical species can act as acids and donate protons or bases and accept protons. They are listed both on the left side of the table as an acid and the right side as a base. Acid, Base, or Amphiprotic PO 4 3- Base can gain H +, cannot lose H + HPO 4 2-

23 Amphiprotic Chemical Species Amphiprotic chemical species can act as acids and donate protons or bases and accept protons. They are listed both on the left side of the table as an acid and the right side as a base. Acid, Base, or Amphiprotic PO 4 3- Base can gain H +, cannot lose H + HPO 4 2- Amphiprotic can gain H + and lose H + H 2 PO 4 -

24 Amphiprotic Chemical Species Amphiprotic chemical species can act as acids and donate protons or bases and accept protons. They are listed both on the left side of the table as an acid and the right side as a base. Acid, Base, or Amphiprotic PO 4 3- Base can gain H +, cannot lose H + HPO 4 2- Amphiprotic can gain H + and lose H + H 2 PO 4 - Amphiprotic can gain H + and lose H + H 3 PO 4

25 Amphiprotic Chemical Species Amphiprotic chemical species can act as acids and donate protons or bases and accept protons. They are listed both on the left side of the table as an acid and the right side as a base. Acid, Base, or Amphiprotic PO 4 3- Base can gain H +, cannot lose H + HPO 4 2- Amphiprotic can gain H + and lose H + H 2 PO 4 - Amphiprotic can gain H + and lose H + H 3 PO 4 Acid cannot gain H +, can lose H +

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