8. Acids and Bases

Question 1

Bronsted-Lowry Acid

Answer 1

Proton donor (H2)

Question 2

Bronsted-Lowry Base

Answer 2

Proton acceptor (NH3)

Question 3

Lewis Acid

Answer 3

electron pair acceptor

(H⁺ in H₂O acts as the electrophile)

Question 4

Lewis base

Answer 4

electron pair donor

(water acts as the nucleophile)

Question 5

Amphoteric

Answer 5

can act as either an acid or a base eg Al2O3

Question 6

Amphiprotic

Answer 6

A type of amphoteric substance that specifically can act as either an acid or base by accepting / donating H+ ions

Question 7

pH equations

Answer 7

pH = -log₁₀[H⁺]

[H⁺] = 10^-pH

Question 8

Ionic product constant of water (Kw)

Answer 8

Kw = [H⁺][OH] = 1 x 10^-14 mol²dm^-6

pKw = 14 = pH +pOH

Question 9

Kw variation with temperature

Answer 9

pH decreases as the temp increases

Question 10

Strong Acid examples

Answer 10

• Hydrochloric acid
• Nitric acid
• Sulfuric acid

Question 11

Weak Acid examples

Answer 11

• Carboxylic acids (eg ethanoic acid)
• Carbonic acid

Question 12

Strong Bases

Answer 12

• Group 1 hydroxides (eg NaOH)
• Barium hydroxide

Question 13

Weak Bases

Answer 13

• Ammonia
• Amines

Question 14

Formation of Carbonic Acid

Answer 14

CO_2(g) + H₂O_(l) <—> H₂CO3(aq)

H₂CO3(aq) <—> H⁺_(aq) + HCO₃^-_(aq)

HCO₃^-_(aq)​ <—> H⁺_(aq) + CO₃^2-_(aq)

precipitation below pH 5.6 is considered acid deposition

Question 15

Acid Deposition - Nitrogen

Answer 15

at high temps such as in engines

N_2(g) + O_2(g) –> 2NO_(g)

this reacts further with oxygen

2NO_(g) + O_2(g) –> 2NO_{<strong>2(g)</strong>}

this then reacts with water

2NO_2(g) + H₂O_(l) –> HNO_3(aq) + HNO_2(aq)

Question 16

Acid Deposition - Sulphur

Answer 16

sulphur diozide is released by burning coal

S_(s) + O_2(g) –> SO_(g)

this reacts with water to form sulfurous acid

SO_2(g) + H₂O_(l) <—> H₂SO_3(aq)

this can also react further with air, then water to form sulphuric acid

2SO_2(g) + O_2(g) <—> 2SO_3(g)

SO_3(g) + H₂O_(l) –> H₂SO_4(aq)

Question 17

Prevention of Acid Deposition

Answer 17

Pre-combustion methods

• involve crushing and cleaning coal to remove up to 90% of solid sulphur

Post-combustion methods

• calcium oxide or lime can remove gaseous sulphur (and other pollutants)

Question 18

Acid Dissociation constant Ka and pH

Answer 18

[H⁺] = sqrt Ka[HA]

pKw = pH + pOH = 14

Kw = KaKb = 10^-14

Question 19

Acidic buffers

Answer 19

weak acid + its sodium/ potassium salt

eg

ethanoic acid sodium ethanoate

Question 20

Alkaline buffer

Answer 20

Weak base + its chloride

eg

ammonia ammonium chloride