Acids and bases 1

Question 1

What is the definition of acid and base (3)

Answer 1

1. acids typically give solvated H⁺(aq) (hydrogen ion)
2. bases typically give HO⁻(aq) (hydroxide ion)
3. Acids and bases react in solution, typically giving salt and water (a neutralisation reaction).

Question 2

What is protonation and deprotonation (3)

Answer 2

1. protonation - gaining H⁺ **
2. deprotonation - losing H⁺
3. A protonated water molecule is known as a hydronium ion H₃O⁺ **(aq) this is aka H⁺ **(aq).

Question 3

What are electrolytes (3)

Answer 3

1. Electrolytes are solutes that give cations (+) &anions (-) when in solution.
2. Strong electrolytes fully ionise (dissociate) in an irreversible reaction.
3. Weak electrolytes partially ionise in a (reversible) equilibrium reaction.

Question 4

What is the Brönsted-Lowry acid-base definition (3)

Answer 4

1. An acid is a substance capable of donating a proton.
2. A base **is a substance capable of accepting a proton.
3. Acids & alkalis (water-soluble bases) are electrolytes.

Question 5

What are conjugated acids and bases (5)

Answer 5

1. conjugated because it is on the right-hand side
2. Base or acid depending on whether it accepts or donates protons.
3. An acid and its conjugate base form a ‘conjugate pair’: they differ only by the presence of a proton.
4. Weak acids have strong conjugate bases.
5. Strong bases have weak conjugate acids.

Question 6

What effect does adding water to acids and bases have on the equilibrium?

Answer 6

For acids and bases, adding more water will shift equilibria to the right due to Le Chatelier’s principle.

Question 7

Given the ionisation in aqueous solution of the following products, which statement is correct:

X + H₂O ⇌ XH⁺ + HO⁻

Y + H₂O → YH⁺ + HO⁻

a. X has a strong conjugate acid.
b. Y has a strong conjugate acid.
c. X has a strong conjugate base.
d. Y has a strong conjugate base.

Answer 7

Answer = A
1. X & Y are bases, so they have conjugate acids.
2. X + H₂O is a reversible reaction, meaning weak electrolytes that give strong conjugate pairs.
3. XH⁺ is a strong H⁺ donor. Therefore, X still remains at an equilibrium.

Question 8

What is the difference between amphoteric and amphiprotic (3)

Answer 8

1. amphiprotic - substance that can both accept or donate protons
2. amphoteric - substance that reacts with both bases and acids
3. All amphiprotic species are amphoteric, but not all amphoteric substances are amphiprotic.

Question 9

What are Lewis acids and Lewis bases and examples (4)

Answer 9

1. A Lewis acid **is an electron pair acceptor.
2. A Lewis base **is an electron pair donor.
3. NH₃ = Lewis base & Brönsted-Lowry base. (can gain H to make NH₄)
4. BF₃ = Lewis acid, but not Brönsted-Lowry acid. Cannot give away protons (doesn’t have H ions)

Question 10

What are the types of solvents that determine whether substances act as acids or bases (5)

Answer 10

1. Amphiprotic: Donates or accepts protons, e.g. H₂O
2. Protogenic: Donates protons, e.g. H₂SO₄
3. Protophillic: Accepts protons e.g. NH₃
4. Aprotic: Neither accepts nor donates protons
5. Aprotic solvents may be non-polar

Question 11

How can aqueous solvents affect acid and base strength (4)

Answer 11

1. Contains dissolved species that can affect apparent acid and base strength.
2. HCl is a strong acid in water the equilibrium lies 100% on the right-hand side.
3. HCl is a weak acid in formic acid because the solvent acts as a provider of H⁺ and pushes the equilibrium to the left.
4. This acid is stronger in solvents that accept H.⁺

Question 12

How is pH and the concentration of H₃O⁺ ([H₃O⁺]) calculated (2)

Answer 12

1. pH = -log[H₃O⁺ + (aq)] - concentration of H₃O⁺
2. [H₃O⁺ + (aq)] = 10ᵖᴴ

Question 13

How is the pH of bodily fluids described (9)

Answer 13

1. Gastric juice- acidic
2. Urine- wide range, mildly acidic - neutral
3. Saliva- mildly acidic
4. Blood - very narrow range, neutral
5. Lachrymal - neutral
6. Bile - neutral
7. Muscle - neutral
8. Sweat - mildly acidic
9. Cerebrospinal - neutral

Question 14

What is the equilibrium constant (2)

Answer 14

1. K = Products concentration/Reactants concentration
2. if K is very small, the equilibrium positions on the left and [H2O] stay approximately the same as if there is no ionisation at all

Question 15

What is the ionic product of water (4)

Answer 15

1. Kw is ionic product of water.
2. Kw = [H₃O⁺] [OH⁻]
3. Kw = 1.0 x 10⁻¹⁴ M² for any solution of H₂O (at 25℃ only).
4. The ionisation of water absorbs heat energy (endothermic), so KW increases with temperature.

Question 16

What are neutral solutions (3)

Answer 16

1. A neutral solution has an equal concentration of hydrogen and hydroxide ions, i.e. [H⁺] = [HO⁻]
2. For neutral solution, [H⁺] = KW (= 1 x 10⁻⁷ M at 25℃).
3. As pH = -log [H⁺], pH = 7 for neutral solutions at 25℃.