Chapter 12 - Acids & Bases

Question 1

Give three examples of common household acids

Answer 1

○Ethanoic acid (CH₃COOH) → found in vinegar
○Citric acid (C₆H₈O₇) → found in oranges and lemons
○Benzoic acid (C₆H₅COOH) → food preservative

Question 2

Arrhenius definition of an acid

Answer 2

A substance that dissociates in water to produce H⁺ ions

Question 3

Arrhenius definition of a strong acid

Answer 3

A substance that would almost completely dissociate in water into its two ions (H⁺ and X⁻)

Question 4

Arrhenius definition of a weak acid

Answer 4

A substance that only slightly dissociates in water into its two ions

Question 5

Monobasic acid

Answer 5

An Arrhenius acid that had one H⁺ in its molecule

Question 6

Dibasic acid

Answer 6

An Arrhenius acid that had two H⁺ in its molecule

Question 7

Tribasic acid

Answer 7

An Arrhenius acid that had three H⁺ in its molecule

Question 8

Arrhenius definition of a base

Answer 8

Substance that dissociates in water to produce OH⁻ ions (hydroxide ions/hydroxyl)

Question 9

Arrhenius definition of a strong base

Answer 9

Substance that would almost completely dissociate in water into its two ions (X⁻ and OH⁻)

Question 10

Arrhenius definition of a weak base

Answer 10

Substance that would only slightly dissociate in water into its two ions

Question 11

Give two examples of common household bases

Answer 11

○Sodium hydroxide (NaOH) → In caustic soda used to unblock drains
○Magnesium hydroxide (Mg(OH)₂) → found in ‘Milk of Magnesia’

Question 12

What were the problems with Arrhenius’ Theory of Acids & Bases?

Answer 12

○The H⁺ ions produced when acid dissociates reacts with the water molecule to form H₃O⁺ (hydronium ion). This is what exists in the solution, not H⁺
○His theory only holds for reactions occurring in water. No other solvents are included
○Not all acid-base reactions include water

Question 13

Brønsted-Lowry definition of an acid

Answer 13

A proton (H⁺) donor

Question 14

Brønsted-Lowry definition of a strong acid

Answer 14

A good proton donor

Question 15

Brønsted-Lowry definition of a weak acid

Answer 15

A poor proton donor

Question 16

Brønsted-Lowry definition of a base

Answer 16

A proton acceptor

Question 17

Brønsted-Lowry definition of a strong base

Answer 17

A good proton acceptor

Question 18

Brønsted-Lowry definition of a weak base

Answer 18

A poor proton acceptor

Question 19

Amphoteric/amphiprotic

Answer 19

A substance that can act as either an acid or a base

Question 20

What are the advantages of the Brønsted-Lowry Theory over Arrhenius’s?

Answer 20

○Brønsted-Lowry doesn’t require water as a solvent
○Brønsted-Lowry has a broader range of species that can be defined as an acid/base
○Brønsted-Lowry can explain how a substance can be amphoteric in terms of proton transfer

Question 21

What are the conditions of the Brønsted-Lowry Theory of Acids & Bases?

Answer 21

○It will only work if there is an acid present to donate a proton and a base to accept it
○Have to work in pairs

Question 22

Conjugate acid-base pair (conjugate pair)

Answer 22

Any pair consisting of an acid and a base that differ by one proton

Question 23

When does an acid change into its conjugate base?

Answer 23

When it donates a H⁺ e.g. HCN → CN⁻

Question 24

When does a base change into its conjugate acid?

Answer 24

When it accepts a H⁺ e.g. HCO₃⁻ → H₂CO₃

Question 25

Identify the following in this equation: ``` C₃HCOOH + H₂O ↔ CH₃COO⁻ + H₃O⁺ B/L acid B/L base Conjugate base Conjugate acid Conjugate pair Conjugate pair ```

Answer 25

``` B/L acid: C₃HCOOH B/L base: H₂O Conjugate base: CH₃COO⁻ Conjugate acid: H₃O⁺ Conjugate pair: C₃HCOOH & CH₃COO⁻ Conjugate pair: H₂O & H₃O⁺ ```

Question 26

Neutralisation

Answer 26

The reaction between an acid and a base to form salt and water

Question 27

Salt

Answer 27

A substance formed when the hydrogen ion from an acid is replaced by a metal or ammonium ion

Question 28

Give an example of neutralisation in medicine

Answer 28

○Excess stomach acid is neutralised using a base substance (antacids) such as Alka-Seltzer which contains sodium hydrogencarbonate (NaHCO₃) ►HCL + NaHCO₃ → NaCl + H₂O + CO₂

Question 29

Give an example of neutralisation in agriculture

Answer 29

○Lime (CaO) can be used to neutralise acidic soil ○Lime reacts with rain water to form calcium hydroxide (Ca(OH)₂) and this is used to neutralise the acid ►CaO + H₂O → Ca(OH)₂ ►H₂SO₄ + Ca(OH)₂ → CaSO₄ [ᶜᵃˡᶜᶦᵘᵐ ˢᵘˡᶠᵃᵗᵉ] + 2H₂O

Question 30

Give an example of neutralisation in environmental protection

Answer 30

○Limestone is added to lakes to neutralise acid rain ○Limestone is added to chimneys of coal burning power plants to neutralise acidic gases produced ►H₂SO₄ + CaCO₃ → CaSO₄ + H₂O + CO₂

Question 31

How does toothpaste involve neutralisation?

Answer 31

Toothpaste is basic to neutralise acids bacteria produce which cause tooth decay

Question 32

How do wasp and bee sting treatments involve neutralisation?

Answer 32

○Wasp stings are strongly alkaline and so vinegar is used to neutralise them ○Bee stings are acidic and a base such as sodium hydrogencarbonate (baking soda) are used to neutralise it

Question 33

How does shampoo and conditioner involve neutralisation?

Answer 33

○Shampoo is slightly basic and can cause scales on the hair to open out ○Conditioner is slightly acidic to neutralise this base, leaving the hair shiny and more manageable