Chapter 12 - Acids & Bases Flashcards
Give three examples of common household acids
○Ethanoic acid (CH₃COOH) → found in vinegar
○Citric acid (C₆H₈O₇) → found in oranges and lemons
○Benzoic acid (C₆H₅COOH) → food preservative
Arrhenius definition of an acid
A substance that dissociates in water to produce H⁺ ions
Arrhenius definition of a strong acid
A substance that would almost completely dissociate in water into its two ions (H⁺ and X⁻)
Arrhenius definition of a weak acid
A substance that only slightly dissociates in water into its two ions
Monobasic acid
An Arrhenius acid that had one H⁺ in its molecule
Dibasic acid
An Arrhenius acid that had two H⁺ in its molecule
Tribasic acid
An Arrhenius acid that had three H⁺ in its molecule
Arrhenius definition of a base
Substance that dissociates in water to produce OH⁻ ions (hydroxide ions/hydroxyl)
Arrhenius definition of a strong base
Substance that would almost completely dissociate in water into its two ions (X⁻ and OH⁻)
Arrhenius definition of a weak base
Substance that would only slightly dissociate in water into its two ions
Give two examples of common household bases
○Sodium hydroxide (NaOH) → In caustic soda used to unblock drains
○Magnesium hydroxide (Mg(OH)₂) → found in ‘Milk of Magnesia’
What were the problems with Arrhenius’ Theory of Acids & Bases?
○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
Brønsted-Lowry definition of an acid
A proton (H⁺) donor
Brønsted-Lowry definition of a strong acid
A good proton donor
Brønsted-Lowry definition of a weak acid
A poor proton donor
Brønsted-Lowry definition of a base
A proton acceptor
Brønsted-Lowry definition of a strong base
A good proton acceptor
Brønsted-Lowry definition of a weak base
A poor proton acceptor
Amphoteric/amphiprotic
A substance that can act as either an acid or a base
What are the advantages of the Brønsted-Lowry Theory over Arrhenius’s?
○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
What are the conditions of the Brønsted-Lowry Theory of Acids & Bases?
○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
Conjugate acid-base pair (conjugate pair)
Any pair consisting of an acid and a base that differ by one proton
When does an acid change into its conjugate base?
When it donates a H⁺ e.g. HCN → CN⁻
When does a base change into its conjugate acid?
When it accepts a H⁺ e.g. HCO₃⁻ → H₂CO₃
Identify the following in this equation:
C₃HCOOH + H₂O ↔ CH₃COO⁻ + H₃O⁺ B/L acid B/L base Conjugate base Conjugate acid Conjugate pair Conjugate pair
B/L acid: C₃HCOOH B/L base: H₂O Conjugate base: CH₃COO⁻ Conjugate acid: H₃O⁺ Conjugate pair: C₃HCOOH & CH₃COO⁻ Conjugate pair: H₂O & H₃O⁺
Neutralisation
The reaction between an acid and a base to form salt and water
Salt
A substance formed when the hydrogen ion from an acid is replaced by a metal or ammonium ion
Give an example of neutralisation in medicine
○Excess stomach acid is neutralised using a base substance (antacids) such as Alka-Seltzer which contains sodium hydrogencarbonate (NaHCO₃)
►HCL + NaHCO₃ → NaCl + H₂O + CO₂
Give an example of neutralisation in agriculture
○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
Give an example of neutralisation in environmental protection
○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
How does toothpaste involve neutralisation?
Toothpaste is basic to neutralise acids bacteria produce which cause tooth decay
How do wasp and bee sting treatments involve neutralisation?
○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
How does shampoo and conditioner involve neutralisation?
○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
