Acid and Base Reactions

Hydrofluoric acid

HF - weak acid

Hydrochloric acid

HCl - strong acid

Nitrous acid

HNO₂ - weak acid

Nitric acid

HNO₃ - strong acid

Sulfurous acid

H₂SO₃ - weak acid

Sulfuric acid

H₂SO₄ - strong acid

Phosphoric acid

H₃PO₄ - weak acid

Carbonic acid

H₂CO₃ - weak acid

Acetic acid

CH₃COOH - weak acid

citric acid

C₆H₈O₇ - weak acid

Sodium hydroxide

NaOH - strong base

Barium hydroxide

Ba(OH)₂ - strong base

Ammonia

NH₃ - weak base

Ammonium

NH₄⁺ - weak acid

two types of inorganic acid groups:

• hydrohalic acids: hydrogen + halogen

• oxyacids: containing oxygen atom/s

hydrohalic acid nomenclature:

prefix + suffix

hydro——ic acid

halogenic oxyacids nomenclature:

• 1 oxygen -

• 2 oxygen -

• 3 oxygen -

• 4 oxygen -

• hypo — ous acid

• — ous acid

• — ic acid

• per — ic aid

define acid

a substance whose molecules or ions are able to donate protons (hydrogen ions).

define base

a substance whose molecules or ions are able to accept protons (hydrogen ions)

acid + base →

salt + water

hydrochloric acid + sodium hydroxide

equation:

NaOH_(aq) + HCl_(aq) → H₂O_(l) + NaCl_(aq)

neutralisation reactions are ____thermic::

exothermic

hydrochloric acid + barium hydroxide

equation:

2HCl_(aq) + Ba(OH)_{2 (aq)} → 2H₂O + BaCl_{2 (aq)}

acid + carbonate →

salt + water + carbon dioxide

hydrochloric acid + sodium carbonate

equation:

2HCl_(aq) + Na₂CO_{3 (aq)} → H₂O_(l) + CO_{2 (g)} + 2NaCl_(aq)

sulphuric acid + copper carbonate

H₂SO_{4 (aq)} + CuCO_{3 (aq)} → CuSO_{4 (aq)} + H₂O_(l) + CO_{2 (g)}

acid + metal →

salt + hydrogen gas

acid + metal oxide →

salt + water

sulphuric acid + magnesium

H₂SO_{4 (aq)} + Mg_(s) → MgSO_{4 (s)} + H_{2 (g)}

equation for dissolution of an acid

acid → positive hydrogen + negative ion

equation for dissolution of vinegar

ethanoic acid → hydrogen ion + acetate ion

CH₃COOH → H⁺ + CH₃COO^-

monoprotic acids

acids that donate one proton

• hydrochloric acid HCl

• nitric acid HNO₃

• ethanoic acid CH₃COOH

amphoprotic substance

a substance that cab both accpet and donate a proton (H⁺)

polyprotic acids

acids that donate more than one proton

• sulfuric acid H₂SO₄ - donate 2 protons - diprotic

• carbonic acid H₂CO₃ - donate 2 protons - diprotic

• phphosphoric acid H₃PO₄ - donate 3 protons - triprotic

dissociation of acids in water

splitting into positive and negative ions when dissolved in water

acids react faster if ____

there a more ions to react

acid strength refers ____

to the extent of dissociation of the acid

strong acids create _____

lots of hydrogen ions

strong acids react _____

easily

weak acids create _____

few or no hydrogen ions

weak acids react _____

poorly

strong acids

• hydrochloric acid, HCl

• sulfuric acid H₂SO₄

• nitric acid, HNO₃

• perchloric acid, HClO₄

• hydrobromic acid, HBr

• hydroiodic acid, HI

strong bases

• sodium hydroxide, NaOH

• potassium hydroxide, KOH

• lithium hydroxide, LiOH

• calcium hydroxide, Ca(OH)₂

• strontium hydroxide, Sr(OH)₂

• barium hydroxide, Ba(OH)₂

strong acid, concentrated solution

strong acid, dilute solution

A strong acid dissociates ____

almost fully in water and there will have high electrical conductivity as there are many ions present.

A weak acid dissociates ____

partially and therefore has less ions present, so has lower electrical conductivity.

acid concentration refers ____

to the number of moles present in a given volume.

chemical properties of acids

• corrode materials

• taste sour

• conduct electricity in solution

• react easily

chemical properties of bases

• caustic

• slippery

• taste bitter

general formula for acid dissociation in water:

HA + H₂O ⇌ H₃O⁺ + A^-

strong acids: reaction completion

• generally reversible

• however some acids donate all hydrogen ions that the reaction is irreversible / gone to completion.

  • equilibrium lies very much to the right

weak acids: reaction completion

• do not go to completion (partially ionise)

• reversible ∴ establishes an equilibrium

  • reverse reaction is favoured (ions react very easily to reform reactants)

strong acid: pH

pH ≈ 1

strong acid: pKa

pKa ≈ 0

weak acid: pH

pH = 2-6

weak acid: pKa

pKa > 3

strong base: pH

pH ≈ 14

strong base: pKb

pKb = low (0 - 3)

weak base: pH

pH = 8-11

weak base: pKb

pKb > 3

pH:

is a measure of the concentration of hydrogen ions in a solution.

pOH:

is a measure of the concentration of hydoxide ions in a solution.

pH equation:

pH = -log [ H⁺]

[H⁺] =

10^-pH

pOH equation:

pOH = -log [OH^-]

[OH^-] =

10^-pOH

relationship between pH and pOH

pH + pOH = 14

Pure Water pH:

pH = 7

[OH^-] = [H₃O⁺] = 10^-7 M

Acid Dissociation Constant:

Ka - the equilibrium constant describing the extent of dissociation fro a weak acid. Ka is measured in mol/L.

conjugate acid-base pairs refer to ____

two substances that differ only by the presence of a proton (H⁺)

Conjugate Acid:

A species formed by adding a proton to a Bronsted-Lowry base e.g. NH₄⁺ from NH_3.

Conjugate Base:

A species formed by the loss of a proton from a Bronsted-Lowry acid e.g. Ch₃COO^- from CH₃COOH.

Acidic Buffer:

A buffer solution comprising a weak acid and its conjugate base, often in the form of a salt, such as a mixture of ethanoic acid (CH₃COOH) and sodium acetate (CH₃COONa).

Basic Buffer:

A buffer solution composed of a weak base and its conjugate acid, often in the form of a salt.

Buffer Solution:

A solution capable of resisting pH changes when small amounts of acid or base are added.

Lavoisier theory:

description:

• acids were substances that contained oxygen atoms

• experimented on oxides of non-metals

limitations:

• many acids do not contain oxygen

  • e.g. HCl

Davy theory:

description:

• acids contained replaceable hydrogen atoms

• HCl did not contain oxygen whilst still acting as an acid

limitations:

• no explanation as to when, or how the molecules interacted

Arrhenius theory:

description:

• acids ionise in water to produce hydrogen ions (H⁺) and bases ionise in water to produce hydroxide ions (OH^-).

limitations:

• only works for acids and bases in aqueous solutions

• some acids and bases operate without being in solution

Bronsted-Lowry theory:

description:

• acids are proton donors

• bases are proton acceptors

limitations:

• theory requires hydrogen atoms to be present within a molecule to be classified as an acid or a base

  • molecules e.g. BF₃ acts an acid

primary purposes of titrations:

• quantitive analysis

• identification of unknown substances

• quality control

PSS

pure soluble stable (primary standard solutions)

primary standard solution:

a solution that has an accuratrly known concentration.

preparation of primary standard solution: summary

1. Measure

2. Transfer

3. Ensure transfer of all

4. Swirl to dissolve

5. Fill and invert to mix

Phenolphthalein

Colourless → Pink

8.3 - 10.0

weak acid + strong base

Bromothymol Blue

Yellow → Green

6.0 - 7.6

strong acid + strong base

Phenol Red

Yellow → Red

6.8 - 8.0

strong acid + strong base

Methyl Red

Red → Yellow

4.4 - 6.2

strong acid + weak base

Methyl Orange

Red → Yellow

3.2 - 4.4

strong acid + weak base

applications of neutralisation reactions in everyday life:

• vinegar to treat wasp or jelly fish stings:

  • toxins are alkaline (basic)

  • vinegar contains acetic acid (weak acid)

• toothpaste:

  • contains various bases

    • sodium hydroxide NaOH

    • calcium carbonate CaCO₃

  • alkalinity of toothpaste helps to neutralise acids produced by bacteria in the mouth

applications of neutralisation reactions in chemical industry:

• chemical spills:

  • bases used to neutralise acid spills

  • acids used to neutralise base spills

  • generally weak acids and bases as strong acid + strong base reaction is highly exothermic.