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

acid + base →

salt + water [ __ + __ ]

metal hydroxide + acid →

salt + water [ __ _____ + __ ]

metal oxide + acid →

salt + water [ __ __ + __ ]

acid + metal carbonate →

salt + water + carbon dioxide

acid + metal →

salt + hydrogen

common inorganic / mineral acids

• hydrochloric acid HCl

• sulfuric acid H₂SO₄

• nitric acid HNO₃

• phosphoric acid H₃PO₃

common organic acids

• citric acid - citrus fruit

• acetic acid - vinegar

• lactic acid - milk

• ascorbic acid - vitamin C

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)

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

weak acids

• citric acid

• acetic acid

• phosphoric acid

• methanoic acid

• hydrofluoric acid

• ethanoic acid

• lactic acid

weak bases

• ammonia, NH₃

• trimethyl ammonia, N(CH₃)₃

• ammonium hydroxide, NH₄OH

• pyridine, C₅H₅N

• aniline C₆H₅NH₂

• sodium bicarbonate, NaHCO₃

• metal hydroxides

  • lead hydroxide Pb(OH)₂

  • aluminium hydroxide Al(OH)₃

  • copper hydroxide Cu(OH)₂

  • ferric hydroxide Fe(OH)₃

  • zinc hydroxide Zn(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: method

1. Use an analytical balance to weigh an appropriate amount of sodium carbonate (Na₂CO₃) with high precision. Refer to the desired molarity and the balanced chemical equation to calculate the required mass.

2. Use a small amount of distilled water to dissolve the sodium carbonate completely using a stirring rod.

3. Transfer the sodium carbonate from the beaker into the volumetric flask. Use a wash bottle with distilled water to ensure all parts are transferred to the volumetric flask.

4. Add more distilled water to the volumetric flask until it is nearly filled, leaving some space at the top.

5. Swirl the mixture to ensure all solid is dissolved. This step helps achieve homogeneity in concentration.

6. Carefully add distilled water drop by drop until the bottom of the meniscus is precisely at the calibration mark on the neck of the volumetric flask.

7. Stopper the volumetric flask and invert it several times to ensure uniform mixing of the solution.

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