Chapter 11 - Acid & Base Reactions In Water

Common Acids

Hydrochloric Acid - Stomach Acid (Strong)

Sulfuric Acid - In car batteries (strong)

Ethanoic Acid - Batteries, fertilizers (strong)

Carbonic Acid - Carbonated Drinks (weak)

Phosphoric Acid - Fertilizers, drinks (weak)

Citric Acid - In citrus fruits (weak)

Ascorbic Acid - In citrus fruits (weak)

Common Bases

Sodium hydroxide - Oven cleaners (strong)

Ammonia - Fertilisers, explosives (weak)

Calcium hyrdoxide - Cement and mortar (strong)

Magnesium Hydroxide - For acid reflux (strong)

Sodium hydroxide - Powder, glass (strong)

Alkalis

Soluble/aqueous bases

Properties Of Acids

Turns litmus paper red

Tend to be corrosive

Taste Sour

Reacts With Bases

Solutions have low pH

Solution conducts an electrical current - because aqeous solution has free moving hydrogen protons (mobile)

Properties Of Bases

Turns litmus paper blue

Caustic, Slippery

Taste bitter

Reacts with acids

Solutions have pH

Solution conducts electrical current

Litmus Test

Robert Boyle deduced acids based on:

Taste

Action as solvents

How they change the color of vegetable extracts

Soluble bases (alkalis) could reverse the effect of acids

Antoine Lavoisier’s Suggestion

Acid properties due to Prescence of oxygen

Sir Humphrey David’s Discovery

Acidic properties are associated with hydrogen

Lime Water Test

Bronsted-Lowry Theory Of Acids and Bases

When substance donates (H⁺) proton - acid

When substance receives (H⁺) proton - base

Conjugate Acid Pairs

Amphiprotic Substances

Substance can receive or donate an electron - must have at least on hydrogen proton

Monoprotic Substances

Can have only one hydrogen that can be donated (eg.HCI or H₂0)

Polyprotic Acids

Acids that can donate more than one hydrogen atom

Don’t donate all protons at once

Donate protons in steps

Ionization Energy Across Steps

Harder to loose hydrogen protons as steps increase, due to the increase of electrostatic attraction.

Triprotic Acids

Have 3 protons that can be donated (done in three steps)

Diprotic Acids

Have 2 protons (done through 2 steps)

Water in all ionisation reactions

Water is a reactant in all ionization reactions

Why do Amphiprotic substances have a double reversible arrow

They can behave as either a base or an acid meaning that the reaction can happen in both ways.

Can only be straight arrow if the first proton (oly if strong acid)

Other protons are less likely to ionise due to increased electrostatic attraction

Why must Hydrogen be next to a highly electronegative atom to be donated?

It creates a partial positive charge

Enables it to be transferred as a proton easily.

e.g. only a bond with O-H can be donated with acids such as CH₃COOH (acidic proton)

What is strength of a acid or base measured by?

By its ability to donate or accept protons

Dissolving into water

Strong acids completely ionize in water

Weak acids partially ionize in water

Weak acids

HCI

H₂S0₄

HN0₃

Strong Acids

CH₃C00H

H₂C0₃

H₃PO₄

Strong Bases

NaOH

KOH

Ca(OH)₂

Weak Bases

NH₃

What is concentration?

Measuring “solute” to “solvent” ration

Solute - Solvent ratio low?

Less solute

More solvent

Diluted solution

Solute - Solvent ratio high?

More solute

Less solvent

Concentrated solution

Acid & Base relationship with conjugates

Stronger the acid - weaker the conjugate base

Stronger the base - weaker the conjugate acid

Neutralization Reactions

Acid + metal hydroxide (base) ——- Salt + water

Acid + bicarbonate ——- Salt + C0₂ + H₂0

Acid + metal carbonate —— Salt + H₂0 +C0₂

Acid + metal hydrogen carbonate —- Salt + H₂0 + C0₂

Acid + Reactive Metal ————- Salt + Hydrogen

Acid + Metal Oxide ——— Salt + Water

Acid + Ammonia ——- Ammonia Salt (eg. NH₄CI)

Neutralization (real life)

Sting of bee (methanoic / formic acid) neutralized by ammonia or lime water

venom of wasp is alkaline - ethanoic acid can be used to treat it

Stomach acid treated with antacid (milk or magnesia)

Harmful bacteria in tooth enamel deteriorate teeth and can be neutralized with a weak base

Dissassociation

Ionic compounds seperate into ions

Water in a reaction

Weak acid and base

Only a small amount reacts

What does “M” stand for?

Concentration of moles per litre

Acidity of water at 25 degrees

[H₃0⁺]=[OH^-]=10^-7M

Hydronium = 10^-7M

Hydroxide = 10^-7M

They both multiply up to 10^-14M (half-half)

Acid Ionisation

[H₃0⁺] > 10^-7M - more hydronium ions than hydroxide ions make the solution more acidic

Base Ionisation

[OH^-] > 10^-7M - more hydroxide ions than hydronium ions make the solution more basic

Neutral

[H₃0] = [OH^-] - Both have 10^-7M

Measuring of acidity

pH = -log₁₀[H₃0⁺]

[H₃0⁺] = 10^-pH

Notes on pH

pH decreases as [H₃0⁺] increases (more hydronium = more acidic)

Indicators

Litmus - purple dye from lichen plant

Rose petals, blackberry, red cabbage - organic indicators

Converting to moles and finding concentration

n=m/n

C = n/v

n= moles

v = volume

c = concentration

Ocean acidity

Increase in C0₂ in atmosphere increases ocean acidity

Steps of CO₂ entering water

CaCO3(s)+H+(aq)−>Ca2+(aq)+HCO3−(aq)

The more H₂C0_{3 (}from C0₂ mixing with H₂0) the more h⁺ ions attack the calcium carbonate

Why Is Ocean Acidity Bad

Krill eggs won’t hatch at lower pH (high acidity)

Stops food chain

Stops calcification for coverings of sea animals (decalcification) - acidity in sea water

Impact of Ocean Acidity On Humans

Social, Economic Impacts

Reduce sea life in water

Destroy coastal reefs - reduce tourism and increases erosion on land

Common Acids

Acid	Formula	Strength
Hydrochloric acid	HCl	Strong
Nitric acid	HNO₃	Strong
Sulfuric acid	H₂SO₄	Strong
Ethanoic (acetic) acid	CH₃COOH	Weak
Carbonic acid	H₂CO₃	Weak
Phosphoric acid	H₃PO₄	Weak
Citric acid	C₆H₈O₇	Weak
Hydrofluoric acid	HF	Weak (but corrosive)

Common Bases

Base	Formula	Strength	Common Uses
Sodium hydroxide	NaOH	Strong	Soap and detergent production, drain cleaner, paper manufacturing
Potassium hydroxide	KOH	Strong	Fertilizers, liquid soap, alkaline batteries
Calcium hydroxide	Ca(OH)₂	Strong	Limewater, water treatment, cement and plaster
Barium hydroxide	Ba(OH)₂	Strong	Laboratory reagent, sugar refining
Ammonia	NH₃	Weak	Fertilizer, cleaning products, refrigeration gas
Methylamine	CH₃NH₂	Weak	Chemical synthesis, pharmaceuticals
Sodium carbonate	Na₂CO₃	Weak	Glass manufacturing, water softening, detergents
Magnesium hydroxide	Mg(OH)₂	Weak	Antacids, laxatives, wastewater treatment
Aluminium hydroxide	Al(OH)₃	Weak	Antacids, water purification, fire retardants
Ammonium hydroxide	NH₄OH	Weak	Cleaning products, pH adjustment, chemical manufacturing

If ph falls or rises based on reaction

Reaction Type	Reaction Example	pH Change	Reason
Acid + Metal hydroxide	HCl + NaOH → NaCl + H₂O	Rises (if acid in excess)	H⁺ ions are neutralised by OH⁻
Acid + Base (general)	HNO₃ + KOH → KNO₃ + H₂O	Rises	H⁺ removed → less acidic
Acid + Metal carbonate	HCl + CaCO₃ → CaCl₂ + H₂O + CO₂	Rises	H⁺ ions react with CO₃²⁻ → acid partially neutralised
Acid + Metal hydrogen carbonate / Bicarbonate	HNO₃ + NaHCO₃ → NaNO₃ + H₂O + CO₂	Rises	H⁺ reacts with HCO₃⁻ → pH increases
Acid + Reactive metal	2HCl + Zn → ZnCl₂ + H₂	Slightly rises	H⁺ removed to form H₂ gas
Acid + Ammonia / Weak base	HCl + NH₃ → NH₄Cl	Rises	NH₃ consumes H⁺ ions → solution less acidic
Acid + Metal oxide	H₂SO₄ + CuO → CuSO₄ + H₂O	Rises	H⁺ reacts with O²⁻ ions to form water → pH rises

Real life Neutralization Reactions

1) Hydrochloric Acid (HCI) + Magnesium hydroxide (Mg(OH)₂) -

Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O

2. Treating acidic soil using lime

• Acid: Sulfuric acid (acidic soil often contains H₂SO₄)

• Base: Calcium hydroxide or Calcium oxide (lime)

• Reaction (with calcium hydroxide):
  Ca(OH)₂ + H₂SO₄ → CaSO₄ + 2H₂O

6. Baking soda for bee sting

• Acid (from sting): Methanoic acid (formic acid)

• Base: Sodium hydrogen carbonate (baking soda)

• Reaction:
  NaHCO₃ + HCOOH → NaCOOH + CO₂ + H₂O

When and how to use stoichiometry for getting correct concentration

for strong bases - just dissassociate - and find the ratio

for strong acids - include water and balance - find ration

ubstance	Reaction for stoichiometry	Include water as a reactant?	Why?
Strong bases (e.g. KOH, NaOH)	KOH→K++OH−\mathrm{KOH \to K^+ + OH^-}KOH→K++OH−	❌ No	Complete dissociation → directly gives OH⁻
Strong diprotic acids (e.g. H₂SO₄)	donates 2 H⁺ in steps	✅ Yes	Use water to track how many H⁺ (or H₃O⁺) are formed
Weak acids/bases	equilibrium with water	✅ Yes	Water donates/accepts protons, affects pH

Universal Indicator