Chemistry 9, 10 acid & bases, findamentals of organic chemistry

Name the different definitions of acids & bases

1. Most important: Arrhenius Definition

Acid: a substance that produces → H⁺ ions in water

Example: HCl → H⁺ + Cl⁻

Tip: when you see a equation with H⁺, it means it is a acid (?)

Base: a sub that produces → OH⁻ ions in water

Example: NaOH → Na⁺ + OH⁻

2. Strong vs weak acids & bases

Strong acids: completely dissociate in water

Example: HCl

HCl → H⁺ + Cl⁻

Weak acids: partially dissociate

Example: Acetic acid

CH₃COOH ⇌ H⁺ + CH₃COO⁻

Strong bases: completely releases OH⁻

Example: NaOH

Weak bases: partially accept H⁺

Example: NH₃

Strong does not mean concentrated (in terms of strong vs weak acids & bases)

Strong = degree of ionisation

Concentrated = amount of substance present

Strong does not mean concentrated highly or low!

Neutralisation reaction

a specific chemical reaction where an acid & base react together to cancel each other out, forming water & a salt

Acid + Base → Salt + Water

Example: classic reaction → hydrochloric acid (HCl) and Sodium Hydroxide (NaOH):

HCl + NaOH → NaCl + H20

1. the acid (HCl) splits into H+ & Cl- ions

2. The base (NaOH) splits into Na+ & OH-

3. The Match: the H+ & OH- find each other instantly to form H20

4. The leftovers: Na+ & Cl- are just floating around → evaporate the water, thermocline back together & form table salt (NaCl)

→ this reaction removes H⁺ + OH⁻ → H₂O

→ so it does not really depends on the charge but rather the reaction from the elements in general but not depending on redox?

What does increased H+ do to the pH?

It decreases the pH

pH scale

pH measures the concentration of hydrogen ions:

[H+] = 10^-pH

So if a solution has pH of 4:

[H+] = 10^-4 moles per Liter

pH scale usually: 0 → 14

Acidic solution pH scale?

pH < 7

High H⁺ concentration

Example: HCl

Neutral solution pH scale?

pH = 7

Example: pure water

Basic (alkaline) solution

pH > 7

Higher OH⁻ concentration

Example: NaOH

pH and H⁺ Relationship

More H⁺:

→ Lower pH

Less H⁺:

→ Higher pH

What is a pH unit change doing?

It means a 10x change in H+ concentration

Example: pH 3 has 10 times more H+ than pH 4

Water ionization

Water can ionise:

H_2O ⇌ H⁺ + OH⁻

in pure water:

H⁺ = OH⁻

Therefore → pH = 7

Hydrolysis

Reaction of ions with water that affects pH

Example: a salt can produce acidic or basic solution depending on its ions

→ NaCl

Na⁺ and Cl⁻ do not significantly react with water

Solution remains approximately neutral

→ sodium acetate:

CH₃COO⁻ reacts with water

Produces OH⁻

Solution becomes basic

Buffer solutions

A buffer is a solution that resists changes in pH

Usually contains: weak acid, its conjugate base OR weaks base, its conjugate acid

Example: acetic acid + acetate

Biological importance of buffers

The body must maintain stable pH

Example: Blood buffer system

Carbonic acid/bicarbonate system

→ maintains blood pH around: 7.4

another fact about enzymes and certain pH ranges

Enzymes work only within certain pH ranges → large pH ranges can denature proteins

What is the basis of organic molecules?

Carbon

Why is carbon the basis of organic molecules?

Because carbon:

• forms covalent bonds

• Bonds with itself

• Forms chains & rings

• Creates complex molecules

Carbon bonding

usually covalent bonds

Examples:

C-C

C-H

C-O

C-N

In which structural formula can you represent organic molecules?

1. molecular formula:

   shows number of atoms

Example: glucose → C₆H₁₂O₆

2. structural formula:

shows how atoms are connected

3. condensed formula:

simplified structural representation

Example: ethanol → CH₃CH₂OH

What are compounds with same molecular formula but different structures? Name the types as well

Isomerism

Types:

structural isomers (different arrangement of atoms, example: C₄H₁₀ can form different structures)

Stereoisomers (same connection but different 3D arrangement, important in biology)

Hydrocarbons

Contain only: Carbon & hydrogen

main groups: alkanes, alkenes, alkynes, aromatic hydrocarbons

Alkanes

only single bonds

General formula: C_nH_2n+2

Examples: methane CH₄, Ethane C₂H₆

Alkenes

at least one double bond

General formula: C_nH_2xn

Example: Ethene C₂H₄

Alkynes

contain triple bonds

Example: Ethyne C₂H₂

Aromatic hydrocarbons

contain aromatic rings

Example: Benzene

Functional groups

They determine chemical properties

Alcohol, Ethers, amines, aldehydes, ketones, carboxylic acids, esters, amides

Alcohol

Alcohol

functional group: -OH

Example: ethanol

CH₃CH₂OH

Properties: polar, can form hydrogen bonds

Ethers

Functional group:

R-O-R

Example:

Dimethyl ether

Amines

Functional group:

-NH₂

Related to ammonia.

Important in amino acids.

Aldehyds

Functional group:

-CHO

Carbonyl group at end of chain.

Example:

Glucose contains an aldehyde form.

Ketones

Functional group:

C=O

Inside carbon chain.

Example:

Acetone.

Carboxylic acids

Functional group:

-COOH

Contain:

• Carbonyl group

• Hydroxyl group

Example:

Acetic acid.

Esters

Functional group:

-COO-

Formed from:

Carboxylic acid + alcohol

Important in: fats, lipids

Amides

Functional group:

-CONH₂

Important in:

• Proteins

• Peptide bonds

Basic organic nomenclature

Number of carbons:

1 → meth-

2 → eth-

3 → prop-

4 → but-

5 → pent-

6 → hex-

Suffix examples:

Alkane:

-ane

Alkene:

-ene

Alcohol:

-ol

Carboxylic acid:

-oic acid

⸻

Examples:

CH₄

Methane

⸻

CH₃CH₂OH

Ethanol

⸻

CH₃COOH

Ethanoic acid

“Organic compounds only come from living organisms.”

WRONG → organic chemistry means carbon containing compounds

“All carbon compounds are organic.”

WRONG → CO2 & carbonates are exceptions

“Isomers have different molecular formulas.”

WRONG → they have same formula but different structures

“Double bonds allow free rotation.”

WRONG → they restrict rotation!