Chemistry acidic 3~

The dissociation of molecules or compounds into smaller charged particles called ions

• -An acid is a proton donor
• -A base is a proton acceptor

- Acids ionise in water to release hydrogen ions

• - Acid molecules react with water by donation a proton to form a hydronium ion (H₃O⁺)

(Ethanoic acid)

• -CH₃COOH
• - Used in vinegar (around 4% of vinegar is acetic acid)

-Manufactured industrially

(2-hydroxypropane-1,2,3-tricarboxylic acid)

- C₆H₈O₇

- Occurs naturally in fruit

- Added to food as preservative and flavouring

(HCl)

- Found in the stomach of humans

-Produced industrailly on a large scale

(H₂SO₄)

- Can be produced from volcanic eruptions

-Can be produced from smelting of ores

- Used as an acid catalyst

-Used as a dehydrating agent

- Allows us to measure acidity of various samples by comparing concentrations of H⁺ and OH^- ions in solution

- "Concentrated" and "Dilute" refer to the amount of acid added relative to volume of water

-"Strong" and "Weak" refer to the extent to which an acid dissociates into its ions in solution in water

-A formula is used to determine pH given the concentration of hydronium ions:

pH= -log[H⁺]

- A change in pH of 1 means a ten-fold change in [H⁺]

-HCl is a strong acid and completely ionises in solution

-Citric acid is a weak acid and only partially ionises in solution

- Acetic acid is an even weaker acid and is monoprotic

Strong acids

• -Strong acids completely ionise in water to produce hydronium ions in solution
• -No equilibrium
• -e.g.

Weak Acids 

• -Weak acids only partially ionise in water
• -Equilibrium is established between acid molecules and its ions

-e.g.

Strong Bases

-Strong bases completely ionise in warter to produce hydroxide ions in solution 

• -e.g. 
• 

Weak Bases

- Some molecules or ions react with water to form hydroxide ions in aq solution

• -e.g. 
• 

• - Improves taste
• - Preserves food

-Common acids added: acetic, citric, phosphoric, propanoic

Proposed that acids were substances that contained oxygen

• Limitations
• -Some acids contained no oxygen e.g. HCl
• -Metal oxides formed bases in solution

Proposed that acids were substances that contained replacable hydrogen

• Limitations
• -Could not explain why some hydrogen containing substances were not acidic

Proposed acids were substances that ionized in solution to produce hydrogen ions

• Limitations
• - Only applied to aqueous solutions
• - Does not explain why some salts act as acids

-Products of acid-base reactions are the conjugate acids and bases

-When an acid donates a proton, it forms its conjugate base

-When a base accepts a proton, it forms its conjugate acid

• Generalisation
• -Strong acids will have weak conj bases
• -Strong bases will have weak conj acids
• -Weak acids will have stronger conj bases
• -Weak bases will have stronger conj acids

-Neutral salts contain ions that do not react with water

-Basic salts contain ions that react with water to from OH^- ions

- Acidic salts contain ions that react with water to form H₃O⁺ions

• 
• 
• 
• 

-Amphiprotic substances can accept or donate protons

-This means they can act as either an acid or a base

- An amphoprotic substance must contain a donateable hydrogen ion

-All amphiportic substances are amphoteric but not all amphoteric substances are amphiprotic

E.g. Water

• Acting as an acid
• 

• Acting as a base
• 

Self ionisation of water

-One molecule of water acts as an acid and one molecule of water acts as a base

-Neutralisation reactions are acid-base reactions involving a proton transfer which is exothermic

-It is exothermic since it forms covalent bonds between hydrogen and oxygen when water is formed

Effect of Buffers

-Buffer solutions resist changes to pH when small amounts of acids or bases are added

-Buffers are an aq mixture in roughly equal amoujnts of a weak acid and its conjugate base or a weak base and its conjugate acid

Buffers in a natural system

-The buffer system used in blood is carbonic acid and hydrogen carbonate ions

-Alkanols have at least one hydroxly (-OH) group bonded to a carbon

-Alkanoic (carboxylic) acids have at least one carboxyl group (-COOH)

Esters are named in 2 parts

• First Part
• - Comes from alkanol
• -e.g. ethyl (suffix '-anol' changes to '-yl')

• Second Part
• - Comes from acid
• -e.g. Butanoate (suffix '-oic' acid changes to 'oate')

A reaction between an alkanol and an alkanoic acid forms an organic compound called an ester

In Alkanols

• -C-O and O-H bonds are polar
• - Able to form hydrogen bonds: strong intermolecular forces between alkanol molecules

-Thus higher b.p. than corresponding alkanes/enes

In Alkanoic Acid

• -Additional C=O bond
• -forms even stronger hydrogen bonds: even stronger intermolecular forces

-Even more energy needed to separate molecules


Both, alkanols and alkanoic acids have higher m.ps than hydrocarbons of similar molecular mass

-Esterification is the condensation reaction between an alkanoic acid and an alkanol to form an ester

-Esterification is reversible

• e.g. 
• 
• conc.H₂SO₄ as catalyst

-Conc. H₂SO₄ is needed to lower activation energy

- Conc. H₂SO₄ increases yield, as it is a dehydrating agent therefore shifts the equilibrium to the right according to Le Chat

Refluxing is the process of ehating a reaction mixture in a vessel with a cooling condenser attached

- Cooling condenser prevents loss of any volatile reactant or product

-Esterification requires thermal energy to reach equilibrium , therefore, without refluxing it would take days to reach equilibrium

Esters are frequently found in many parts of nature

Esters have pleasant, sweet, fruity odours

Occurence

-Many odours and scents of fruits and flowers are caused by the presence of esters

-Solid animal fats and plant oils are esters

Production

-There is a substantial industry that manufactures and develops synthetic flavours and perfumes

Uses

• -Food: margarine, flavours, fragrances
• -Soaps
• -Solvents
• -Cosmetics

-Esters are widely used as flavours and perfumes in processed foods and cosmetics

• Ethyl Ethanoate
• -has a pear and wine-like odour
• -used in nail polish remover and perfumes

• Butyl Ethanoate
• -Pleasant odour
• -used in flavouring of confectionary and ice cream
• -alse used as solvent