Acids, Bases and Salts

CSEC Chemistry - Grade 10

What is the Bronsted-Lowry definition of an acid?

An acid is a proton donor.

It releases hydrogen ions (H⁺) in aqueous solution.

List 5 general characteristics of acids.

• Sour taste pH less than 7

• They change blue litmus to red

• They are corrosive

• They are electrolytes (they conduct an electric current)

Hydrochloric acid

Nitric acid

Sulfuric acid

Perchloric acid

Hydrofluoric acid

Carbonic acid

Ethanoic (acetic) acid

Methanoic (formic) acid

Phosphoric acid

Sulfurous acid

ALL acids have this in their formula

Hydrogen ions (H⁺)

Acid + Base →

Salt + Water

Acid + Metal →

Salt + Hydrogen gas

Acid + Metal Carbonate →

Salt + Water + Carbon Dioxide

Acid + Metal Hydrogen Carbonate →

Salt + Water + Carbon Dioxide

Acid + Metal Oxide →

Salt + Water

Acid + Ammonia →

Ammonium Salt

Name the type of reaction which occurs when acids react with bases.

Neutralization

What is basicity/proticity of an acid?

• It is the number of moles of H+ ions that one molecule of an acid can donate when in aqueous solution.

• Basicity tells how many protons an acid can release per molecule.

Monobasic acids release one H⁺ ion per molecule when dissolved in water. List 4 monobasic acids.

• HCl - hydrochloric acid

• HNO₃ - nitric acid

• HF - hydrofluoric acid

• HClO₄ - perchloric acid

• HCOOH - methanoic acid

• CH₃COOH - ethanoic acid

Dibasic acids release two H⁺ ions per molecule when dissolved in water. List 3 dibasic acids.

H₂SO₄ - sulfuric acid

H₂SO₃ - sulfurous acid

H₂CO₃ - carbonic acid

Tribasic acids release three H⁺ ions per molecule when dissolved in water. Name one tribasic acid.

H₃PO₄ - phosphoric acid

Define acid anhydride

A substance (a non-metal oxide) that reacts with water to form an acid.

E.g. SO₃, CO₃, N₂O₅

What is a dilute acid?

It is one that contains a lot of water.

What is a concentrated acid?

It is one that contains very little water.

What is a strong acid?

An acid which is fully ionized when dissolved in water e.g. hydrochloric acid and sulfuric acid.

What is a weak acid?

An acid which is only partially ionised when dissolved in water e.g. carbonic acid and ethanoic acid.

Differentiate between inorganic and organic acids.

• Organic acids contain carbon, usually with a –COOH group. They are generally weak acids (partially ionize in water)

• Inorganic acids do not usually contain carbon (exception H₂CO₃). Most of them are strong acids. They completely ionize in water.

Where can ascorbic acid/vitamin C (C6H8O6) be found naturally?

In many foods, e.g. citrus fruits, West Indian cherries, sweet peppers, tomatoes, green leafy vegetables.

Where can methanoic acid (HCOOH) be found naturally?

In the venom of bee and ant stings

Where can lactic acid(C3H6O3) be found naturally?

Produced in muscle cells during strenuous activity

Where can ethanoic acid (CH3COOH) be found ?

In vinegar

Where can citric acid(C6H8O7) be found?

In citrus fruits, e.g.limes

What is the result of vitamin C deficiency in the diet?

Scurvy

What happens to vitamin C during cooking?

Vitamin C is destroyed by becoming oxidised.

Why is sodium hydrogen carbonate sometimes added to fruits and vegetables?

It causes them to improve their appearance and texture since it neutralizes any vitamin C present thereby reducing the vitamin C content.

Stings can be treated by applying a paste of sodium hydrogen carbonate or calamine lotion which contains zinc hydrogen carbonate. Why?

These neutralize methanoic acid.

Why can vinegar be used to preserve certain food items?

Being acidic, it has a low pH, which denatures (destroys) the enzymes that cause decay and inhibits the growth of bacteria and fungi.

Why can limes be used to remove rust stains from clothing?

The acid in the lime juice reacts with the iron(III) oxide(Fe2O3) in the rust making a soluble compound which can be washed out of the clothes. Fe2O3(s) + 6H+(aq) -> 2Fe2+ (aq) + 3H20(l)

What is the Bronsted-Lowry definition of a base?

A proton(H+) acceptor.

It is a substance that releases hydroxide ions (OH⁻) in aqueous solution

What is a alkali?

A base which dissolves in water to form a solution containing OH- ions

Distinguish between a strong alkali and a weak alkali.

Strong alkali - Fully ionized when dissolved in water e.g. KOH and NaOH

Weak alkali - Partially ionized when dissolved in water e.g. NH3

Base + Ammonium salt

Salt + Water + Ammonia Gas

What are amphoteric oxides?

A substance which can react with both acids and alkali to form salt and water. Examples: Al₂O₃, PbO, ZnO

What are acidic oxides?

Oxides of certain non-metal which react with alkalis to form salt and water

Examples: CO₂, SO₃

What are basic oxides?

Oxides of metals which react with acids to form a salt and water

What are neutral oxides?

Oxides of certain non-metals which do not react with acids or alkali

Examples: CO, NO, N₂O