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

What is a salt?

A compound formed when some or all of the replaceable hydrogen ions in an acid are replaced by metal or ammonium ions

What is a normal salt?

A salt formed when ALL of the replaceable hydrogen ions in an acid are replaced by metal or ammonium ions. All acids can form normal salts

What is an acid salt?

A salt formed when the replaceable hydrogen ions in an acid are only partially replaced by metal or ammonium ions. Only dibasic and tribasic acids can form acid salts.

What is a hydrated salt?

Salts with fixed number of water molecules in their crystal lattice/salts containing water of crystallization

What is an anhydrous salt?

Salts without water of crystallization

What is ionic precipitation?

The reaction of two soluble salts in solution to form an insoluble salt. One solution contains the cation of the desired salt, the other solution contains the anion of the desired salt

Outline the steps involved in preparing an insoluble salt using direct combination.

1. Choose two soluble salts, one containing the cations required to make the salt the other containing the anions required

2. Dissolve the two salts in water to make solutions

3. Mix the two solutions to form the insoluble salt as a precipitate

4. Filter the mixture and collect the precipitate as the residue

5. Wash the residue with distilled water while it is still in the filter funnel and leave it to dry

Complete the solubility rule:

All nitrates are _______

soluble

Complete the solubility rule:

All Group 1 salts are ________

soluble

List 3 main ways of preparing soluble salts

1. Direct combination

2. React a reactive metal/insoluble carbonate/insoluble base with an acid

3. React an alkali and an acid using titration method

Describe the flow chart used to determine method of salt preparation.

Outline the steps involved in the titration method of salt preparation.

1. Choose an appropriate alkali or soluble carbonate to provide the cations and an appropriate acid to supply the anions

2. Measure a fixed volume of the aqueous alkali or carbonate using a pipette. Run it into a conical flask and a few drops of an indicator solution e.g. phenolphthalein

3. Place the acid in a burette and take the initial burette reading

4. Add the acid to the aqueous alkali or carbonate until the neutralization point is reached ( indicator changes color)

5. Take a final burette reading and determine the volume of acid added

6. Repeat the titration of acid until you have three volumes of acid with precise readings. Average these volumes to determine the volume if acid needed

7. Add this volume of acid to the fixed volume of aqueous alkali or carbonate without the indicator

8. Evaporate the water from the solution

This salt is used as an ingredient in baking powder

Sodium hydrogen carbonate (NaHCO3)

This salt is used to soften hard water

Sodium carbonate (Na2CO3)

This salt is used in the manufacture of cement for use in the construction industry

Calcium carbonate

This salt has various medicinal and therapeutic uses

Magnesium sulfate (MgSO4)- Epsom salt

Three salts used in food preservation

Sodium chloride(NaCl), sodium nitrate (NaNO3) and sodium nitrite (NaNO2), sodium benzoate

This salt is used in the manufacture of plaster of Paris, which is used when setting broken bones and as a building material

Calcium sulfate - gypsum

State one danger of consuming NaCl

Excessive consumption can lead to hypertension (high blood pressure)

State one danger of consuming NaNO3 and NaNO2

May increase a risk for developing cancer. Has been linked to causing brain damage in children

State one danger of consuming sodium benzoate

Has been linked to increasing hyperactivity and asthma in children. May increase a person's risk of developing cancer