Acids, bases and salts

What is an acid?

1. This is a substance containing hydrogen which can be replaced directly or indirectly by a metal to form a salt.

2. This is a proton donor

What are some common acids?

1. Hydrochloric acid (HCl)

2. Sulphuric acids (H2SO4)

3. Nitric acid (HNO3)

4. Phosphoric acid (H3PO4)

5. Methanic acid (HCOOH) Organic

6. Ethanoic acid (CH3COOH) Organic

What are the general properties of acids in aqueous solution?

1. They are corrosive

2. They have a sour taste

3. They have a pH value of less than 7

4. They conduct an electric current (They are electrolytes)

What are indicators used to identify acids?

1. Blue litmus paper which turns RED

2. Methyl orange which turns RED

3. Phenolphthalein which remains COLOURLESS

4. Universal indicator turns RED for strong acids (pH 0-3) and YELLOW to ORANGE for moderate to weak acids (pH 4-6)

What happens during chemical reactions of acids in aqueous solution?

The H+ ions in the acid are replaced by metal or ammonium ions to form a salt. As a result, salts contain metal ammonium cations and negative anions from the acid.

What happens when acids react with reactive metals?

Other than nitric acid, when acids react with metals above hydrogen in the reactivity series a salt and hydrogen is produced

What happens when acids react with bases (Mainly metal hydroxides and oxides)?

A salt and water are produced

What happens when acids react with metal carbonates and metal hydrocarbonates (Hydrogen carbonates)?

This forms salt, carbon dioxide and water

Metal carbonates:

Na2CO3 (aq)+ H2SO4 → NA2SO4 (aq) + CO2 (g) + H2O (l)

What are the groups in which acids are classified?

Organic and Inorganic

What are inorganic acids?

These are acids that contain a non-metallic element or polyatomic group as well as hydrogen

What are organic acids?

These are acids that contain the carboxyl group COOH. In these acids, it is the hydrogen at the end of the carboxyl group which forms the H+ ion when the acid dissolves in water.

What are some common organic acids?

1. Methanoic acid (Present in ant bites)- HCOOH

2. Ethanoic acid (Vinegar)- CH3COOH

3. Latic acid (In milk)- CH3CH(OH)COOH

4. Ascorbic acid (Vitamin C)- C6H8O6

5. Citric acid (In fruits and citrus fruits)- C6H8O7

What are some common inorganic acids?

1. Hydrochloric acid- HCl

2. Nitric acid- HNO3

3. Sulphuric acid- H2SO4

4. Phosphoric acid- H3PO4

5. Nitrous acid- HNO2

6. Sulfurous acid- H2SO3

7. Carbonic acid- H2CO3

How can acids be classified?

1. Based on their basicity

2. Based on their strength

3. Based on the degree of ionization that occurs when the acid dissolves in water

4. Based on if they are organic or inorganic

Define the term basicity

This is the number of H+ ions produced per molecule of acid when the acid dissolves in water.

In terms of basicity, what are types of acids?

Monobasic acids

Dibasic acids

Tribasic acids

What are monobasic acids?

These are acids that produce one H+ ion per molecule. Example: Hydrochloric acid (HCL) and nitric acid (HNO₃)

What are dibasic acids?

These are acids that produce two H+ ions per molecule. Example: Sulphuric acid (H₂SO₄)

What are tribasic acids?

These are acids that produce three H+ ions per molecule. Example: Phosphoric acid (H₃PO₄)

In terms of strength, what are the types of acids?

Dilute and concentrated acids (quantity of water present)

What is a dilute acid?

This is an acid that contains a lot of water, e.g hydrochloric acid, which has a concentration of 0.1 mol/dm3

What is a concentrated acid?

This is an acid that contains very little water, e.g hydrochloric acid, which has a concentration of 12 mol/dm3

In terms of degree of ionization, what are the types of acids?

Strong and weak acids

What is a strong acid?

This is an acid that is fully ionized when dissolved in water. E.g. hydrochloric acid (HCl_(aq)) and sulfuric acid (H₂SO_{4 (aq)})

What is a weak acid?

This is an acid that is only partially ionized when dissolved in water. E.g. carbonic acid (H₂CO₃) and ethanoic acid (CH₃COOH).

What is an acid anhydride?

This is a compound that reacts with water to form an acid. Most of these compounds are acidic oxides of nonmetals.

What are examples of acid anhydride?

Carbon dioxide (CO2)

Sulphur dioxide (SO2)

Sulphur trioxide (SO3)

Nitrogen dioxide (NO2)

What are some acids present in living systems?

Ascorbic acid (C6H8O6)

Methanoic acid (HCOOH)

Ethanoic acid (CH3COOH)

Lactic acid (C3H6O3)

Where does Ascorbic acid occur (Vtamin C)?

This occurs in many citrus fruits. A shortage of this vitamin can cause scurvy. It is destroyed by oxidisation when exposed to heat.

Where does methanoic acid occur?

This occurs in the venom of bee and ant stings. It causes itching, swelling, redness and pain around the sting.

Where does ethanoic acid occur?

This occurs in vinegar which is used as a food preservative. Its acidic nature gives it a lower pH which denatures the enzymes that cause decay and inhibits the growth of bacteria and fungi.

Where does lactic acid occur?

This is produced in muscle cells during strenuous activity. If there is an over-accumulation it can prevent the muscles from contracting and the person will callapse.

What is a base?

This is chemically opposite to acids

OR

These are proton receivers.

What happens when a base reacts with an acid?

The O^2- ions or OH^- ions in the base accept the H⁺ ions, or protons, from the acid, forming water.

What is an alkali?

This is a base that dissolves in water to form a solution containing OH^- ions.

What are examples of alkalis?

1. Potassium, sodium, and calcium hydroxide.

2. Ammonium gas, potassium oxide, sodium oxide, and calcium oxide which reacts with water to form a solution containing hydroxide ions

What are the general properties of aqueous solutions of alkalis?

1. They have a bitter taste

2. They are corrosive

3. They feel soapy

4. They have a pH value greater than 7

5. They conduct an electric current (They’re electrolytes)

What are the colours of indicators when in contact with alkalis?

1. Red litmus paper- Blue

2. Methyl orange- Yellow

3. Phenolphthalein- Bright pink

4. Universal indicator- Blue in weak bases, dark blue in moderate bases, Purple/violet in strong bases.

What are the chemical reactions of bases?

1. They react with acids to form a salt and water. Examples:

   MgO (s) + HCl (aq) → Mg₂Cl (aq) + H₂O (l)

   2KOH (aq) + H₂SO₄ (aq) → K₂SO₄ + H₂O (l)

2. When heated, they react with ammonium salts to produce a salt, ammonia and water. Examples:

   MgO₂ (s) + 2HN₄ (s) → MgCl₂ (S) + 2NH3 (g) + H₂O (l)

   CaO (s) + (NH₄)2SO₄ (s) → CaSO₄ (S) + 2NH₃ (g) + H₂O (g)

What amphoteric substances forms salt and water?

Amphoteric oxides or hydroxides can react with both acids and strong alkalis to form a salt and water.

What are the amphoteric substances?

The oxides and hydroxides of alumimium, zinc, and lead

What are the amphoteric oxides and hydroxides of aluminum and state the salt formed and the anion present in the salt.

Aluminum oxide (Al₂O₃) and aluminum hydroxide [Al(OH)₃]. The salts formed are aluminates and the anion present in the salt is AlO₂^-.

What are the amphoteric oxides and hydroxides of zinc and state the salt formed and the anion present in the salt.

Zinc oxide (ZnO) and zinc hydroxide [Zn(OH)₂]. The salts formed are zincates and the anion present in the salt is ZnO_2^2-

What are the amphoteric oxides and hydroxides of lead and state the salt formed and the anion present in the salt.

Lead oxide (PbO) and lead (ll) hydroxide [Pb(OH)₂]. The salts formed are plumbates and the anion present in the salt is PbO_2^2-

What are the classification of oxides?

Oxides are classified as:

1. Oxides that react with an acid or base- Metal oxides/Basic oxides and nonmetal oxides/Acidic oxides

2. Neutral oxides (Oxides that don’t react)

What are acidic oxides/nonmetal oxides?

These are oxides of some nonmetals which react with alkalis to form a salt and water. Examples include carbon dioxide, sulphur dioxide, sulphur trioxide, nitrogen dioxide and silicon dioxide.

What are basic oxides/metal oxides?

These are oxides of metals which react with acids to form salt and water. Examples include magnesium oxide (MgO), iron (lll) oxide (Fe₂O₃), and copper (ll) oxide (CuO)

What are neutral oxides?

These are oxides of some nonmetals that don’t react with acids or alkalis. Examples include carbon monoxide (CO), nitrogen monoxide (NO), dinitrogen monoxide (N₂O), and water (H_2O)

What is used to distinguish between acids and alkalis in aqueous solutions?

An indicator. It has one colour in an acidic solution and another colour in an alkali solution.

What is the colour of litmus paper when exposed to acids versus alkalis?

Acidic solution- Blue litmus paper turns red

Alkali solution- Red litmus paper terns blue

What is the colour of methyl orange when exposed to acids versus alkalis?

Acidic solution- Blue

Alkali solution- Yellow

What is the colour of screaned methyl orange when exposed to acids versus alkalis?

Acidic solution- Red

Alkali solution- Green

What is the colour of phenolphthalein when exposed to acids versus alkalis?

Acidic solution- Colourless

Alkali solution- Pink

What is the colour of universal indicator when exposed to acids versus alkalis?

Acidic solution- Red

Alkali solution- ?

What is a strong alkali?

This is an alkali that is fully ionized when dissolved in water. The concentration of OH^- ions in the solution is high. E.g. Potassium hydroxide (KOH) and sodium hydroxide (NaOH)

What is a weak alkali?

This is an alkali that is only partially ionized when dissolved in water. The concentration of OH^- ions in the solution is low. Example: Ammonia (NH₃)

What is a salt?

1. These are ionic compounds that contain a metal and a nonmetal

2. These are ionic compounds that contain a cation and an anion

3. These are ionic compounds formed when metal ions and the ammonium ions take the place of the hydrogen ions in an acid.

What are the classifications of salts?

These are classified as normal and acid salts

What are normal salts?

This is a salt formed when all the hydrogen ions are replaced by metal or ammonium ions. Example

NaOH(aq) + HCl (aq) → NaCl (aq) + H₂O (l)

What are acid salts?

These are acids formed if the hydrogen ions are partially replaced by metal or ammonium ions. Example:

NaOH (aq) + H₂SO₄ (aq) → NaHSO₄ (aq) + H₂O (l)

What must be taken into consideration when preparing salts?

1. The solubility of the salt being prepared

2. The solubility of the reactants being used to prepare the salt

3. The hydration of the salt being prepared.

What is formed when two solutions of soluble salts are mixed?

An insoluble salt

What is the method used to prepare insoluble salts?

The ionic precipitation method

Describe the ionic precipitation method

1. Dissolve 2 soluble salts separately

2. Mix the 2 soluble salts

3. A solid precipitate is formed

4. Filter the mixture to separate the solid

5. Wash the solid with distilled water

6. Dry the solid

Example: Pb (NO₃)_{2 (aq)} + CuSO_{4 (aq)} → PbSO₄ + Cu(NO₃)₂

When is the titration method used?

This is used to make soluble salts from acids and alkalis or acids and carbonates (when both are soluble).

Describe the titration method

1. Use a burette to add acid to a known volume of alkali with indicator

2. Find the exact volume of acid needed to neutralize the alkali

3. Repeat with the indicator

4. Evaporate the solution to get the crystals

Example 1: KOH (aq) + H₂SO₄ (aq) →K₂HSO₄ (aq) + H₂O (l)

Example 2: 2KOH (aq) + H₂SO₄ (aq) → K₂SO₄ (aq)+ H₂O (l)

When is the direct combination method used?

This is used to prepare soluble salts of zinc, aluminum, iron and magnesium

Describe the direct combination titration method

1. Add metal to dilute solution until bubbling stops

2. Filter off the excess metal

3. Evaporate solution to get crystals

Example: Mg (s) + 2HCl (aq) → MgCl₂ (aq) ₊ H₂ (l)

Describe the base + acid (using insoluble bases) titration method

1. Add insoluble base to the acid

2. Warm the mixture gentle and stir

3. When there is excess base and no more dissolves, filter off the solid

4. Evaporate the solution to form crystals

Example: MgO (s) + H₂SO₄ (aq) → MgSO₄ (aq)+ H₂O (l)

When is the carbonate + acid titration method used?

This is used to prepare all carbonate salts except those of sodium, potassium, and ammonium.

Describe the carbonate + acid method

1. Add insoluble carbonate to the acid

2. Effervescence (formation of gas bubbles in a liquid due to a chemical reaction) shows CO₂ is being released

3. When bubbling stops, filter off the excess solid

4. Evaporate to get the salt crystals

Example: CuCO₃ (s) + 2HNO₃ (aq) → Cu (NO₃)₂ (aq) + CO₂ (aq) (l) + H₂O (l)