ACIDSWhat is acid?An acid is a chemical substance, which ionizes in water to produce hydrogen ions, H+ When acids dissolved in water, the hydrogen atoms in acids are released as hydrogen ions, H+. The hydrogen ion combined with water molecule, H2O to form a hydroxonium ion, H3O+. However, this ion can be written as H+.

We can classify an acid as a monoprotic acid or a diprotic acid based on basicity. Basicity of an acid is the number of mole of H+ ion that can be produced by one mole of acid when it dissolves in water.

Monoprotic acid Ionisation

Hydrochloric acid, HCl HCl → H+ + Cl-

Ethanoic acid, CH3COOH CH3COOH → H+ + CH3COO-

Diprotic acid Ionisation

Sulphuric acid, H2SO4 H2SO4 → 2H+ + SO42+

BASESWhat is base?A base is a chemical substance that can neutralize an acid to produce a salt and water.

Examples of bases are; i. metal hydroxidesii. metal oxide

Most bases are not soluble in water. Bases that are soluble in water are known as alkalis.

Bases that are insoluble in water Bases that are soluble in water

Zinc oxide, ZnO Sodium oxide, Na2OZinc hydroxide, Zn(OH)2 Sodium hydroxide, NaOHCopper(II) oxide, CuO2 Potassium oxide, K2OCopper(II) hydroxide, Cu(OH)2 Potassium hydroxide, KOH

Calcium hydroxide, Ca(OH)2

Ammonia, NH3

In water, an alkali dissociates to hydroxide ions, OH- and cations.

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Role of water and the properties of acids

Results Acid Condition Observation Inference

Ethanoic acid(molecule)

Glacial (dry)

- No colour change in the litmus paper- Light bulb is not lighted up

Does not show any acidic properties

Aqueous - Blue litmus paper is changed to red- Light bulb is lighted up

Shows acidic properties

Hydrogen chloride

(molecule)

Dissolved in methylbenzene

- No colour change in the litmus paper - Light bulb is not lighted up

Does not show any acidic properties

Aqueous- Blue litmus paper is changed to red- Light bulb is lighted up

Shows acidic properties

Discussion

The hydrogen ions, H+ are responsible for acids to show their properties

1. Glacial/dry ethanoic acid does not show acidic properties because without water, ethanoic acid remains or exists as molecules and there are no hydrogen ions present. 2. Aqueous ethanoic acid shows acidic properties because in water, ethanoic acid ionises to form hydrogen ions, H+.4. Hydrogen chloride gas in methylbenzene does not show acidic properties and does not conduct electricity, because it exists as covalent molecules. 5. Hydrogen chloride gas in water shows acidic properties and conduct electricity. This is because hydrogen chloride ionises in water to form hydrogen ions, H+ thus hydrochloric acid is formed.

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○ Light bulb

Carbon Carbon

AqueousEthanoic acid

○ Light bulb

Carbon Carbon

Glacial Ethanoic acid

Switch Switch

6. Aqueous ethanoic acid and hydrochloric acid can conduct electricity because in the solutions the ions can move freely.

Ionisation equation for hydrochloric acid;

Ionisation equation for ethanoic acid;

Conclusion

Chemicals Properties of Acida. Acids react with bases to form salts and water. Examples;

i. H2SO4 + ZnO → ZnSO4 + H2O

ii. 2HCl + CuO → CuCl2 + H2O

b. Acids react with alkalis to form salts and water. Examples;

i. HCl + NaOH → NaCl + H2O

ii. H2SO4 + Ca(OH)2 → CaSO4 + 2H2O

c. Acids react with reactive metal to produce salts and hydrogen gas. Examples;

i. 2HCl + Mg → MgCl2 + H2

ii. H2SO4 + Zn → ZnSO4 + H2

Reactive metals: Mg, Al, Zn (use this metals only)

d. Acids react with carbonate compound to produce salts, water and carbon dioxide. Examples;

i. 2HCl + PbCO3 → PbCl2 + CO2 + H2O

ii. H2SO4 + CuCO3 → CuSO4 + CO2 + H2O

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CH3COOH (l) H+ (aq) + CH3COO- (aq) Ethanoic acid hydrogen ion ethanoat ion

+ H2O

HCl (g) H+ (aq) + Cl- (aq) Hydrogen chloride gas hydrogen ion chloride ion

+ H2O

An acid only shows its acidic properties when dissolved in water.

Role of water and the properties of alkalis

Results

Acid Condition Observation Inference

Ammonia (molecule)

In tetra chloromethane

- No colour change in the litmus paper- Light bulb is not lighted up

Does not show any alkalis properties

Aqueous - Blue litmus paper is changed to red- Light bulb is lighted up

Shows alkalis properties

Discussion

The hydroxide ions, OH- are responsible for alkalis to show their properties

1. Ammonia liquid in tetrachloromethane does not show alkalis properties because it exists as molecules.2. Aqueous ammonia acid shows acidic properties because in water, ethanoic acid ionises to form hydroxide ions, OH-.

Ionisation equation for ammonia;

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Carbon Carbon

○ Light bulb

Carbon Carbon

Switch Switch

Ammoniain tetrachloromethane

Ammonia in water

NH3 (l) NH4+ (aq) + OH− (aq)

Ammonia ammonium ion hydroxide ion

+ H2O (l)

3. Hydroxide ion, OH- in ammonia solution / solution hydroxide cause solution shows alkalis properties. 4. Ammonia gas in methylbenzene does not show alkalis properties and does not conduct electricity because it exits as a molecules. 5. Ammonia gas in water shows alkalis properties and conduct electricity because in the solutions the ions can move freely.

Conclusion

Chemicals Properties of Alkalisa. Alkalis react with acids to form salts and water. Examples;

i. NaOH + HCl → NaCl + H2O

ii. Ca(OH)2 + H2SO4 → CaSO4 + 2H2O

b. When a mixture of an alkali and an ammonium salt is heated, ammonia gas is, NH3 is liberated. Examples;

i. NaOH + NH4Cl → NaCl + H2O + NH3

ii. Ca(OH)2 + 2NH4Cl → CaCl2 + 2H2O + 2NH3

The Strength of Acids and Alkalis1. The pH scale us used to indicate the degree of acidity or alkalinity of a solutions.

Please check the colour for each box… pH value less than 7 indicates an acidic solution pH value equals 7 indicates a neutral solution pH value greater than 7 indicates an alkaline solution

Strong and Weak Acids/Alkalis1. The strength of an acid or alkali depends on the degree of ionisation or dissociation of the acid or alkali in water.

2. Strong Acid: An acid which ionises completely in water. Example; HCl → H+ + Cl- (monoprotic acid)

H2SO4 → 2H+ + SO42- (diprotic acid)

3. Weak Acid: An acid which ionises partially in water.

Example; CH3COOH H+ + CH3COO-

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14pH

NeutralIncreasingly acidic Increasingly alkaline

Bases and alkalis only show its alkalis properties when dissolved in water.

4. Strong Alkali: An alkali which ionises completely in water. Example; NaOH → Na+ + OH-

5. Weak Alkali: An alkali which ionises partially in water.

Example; NH3 + H2O NH4 + + OH-

Ca(OH)2 Ca2+ + 2OH-

Concentrations of Acids and Alkalis1. Concentration of solution can be expressed in gdm-3 or mol dm-3.

2. Molarity or molar concentration is the number of moles of solute that are present in 1 dm3 of solution.

Example. 1:A student dissolves 50.0 g of anhydrous copper(II) sulphate in water to make a 250 cm3 of solution.What is the concentration of the solution in g dm3?

Solution: Mass of anhydrous copper(II) sulphate, CuSO4 = 50.0 g

Volume of solution = = 0.25 dm3

Concentration of CuSO4 solution = = 200.0 g dm3

200 gdm-3 = 200 mol dm-3 64 + 32 + 4x16 molar mass

Example 2:28.0 g of potassium hydroxide is dissolved in water to make 200 cm3 of solution. Calculate the molarity of potassium hydroxide solution obtained. (Ar: H, 1; O, 16; K, 39)

Solution:

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Concentration (mol /dm-3)

Number of mole of solute (mol)

=Volume of solution (dm3)

Concentration (g /dm-3)

Mass of solute/substance (g)

=Volume of solution (dm3)

Question 1Find (a) the concentration of a sodium in grams per dm3 when 36.5 g of hydrogen chloride, HCl is dissolved in water to make up 500 cm3 of solution.

(b) the molarity of a solution which is prepared by dissolving 0.30 mol of sodium hydroxide, NaOH in distilled water to make up 250 cm3 of solution.

Solution:(a)

(b) Volume of solution =

Question 2The molarity of a bottle of nitric acid, HNO3 solution is 2.0 mol dm-3. What is the concentration of sodium in g dm-3 [Relative atomic masses: H, 1; N, 14; O, 16]

Solution;

Question 3Calculate the molarity of a sodium sulphate, Na2SO4 solution with a concentration of 28.4 g dm-3. [Relative atomic masses: O, 16; Na, 23; S, 32]

Solution;

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Question 4A student pipettes 25.0 mol dm3 of sodium hydroxide, NaOH solution into a conical flask. The concentration of the alkali was 1.5 mol dm-3. Calculate the number of moles of sodium hydroxide, NaOH in the flask.

Solution;

Preparation of Standard Solutions by Dilution Method

Standard solution is a solution in which its concentration is accurately known.

Use this formula ok..

M1 × V1 = M2 × V2

M1 = molarity of the solution before water is addedV1 = volume of the solution before water is added M2 = molarity of the solution after water is addedV2 = volume of the solution after water is added

a) Preparation of standard solution

- prepared by using a volumetric flask

b) Preparation of a solution by dilution method

- adding distilled water to a concentrated solution- changes the concentration of the solution- does not change the amount of solute

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Calibration mark

Example 1:Find the volume of 2.0 mol dm3 sulphuric acid, H2SO4 needed to prepare 100 cm3 of 1.0 mol dm-3 sulphuric acid, H2SO4. Solution; M1 × V1 = M2 × V2

2.0 mol dm-3 × V1 = 1.0 mol dm-3 × 100 cm3

V1 = 1.0 mol dm -3 × 100 cm 3 = 50 cm3 2.0 mol dm-3

Example 2: Volume of 2.0 mol dm3 nitric acid needed to be diluted with distilled water to make 250 cm3 of 0.5 mol dm3 nitric acid?

Solution: M1V1 = M2V2

Example 3:50 cm3 of water is added to 200 cm3 of a 2 mol dm3 solution of sodium hydroxide. Determine the molarity of the diluted solution.

Solution: M1V1 = M2V2

NeutralizationDefinition: The reaction between an acid and a base to produce a salt and water only.

Example : i. HCl + NaOH → NaCl + H2O

ii. H2SO4 + CuO → CuSO4 + H2O

The ionic equation for neutralization;

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H+ + OH- → H2O

Neutralisation in Daily Life

Neutralisation is used in various fields such as agriculture, industries and health.

Agriculture Acidic soil is treated with powdered lime, CaO, limestone, CaCO3 or ashes of burnt wood.

Basic soil is treated with compost. The acidic gas from the decomposition of compost neutralises

the alkalis in basic soils.

Lime, CaO is used to control the acidity in aqua farming.

Industries

Acidic effluent from factories is treated with lime, CaO before being discharged.

Acidic gas such as sulphur dioxide, SO2 emitted by power stations and industries is neutralised

with lime, CaO before the gas is discharged into the air.

Ammonia, NH3 prevents the coagulation of latex by neutralising the acid produced by bacteria in

the latex.

Health

Anti-acids contain bases such as aluminium hydroxide, Al(OH)3 and magnesium hydroxide,

Mg(OH)2 to neutralise the excess acid in the stomach.

Vinegar is used to cure wasp stings that are alkaline in nature.

Baking powder is used to cure bee stings and ant bites that are acidic in nature.

Toothpaste contains bases that neutralise the acid produced by bacteria in our mouth.

Acid-Base Titration

Titration is a quantitative analysis that involves the gradual addition of chemical solution from a burette to another chemical solution of known quatity in a conical flask.

In an acid-base titration, the volume of an alkali is measured using a pipette and transferred into a conical flask. The acid solution from a burette is then added slowly into the alkali in the conical flask until neutralisation occurs.

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The end-point of neutralisation is achieved when all the OH- ions combine with all the H+ ions in the solution to form water which is neutral.

Since both the reactants (acids and alkali) and the products formed (salt and water) are all colourless, the end-point of neutralisation is determined by three methods as follow:

- The use of acid-base indicators such as methyl orange, phenolphthalein and litmus.- Measurement of the pH values of the solution on computer interface during titration.- Measurement of the electrical conductivity of the solution during titration.

Indicator Colour in alkalis Colour in neutral Colour in acids

Methyl orange Yellow Orange RedPhenolphthalein Pink Colourless ColourlessLitmus Blue Purple Red

Calculation involving neutralization using balanced equations.

Question 1: A student pipettes 25.0 mol dm-3 of sodium hydroxide, NaOH solution into a conical flask and filled a burette with 0.10 mol dm-3 hydrochloric acid, HCl to carry out titration. He obtained an average volume of 22.0 cm3 hydrochloric acid, HCl. What was the molarity of the sodium hydroxide, NaOH solution?

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Retort stand

Burette

Hydrochloric acid, HCl

Conical flask

25 cm3 sodium hydroxide, NaOH + phenolphthalein

MA × VA MB × VB=

a b

MA = Molarity of alkali MB = Molarity of base VA = Volume of alkali VB = Volume of base

a = number of mole of acid from balanced chemical equation b = number of mole of base from balanced chemical equation

Solution: Chemical equation: HCl + NaOH → NaCl + H2O

MA = 0.10 mol dm-3 HCl MB = unknown [Molarity NaOH] VA = 22.0 cm3 HCl VB = 25.0 mol dm-3 NaOH

a = 1 [no. of mole of HCl FBCE] b =1 [no. of mole of NaOH FBCE]

MB = 0.1 × 22.0 × 1 = 0.088 mol dm-3 1 × 25.0 Molarity of NaOH = 0.088 mol dm-3

Question 2: What is the volume of 0.5 mol dm-3 sulphuric acid, H2SO4 needed to neutralize 25.0 cm3 of 0.8 mol dm-3 ammmonia, NH3 solution?

Solution: Chemical equation: H2SO4 + 2NH3 → (NH4)2SO4 or H2SO4 + 2NH4OH → (NH4)2SO4 + 2H2O

MA = 0.5 mol dm-3 H2SO4 MB = 0.8 mol dm-3 NH3

VA = unknown volume of H2SO4 VB = 25.0 mol dm-3 NH3

a = 1 (mole of H2SO4 FBCE) b = 2 ( mole of NaOH FBCE)

Question 3: A sample of copper(II) oxide, CuO was found to completely neutralize 100 cm3 of 0.5 mol dm-3 hydrochloric acid. Calculate the mass of sample.

Solution: Chemical equation: CuO + 2HCl → CuCl2 + H2O Number of mole of HCl = M × V = 0.5 × 100 = 0.05 mol of HCl

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0.1 × 22.0 MB × 25.0=

1 1

MA × VA MB × VB=a b

MA × VA MB × VB=

a b

1000 1000 2 mol HCL = 1 mol CuO 0.05 mol HCl = 1 × 0.05 = 0.025 mol of CuO

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Mass of CuO = 0.025 × [64 + 16] = 0.025 × 80 = 2.0 g

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