Acid-base Titration

Sodium hydroxide

Acid-base Titration

• Titration – a quantitative analysis method to determine the volume of an acid that is required to neutralise a fixed volume of an alkali / a quantitative analysis method to determine the volume of an alkali that is required to neutralise a fixed volume of an acid.
• End point of a titration – a point which neutralisation occurs when the acid has completely neutralised the alkali / the alkali has completely neutralised the acid.
• Reactants: Acid and alkali
• Products: Salt and water
• End point can be determined by (i) the use of acid-base indicators during titration, (ii) measuring the pH values of the solution during titration and (iii) measuring the electrical conductivity of solution during titration.

Indicator	Alkali	Neutral	Acid
Litmus	Blue	Orange	Red
Methyl orange	Yellow	Orange	Red
Phenolphthalein	Pink	Colourless	Colourless

Read More

Neutralisation

Sodium hydroxide

Neutralisation

• Neutralisation = a reaction between an acid and a base/alkali to produce salt and water only.
• Acid + alkali –> salt + water
• Ionic equation of neutralisation: H⁺(aq) + OH^-(aq) –> H₂O(l)

Application of Neutralisation Reactions in Daily Life

Digestive juices in stomach	Break up food (only in acidic condition) and maintained at pH of between 1 and 2,
Insect stings	Bees and ants inject an acidic liquid into the skin but wasps inject an alkaline liquid.
Toothpaste	An alkaline compound (magnesium hydroxide) in toothpastes neutralises the organic acids produced by the food.
pH of the swimming pool	Calcium hypochlorite, Ca(OCl)2 is added to the water.
Latex industries	Ammonia is used to neutralise the organic acid produces by bacteria to prevent coagulation.
Neutralisation	Manufacture fertilisers, soaps and detergents
Effluent from factories	It can be treated with lime.
Sulphuric acid	Manufacture of dyes, explosives, steel, fertilisers, paints and plastics.
Soil treatment	Plants grow best when the pH of the soil is about 7. The soil is too acidic, quick lime (calcium oxide) or slaked lime (calcium hydroxide) is added to the soil to neutralise the excess acid.

Read More

Concentration of Acids and Alkalis

Sodium hydroxide

Concentration of Acids and Alkalis

• Quantity of solute can be measured in grams or moles: g dm^-3 or mol dm^-3.
• Concentration (g dm^-3) = mass of solute (g) / volume of solution (dm³)
• Concentration (mol dm^-3) = number of moles of solute (mol) / volume of solution (dm³)

Relationship between Number of Moles with Molarity and Volume of a Solution

• Molarity (mol dm^-3) = number of moles of solution (mol) / volume of solution (dm³)
• M = molarity of solution (mol dm^-3), V = Volume of solution (dm³), n = Number of moles of solute (mol)
• M = n/V

Preparation of Standard Solutions

• Standard solution = a solution in which its concentration is accurately known.
• Standard solution is prepared by using volumetric flask with a fixed volume (100 cm³, 200 cm³, 250 cm³, 500 cm³ and 1000 cm³)

Preparation of a Solution by Dilution Method

• Dilution = a process of diluting a concentrated solution by adding a solvent (water) to obtain a more diluted solution.
• The concentration of the solution decreases after dilution.
• The number of moles of solute in the solution remains unchanged after dilution.
• (M_aV_a) / 1000 = (M_bV_b) / 1000
• M_a = Initial molarity of solution, M_b = Final molarity of solution, V_a = Initial volume of solution and V_b = Final volume of solution

Relationship between pH Values and Molarities of Acids or Alkalis

• pH values depends on degree of dissociation and molarity / concentration of hydrogen ions, H⁺/ hydroxide ions, OH^- in the solution.
• The higher the molarity of a strong acid, the lower is its pH value.
• The higher the molarity of a strong alkali, the higher is its pH value.
• The molarity of an acid can be changed when (i) water is added, (ii) an acid of different concentration is added and (iii) an alkali is added.

Read More

Strong Acids

Sodium hydroxide

Strong Acids

• Strength of an acid – the degree of ionisation or dissociation of the acid in water.
• Strong acid – an acid which ionises / dissociates completely in water to form high concentration of hydrogen ions (H⁺).
• Example of strong acid: Mineral acid – hydrochloric acid (HCl), nitric acid (HNO₃) and sulphuric acid (H₂SO₄).
• Example of the strong acid reaction in water: HCl(aq) –> H⁺(aq) + Cl^-(aq)  (The concentration of hydrogen ions is equal to the concentration of hydrochloric acid)

Weak Acids

• Weak acid – an acid which ionises / dissociates partially in water to form low concentration of hydrogen ions (H⁺).
• Example of weak acid: ethanoic acid (CH₃COOH) and methanoic acid (HCOOH)
• Example of the weak acid reaction in water: CH₃COOH <—-> CH₃COO^-(aq) + H⁺(aq) {The concentration of hydrogen ions is low and the ions (CH₃COO^- and H⁺) reacts to reform the ethanoic acid molecule = reversible reaction}

Strong Alkalis

• Strength of an alkali – the degree of ionisation or dissociation of the alkali in water.
• Strong alkali – an alkali which ionises / dissociates completely in water to form high concentration of hydroxide ions (OH ^– ).
• Example of strong alkali: Sodium hydroxide (NaOH) solution, potassium hydroxide (KOH) solution and barium hydroxide (Ba(OH)₂) solution.
• Example of the strong alkali reaction in water: NaOH(aq) –> Na⁺(aq) + OH^-(aq)

Weak Alkalis

• Weak alkali – an alkali which ionises / dissociates partially in water to form low concentration of hydroxide ions (OH ^– ).
• Example of weak alkali: ammonia (NH₃) solution.
• Example of the weak alkali reaction in water: NH₃(g) + H₂O(l) <—-> NH₄⁺(aq) + OH^- (aq)

Read More

The pH scale and the Measurement of pH Value of a Solution

The pH scale and the Measurement of pH Value of a Solution

• pH scale is a set of numbers used to represent the degree of acidity or alkalinity of a solution.
• pH is a measurement of the concentration of hydrogen ions (H⁺) in the solution.
• pH value greater than 7: alkaline solution
• pH value of exactly 7: neutral solution
• pH value less than 7: acidic solution
• In an acidic solution = higher in the concentration of the H⁺ ions, the lower the pH value.
• In an alkaline solution = lower in the concentration of the H⁺ ions, the higher the pH value.
• pH solution can be measured by using universal indicator, pH paper and pH meter.

pH value	Colour of Universal Indicator
0, 1, 2	Red
3	Orange red
4	Orange
5	Orange yellow
6	Yellow
7	Green
8	Greenish-blue
9	Blue
10	Blue
11	Bluish-purple
12, 13, 14	Purple

Read More

Important Definition for Acids

Sodium hydroxide

Important Definition for Acids
Monoprotic acid (monobasic acid) is an acid which produce one mole of H⁺ ion when one mole of the acid ionise in water.

Monoprotic acid	Monoprotic acid name
HCl	Hydrochloric acid
HNO3	Nitric acid
CH3COOH	Ethanoic acid

.
Polyprotic acids

Diprotic acid (dibasic acid) is an acid which produce two moles of H⁺ ios from one mole of the acid in water.

Diprotic acid	Diprotic acid name
H2SO4	Sulphuric acid
H2CO3	Carbonic acid
H2CrO4	Chromic acid
H2C2O4	Ethanedioic acid / Oxalate acid

Triprotic acid (tribasic acid) is an acid which produce three moles of H⁺ ions from one mole of the acid in water.

Triprotic acid	Triprotic acid name
H3PO4	Phosphoric acid
C6H8O7	Citric acid

Read More

Chemical Properties

Sodium hydroxide

Chemical Properties

Acid	Alkali
In the presence of water, an acid will ionise to form hydrogen ion, H+.	In the presence of water, an alkali will ionise to form hydroxide ion, OH -.
Sour in taste	Bitter in taste
pH values less than 7	pH values more than 7
Indicator: Blue litmus paper (Red)	Indicator: Red litmus paper (Blue)
Indicator: Universal indicator (Orange and red)	Indicator: Universal indicator (Blue and purple)
Indicator: Methyl orange (Red)	Indicator: Methyl orange (Yellow)
React with bases to produce salts and water. 2HCl(aq) + CuO(s) –> CuCl2(aq) + H2O(l)	React with acids to produce salts and water. NaOH(aq) + HCl(aq) –> NaCl(aq) + H2O(l)
React with metals (reactive metal, higher position than H+ in the electrochemical series) to produce salts and hydrogen gas. 2HCl(aq) + Zn(s) –> ZnCl2(aq) + H2(g)	React with an ammonium salt (alkali is heated) to produce ammonia gas. Ba(OH)2(aq) + 2NH4Cl(s) –> BaCl2(aq) + 2H2O(l) + 2NH3(g)
React with carbonates to produce salts, carbon dioxide gas and water. H2SO4(aq) + ZnCO3(s) –> ZnSO4(aq) + H2O(l) + CO2(g)	React with aqueous salt solutions to produce metal hydroxides (as precipitate). 2NaOH(aq) + CuSO4(aq) –> Na2SO4(aq) + Cu(OH)2(s)

Read More

The Uses of Acids in Our Daily Life

Sodium hydroxide

The Uses of Acids in Our Daily Life

Benzoic acid	Its salt are used to preserve food
Carbonic acid	To make carbonated drinks
Ethanoic acid	A main compound of vinegar
Hydrochloric acid	To clean metals before electroplating / household cleaning / leather processing / swimming pool maintenance
Nitric acid	Production of fertilisers, explosives, etching and dissolution of metals (purification and extraction of gold)
Sulphuric acid	To make detergent, polymer and fertilisers.
Tartaric acid	Manufacturing of soft drinks, provide tartness to food, as an emetic (a substance to induce vomiting)

The Uses of Bases in Our Daily Life

Ammonia	Production of fertilisers (ammonium and nitrate salts), used in the manufacture of nitric acid, neutralise the acid (in the petroleum industry) and prevent premature coagulation in natural / synthetic latex.
Aluminium hydroxide	Manufacture other aluminium compound and to make gastric medicine (antacid)
Calcium hydroxide	To make cement, limewater, neutralise the acidity of soil and application of sewage treatment.
Sodium hydroxide	Used in the manufacturing of soaps, detergents, and cleaners.
Magnesium hydroxide	Suspension of magnesium hydroxide in water are used as an antacid, used as an antiperspirant armpit deodorant and as a non-hazardous alkali to neutralise acidic wastewater.

Read More

Acids

Acids

• An acid is a chemical substance which ionises in water to produce hydrogen ions, H⁺ / hydroxonium ions, H₃O⁺.
• H⁺(aq) + H₂O(l) –> H₃O⁺(aq)
• Example: HCl(g) + H₂O(l) –> H₃O⁺(aq) + Cl ^-(aq)

Acid	Acid name	Ions
HCl	Hydrochloric acid	H+, Cl -
HNO3	Nitric acid	H+, NO3-
H2SO4	Sulphuric acid	H+, SO42-
CH3COOH	Ethanoic acid	H+, CH3COO -

• Monoprotic acid = acid can produce only one hydrogen ion per molecule in water. (Example: HCl)
• Diprotic acid = acid can produce two hydrogen ions per molecule in water. (Example: H₂SO₄)
• Triprotic acid = acid can produce three hydrogen ions per molecule in water. (Example: H₃PO₄)

Sodium hydroxide

Bases / Alkalis

• A base is a chemical substance which reacts with an acid to produce a salt and water only.
• Base(s) + acid(aq) –> salt + water (l).
• Example: NaOH(s) + HCl(aq) –> NaCl(aq) + H₂O(l)

Base	Formula	Solubility in water	Ions in the aqueous solution
Copper(II) oxide	CuO	Insoluble base	-
Lead(II) oxide	PbO	Insoluble base	-
Magnesium oxide	MgO	Insoluble base	-
Zinc hydroxide	Zn(OH)2	Insoluble base	-
Aluminium hydroxide	Al(OH)3	Insoluble base	-
Sodium oxide	Na2O	Soluble base (alkali)	Na+, O2-
Calcium oxide	CaO	Soluble base (alkali)	Ca2+, O2-
Sodium hydroxide	NaOH	Soluble base (alkali)	Na+, OH-
Potassium hydroxide	KOH	Soluble base (alkali)	K+, OH-
Barium hydroxide	Ba(OH)2	Soluble base (alkali)	Ba2+, OH-

Read More