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CHEMISTRY LEVEL 3
1. GAS LAWS
- 1.1 Boyle's Law
- 1.2 Charles'law
- 1.3 Combined gas law
- 1.4 Standard conditions
- 1.5 Diffusion and Graham's law
2. THE MOLE: Formulae and Chemical Equations
- 2.1 Relative Mass
- 2.2 Atoms, Molecules and Moles
- 2.3 Compounds and the mole
- 2.4 Empirical and Molecular formula
- 2.5 Concentration of a solution
- 2.6 Molar solutions
- 2.7 Preparation of molar solutions
- 2.8 Dilution of a solution
- 2.9 Stoichiometry of chemical reactions
- 2.10 Volumetric analysis
- 2.11 Titration
- 2.12 Redox titration
- 2.13 Atomicity and molar gas volume
- 2.14 Combining volumes of gases
3. ORGANIC CHEMISTRY 1
- 3.1 Alkanes
- 3.1.1 Formulae of alkanes
- 3.1.2 Cracking of alkanes
- 3.1.3 Nomenclature (systematic naming) of alkanes
- 3.1.4 Isomerism in alkanes
- 3.1.5 Laboratory preparation of alkanes
- 3.1.6 Physical properties of alkanes
- 3.1.7 Chemical properties of alkanes
- 3.1.8 Uses of alkanes
- 3.2 Alkenes
- 3.2.1 Nomenclature of alkenes
- 3.2.2 Isomerism in alkenes
- 3.2.3 Laboratory preparation of ethene
- 3.2.4 Physical properties of alkenes
- 3.2.5 Chemical properties of alkenes
- 3.2.6 Test for alkenes
- 3.2.7 Uses of alkenes
- 3.3 Alkynes
- 3.3.1 Nomenclature of alkynes
- 3.3.2 Isomerism in alkynes
- 3.3.3 Laboratory preparation of ethyne
- 3.3.4 Physical properties of alkynes
- 3.3.5 Chemical properties of alkynes
- 3.3.6 Test for alkynes
- 3.3.7 Uses of alkynes
- 3.4 Recommended practice of topic summary
4. NITROGEN AND ITS COMPOUNDS
- 4.1 Extraction of nitrogen from air
- 4.2.1 Laboratory preparation of nitrogen gas from the air
- 4.2.2 Laboratory preparation of nitrogen gas from ammonium nitrite (NH4NO2)
- 4.2.3 Uses of nitrogen
- 4.3 Oxides of nitrogen
- 4.3.1 Nitrogen (I) oxide
- 4.3.2 Nitrogen (II) oxide
- 4.3.3 Nitrogen (IV) oxide
- 4.4.1 Laboratory preparation of ammonia
- 4.4.2 Solubility of ammonia in water
- 4.4.3 Reactions of aqueous ammonia (ammonia solution)
- 4.4.4 Reactions of ammonia gas
- 4.4.5 Industrial manufacture of ammonia: The Haber Process
- 4.4.6 Uses of ammonia
- 4.4.7 Nitrogenous fertilizers
- 4.5.1 Laboratory preparation of nitric (V) acid
- 4.5.2 Industrial manufacture of nitric (V) acid
- 4.5.3 Reactions of dilute nitric (V) acid
- 4.5.4 Reactions of concentrated nitric (V) acid
- 4.5.5 Uses of nitric (V) acid
- 4.6.1 Action of heat on nitrates
- 4.6.2 Test for nitrates (nitrate ions, NO3-)
- 4.6.3 Air pollution by nitrogen compounds
- 4.7 Summary on nitrogen and its compounds
5. SULPHUR AND ITS COMPOUNDS
- 5.0 Sulphur and its Compounds
- 5.1.1 Extraction of sulphur
- 5.1.2 Allotropes of sulphur
- 5.1.3 Physical properties of sulphur
- 5.1.4 Chemical properties of sulphur
- 5.2.1 Preparation of sulphur (IV) oxide
- 5.2.2 Physical properties of sulphur (IV) oxide
- 5.2.3 Chemical properties of sulphur (IV) oxide
- 5.2.4 Reducing action of sulphur (IV) oxide
- 5.2.5 Oxidization of SO2 to SO3
- 5.2.6 Oxidizing action of sulphur (IV) oxide
- 5.2.7 Test for sulphite (SO32-) and sulphate (SO42-) ions
- 5.2.8 Uses of sulphur (IV) oxide
- 5.3 Large scale (industrial) manufacture of sulphuric (VI) acid
- 5.3.1 Physical properties of concentrated sulphuric (VI) acid
- 5.3.2 Chemical properties of concentrated sulphuric (VI) acid
- 5.3.3 Reactions of dilute sulphuric (VI) acid
- 5.4 Hydrogen sulphide
- 5.4.1 Chemical properties of hydrogen sulphide
- 5.4.2 Air pollution by compounds of sulphur
- 5.5 Summary on sulphur and its compounds
6. CHLORINE AND ITS COMPOUNDS
- 6.1 Occurrence of chlorine
- 6.2 Laboratory preparation of chlorine
- 6.3 Physical properties of chlorine
- 6.4 Chemical properties of chlorine
- 6.5 Oxidizing properties of chlorine
- 6.6 Reaction of chlorine with alkaline solutions
- 6.7 Test for chloride ions
- 6.8 Uses of chlorine and its compounds
- 6.9 Preparation of hydrogen chloride gas
- 6.10 Physical properties of hydrogen chloride
- 6.11 Chemical properties of hydrogen chloride
- 6.12 Industrial manufacture of hydrochloric acid
- 6.13 Uses of hydrochloric acid
7. A guide to chemical tests based on this module
Content developer
The Mole: Formulae and Chemical Equations: Empirical and Molecular formula
2.0 The Mole: Empirical and Molecular formula
2.4 Empirical and Molecular formula
Elements combine in definite ratios of atoms. This can be seen in the formulae of the compounds we have dealt with so far. Examples are H2O, CO2, SO2, NO2, NaCl, MgCO3, H2O2, Na2O2, and Al2Cl6.
Questions 2.4(a)
- How do the formulae H2O2, Na2O2, and Al2Cl6 differ from the rest?
- Rewrite these formulae to show the simplest ratio in which the elements are combined.
- The formulae you have written (in Question 2) are called empirical formulae. What is an empirical formula?
- The formulae H2O2, Na2O2, and Al2Cl6 show the actual numbers of atoms in each molecule of the compound. They are called molecular formulae. What is a molecular formula?
- How is molecular formula related to empirical formula?
Answers to Questions 2.4(a) 
An empirical formula shows the simplest ratio in which elements are combined in a compound.
Examples are HO, NaO, and AlCl3. The actual formulae in which they exist, that is, H2O2, Na2O2, and Al2Cl6, are called molecular formulae. Empirical Formula (E.F.) and Molecular Formula (M.F.) are related as n(E.F.) = M.F., n being a whole number, sometimes 1. In the three examples, n = 2.
For H2O, CO2, SO2, NO2, NaCl, MgCO3, and many other substances, n = 1; so molecular and empirical formulae are the same.
We can easily determine empirical formula if we know the masses of elements combined.
Example
A compound consists of 2 g of carbon and 0.5 g of hydrogen as its only components. Find the empirical formula of the compound (H = 1; C = 12).
Plate 2.4(a) Empirical formula
Questions 2.4(b)
- A compound X, consists of 3.5 g of nitrogen and 8 g of oxygen as the only components. Determine the empirical formula of X (N = 14; O = 16).
- If the molar mass of X (in question 1) is 92 g, find its molecular formula.
- In a compound, 4 g of hydrogen is found to be combined with 32 g of oxygen. Determine the empirical formula of the compound (H = 1; O = 16).
- The empirical formula of a compound is ZQ2. The masses of Z and Q in a sample of the compound are 2.5 g and 17.75 g respectively.
Determine the molar mass of (a) Z and (b) ZQ2
(Q = 35.5).
Answers to Questions 2.4(b)