CHEMISTRY LEVEL 3
- 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
- 2.1 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
- 3.1 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
- 4.1 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
- 5.0 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
- 6.1 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
THE MOLE: Formulae and Chemical Equations: Compounds and the mole
2.0 THE MOLE: Formulae and Chemical Equations
2.3 Compounds and the mole
Given the number of moles of a compound, we can easily convert them to mass in grams and vice versa, in the same manner done in Section 2.2.
Examples
- Find the mass of one mole of sodium chloride.
- What is the mass of 0.25 moles of sodium chloride?
- Determine the number of moles in 5.85 g of sodium chloride.
(Na = 23; Cl = 35.5.)
Solutions
- Mass of one mole (molar mass) of NaCl = 23 + 35.5 = 58.5 g
- 1 mole weighs 58.5 g
Therefore 0.25 moles weigh (0.25/1) x 58.5 = 14.625 g - 58.5 g is 1 mole
Therefore 5.85 is 5.85/58.5 = 0.1 mol.
Questions 2.3(a)
- Find the mass of one mole of (a) magnesium oxide (b) water (c) sodium sulphate (Na2SO4)
(H = 1; C = 12; O = 16; Mg = 24; S = 32) - Find the number of moles of molecules in (a) 2 g of carbon (IV) oxide (b) 0.34 g of ammonia
(H = 1; C = 12; O = 16; N = 14) - Find the mass in grams of (a) 0.5 moles of nitrogen (IV) oxide (b) 0.3 moles of sulphur (IV) oxide. (N = 14; O = 16; S = 32)
- Determine the number of moles of molecules in (a) 6 g of sodium sulphate (b) 2 g of magnesium carbonate (C = 12; Na = 23; S = 32).
- State the number of atoms of each element in the formula, NaHSO4.
- Determine the mass of each element in one mole of NaHSO4.
- Determine the number of moles of each kind of atom in 12g of NaHSO4.
(H = 1; Na = 23; O = 16; S = 32)
Answers to Questions 2.3(a) 
NB: Calculations involving moles are normally easy, involving simple direct proportions of the form "a leads to b; therefore c leads to ((c/a) x b)". The rest is about understanding the question, and knowing the information given, sometimes indirectly, to solve it.
It is advisable to solve problems on moles by reasoning, as we have done in the sample answers, because memorized equations can be confusing. Moreover, they do not reflect our understanding.
Because the term mole applies to any particles, we always specify the particles we are referring to: whether atoms, molecules, ions or formula units. For example, in one mole of carbon (IV) oxide (CO2), there is one mole of carbon atoms but two moles of oxygen atoms.
One mole of potassium sulphate (K2SO4) has two moles of potassium ions (K+), one mole of sulphur atoms, four moles of oxygen atoms and one mole of sulphate ions (SO42-).
Questions 2.3(b): Previous experience
What mass of magnesium sulphate (MgSO4) has the same number of moles as 1.06 g of anhydrous sodium carbonate (Na2CO3)? (C = 12; O = 16; Mg = 24; Na = 23; S = 32.)
Answers to Questions 2.3(b)