I. BASIC CONCEPTS OF CHEMISTRY Prepared by PhD Halina Falfushynska

Branches of chemistry Physical chemistry Organic chemistry Inorganic chemistry Analytical chemistry Industrial chemistry Bio chemistry Nuclear chemistry Agricultural chemistry Geo chemistry

Uses of chemistry

Abuses of chemistry

A compound is a substance which can be decomposed into two or more dissimilar substances. Compound and mixture Mixture contains two or more components. Homogenous mixture: Same or uniform composition. Air is a mixture of gases like O 2, N 2, CO 2, etc. Heterogeneous mixture: Different compositions in different phases. Smog.

Law of conservation of mass Total mass of the product remains equal to the total mass of the reactants. H 2 + Cl 2 2 HCl 2g 71g73g

A chemical compound always contains same elements combined together in same proportion of mass. Law of definite proportions Ice water H 2 O 1 : 8River water H 2 O 1 : 8 Sea water H 2 O 1 : 8

Law of Multiple Proportions If two elements form more than a single compound, the masses of one element combined with a fixed mass of the second are in the ratio of small whole numbers (John Dalton, 1803).

It is found elemental iron combines with elemental chlorine to form two different compounds; ferric chloride and ferrous chloride. The definite composition of these two compounds is: This data can be used to determine the mass of chlorine per 1.00g of iron needed to produce these compounds.

Dalton’s Atomic Theory 1) All matter is made of atoms. Atoms are indivisible and indestructible. 2) All atoms of a given element are identical in mass and properties 3) Compounds are formed by a combination of two or more different kinds of atoms. 4) A chemical reaction is arearrangement of atoms.

Avogadro's Law Equal volumes of gases under identical temperature and pressure conditions will (atoms, ion, molecules, electrons, etc.).

Avogadro's Number! How many carbon-12 atoms are needed to have a mass of exactly 12 g? That number is Na - Avogadro's number. Careful measurements yield a value for Na = x10^ mole = x particles of any substance

Moles n = mass (m)/Molar mass (M) n= m/M n = number of particles (N)/ Avogadro's Number (Na) n= N/Na.

Simplest and molecular formulae Consider NaCl (ionic) vs. H 2 O 2 (covalent) Cl Na Cl Na Chemical formulas are either “simplest” (a.k.a. “empirical”) or “molecular”. Ionic compounds are always expressed as simplest formulas. Covalent compounds can either be molecular formulas (I.e. H 2 O 2 ) or simplest (e.g. HO) Q - Write simplest formulas for propene (C 3 H 6 ), C 2 H 2, glucose (C 6 H 12 O 6 ), octane (C 8 H 14 ) Q - Identify these as simplest formula, molecular formula, or both H 2 O, C 4 H 10, CH, NaCl H O O H H O O H H O O H

Equivalent weight Molecular weight / Valency Valency is equal to: - absolute number of ion charge - number of H+ or OH- ions that can combine with the ion - absolute number of change in charge of ion in a reaction Quantity of chemicals equivalent to each other One chemical expressed as another Same number of equivalents of reactants in a chemical reaction

Equivalent weight

Example: for the balanced reaction 2NaOH + H2SO4 =Na2SO4 +2H2O - 2 moles NaOH react with 1 mole H2SO4 - 80g NaOH react with 98g H2SO4 - 2eq NaOH react with 2 eq H2SO4

Law of Equivalence For a chemical reaction: aA + bB -> cC + dD Equivalent of A = Equivalent of B = Equivalent of C = Equivalent of D where n, and M is n factor, molecular mass of the species

If the reaction is carried out in solution, then N A V A = N B V B = N C V C = N D V D or n A M A V A = n B M B V B = n C M C V C = n D M D V D For a given solution, number of equivalents per litre is same as the number of milliequivalents per ml, Moles, millimoles, equivalent, milli equivalent of solute does not change on dilution.