i. basic concepts of chemistry prepared by phd halina falfushynska
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I. BASIC CONCEPTS OF CHEMISTRY
Prepared by PhD Halina Falfushynska
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Branches of chemistry
Physical chemistryOrganic chemistry
Inorganic chemistryAnalytical chemistryIndustrial chemistry
Bio chemistryNuclear chemistry
Agricultural chemistryGeo chemistry
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Uses of chemistry
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Abuses of chemistry
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A compound is a substance which can be decomposed into two or more dissimilar substances.
2 2 2Compound
Elements
2H O 2H O
Compound and mixture
Mixture contains two or more components.
Homogenous mixture: Same or uniform composition.Air is a mixture of gases like O2, N2, CO2, etc.
Heterogeneous mixture: Different compositions in different phases. Smog.
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Law of conservation of mass
Total mass of the product remains equal to the total mass of the reactants.
H2 + Cl2 2 HCl2g 71g 73g
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A chemical compound always contains same elements combined together in same proportion of mass.
Law of definite proportions
Ice water H2O 1 : 8
River water H2O 1 : 8
Sea water H2O 1 : 8
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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).
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• 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.
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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.
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Avogadro's Law
• Equal volumes of gases under identical temperature and pressure conditions will (atoms, ion, molecules, electrons, etc.).
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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 = 6.0221367x10^+23.
• 1 mole = 6.022 x 1023 particles of any substance
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Moles
• n = mass (m)/Molar mass (M) n= m/M• n = number of particles (N)/
Avogadro's Number (Na) n= N/Na
.
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Simplest and molecular formulaeConsider NaCl (ionic) vs. H2O2 (covalent)
Cl Na
Na Cl
Cl
Cl
Na
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. H2O2) or simplest (e.g. HO)
Q - Write simplest formulas for propene (C3H6), C2H2, glucose (C6H12O6), octane (C8H14)
Q - Identify these as simplest formula, molecularformula, or both H2O, C4H10, CH, NaCl
HOO
H HOO H H
OO H
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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
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Equivalent weight
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Equivalent weight
• Example: for the balanced reaction2NaOH + H2SO4 =Na2SO4 +2H2O
- 2 moles NaOH react with 1 mole H2SO4
- 80g NaOH react with 98g H2SO4- 2eq NaOH react with 2 eq H2SO4
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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
•
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• If the reaction is carried out in solution, then NAVA = NBVB = NCVC = NDVD or
nAMAVA = nBMBVB = nCMCVC = nDMDVD
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.