Stoichiometry Student Copy PDF

Fundamental of Organic Chemistry (PHC414) Stoichiometry Hannis Fadzillah bt Mohsin (Dr.) Content  Early views of atomic theory.  Molecular forces - Intro  The mole concept.  Chemical equation & calculations. YES? NO?  Stoichiometry problems are a typical par...

Fundamental of Organic Chemistry (PHC414) Stoichiometry Hannis Fadzillah bt Mohsin (Dr.) Content  Early views of atomic theory.  Molecular forces - Intro  The mole concept.  Chemical equation & calculations. YES? NO?  Stoichiometry problems are a typical part of a pharmacist's daily routine.  This type of chemistry can be extremely useful, and is essential to pharmacists.  Pharmacists use the mole and various calculations that use this value to mix chemicals that form powders, tablets, and ointments.  These measurements are essential to make sure that the right relative amount of a certain chemical can be found in the medicine that they dispense. How chemistry connected to pharmacy  Stoichiometry  Solubility  Dilutions and Concentration  Molecular Stability  Pro drug Chemistry  Molecular Structure  X-Ray Diffraction  Synthetic Compounds/Polymers  Functional Groups (Organic Chemistry)  Unit Conversions  Atomic Theory JOHN DALTON (1766 - 1844) J.J. THOMPSON (1856 - 1940) ERNEST RUTHERFORD (1871 - 1937) NIELS BOHR (1885-1962 ) LOUIS DE BROGLIE (1892 - 1987 ) ERWIN SCHRÖDINGER (1887 - 1961) MODERN THEORY OF ATOMIC STRUCTURE Atomic Theory Atomic numbers, Z, as basic classification to elements in Periodic Table. Atomic numbers (Z) = protons. Mass number (M) = protons + neutrons. 8 Atomic number, Z O Chemical symbol Atomic weight 15.94 www.themegallery.com Four chemical families of the periodic table: the alkali metals (IA) the alkaline earth metals (IIA) halogens (VII) the noble gases (VIIIA)  Molecular Forces Ionic Bond 2. Covalent Bond Between atoms of metals and Between nonmetallic elements of nonmetals with very different similar electronegativity. electronegativity Examples; O2, CO2, C2H6, H2O, SiC Examples; NaCl, CaCl2, K2O  Molecular forces Various drug-receptor interactions such as 1. Covalent bonding 2. Ionic (electrostatic) interaction 3. Dipole-dipole interaction 4. H-bonding 5. Hydrophobic interaction  Functional groups use their electronic & shape 6. Van der Waals forces. characters in the binding process.  Bonds could be inter-molecular or intramolecular.  Neratinib (red), a Pfizer drug candidate, Example forms a covalent bond with a cysteine (yellow) of epidermal growth factor receptor (blue) 1. Covalent bonds For covalent bond formation, there should be two poles; the electrophile and the nucleophile. Nucleophiles in biology have the following functional groups:  Thiol in the amino acid cysteine  Hydroxyl in the amino acid serine  Amine in the amino acid lysine  Carboxylate in the amino acid glutamic acid. Electrophiles  Epoxide ring  Alkyl group attached to halogen  Positively charged centre Polar Covalent Non-polar Bonds Covalent Covalent Bonds When electrons Bonds are shared but When electrons shared are shared unequally. equally. H2O H2 or Cl2 The greater the difference in electronegativity between the bonded atoms, the greater is the polarity of the bond.  2. Ionic or electrostatic interactions The drug molecule must have an opposite charge to the ionized amino acids found in the receptor or enzyme. The extent of ionization affects the occurrence of this bond, and the distance between opposite charges also plays a role. Example In biological systems, it happens between residues having carboxylate group such as aspartic acid & glutamic acid (acidic amino acids), and aminium ions such as Histidine, Lysine and Arginine (basic amino acids).  3. Ion-dipole and dipole-dipole interactions Electronic dipole is formed when we have polarized bond due to electronegativity of atoms. In the polarized bond, one of the poles will be partially positive and the other partially negative. These partially positive or negative charges might form an electrostatic bond with either partially charged atoms OR ionized elements. solid liquid 18 4. H-bonding  Hydrogen Bond - A special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.  H-bonding - Should have H-Bond acceptor (the electron rich atom, slightly negative) and H-Bond donor (electron-deficient hydrogen, slightly positive). 20 Intramolecular hydrogen bonding Intermolecular hydrogen bonding  5. Hydrophobic interaction  When two nonpolar groups (a lipophilic group on a drug and a nonpolar receptor group), are each surrounded by water molecules, they become disordered to associate with each other.  Another type of hydrophobic interaction is called π- π interaction.  This involves a parallel arrangement of aromatic rings in which the π-electrons interact in a face-to- face arrangement. Example: Anticonvulsant drug Lacosamide has a phenyl ring (π electrons) The receptor has phenylalanine containing phenyl ring (π electrons)  6. Van der Waals forces Occurs due to temporary non-symmetrical distribution of electron density; this will form a temporary dipole that will interact with the nearby dipole. Weaker than other bonds Electron clouds are temporarily polarized, inducing dipoles to form in other molecules  temporary attraction (Eg: Br2, H2) 24 Van der Waals forces Significance of chemical bonding in drug–receptor interactions  Most drugs interact with receptor sites localized in macromolecules that have protein-like properties and specific three-dimensional shapes.  A receptor is the specific chemical constituent of the cell with which a drug interacts to produce its pharmacological effects. Drug – Drug + Altered Receptor Receptor Function Complex  Additional Notes Many drugs are acids or amines, easily ionized at physiological pH, and able to form ionic bonds by the attraction of opposite charges in the receptor site, for example the ionic interaction between the protonated amino group on salbutamol or the quaternary ammonium on acetylcholine and the dissociated carboxylic acid group of its receptor site. Similarly, the dissociated carboxylic group on the drug can bind with amino groups on the receptor. Ion–dipole and dipole–dipole bonds have similar interactions, but are more complicated and are weaker than ionic bonds. Polar–polar interaction, e.g. hydrogen bonding, is also an important binding force in drug– receptor interaction, because the drug–receptor interaction is basically an exchange of the hydrogen bond between a drug molecule, surrounding water and the receptor site. Formation of hydrophobic bonds between nonpolar hydrocarbon groups on the drug and those in the receptor site is also common. Although these bonds are not very specific, the interactions take place to exclude water molecules. Repulsive forces that decrease the stability of the drug–receptor interaction include repulsion of like charges and steric hindrance. The Mole Concept  Proportional Relationships Stoichiometry mass relationships between substances in a chemical reaction based on the mole ratio Mole Ratio indicated by coefficients in a balanced equation. 2 Mg + O2 2 MgO  The Mole The mole (mol) is a unit of measure for an amount of a chemical substance. A mole is Avogadroʼs number of particles, which is 6.02 x 1023 particles. 1 mol = Avogadroʼs number = 6.02 x 1023 units We can use the mole relationship to convert between the number of particles and the mass of a substance. Chapter 9 30  Mole Calculations 1. How many sodium atoms are in 0.120 mol Na? 6.02 x 1023 atoms Na 0.120 mol Na x = 7.22 x 1022 atoms Na 1 mol Na 2. How many moles of potassium are in 1.25 x 1021 atoms K? 1 mol K 1.25 x 1021 atoms K x = 2.08 x 10-3 mol K 6.02 x 1023 atoms K Chapter 9  Molar Mass The atomic mass of any substance expressed in grams is the molar mass of that substance. Eg: The atomic mass of iron (Fe) is 55.85 amu. Therefore, the molar mass of iron is 55.85 g/mol. Since oxygen occurs naturally as a diatomic, O2, the molar mass of oxygen gas is two times 16.00 g or 32.00 g/mol. Chapter 9 32 Calculation Calculate the number of moles in 1.4g of ibuprofen and mefenamic acid. To summarize…  Percent Composition The percent composition of a compound lists the mass percent of each element. For example, the percent composition of water, H2O is 11% hydrogen and 89% oxygen. All water contains 11% hydrogen and 89% oxygen by mass. Chapter 9 36 Calculating Percent Composition Find the percent composition of water by comparing the masses of hydrogen and oxygen in water to the molar mass of water. H2O 2.02 g H x 100% = 11.2% H 18.02 g H2O 16.00 g O x 100% = 88.79% O 18.02 g H2O Chapter 9 37  Working between weights and molarity Weights are much easier to appreciate than molar concentrations but sometimes, particularly in bioanalytical methods, molar concentrations are used. Definitions Molar: molecular weight in g/l (mg/ml) mMolar: molecular weight in mg/l (µg/ml) µMolar: molecular weight in µg/l (ng/ml) nMolar: molecular weight in ng/l (pg/ml) 38  Solution & Dilution Volume per volume, % (v/v) Weight per volume, g/ml or % (w/v) Percent weight-in-weight (w/w) Sample or stock solution preparation - dilution Cundiluted. Vundiluted = Cdiluted. Vdiluted *Volatile liquid – always cap the flask as soon as possible 39 Pharmacist Knowledge of drug composition, modes of action, and possible harmful interactions with other substances allows a pharmacist to counsel patients on their care. Pharmacists also mix chemicals to form powders, tablets, ointments, and solutions. CHEMICAL EQUATION  Chemical Equations Reactants – the substances that exist before a chemical change (or reaction) takes place. Products – the new substance(s) that are formed during the chemical changes. CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS  PRODUCTS  Anatomy of a Chemical Equation CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)  Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product Determine whether the following equation is balanced. 2 Na + 2 H2O  2 NaOH + H2  Limiting Reactants The limiting reactant is the reactant present in the smallest stoichiometric amount.  Limiting Reactants 3 Br2 (l) + 2 Al (s) → Al2Br6 (s) excess limiting Given the amounts below  In other words, it’s the reactant you’ll run out of first (*in this case, the Al) 45  Example Calculation Involving a Limiting Reactant Suppose that 1.00 g of sodium and 1.00 g of chlorine react to form sodium chloride (NaCl). Which of these is limiting, and what is the mass of the product?  Example Calculation Involving a Limiting Reactant Suppose that 1.00 g of sodium and 1.00 g of chlorine react to form sodium chloride (NaCl). Which of these is limiting, and what is the mass of product. 2 Na + Cl2 → 2 NaCl nNa = 1.00 g x (1 mol Na / 23.0 g Na) = 0.0435 mol Na nCl2 = 1.00 g × (1 mol / 70.9 g Cl2) = 0.0141 mol Cl2 nNa/2 = 0.022 (normalized) nCl2/1 = 0.0141 (normalized)  Cl2 is the limiting reagent 1 mol Cl2  2 mol NaCl 0.0141 mol Cl2  0.0141 mol x 2 = 0.0282 mol NaCl  Mass of product (NaCl) = 0.0282 mol NaCl x 58.44 g/mol = 1.6480 g of NaCl 47  Theoretical Yield The theoretical yield is the amount of product that can be made  In other words it’s the amount of product possible as calculated through the stoichiometry problem This is different from the actual yield, the amount one actually produces and measures Percentage Yield A comparison of the amount actually obtained to the amount it was possible to make Actual Yield Percent Yield (%) = x 100 Theoretical Yield THANK YOU FOR YOUR ATTENTION 49