Medical Chemistry Lecture 1 PDF

University of Sumo College of Dentistry First Stage Medical Chemistry First Lecture Acid, Base and Salts Before discussing the topic of acids and bases, we must give a brief idea about chemistry and its branches Chemistry: is a science that studies the matter and its properties....

University of Sumo College of Dentistry First Stage Medical Chemistry First Lecture Acid, Base and Salts Before discussing the topic of acids and bases, we must give a brief idea about chemistry and its branches Chemistry: is a science that studies the matter and its properties. There are five main branches of chemistry: Organic Chemistry: Organic Chemistry is one of the most important branches of chemistry that studies chemical compounds containing carbon elements combined with ‘carbon-hydrogen’ bonds (hydrocarbons such as CH4) Inorganic Chemistry: studies the structure, properties and reactions of noncarbon chemical compounds or those that do not contain carbon- hydrogen bonds. Example,NaCl. Analytical Chemistry: is one of the quantitative branches of Chemistry that deals with the ‘identification, separation and quantification’ of chemical substances. ‫تشخيص وفصل وتقدير كمية المواد الكيميائية‬ The knowledge of Analytical Chemistry enables chemists and scientists to determine the amount of chemical substances in a given material. The subject has been further classified into:  Qualitative Analysis: It involves processes that are carried out to identify a chemical substance in a given sample.  Quantitative Analysis. It involves finding out the concentration or amount of the substance in the given sample. Physical Chemistry Physical Chemistry covers the ‘physical properties’ of chemical compounds using law and various concepts of Physics, such as motion, energy, force, time, statistical mechanics, quantum chemistry and thermodynamics. Biochemistry Known to be one of the most important branches of Chemistry, Biochemistry studies the biological structure, composition and chemical reactions at the cellular and molecular level. This covers a range of living organisms such as plants, insects, viruses, microorganisms, etc ‫ حُث تدرس التركُب البُىلىجٍ والتركُب‬،‫تُعرف الكُمُبء الحُىَة بأنهب أحد أهم فروع الكُمُبء‬ ‫ وَشمل ذلك مجمىعة من الكبئنبت الحُة مثل‬.ٍ‫والتفبعالت الكُمُبئُة علً المستىي الخلىٌ والجزَئ‬ ‫النببتبت والحشرات والفُروسبت والكبئنبت الحُة الدقُقة ومب إلً ذلك‬  History of Acids and Bases In the early days of chemistry chemists were organizing physical and chemical properties of substances. They discovered that many substances could be placed in two different property categories: Substance A Substance B 1. Sour taste ‫طعم حامض‬ 1. Bitter taste ‫طعم مر‬ 2. Reacts with carbonates to make 2. Reacts with fats to make soaps CO2 3. Do not react with metals 3. Reacts with metals to produce H2 4. Turns red litmus blue 4. Turns blue litmus pink 5. Reacts with A substances make 5. Reacts with B substances to make salt and water salt and water The definition of acid and base has changed according to different theories as follow:  Arrhenius Theory Arrhenius proposed the first definition of acids and bases. (Substances A and B became known as acids and bases) Acids: are substances that dissociate in water to produce H+ ions bases are substances that dissociate in water to produce OH- ions NaOH (aq) Na+ (aq) + OH- (aq) Base HCl (aq) H+ (aq) + Cl- (aq) Acid  Bronsted Lowry Theory Johannes Brønsted and Thomas Lowry revised Arrhenius’s acid-base theory to include other solvents besides water. They defined acids and bases as follows: An acid is a hydrogen containing species that donates a proton. A base is any substance that accepts a proton” HCl (aq) + H2O (l) Cl- (aq) + H3O+ (aq) In the above example, what is the Brønsted acid? what is the Brønsted base?  the reaction of HCl with H2O is an equilibrium and occurs in both directions, although in this case the equilibrium lies far to the right. HCl (aq) + H2O (l) Cl - ( aq) + H3O+ (aq) For the reverse reaction Cl - behaves as a Brønsted base and H3O+ behaves as a Brønsted acid. The Cl- is called the conjugate base of HCl. Brønsted acids and bases always exist as conjugate acid-base pairs. Their formulas differ by only one proton. Conjugate Pairs Strong acids ionize completely while weak ones do not! A single arrow is used to represent the ionization of strong acids. HCl (g) H+ (aq) + Cl - (aq) double arrows are used to represent ionization of weak acids because an equilibrium is created. HF (g) H+ (aq) + F – (aq)  Common Strong Acids and Bases There are two basic types of acids: organic and inorganic organic acids are generally not as strong as inorganic acids. The main difference between the two is the presence of carbon in the compound; inorganic acids do not contain carbon.  Autoionization of Water In pure water molecules behave as both an acid and base It is called amphoteric meaning it will act as either an acid or a base depending on the situation. H2O (l) + H2O (l) H3O+ (aq) + OH- (aq) For pure water [OH-] = [H+] Kw is called ionization constant of water and is very small. As with all Kw values, it is temperature dependent. Kw = 1.0 x 10 -14 at 25oC, Kw = [H+][OH-] Kw =(1 x 10-7 )(1 x10-7 ) This only means that the neutral value for pH is getting lower, it does not mean that the solution is becoming more acidic as the temperature increase We define an aqueous solution as being neutral when the [H+] = [OH-] acidic when [H+] > [OH-] basic when [H+] < [OH-] [H+] = 0.0000001 = 10-7 By just describing the power called the POWER of H, pH = 7 Lewis' theory: used electrons instead of proton transfer and specifically stated that an acid is a species that accepts an electron pair while a base donates an electron pair. The reaction of a Lewis acid and a Lewis base produces a coordinate covalent bond. 4-Element Has 6 electron in outer shell: Example S element in SF4  Summary of Acid-Base Definitions Type Acid Base Arrhenius H+ ions in solution OH- Ions in solution Bronsted-Lowry H+ donor H+ acceptor Lewis Electron-pair Electron-pair donor acceptor