Lecture 9b: Acid and Bases Chemistry – FALL 2016 Course lecturer : Jasmin Šutković 15th Dec 2016

Acids: Acid-Base Reactions Ionize in H2O, causes increase in H+ ions. H+ ions are bare protons. Acids are proton donor Reacts with some metals to produce H2 Dissolves carbonate salts, releasing CO2 Acids that can only yield one H+ per molecule upon ionization. HCl  H+ + Cl-

IONIZATION Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or ions.

What mean actually strong and weak acid/base? The terms "strong" and "weak" do NOT refer to the concentration of the acid or base, but instead, refer to whether the acid or base dissociates completely in water.

Examples of strong acids For strong acids, try to remember them, there are 6 : Strong acids: HCl Hydrogen chloride HBr Hydrogen bromide HI Hydrogen iodide HClO4 Perochloric acid HNO3 Nitric acid H2SO4 Sulfuric acid

Bases Bases: Substances that increase the OH- when added to water. (NaOH) Strong bases: Any groups in 1A or 2A elements with OH elements with O2 elements and NH2

Definitions of Acids and Bases  Brønsted – Lowry definition of acids and bases – A more general definition of acids and bases – An acid is any substance that can donate a proton. – A base is any substance that can accept a proton. – Not restricted to aqueous solutions

Acids differ in the number of hydrogen ions they can donate. Polyprotic Acids Acids differ in the number of hydrogen ions they can donate. – Monoprotic acids are compounds capable of donating a single proton per molecule. – Polyprotic acids can donate more than one hydrogen ion per molecule.

Strengths of Acids and Bases Strong acids react essentially completely with water to give H+ and the corresponding anion. Strong bases dissociate essentially completely in water to give OH– and the corresponding cation. Both strong acids and strong bases are strong electrolytes.

Some Properties of Acids and Bases Acid Properties Sour taste Turn blue litmus red pH < 7 Base properties Bitter taste Turns red litmus blue pH >7 slippery

The Hydronium Ion When a strong acid dissolves in water, the proton that is released is transferred to a water molecule that acts as a proton acceptor or base, the Resulting molecule is H3O+ ion is called the hydronium ion. Substances that can behave as both an acid and a base are said to be amphoteric.

An acid reacts with a metal hydroxide to form a salt plus water. Neutralization reactions Acid + Base Neutralization HBr(aq) + NaOH(aq) H2O(l) + NaBr(aq) Products of a neutralization reaction have none of the properties of an acid or a base. An acid reacts with a metal hydroxide to form a salt plus water.

Neutralization reactions cont.. A reaction in which an acid and a base react to produce water and a salt Strengths of the acid and base determine whether the reaction goes to completion 1. Reactions that go to completion a. Reaction of any strong acid with any strong base b. Reaction of a strong acid with a weak base c. Reaction of weak acid with a weak base 2. Reaction that does not go to completion is a reaction of a weak acid or a weak base with water

The pH Scale It is one of the main factors that affects the chemical reaction that occur in dilute solutions . It is a convenient way to express the hydrogen ION (H+) concentration of a solution and enables as to understand if a solution is an acid or base!!

Example with pure liquid water Pure liquid water contains low but measurable concentrations of H3O+ and OH- ions produced via auto-ionization reaction in which water acts in the same time as an acid and a base . H2O (aq) + H2O (l) H3O+ (aq) + OH- (aq)

The pH scale pH is defined as the negative base-10 logarithm of the hydrogen ion concentration pH = – log [H+] or [H+] = 10-pH Hydrogen ion concentration in pure water is 1 x 10-7 M at 25ºC; the pH of pure water is – log [1.0 x 10-7] = 7.00. pH decreases with increasing [H+] — adding an acid to pure water increases the hydrogen ion concentration and decreases the hydroxide ion concentration. Adding a base to pure water increases the hydroxide ion concentration and decreases the hydrogen ion concentration—pH increases with decreasing [H+].

Lecture 10: Hydrocarbons Chemistry – FALL 2016 Course lecturer : Jasmin Šutković 15th Dec 2016

Contents Alkanes Properties of Alkanes Alkenes and Alkynes International University of Sarajevo Alkanes Properties of Alkanes Alkenes and Alkynes Naming of hydrocarbons Cis-Trans isomers Aromatic compounds

Organic compounds Organic compounds is the study of carbon containing molecules. Organic compounds ALWAYS contain carbon and hydrogen. We found Organic compounds everywhere around: common products we use (gasoline, medicine, shampoos, plastics etc), in food we eat (carbohydrates, fats and proteins)

Bonding in Organic compounds Hydrocarbon: compound made of carbon and hydrogen Hydrocarbon is saturated where all bonds in the molecule all single bonds CH4

Alkanes The simples hydrocarbons are alkanes, having only single bonds (C-C) like CH4, C2H6, C3H8 etc.. The alkanes ethane, propane, and butane contain two, three, and four carbon atoms, respectively, connected in a row or a continuous chain. As we can see, the names for alkanes end in ane. Such names are part of the IUPAC (International Union of Pure and Applied Chemistry) system used by chemists to name organic compounds.

IUPAC names of Alkanes

Molecular and Structural formulas

Drawing of structural formulas Page 365, example 11.2 Pentane

Butane

Cyclic or ring structures of alkanes are called cycloalkanes The simplest is cyclopropane

Alkanes with substituent's When an alkane has four or more carbon atoms, the atoms can be arranged so that a side group called a branch or substituent is attached to a carbon chain.

Examples

Naming

Haloalkanes

Properties of Alkanes They make up: different types of fuels and mineral oils and their usage is supported by their physical properties (density and solubility) The first four alkanes—methane, ethane, propane, and butane—are gases at room temperature and are widely used as heating fuels. Alkanes having five to eight carbon atoms, pentane, hexane, heptane, and octane, are liquids at room temperature. They are highly volatile, which makes them useful in fuels such as gasoline

Alkenes and Alkynes Alkenes are hydrocarbons that contain one or more carbon-to-carbon double bonds (C=C). Double bonds are very reactive, they easily add hydrogen atoms (hydrogenation) or water (hydration) to the carbon atoms in the double bond. Example ethylene (ethene) C2H4

Example : Ethene (Acetylene)

Naming

Cis and Trans isomerism In any alkene, the double bond is rigid, which means there is no rotation around the double bond. As a result, the atoms or groups are attached to the carbon atoms in the double bond on one side or the other, which gives two different structures called geometric isomers or cis – trans isomers.

Example

Cis–Trans Isomers for Night Vision The retinas of the eyes consist of two types of cells: rods and cones. The rods on the edge of the retina allow us to see in dim light, and the cones, in the center, produce our vision in bright light. In the rods, there is a substance called rhodopsin that absorbs light. Rhodopsin is composed of cis-11-retinal, an unsaturated compound, attached to a protein. When rhodopsin absorbs light, the cis-11-retinal isomer is converted to its trans isomer, which changes its shape. The change from the cis to trans isomer and its separation from the protein generate an electrical signal that the brain converts into an image.

Addition reactions The most characteristic reaction of alkenes is the addition of atoms or groups of atoms to the carbon atoms in a double bond. Addition occurs because double bonds are easily broken, providing electrons to form new single bonds. The addition reactions have different names that depend on the type of reactant we add to the alkene, as Table 11.7 shows.

Hydrogenation In a reaction called hydrogenation, H atoms add to each of the carbon atoms in a double bond of an alkene. During hydrogenation, the double bonds are converted to single bonds in alkanes. A catalyst such as finely divided platinum (Pt) nickel (Ni), or palladium (Pd) is used to speed up the reaction. The general equation for hydrogenation can be written as follows:

Examples:

In hydration, an alkene reacts with water (H-OH). A hydrogen atom (H-) from water forms a bond with one carbon atom in the double bond, and the oxygen atom in (-OH) forms a bond with the other carbon. The reaction is catalyzed by a strong acid such as H2SO4. Hydration is used to prepare alcohols, which have the hydroxyl (-OH) functional group.

Examples

Aromatic Compounds Benzen – C6H6,1825 isolated by Michael Faraday Because many compounds containing benzene have fragrant odors, the family of benzene compounds became known as aromatic compounds.