ACIDS AND BASES IN CHEMISTRY

ACIDS AND BASES IN CHEMISTRY - Transcript

CHAPTER 20 ACID BASE THEORIES

Properties of acids and bases Your body needs both acids and bases to function properly Maintaining proper pH value throughout your body system is critical to good health Acids give food a tartness Bases bitter Aqueous solutions of acids and bases are electrolytes An electrolyte is a solution that conducts electricity Both acid and bases can be detected by a color change using certain chemical dyes These dyes are called indicators An acid reacts with compounds containing hydroxide ions to form water and salt A base reacts with an acid to form water and

Why do we need to be able to conduct electricity in our bodies Send messages to the brain for both voluntary and involuntary muscle movements for example Important muscle heart Just to name a few

Acid An acid is a compound that produces hydrogen ions when dissolved in water Therefore the chemical formulas of acids are of the general form HX X representing a monatomic or polyatomic anion Rules for assigning names to acids 1 when the name ends in ide the acids name begins with hydro the stem of the anion has the suffix ic and is followed by the word acid Example HCl Xchloride chloride Name hydrochloric acid Example 2 H2S X sulfide hydrosulfuric acid

2 when the anion name ends in ite the acid name has the stem name of ous Example H2SO4 sulfurous acid 3 anion ending in ate the stem of the acid is given ic Example HNO3 nitric acid

Identify each property as applying it to an acid base or both A bitter taste Base B electrolyte Both C indicator color change Both Sour taste acid

Name each acid or base A HF Hydrofluoric acid B HClO3 Chloric acid H2CO3 Carbonic acid Al OH 3 hint begin with the word aluminum Aluminum hydroxide

Now write the formula for the following Barium hydroxide Ba OH 2 Hydrobromic acid HBr Rubidium hydroxide RbOH Hydroselenic acid Se is for selenium row 6A H2Se

HYDROGEN IONS FROM WATER Collisions between water molecules can occur that result with enough energy to transfer a hydrogen ion to another water molecule The result is the formation of a hydroxide ion OH and hydronium ion H3O The hydronium ion has been given a few different names 1 Hydrogen ions 2 Hydronium ions 3 solvated protons this is because hydrogen with a loss of its only electron is left with just a proton

Self ionization of water is the process of converting a molecule of water to either of these resulting ions In pure water although there are two different ions present they balance each other out and the pH value for pure water is 7 Another name given to this situation is Neutral solution H and OH are interdependent Meaning when OH increases H decreases and vise versa Le Chatlier s principle named for the French chemist who proposed the concept states that when there is a shift in a equilibrium due to a stress brought on by a change in temperature

If additional ions are introduced to an aqueous environment either H or OH there is a shift and depending on which is added the other decreases When possible more water molecules will form to neutralize the solution In a neutral aqueous solution the product of H X OH 1 0 X 10 14 this is called the ion product constant of water or K w When the environment can not neutralize with the addition of either ion then a basic alkaline or acidic situation occurs

To determine OH content or H content you can manipulate the formula as such Kw H OH Example If H in a solution is 1 0 X 10 5 M is the solution acidic basic or neutral pH 5 and it is acidic What is the OH of this solution OH 1 0 X 10 14 1 0 X 10 9 1 0 OH X 10 5 The exponent tells you the OH is 9 The pH will then be 14 9 5

Acid Base theories 1 Arrhenius defined acids as hydrogencontaining compounds that ionize to yield hydrogen ions in aqueous solutions and bases as are compounds that yield hydroxide ions in aqueous solutions This theory works well to explain HCl converting to H and Cl in aqueous solution as well as Na H2O yielding NaOH H2 but is limited for other types of bases such as NH 3 that don t contain OH ions Common acids Monoprotic 1 ionizable hydrogen Diprotic 2 ionizable hydrogens

2 Bronsted Lowry Acids and Bases is a bit broader in its definition Named after the two chemists who independently came up with the definition This theory defines acids as a hydrogen ion donor and bases as a hydrogenion acceptor Behavior of ammonia as a base is defined by this theory but not covered in the Arrhenius theory Ammonia when dissolved in water acts as a base because it becomes a hydrogen acceptor from water Water the hydrogen ion donor is the acid

When ammonia is dissolved in water the resulting NH4 is referred to as a conjugate acid by definition a conjugate acid is a particle formed when a base gains a hydrogen ion A conjugate base is the particle that remains after it donates a hydrogen ion NH3 H2O NH4 OH NH3 is the base water the acid and NH4 is the conjugate acid and OH the conjugate base

3 A third theory is more general than either of the previously mentioned A Lewis acid is defined as a substance that can accept a pair of electrons to form a covalent bond A Lewis base is a substance that can donate a pair of electrons to form a covalent bond H OH H2O H is the Lewis acid and OH is the Lewis base