<p>300 Chemistry Acids and Bases </p><p>Intro to Acids and Bases </p><p>Definitions: </p><p>Acids… Bases… Have a low pH Have a high pH Taste sour Taste bitter React with metals to produce a salt and --- hydrogen gas React with bases to produce a salt and React with acids to produce a salt and water (neutralization reaction) water (neutralization reaction) Are electrolytes, conduct electricity Are electrolytes, conduct electricity Turn blue litmus paper red Turn red litmus paper blue --- Feel slippery </p><p>Different scientists have come up with a number of definitions regarding acids and bases due to the observation they made in their research. We will study the following: Arrhenius and Bronstead-Lowery Theories. ======Arrhenius Theory Around 1884, a Swedish scientist, Svante Arrhenius developed the theory that acids, when placed in water, acids form H+1ions and bases form OH-1 ions. This was the first modern definition of acids and bases and he won the Nobel Prize for it in 1903.</p><p>Arrhenius Acid = a substance that produces H+ ions in aqueous solution - Ex: HCl → H+1 + Cl 1 Note: Remember, a hydrogen atom only contains one electron and one proton and NO neutrons in its nucleus. As a result, when it forms and H+1 ion, it loses its only electron, and all that is left is the proton in the nucleus. As result, +1 H is called a “proton” as well as a “hydrogen ion.” A monoprotic (mono = 1) acid only has 1 acidic proton (H+); a diprotic (di = 2) has 2… etc. </p><p>Arrhenius Base = a substance that produces OH-1 ions in aqueous solution -1 Ex: NaOH → Na+1 + OH</p><p>Svante Arrhenius ======Bronsted-Lowry Theory</p><p>The Bronsted-Lowry definition is named for Johannes Bronsted and Thomas Lowry, who independently proposed it in 1923. A Bronsted-Lowry (BL) acid is defined as any substance that can donate a hydrogen ion (proton) and a Bronsted-Lowry base is any substance that can accept a hydrogen ion (proton). Thus, according to the BL definition, acids and bases must come in what is called conjugate pairs. (http://www.nyu.edu/classes/tuckerman/honors.chem/lectures/lecture_21/node3.html)</p><p>BL Acid = proton (H+) donor </p><p>BL Base = proton (H+) acceptor </p><p>Conjugate acid = what the base becomes after it accepts a proton Conjugate base = what the acid becomes after it donates a proton </p><p>+1 -1 Ex: NH3 + H2O → NH4 + OH </p><p>Ammonia is the Bronsted-Lowry base (it will accept a proton) Water is the Bronsted-Lowry acid (it will donate a proton) Ammonium ion is the conjugate acid of ammonia (it has accepted a proton) Hydroxide ion is the conjugate base of water (it has donated a proton) </p><p>Great link for further reading and many examples: http://www.mpcfaculty.net/mark_bishop/Bronsted_Lowry.pdf Fun website – easier to understand: http://www.blobs.org/science/article.php?article=3</p><p>======What are considered acids and bases?</p><p>Acids The six strong acids are: HCl (hydrochloric), HBr (hydrobromic), HI (hydroiodic), HNO3 (nitric), H2SO4 (sulfuric), and HClO4 (perchloric) Remember: Strong acids and bases are strong electrolytes, weak acids and bases are weak electrolytes (can break into ions and carry electric current. No ions = no current!) If a substance is not one of the strong acid listed above, it’s a weak acid! The weak acids are: HF (hydrofluoric), HC2H3O2 (acetic), H2CO3 (carbonic), and H3PO4 (phosphoric) </p><p>------</p><p>Bases The strong bases are: any alkali metal hydroxides (LiOH, NaOH, KOH, RbOH, etc.), Ca(OH)2 (calcium hydroxide), Ba(OH)2 (barium hydroxide), and Sr(OH)2 (strontium hydroxide) If a substance is not a strong base, it’s a weak base! The most common weak one you’ll see if NH3 (ammonia) What is pH? pH (potential of hydrogen – or – how much hydrogen is in a substance) is very important biologically (pH of blood, pH of the ocean or lakes, pH of rain, etc). It is a measure of acidity (how much H+1) and basicity (how much OH-1) there is in a water solution. </p><p>If: pH = 7 the solution is neutral pH > 7 the solution is basic pH < 7 the solution is acidic</p><p>If we use Universal Paper to determine pH, the following colors will appear:</p><p>If litmus paper is used:</p><p>Red litmus: Base: turns paper blue Acid: paper stays red (looks wet)</p><p>Blue litmus: Base: paper stays blue (looks wet) Acid: paper turns red Determining pH For strong acids and bases, it is easy to determine their strength, using pH For weak acids and bases, it is a bit more complex to determine their strength and pH (we’re not going to worry about those) </p><p>Acid and Base Strength for Strong Acids and Bases Strong acids and bases dissociate 100% (equilibrium position is far to the right, reaction goes nearly completely to the products (ions)) </p><p>For all aqueous solutions water also dissociates a little: H2O ↔ H+1 + OH-1 We can write Keq = Kw = [H+1] x [OH-1] = 1.0 x 10-14 [It sounds strange… but this means even in a basic solution, there are hydrogen ions, and even in an acidic solution, there are hydroxide ions… they come from the water] pH below 7 indicates an acidic solution ([H+1] > [OH-1]) pH of 7 indicates a neutral solution (not an acid or a base) ([H+1] = [OH-1] = 1.0x10-7) pH above 7 indicates a basic (alkaline) solution ([OH-1] > [H+1]) </p><p>Neutralization In a neutralization reaction, an acid and base react to produce some salt and water… at what is called the “equivalence point”, we can say that: Moles of H+ = Moles of OH- For a monoprotic acid and a base with one hydroxide, use the following equation: Ma x Va = Mb x Vb </p><p>Titrations and Indicators Titration = a process used to determine the amount (concentration) of acid or base in a solution Indicator = a substance that marks the equivalence point of a titration (or identifies a pH range) by changing color Common indicators: litmus paper (red in acid, blue in base), phenolphthalein (clear in acid, pink in base), and universal indicator (a rainbow of colors depending on the pH) pH meter = device used to make rapid, accurate pH measurements Titration curve = a graph used to show how the pH of the unknown solution changes as various amounts of titrant are added How they are used: -A solution of known concentration (the titrant) is delivered from a buret into an unknown solution containing an indicator -At the endpoint of the titration, when the unknown substance is just consumed, the stoichiometric (equivalence) point is reached, and the indicator changes color -Then, the amount of titrant added can be used to determine the concentration of the unknown</p>