Acids & Bases 2023 PDF

prepared by: Ellen O. Mercado, MS The theory of acids and bases has changed over time due to research and experimentation. Arrhenius Acids and Bases - oldest Brønsted-Lowry Acids and Bases - newer Lewis Acids and Bases - newest Ellen Mer...

prepared by: Ellen O. Mercado, MS The theory of acids and bases has changed over time due to research and experimentation. Arrhenius Acids and Bases - oldest Brønsted-Lowry Acids and Bases - newer Lewis Acids and Bases - newest Ellen Mercado  Arrhenius and Svante Arrhenius: the first useful definition in 1884 Nobel Prize for Chemistry in 1903 Acid is a substance that dissolves in water to produce H+ Base dissolves in water to produce OH ions (OH-) Today we know that a H+ does not exist in water because it reacts immediately with H2O molecule to give H3O+. H+ + H 2 O H 3 O+ Ellen Mercado Ellen Mercado Arrhenius Base: a compound that increases OH- in water Ellen Mercado Ellen Mercado  A broader definition than Arrhenius Acid is H+ or proton donor Base is H+ acceptor Acids and bases always come in pairs When HCl dissolves in water, it gives proton to water. HCl + H2O ↔ H3O+ + Cl- Ellen Mercado Neutralization of an acid by a base is a proton-transfer reaction in which the acid is transformed into its conjugate base, and the base is transformed into its conjugate acid. Ellen Mercado Conjugate acid results from a base that acquires a proton or H+ from an acid it is a base with a hydrogen ion added to it Conjugate base what is left over after an acid donated a proton during a chem’l reaction or a species formed after acid lost its protons a species formed by the removal of a proton from an acid Summary: Acid + Base ⇌ Conjugate Base + Conjugate Acid Ellen Mercado  Lewis Acid: electron-pair acceptor = electrophile = a species that forms a new covalent bond by accepting a pair of electrons during reaction Lewis Base: electron-pair donor = nucleophile = a species that forms a new covalent bond by donating a pair of electrons Ellen Mercado A Lewis Base (B) donates it electrons to a Lewis Acid (A) resulting in a coordinate covalently bonded compound, also known as an adduct.  The reaction of a Lewis acid and a Lewis base will produce a coordinate covalent bond.  Coordinate covalent bond: a type of covalent bond in which one reactant gives it electron pair to another reactant.  Lewis base donates its electrons to the Lewis acid. When they do react this way the resulting product is called an addition compound, or an adduct. Ellen Mercado Lewis Acids  acid that accepts an electron pair  electrophilic (electrophile): they are electron attracting  All metal cations are Lewis acids: they’re able to accept electrons Examples: Cu2+ Fe2+ Fe3+  Lone-pair acceptors: atom, ion, or molecule with an incomplete octet of electrons can act as Lewis acid Examples: AlCl3 BF3 AlF3  Molecules where the central atom can have more than 8 valence shell electrons can be electron acceptors, and thus are classified as Lewis acids. Examples: SiBr4 SiF4  Molecules that have multiple bonds between two atoms of different electronegativities. Examples: CO2 SO2 Ellen Mercado Ellen Mercado  AlCl4- Tetrachloroaluminate Ellen Mercado Ellen Mercado Ellen Mercado Ellen Mercado  ELECTROPHILE NUCLEOPHILE Positively charged or neutral, but Negatively charged or neutral, but electron deficient atom or group electron rich atom or group of of atoms atoms Neutral but electron deficient Neutral but electron rich species: species: BF3 AlCl3 FeCl3 H2O NH3 RNH2 ROH Positively charged species: Negatively charged species: H+ (hydrogen ion/proton) Cl- (chloride ion) H3O+ (hydronium ion) Br- (bromide ion) +CH (carbonium ion) 3 CN- (cyanide ion) + Br (bromonium ion) I- (iodide ion) Cl+ (chloronium ion) OH- (hydroxide ion) NH4+ (ammonium ion), etc. NO2- (nitrite ion), etc. Ellen Mercado How do we measure the strength of a base? Strong base: when all molecules of a base break apart or completely dissociates in water to give off plenty of OH- Weak base: when only few basic molecules dissociate in water and give off much less OH- Ellen Mercado Ellen Mercado  Strong Acid vs Weak Acid strong acid: when all the molecules of an acid break apart weak acid: when few molecules of an acid break apart Ellen Mercado Ellen Mercado  pH less than 7 taste sour change the color of indicators >> blue litmus turns red/pink neutralize bases + form H in aqueous solution corrosive >> react with most metals and carbonates to form H2 good conductors of electricity Ellen Mercado  HCl - Hydrochloric acid - stomach acid - commercially sold as Muriatic acid H2SO4 - Sulfuric acid - car batteries HNO3 - Nitric acid - explosives HC2H3O2 - Acetic acid - vinegar H2CO3 - Carbonic acid – sodas H3PO4 - Phosphoric acid –flavorings H3C6H5O7 - Citric acid – citrus fruits Ellen Mercado Ellen Mercado  taste bitter give slippery feel contain Hydroxide ions (OH-) can burn skin as badly as strong acids react with acid to form salt and water turn red/pink litmus paper blue Strong Bases Ellen Mercado  Acids Bases Taste sour Taste bitter No slippery feel Have slippery feel pH < 7 pH > 7 Release H+ in aqueous solution Release OH- in aqueous solution Corrode metals Do not corrode metals React with metals to produce a Do not react with metals compound and hydrogen gas turn blue litmus paper into pink Turn pink litmus paper into blue Ellen Mercado  A chemical reaction between an acid and a base to produce a salt (an ionic compound) and water Ellen Mercado  Ethanoic + Sodium Sodium acetate + water acid hydroxide Ellen Mercado Ellen Mercado  acids and bases neutralize each other antacid tablet neutralizes gastric hyperacidity Parietal cells in the mucosa, the inner cell layer of human digestive tract, secrete HCl into the stomach's lumen. The solution in the lumen may have a pH of 1 or less - 10 times more acidic as pure lemon juice. Ellen Mercado  Sal ammoniac Salt Formula Common Name Sodium chloride NaCl table salt Sodium nitrate NaNO3 Chile saltpeter Sodium bicarbonate NaHCO3 baking soda Potassium carbonate K2CO3 Carbonate of Potash Ammonium chloride NH4Cl Sal ammoniac Ellen Mercado pH power of Hydrogen; commonly used to represent H+ activity in logarithmic scale At pH 7 = H+ and OH- activities are equal A change on the pH scale by 1 pH unit indicates that the H+ activity differs by a factor of 10 (tenfold). Example: >> H+ activity at pH 4 is 10 times greater than at pH 5 >> A difference of 2 pH units, for example from 6 to 4, means that the acidity of pH 4 is 100 times greater than pH 5. Ellen Mercado Ellen Mercado The relationship between OH- , H+ , and pH Ellen Mercado pH Values of Some Common Materials Ellen Mercado  Importance of pH 1. pH and the body Substances in the body have different pH values. Acidic conditions in the stomach (pH ~1.5) and alkaline conditions in the small intestine (pH ~8.4) are needed for good digestion. Slightly acidic condition in the blood (pH ~6.5) that goes to the heart and lungs is due to CO2 in the blood. 2. pH and food preservation Many fresh food quickly go bad mainly due to microorganisms such as bacteria present in food. Acids can be used to preserve food because microorganisms cannot grow well in solutions of quite low pH. Ellen Mercado  How to “measure” pH? Acid-Base Indicators are compounds that will change color in the presence of an acid or base Several acid-base indicators exist, each producing a color change at a specific pH level. Litmus is a plant extract that can be blue or red/pink It turns red/pink in an acidic solution It turns blue in a basic/alkaline solution ACID BASE RED BLUE Ellen Mercado  Some Acid-Base Indicators ***Note that some indicators have 2 color changes Color Variation in Hydrangeas Soil pH indirectly changes flower color. When the soil is acidic (pH below 7), aluminum can be dissolved in water supply making it more available to the roots, resulting in blue flowers. If aluminum is present in small quantities, the color is variable strongly acidic soil (below pH6) blue flowers between pink and blue. If aluminum alkaline soil (pH above 7) pink flowers is absent, the flowers are pink. Ellen Mercado Ellen Mercado Ellen Mercado  An even more precise way of determining pH is the use a pH meter - measures small voltages in solution - calibrated to convert voltages into pH Ellen Mercado Ellen Mercado