Chapter 8- Acids, Bases, & salts

HCl + H2O  H3O+ + Cl– Definitions Acids Ionize to form hydronium ions (H3O+) in water (Arrhenius) Donates a proton to the base (Bronsted) Accepts a pair of electrons from base (Lewis) HCl + H2O  H3O+ + Cl–

NH3 + H2O  NH4+ + OH- Definitions Bases Dissociate or ionize to form hydroxide ions (OH-) in water (Arrhenius) Accepts a proton from acid (Bronsted) Donates pair of electrons to acid (Lewis) NH3 + H2O  NH4+ + OH-

Definitions Indicator substance that changes color in an acid or base Examples: litmus - red/blue phenolphthalein - colorless/pink goldenrod - yellow/red red cabbage juice - pink/green

Properties BASES ACIDS bitter taste corrosive electrolytes sour taste corrosive Electrolytes (solns that conduct electricity when dissolved in water) turn blue litmus paper red react with metals to form H2 gas pH below 7 bitter taste corrosive electrolytes turn red litmus paper blue slippery feel Many contain –OH groups pH above 7

Weak ACIDS Strong ACIDS Ionize completely in water Strong electrolyte Solutions of these acids have as many hydronium atoms as the acid can possible form Do not ionize completely in water Weaker electrolyte Some acid molecules will combine with water to form ions Some of these ions will recombine to form molecules of the weak acid

Uses ACIDS H3PO4 - soft drinks, fertilizer, detergents H2SO4 - fertilizer, car batteries HCl - gastric juice, swimming pools HC2H3O2 - vinegar

Strong Bases Weak Bases Metal + OH All IA and IIA hydroxides are strong Dissociate completely in water into ions Strong electrolyte Do not dissociate completely in water Weaker electrolyte

Uses BASES NaOH - lye, drain and oven cleaner Mg(OH)2 - laxative, antacid NH3 - cleaners, fertilizer Ca(OH)2- treating acid soil, cement, mortar

SAFETY Any acid or base can be very dangerous in concentrated form Always wear goggles and gloves if you must work with these!!!!

pH Scale pH a measure of the concentration of H3O+ ions in solution measured with a pH paper, pH meter or an indicator with a wide color range Ranges from 0-14 INCREASING ACIDITY INCREASING BASICITY NEUTRAL

pH of Common Substances pH Scale pH of Common Substances

CALCULATING PH Can calculate using the molarity of H+ ions Equation is as follows: pH= -log ([H+]) Type in negative sign, press log button, left parenthesis, H+ concentration, right parenthesis Example: Determine the pH of an HCl solution with a concentration of 0.0001 M pH= -log (0.0001) pH= 4

ConcepTest Which of the following "molecular" pictures best represents a concentrated solution of the weak acid HA? A B

ConcepTest Is the following statement TRUE or FALSE? A strong acid has a lower pH than a weak acid. FALSE - Strong/weak refers to amount of ionization whereas pH refers to concentration of H+.

Common chemicals

SOAP & Detergent Chemical composition How they work Improve water’s ability to clean Soaps are salts of potassium and fatty acids, basic with –COO- chains Detergents are salts of sodium, potassium, and sometimes ammonium, basic with –SO3- chains Negatively charged ends dissolve in water, other end dissolves in oil, dirt, and grease

Household CLeaners Ammonia Bleach Ammonia is a weak base [OH-] concentration low, but there is enough ions to help emulsify thin layers of dirt and fingerprints NH3 + H2O  NH4+ + OH- A strong disinfectant A chemical substance that kills harmful bacteria or viruses Changes stains to colorless form because of the oxygen atom in the hypochlorite ion, ClO- Ammonia and Bleach should not be mixed because noxious chloramine gas, NH2Cl is formed!!!

Healthcare Antacids Shampoo We will see how these work in labs Made of magnesium hydroxide or sodium bicarbonate pH balanced between 5-8 If shampoo is too basic, will cause strands of hair to swell Shampoo that is too acidic dries out hair

The refrigerator trick The apple was cut at the same time One side was moistened with lemon juice Why does this work? The citric acid in lemon juice helps antioxidants in the apple that react with oxygen can react with other substances in the apple

Reactions with acids and bases

Neutralization Reaction Chemical reaction between an acid and a base. Products are a salt (ionic compound) and water.

Neutralization Reaction ACID + BASE  SALT + WATER HCl + NaOH  NaCl + H2O = Neutralization does not always mean pH = 7.

Neutralization Reaction KOH + HNO3  H2O + KNO3 Acid? Base? Salt? HNO3 KOH KNO3

Neutralization reactions Not all produce neutral solutions final pH depends on amounts and strength of acids and bases that are combined If a strong acid reacts with an equal amount of weak base, the resulting solution will still be acidic If a strong base reacts with an equal amount of weak acid, the resulting solutions will still be basic

Titration Titration standard solution unknown solution Titration Process in which a standard solution is used to determine the concentration of an unknown solution.

Titration dramatic change in pH Equivalence Point Point at which equal amounts of H3O+ and OH- have been added. Determined by… indicator color change dramatic change in pH

Equivalence point The equivalence point is not always neutral When strong base reacts with strong acid, EP is neutral When strong base reacts with a weak acid or strong acid reacts with weak base, EP will not be at pH 7

Equivalence points Weak Acid titrated with strong base Weak base titrated with strong acid

Salts Origin of NaCl in US Uses of NaCl Underground deposits from dried up ancient seas Uses of NaCl Sodium in your diet Seasoning and preserving food Ceramic glazes Soap Water softeners De-icing of highways Fire extinguishers