GENERAL CHEMISTRY 1 ACID BASE REACTIONS

Class Objectives To outline the properties of acids and bases To differentiate between Arrhenius and Bronsted- Lowry definitions for acids and bases To explain neutralization reactions To determine concentrations and dilutions of solutions

ACIDS Substance that ionize in aqueous solutions to for H+ ions. They increase the conc of H+ ions in solution. Properties Sour taste Change litmus from blue to red They usually react with metals to yield H2 gas Generally have H first in their chemical formula

Naming Acids Acids are named based on the anions they contain; They usually end in –ic; or –ous When the anion ends with –ide or –ate the acid end with –ic When the anion ends with –ite the acid ends with –ous. Formula Anion Name HCl Chloride ion Hydrochloric acid H2SO4 Sulfate ion Sulfuric acid HNO2 Nitrite ion Nitrous acid H2SO3 Sulfite ion Sulfurous acid

BASES Substances that accept (react with) H+ ions. Produce hydroxide ions (OH−) in solution Bases react with acids Properties Bitter taste Slippery feel Change litmus from red to blue

BASES Soluble hydroxide are alkalis e.g NaOH, KOH, Ca(OH)2, Ba(OH)2 NH3(aq) is a weak base H2O(l) is a weak acid (or weak base) H2O(l) ⇆ H+(aq) + OH−(aq) When ammonia and water are mixed a proton is transferred e.g. NH3 + H2O  NH4+ + OH−

MONOPROTIC ACIDS Can be Monoprotic, Diprotic, Triprotic Yield one H+ ion per molecule of Acid Examples HCl, HNO3, HC2H3O2 Diprotic Acids: Yield two H+ ions per molecule of Acid Example: H2SO4 Triprotic Acids: Yield one 3H+ ions per molecule of Acid Examples :H3PO4 Diprotic and triprotic Acids produce acid salts

Strong vs Weak Acids & Bases Strong acids and bases are also strong electrolytes i.e almost 100% ionized The solubility of compounds helps in identifying strong and weak electrolytes Weak acids and bases are weak electrolytes i.e. few ions in solution For strong acids the conc of H+ ions will be very high Strong Acids HX (except HF), HClO3, HClO4,HNO3,H2SO4, Strong Bases Group 1A and 2A, metal hydroxides ( except Be and Mg) – soluble hydroxides Weak base: NH3

ACID-BASE REACTIONS Acid base reactions are proton transfer reactions When an acid and a base are mixed in the correct stoichiometric proportions both acidic and basic properties disappear. The product is a salt. The Anion of the salt comes from the acid The cation of the salt comes from the base Example: HNO3 + KOH  KNO3 + H2O (HOH)

Acid Base Reactions Are Neutralization reactions Acids and bases react as follows Forming salt and water only (hydroxide) HCl(aq)+ NaOH(aq)  NaCl(aq) + H2O(l) Forming salt, water and gas ( carbonate, hydrogen carbonate) HCl(aq)+ NaHCO3(aq)  NaCl(aq) + H2O(l) + CO2(g) Forming salt and gas (sulfide) HCl(aq)+ Na2S(aq)  NaCl(aq) + H2S(g)

CONCENTRATION Concentration is the amount of solute dissolved in a given amount of solvent Concentration can be expressed in several ways: Volume percent Weight percent Weight/volume (mass/volume) percent Molarity

Volume percent Volume percent = volume of solute x 100 volume of solution Example: rubbing alcohol is generally 70% by volume isopropyl alcohol. That means that 100 ml of solution contains 70 ml of isopropyl alcohol.

Weight/volume percent =   weight of solute (in g) x 100 volume of solution (in mL) An example would be a 5%(w/v) NaCl solution. It contains 5 g of NaCl for every 100 mL of solution.

Weight Percent Weight percent = weight of solute x 100 weight of solution To get weight percent we need the weight of the solute and the total weight of the solution.

MOLARITY Molarity (M) – Molar concentration The concentration of a solution expressed as moles of solute per liter of solution Molarity = moles solute volume of solution in liters

DILUTION The process of preparing a less concentrated solution from a more concentrated one Moles solute before dilution = Moles solute after dilution MCVC = MDVD

TITRATIONS The process of reacting a solution of unknown concentration with one of known concentration. Standard solution: solution of known concentration

TITRATIONS Can be used in the following reactions: Acid-Base Precipitation Oxidation-Reduction.

Homework Textbook Chapter 4 Section: 4.3; 4.5 & 4.6 End of chapter questions 4.27 – 4.43