IB SL Chemistry Unit 8

UNIT EIGHT ● Arrhenius Acids and Base ○ Most basic definition of Acid/Base ○ Acids have H+ ○ Bases have OH● Bronsted Lowry Acids and Bases ○ Acids are usually positive ions that have a hydrogen ion (H3O+) to give off ○ Bases accept a Hydrogen ion. They have a lone pair of electrons that wishes to accept a hydrogen ion. ○ Strong means that it dissociates in water almost completely ○ Weak means that it barely dissociates in water ○ Do not confuse strong/weak with concentrated/dilute ● Conjugates ○ Conjugate Acid- the acid that is produced from a reaction with the base. ○ Conjugate Base- base produced through reaction with water. ● Amphoteric substances ○ Molecules that can be both an acid and a base. Water is amphoteric. It can act as an acid and give a hydrogen. It then becomes a hydroxide ion and can act as a base. ● Acid Base Reactions ○ Acid Reactions with metal ■ Acids react with metals to produce a conjugate salt and hydrogen. ■ For example ■ Zn (s) + 2HNO3 (aq) → Zn(NO3)2 (aq) + H2 (g) ■ Zinc reacts with nitric acid to make Zinc nitrate ○ Acid/Base Neutralization ■ Acid goes through a neutralization reaction with a metal hydroxide or metal oxide to produce salt and water. ■ CuO (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l) ■ NaOH (aq) + HNO3 (aq) → NaNO3 (aq) + H2O (l) ○ Acid with Metal Carbonates/ hydrogen carbonates ■ Acid reacts with these species to produce a salt, Co2 and H2O ■ MgCO3(s) + 2HCl (aq) → MgCl2 (aq) + H2O (l) + CO2 (g) ■ NaHCO3 (s) + HCl (aq) → NaCl (aq) + H2O (l) + CO2 (g) ○ Calculating pH ■ -log[H+ ion concentration] ■ pOH calculated by -log[OH concentration] ○ Calculation H+ concentration ■ 10-pH ■ OH- concentration calculated by 10-pOH ● Indicators ○ Weak acid or base that helps indicate the ending pH of a neutralization ○ We use a universal indicator that helps show pH ● Ionic Value of water ○ Water dissociates into hydrogen and hydroxide ions. ○ H2O (l) ⇌ H+ (aq) + OH– (aq) ○ Kw= [𝐻+][𝑂𝐻−] [𝐻2𝑂] ■ We can deem water negligible as it’s basically a constant. We can restate equation as ○ Kw=[H+][OH-] ○ At 298 kelvin, pure water is an equal 50/50 split of hydroxide and hydrogen ions. ○ Kw=1.00 × 10-7 mol dm-3 × 1.00 × 10-7 mol dm-3 = 1 × 10-14 mol2 dm-6 ○ You can use this equation to solve for the concentration of ions. ● Acid Deposition ○ Acid Rain - IB example ○ Carbon dioxide reacts with water in the air to create carbonic acid. ○ Nitric acid is formed through many steps ■ Step 1 ● Nitrogen gas reacts with Oxygen gas to make Nitrogen Monoxide Free radicals(Free electrons in the nitrogen) ● N2 (g) + O2 (g) → 2NO• (g) ■ Step 2 ● Nitrogen Monoxide radical reacts with water to form nitrous and nitric acid. ● 2NO2• (g) + H2O (l) → HNO3 (aq) + HNO2 (aq) ○ Those two come together as acid rain. ○ Acid rain adversely affects the environment. ■ By lowering pH of aquatic environments to around 5, many fish begin to die off. ■ Salmon cannot survive in pH’s created by acid rain. ■ Acid can leach off aluminum ions into the water stream and hurt fish gills. ■ Has adverse corrosive effects on buildings ■ Has effects on the mucous lining in our membranes and lungs, leads to irritation and sickness. ● Dry deposition ○ Acidic fumes or particles from factories fall onto the environment ● How to reduce acid deposition ○ Precombustion vs post combustion methods ■ Hydrodesulfurization- precombustion method that takes sulfur out of gasoline and refined fuel by creating hydrogen sulfide ■ Flue gas desulfurization- post combustion that puts a filter that removes sulfur from the fumes. It’s scrubbed off by calcium carbonate and calcium oxide ■ This produces calcium sulfite (sulfate(IV)) which is further oxidized into a solid calcium sulfate