Acids and Bases.pdf

link on Schoology; username: asparis; password: pasteur Identifying acids and bases Where do these substances fall on the pH scale? ● tap water / rain water (H2O) ● hydrogen chloride (HCl) sodium hydroxide (NaOH) Coke (contains H2CO3 + H3PO4 ) bleach (contains ClO-) milk (contains CH3CH2COOH)...

link on Schoology; username: asparis; password: pasteur Identifying acids and bases Where do these substances fall on the pH scale? ● tap water / rain water (H2O) ● hydrogen chloride (HCl) sodium hydroxide (NaOH) Coke (contains H2CO3 + H3PO4 ) bleach (contains ClO-) milk (contains CH3CH2COOH) soap (contains NaOH) ● ● ● ● ● Classifying acids and bases both acids and bases are chemicals found in aqueous solution (aq), i.e. dissolved in H2O. Acid examples: • hydrochloric acid HCl Base examples: ● sodium hydroxide NaOH • sulfuric acid H2SO4 • ethanoic acid CH3COOH • lactic acid CH3CH2COOH • all release H+ ions into solution • increase in H+ ions causes ● calcium hydroxide Ca(OH)2 ● ammonia NH3 ● bleach ClO- ● most release OH- ions directly into solution ● NH3 and ClO- increase OH- ions indirectly by removing H+ ions from water (leaving OH-) ● bases increase pH Dissociation in aqueous solution, many chemicals (ex. salts, acids and bases) dissociate, or separate into component ions: examples: ● NaCl + H2O → Na+ + Cl- + H2O ● CaCl2 + H2O → Ca2+ + 2Cl- + H2O ● HCl + H2O → H+ + Cl- + H2O (acid dissociation) ● NaOH + H2O → Na+ + OH- + H2O (base dissociation) even water dissociates in small quantities (about 1 in every 10 million molecules of water): H2O → H+ + OHthis explains why water can act as both an acid AND a base Dissociation of acids & bases acids dissociate, adding H+ ions to solution: HCl + H2O → H+ + Cl- + H2O H2SO4 + H2O → 2H+ + SO42- + H2O CH3COOH + H2O → H+ + CH3COO- + H2O ● ● ● result: ALL increase concentration of H+ ions in solution ● bases dissociate, adding OH- ions to solution: either directly... ● NaOH + H2O → Na+ + OH- + H2O ● Ca(OH)2 + H2O → Ca2+ + 2(OH-) + H2O or indirectly, due to taking H+ ions from water... ● NH3 + H2O → NH+4 + OH- ● ClO- + H2O → ClOH + OH- ● result: ALL increase concentration of OH- ions in solution Acids: characteristics: • typically sour tasting corrosivehydrogen ions (H+) when dissolved •• release in water, or when mixed with base solutions • can be manufactured (man-made) ex. sulfuric acid in the lab or released as pollution from coal burning plants • or naturally occurring ex. hydrochloric acid (HCl) in the stomach; citric Bases: characteristics: • typically bitter tasting slippery hydroxide ions (OH-) when dissolved •• release in water, or when mixed with acid solutions • can be manufactured (man-made) ex. NaOH in the lab or any metal hydroxide which has many uses like food preparation, soap, unclogging drains etc. • making or naturally occuring ex. sodium hydrogen carbonate - NaHCO3 found measuring pH indicators - change color in the presence of acids and/or bases (generally weak acids or bases derived from plants / fungus / bacteria which change color with pH change) pH paper / universal indicator acidic soil < pH 5.5 digital pH probe litmus paper acid = blue to red base = red to blue basic soil > pH 6.5 Hydrangeas pH, which stands for “potential of Hydrogen” measures H+ concentration in solutions pH scale is logarithmic, so difference between pH values is 10x (ex. pH 1 is 10x more acidic than pH 2 and 100x more acidic than pH 3) Observing Acid Reactions with Carbonates & Metals Lab metals testing for CO2 and H2 gases demo CO2 limewater test H2 “pop” test groups G block: H block: Vedha/Rebecka Antoine/Augusto Izzy/Esha Yotam/Aima Kevin/Ciaran Ayan/Madeleine Mamoun/Matias Ilyssa/Amelia Aditya/Gabe Emma/Julia Aida/Willow Rebecca/Agnes Sophia/Niko Mia/Zoe/Aizy Silvia/Lola/Matheo Neutralization what do you think happens when we combine hydrochloric acid (HCl) with sodium hydroxide (NaOH)? HCl + NaOH → NaCl + H2O more practice (be sure to balance): ● HBr + NaOH → ● HCl + Ca(OH)2 → ● HNO3 + NaOH → more Salts and Neutralization Practice ● Forming H2SOChemical + Mg(OH) → 4 2 balanced chemical equations give us the MOLAR RATIOS of chemicals in a reaction examples (using balanced equations from previous slide - consider coefficients as MOLES): HBr + NaOH → NaBr (salt) + H2O (water) - ex. this equation shows that: 1 mole HBr + 1 mole NaOH produces 1 mole NaBr + 1 mole H2O 2HCl + Ca(OH)2 → CaCl2 + 2H2O HNO3 + NaOH → NaNO3 + H2O H2SO4 + Mg(OH)2 → MgSO4 + 2H2O Titration Titration is a process used to determine the concentration of an acid or a base. Uses buret, buret clamp, ring stand, flask. process involves adding a known concentration of acid (or base) to an unknown concentration of base (or acid) slowly until the point of neutralization is reached (pH =7). using the volumes used to neutralize and the known concentration, we cantitration determine thelink concentration watch interactive (#1 - in class)) of dothe titration interactive link (#2) unknown acid or base. neutralization practice using moles: You have a 0.05 L of a 1.0 mol/L HCl solution leftover from an experiment, which needs to be neutralized. You are given a 0.50 mol/L NaOH solution in order to neutralize it. a) Write a balanced equation for this neutralization reaction b) Calculate how many moles of HCl are in this leftover solution: c) Determine how many moles of NaOH will be required to neutralize the HCl (hint: use the balanced chemical equation). d) Calculate the volume of NaOH needed to neutralize the HCl. Swimming pool lab using acid base neutralization and titration to determine how to neutralize a swimming pool sodium hydroxide (NaOH) pellets review reactions you should know ● acid + metal → salt + H2 gas ex: 2HCl + Mg → MgCl2 + H2 (note: no water produced) confirm with “pop” test for H2 gas (light with burning splint) ● acid + carbonates → salt + water + CO2 gas ex: 2HCl + CaCO3 → CaCl2 + H2O + CO2 confirm with limewater test which changes from clear to cloudy white with CO2 gas ● acid + base → neutralisation (salt + water) ex: HCl + NaOH → NaCl + H2O confirm with pH probe at pH 7 (or indicator color change); used in titration to determine unknown acid or base