Bryce Greenwald - Science Unit 5 Study Guide.pdf

Unit 5 Study Guide; Acids and Bases Learning Objectives: Classify acids and bases based on chemical structure and behavior Recognize and use common acids and bases in written reactions (HCl, H2­SO4, HNO3, CH3COOH, NaOH, NH3) Determine if a substance contains an acid or a base depending upon its prop...

Unit 5 Study Guide; Acids and Bases Learning Objectives: Classify acids and bases based on chemical structure and behavior Recognize and use common acids and bases in written reactions (HCl, H2­SO4, HNO3, CH3COOH, NaOH, NH3) Determine if a substance contains an acid or a base depending upon its properties. Measure pH using various methods Describe and identify reactions involving acids and metals and acids and carbonates. Explain real-life examples of neutralization reactions (inc. writing out balanced equations for neutralization reactions) Perform an acid-base titration Calculate the amount (volume, moles) of acid or base needed for neutralization Perform acid base titrations to accurately determine the completion of a neutralisation reaction, and use the mole concept to identify an unknown concentration The pH Scale - pH → potential of hydrogen - Way to measure a substance's acidity - Both acids and bases are found in aqueous solutions (aq) (therefore dissolves in H2O) Acids a. Some examples Sulfuric acid H2SO4 Lemon juice Hydrochloric acid HCL Ethonic acid CH3COOH Lactic acid CH3CH3COOH b. - Characteristics All taste sour Conduct electricity as they contain ions The closer you get to 1 on the pH scale, the more acidic / dangerous Are corosive → damage everything they touch All contain Hydrogen ions The more hydrogen ions, the more acidic c. When in water - When in water, acids lose one positive hydrogen ion - When this takes place, the water and hydrogen ions form to create hydronium ions (H2O + H → H3O) d. Interactions relating to pH - If you have a base and you add an acid, you will decrease the pH - For example: You pour yourself a cup of milk, (neutral on pH scale), and then pour in coffee (an acid of 5), the milk will become more acidic, and the overall pH of the substance will decrease, to a 6 Bases a. Examples Sodium hydroxide (NaOH) Calcium Hydroxide Ca(OH)2 Ammonia NH3 Bleach ClO b. - Characteristics Another name is an alkali Conduct electricity as they contain ions Tastes bitter Eats away at protein Slippery c. When in water - When in water, a base often will lose a negative OH ion Dissociation - Breaking apart from something ( if you have an associate and you disassociate yourself with them, you separate with them) a. In equations NaCl + H2O → Na+ + Cl- + H2O CaCl2 + H2O → Ca2+ + 2Cl- + H2O HCl + H2O → H+ + Cl- + H2O (acid dissociation) NaOH + H2O → Na+ + OH- + H2O (base dissociation) b. In acids - Remember, they are trying to form a hydrogen cation HCl + H2O → H+ + Cl- + H2O H2SO4 + H2O → 2H+ + SO42- + H2O CH3COOH + H2O → H+ + CH3COO- + H2O result: ALL increase concentration of H+ ions in solution c. In bases - Remember, they are trying to form a OH anion, the only thing that breaks up, is the base NaOH + H2O → Na+ + OH- + H2O Ca(OH)2 + H2O → Ca2+ + 2(OH-) + H2O - result: ALL increase concentration of OH- ions in solution d. Questions As we know, bases, in water, break up to form a OH anion, but how is this possible for NH3? Well, it will use the water (H2O), to create the anion, through dissociation: NH3 + H2O → NH+4 + OHOr ClO- + H2O → ClOH + OH→ you can break everything up: Cl + O + 2H + O → OH + ? →ClOH + OH ● - Concentration in water For both acids and bases, the more concentrated, the stringer the substance a. For acids - The more H cations, the lower the pH, and the stronger the acid b. For bases - The more OH anions, the higher the pH and the stronger the base Reminders from Last Year https://docs.google.com/document/d/1rCB9tX6iJWCwyLFJTIgBtbyjVJ4fJC7APyJ88SfS-Xg/ edit?usp=sharing Neutralization - When acids & bases react, they form salt and water ● Other reactions you should know 1. 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) 2. 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 3. 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 4. Metal + non-metal → salt Titration - used to determine the concentration of an acid or a base 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 can determine the concentration of the unknown acid or base. a. Example - if testing HCl, add a base to a flask. - Use distilled water to clean buret - Add HCl to Buret - Add drops of HCl into the base - the H and OH will bond to form water HCl + NaOH H + Cl + Na + OH → Na + Cl + H2O Then, remove all “spectator ions” (the ones that do not change throught the experiment) H + OH → H2O - Color indicator will change color, when neutrality is reached - Calculate the amount of HCl added by doing the formula in concentration category b. Concentration - Amount of substance, dissolved into a volume (measured in mol/dm^3) - Formula: - c. Materials - Uses buret, buret clamp, ring stand, flask. How to measure the pH 1. - Digital pH probe Most accurate device Gives you a number Very expensive 2. - Litmus paper Identifies if something is an acid or a base Does not measure how strong the level of the Pink litmus paper stays pink in an acid, but turns acid/base is blue in a base - Blue litmus paper stays blue in a base, but turns pink in an acid 3. - Universal pH indicator More precise than litmus paper Based on color, gives one around No exact number on the pH cheap 4. Cabbage juice - Tells one approximately - through the following the level scale the pH table → Materials used During Labs - Plastic dropper - rubber stopper - Volumetric flask - Buret . - buret clamp - ring stand