Ch. 20 Notes -- Acids and Bases What makes something an acid? Acid Properties: (1) tastes _______-- _______________ (2) corrosive to _________ (3) contains [ ___ ] (or [ _____ ] = “_______________” ions) (4) proton ([ ___ ]) __________-- Brønsted-Lowry Theory Example: HCl + H 2 O  ______ + ______ sourlemons metals H+H+ H3O+H3O+ hydronium H+H+ donor Cl − H3O+H3O+

Examples of Common Acids: Pepsi, _________ juices, ___________, stomach acid, battery acid, _____________, ______ citrusaspirin vinegarDNA

Indicators An indicator is a chemical that will change ___________ when placed in an acidic, basic or neutral environment. Indicator Colors For Acids litmus paper = _______ phenolphthalein = ___________ red cabbage juice (universal indicator) = ________ methyl orange = _______ colors red clear red

pH Paper : Indicator Colors Acidic Basic Neutral

Properties of Bases What make something a base? Base Properties: (…the opposite of acid properties) (1) tastes ________ -- ___________ peel, parsley, dark chocolate (2) feels _____________ -- ________ (3) contains [ _____ ] ions (4) proton ([H + ]) ______________-- Brønsted-Lowry Theory Example: NH 3 + H 2 O  ______ + _______ bitterbanana slipperysoap OH − acceptor NH 4 + OH −

Indicator Colors for Bases litmus paper = _______ methyl orange = ____________ red cabbage juice (universal indicator) =________ phenolphthalein = ______ AcidBase phenolphthalein blue yellow blue pink

Common Bases Examples of Common Bases: milk of magnesia, ___________, drain cleaner, soap, blood, ____________ tablets, ___________ ________. ammonia antacidbaking soda

Measuring the Amount of H + and OH − Ions in a Solution _____ Scale- measures the _____________ of [H + ] ions in a solution Formulas pH = − (log [H + ]) [H + ] = 10 −pH pH + pOH = 14 With the pH scale, we have another way to define acids and bases: Acids have a pH _________7.0 Bases have a pH _________7.0 Neutral pH ___7.0 pHconcentration below above =

Practice Problems: 1) a) Calculate the pH of a M HCl solution b) Calculate the pH of rain water with a concentraion of M c) What would be the [H+] of a vinegar solution with a pH of 2? [H + ] = MSo…pH = − (log M)pH = 3 [H + ] = M So…pH = − (log M) pH = 7.8 pH=2So…[H + ]= [H + ] = 0.01M

Titration Mixing an acid with a base to determine a __________________ is called “titration.” An ____________ is used to determine when neutralization has occurred. ________________ Solution - the solution of known concentration ______ _________ - the point of neutralization when titrating At the ______ point, the moles of [H + ] ions = moles of [OH − ] ions. concentration indicator Standard End Point end

(M acid )x(V acid ) = (M base )x(V base ) Practice Problems: (1)A 25 mL solution of HNO 3 is neutralized by 18 mL of 1.0 M NaOH standard solution using phenolphthalein as an indicator. What is the concentration of the HNO 3 solution? (2) How many mL of 2.0 M KOH will it take to neutralize 55 mL of a 0.76 M HCl standard solution? Determining the Concentration of an Acid (or Base) by Titration ( ) x ( ) = ( ) x ( ) M acid 25 mL1.0 M18 mL M acid = 0.72 Molar 0.76 M55 mL2.0 MV base V base = 20.9 mL

Thermochemistry: The heat energy of chemical reactions Enthalpy is the amount of ________ transferred during a reaction. The symbol for the change in enthalpy is ∆H. An endothermic reaction is one that ___________ heat from the surroundings. (___ ∆ H) An endothermic reaction feels ______. Example--an “instant” ice pack An exothermic process is one that _____________ heat to the surroundings. (___ ∆ H) An exothermic reaction feels _____. Example--burning paper heat gains +cold loses –hot

Thermochemical Reactions A thermochemical reaction is written as follows: 2S + 3O 2  2SO kJ This equation represents an ___________ reaction since the heat is a ________. H 2 + Br kJ  2HBr This equation represents an ___________ reaction since the heat is a __________. exothermic product endothermic reactant

Thermochemistry Problems Example 1: When Sulfur and Oxygen are combined in the following reaction heat is given off. What kind of reaction is this? 2S + 3O 2  2SO 3 ∆H = kJ Example 2: When a instant cold pack is broken, Ammonium Nitrate is mixed with water. The cold pack feels cold to the touch. What kind of reaction is this? NH 4 NO 3 + H 2 O = NO 2 H + HNO 3 ∆H = 1800 kJ Exothermic Endothermic

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Calculations in Thermodynamics In order to calculate how much heat is transferred by a thermochemical reaction the equation we use is q = mc∆T q = the ______ lost or gained in the process m = the _____ of the substance c = the ________ _____ ________ The Specific heat of water is Joules/gram °C ∆T = ________ Temp. – ________Temp. heat mass Specificheat capacity InitialFinal

Calculations Practice If the same amount of heat is applied to 5 grams of the following substances, which substance will increase in temperature the fastest? –Carbon with a specific heat of 0.17 cal/g ° C –Water with a specific heat of 1.00 cal/g ° C –Iron with a specific heat of 0.11 cal/g °C –Titanium with a specific heat of cal/g °C

Chemical Equilibrium Some reactions are reversible, so as products accumulate they can begin to turn back into reactants. When the rate of the forward reaction ____________ the rate of the reverse reaction, it is at equilibrium. Here’s an example: Each is constantly being formed at the same rate that it is being consumed. It is therefore called a “_____________ equilibrium”. Chemical equilibrium is the point at which the concentrations of all species are ________________. equals dynamic constant

Dynamic Equilibrium

Le Chatelier’s Principle: If a stress is applied to a system that is already at equilibrium, the equilibrium will shift to reduce the effect of the stress. We will now look at changing various things on a system at equilibrium. Consider this reaction: A + B C + D Here are some things that one can change in order to shift the equilibrium: (1) Changing _______________________ of the Solutions (2) Changing the _____________________ of the Gases (3) Changing the _____________________ Changes in Equilibrium Concentration Pressure Temperature

Le Chatelier’s Principle: Consider this reaction: A (aq) + B (g) C (aq) + D (aq) + 92 kJ Here are some things that one can change in order to shift the equilibrium: (1) Adding more A shifts the equilibrium to the ________ (2) Removing A shifts the equilibrium to the ________ (3) Adding more gas pressure of B shifts the equilibrium to the ________ (4)Removing gas pressure of B shifts the equilibrium to the ________ (5) Decreasing the temperature shifts the equilibrium to the ________ (6) Increasing the temperature shifts the equilibrium to the ________ Changes in Equilibrium right left right left right left

For the reaction below, predict the direction the equilibrium will shift given the following changes. Temperature and volume are held constant. Fe 3+ (aq) + SCN –1 (aq) FeSCN 2+ (aq) (colorless) (red) More Fe 3+ is added to the reaction. ____________________ NO 2 (g) + 7 H 2 (g) ↔ 2 NH 3 (g) + 4 H 2 O (g) Predict the shift in equilibrium given the following changes: a. addition of ammonia ____________________ b. removal of nitrogen dioxide ____________________ c. removal of water vapor ____________________ Changes in Equilibrium Shifts to the right (…more red) Shifts to the left Shifts to the right