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Chemistry 30 Equilibrium, Acids & Bases A. Dynamic Equilibrium 30-D1.1k define equilibrium and state the criteria that apply to a chemical system in equilibrium; ie. closed system, constancy of properties, equal rates of forward and reverse reactions 30-D1.1sts explain that the goal of science is knowledge about the natural world equilibrium theories and principles apply to a variety of phenomena in our world eg) blood gases in scuba diving CO2 in carbonated beverages buffers in our blood reactions are often _______________________ which means that not only are the _____________________________________________ but the _________________________________________________ we use the double arrow to show this relationship eg) the forward and reverse reaction will proceed at different rates…it depends on the concentration of the reactants and products o if we start with only the reactants A and B, the _____________ ___________________ will initially be the ________________ as it is the __________________________________________ o as the products C and D are formed, the ___________________ _____________________________________________ and the ___________________________________________________ o at some point, the rates of forward and reverse reactions ______ ________________________ Chemistry 30 EAB Notes 1 Jill Agnew a system is said to be in a state of _______________________ when: 1. the _________ of the forward and reverse reactions are ___________ 2. the ____________________________________________________ of the system, such as temperature, pressure, concentration, pH are _____________________ 3. the system is a _______________ system at ____________________ __________________________________ B. Classes of Reaction Equilibria 30-D1.2k identify, write and interpret chemical equations for systems at equilibrium there are three classes of chemical equilibria: 1. ________________ favored (percent rxn __________) 2. _______________ favored (percent rxn ___________) 3. _______________ to the right (percent rxn _____________) or C. The Equilibrium Constant 30-D1.4k define Kc to predict the extent of the reaction and write equilibrium law expressions for given chemical equations, using lowest whole-number coefficients 30-D1.3s write the equilibrium law expression for a given equation experiments have shown that under a given set of conditions (P and T) a specific quantitative relationship exists between the equilibrium concentrations of the reactants and products one reaction that has been studied intensively is that between H2(g) and I2(g) (simple molecules and takes place in gas phase no solvent necessary!) H2(g) + I2(g) ⇌ 2 HI(g) when different combinations of H2(g), I2(g), and HI(g) were mixed and the concentrations measured, it was discovered that ______________ was reached in _______________________ Chemistry 30 EAB Notes 2 Jill Agnew even though the equilibrium [ ] are_______________________, the _____________________________________ was the same each time (within experimental error) this led to the empirical generalization known as the ______________ ___________________________________________ which says that there is a ________________________________ between the concentrations of the products and the concentrations of the reactants at equilibrium this law can be expressed mathematically: For the reaction aA + bB ⇌ cC + dD The law is: where: Kc = ______________________________________ A, B = __________________________ C, D = ________________________ a, b, c, d = _______________________ coefficients ________ is constant for a reaction at a given ___________________ …if you change the temperature, Kc also changes it is common to ignore the units for Kc and list it only as a numerical value (since depends on the powers of the various [ ] terms) when determining Kc use only the species that are in ____________ or _______________________ the ________________ the value of Kc, the greater the tendency for the reaction to favor the ____________________________________ if Kc is ________________________________, then the reaction is _________________ favoured if Kc is _________________________________, then the reaction is _________________ favoured Kc indicates the ____________________________________and not the ____________________________________________________ Chemistry 30 EAB Notes 3 Jill Agnew catalysts will not affect the [ ] at equilibrium…__________________ ________________________________________________________ Example 1 Write the equilibrium law for the reaction of nitrogen monoxide gas with oxygen to form nitrogen dioxide gas. 2 NO(g) + O2(g) ⇌ 2 NO2(g) Example 2 Write the equilibrium law for the following reaction: CaCO3(s) ⇌ CaO(s) + CO2(g) Example 3 Write the equilibrium law for the following reaction: 2 H2O(l) ⇌ 2 H2(g) + O2(g) Example 4 Phosphorus pentachloride gas can be decomposed into phosphorus trichloride gas and chlorine gas. a) Write the equilibrium law for this reaction. b) If the [PCl5(g)]eq = 4.3 x 10-4 mol/L, the [PCl3(g)]eq = 0.014 mol/L and the [Cl2(g)]eq = 0.014 mol/L then calculate Kc. Chemistry 30 EAB Notes 4 Jill Agnew Example 5 Find the [SO3(g)] for the following reaction if Keq = 85.0 at 25.0C. 2 SO2(g) 0.500 mol/L + O2(g) ⇌ 2 SO3(g) 0.500 mol/L ??? Sample Diploma Question The equilibrium law expression for the reaction represented below is H2CO3(aq) + H2O(l) ⇌ HCO3(aq) + H3O+(aq) A. Kc = [H2CO3(aq)][ H2O(l)] [HCO3(aq)][H3O+(aq)] B. Kc = C. Kc = [HCO3(aq)][H3O+(aq)] [H2CO3(aq)][ H2O(l)] D. Kc = [HCO3(aq)][H3O+(aq)] [H2CO3(aq)] [H2CO3(aq)] [HCO3(aq)][H3O+(aq)] Your Assignment: pg 1 #1-4 “Chemical Equilibrium” D. Graphical Analysis 30-D1.3s interpret data from a graph to determine when equilibrium was established and to determine the cause of a stress on the system a graph of ___________________ vs. _____________ can be used to see when equilibrium has been reached…as soon as the concentrations_________________________________________, you can read this time off the graph Chemistry 30 EAB Notes 5 Jill Agnew Example 1 Consider this rxn: Concentration (mol/L) 2 SO2(g) + O2(g) 2 SO3(g) SO3(g) 75 50 25 SO2(g) O2(g) 0 10 20 30 Time (s) At what time does equilibrium get reached and what is the value for Kc? Your Assignment: pg 2 “Graphical Analysis” E. Le Chatelier’s Principle 30-D1.3k predict, qualitatively, using Le Chatelier’s principle, shifts in equilibrium caused by changes in temperature, pressure, volume, concentration or the addition of a catalyst and describe how these changes affect the equilibrium constant _________________________________________________ states that when a chemical system at ________________________ is disturbed by a ____________________________________________ _____________________, the system adjusts in a way ____________ __________________________________________ this takes place in a three-stage process 1. initial equilibrium state 2. shifting non-equilibrium state 3. new equilibrium state a system can be affected by a change in concentration, temperature and or volume (pressure) Chemistry 30 EAB Notes 6 Jill Agnew 1. Concentration Changes an increase in the [ ] of the products or reactants favours _______________________________________________ a decrease in the [ ] of the products or reactants favours _______________________________________________ eg) N2(g) + 3 H2(g) ⇌ 2 NH3(g) 30-D1.3sts explain that the goal of technology is to provide solutions to practical problems eg. the Haber-Bosch process for producing ammonia changes in concentration have _____________________ on the value of ____________ 2. Temperature Changes energy is treated like a ________________or __________________ eg) reactants + energy ⇌ products reactants ⇌ products + energy if cooled, the equilibrium shifts so ____________________________ ________________________________________________ if heated, the equilibrium shifts _______________________________ ________________________________________________ a change in temperature is the only stress that ___________________ the value of Kc!!!!!!! if the shift is towards the ____________ side, Kc will _____________ if the shift is towards the ____________ side, Kc will _____________ 3. Volume (Pressure) Changes with gases, volume and pressure are related ie) volume ____, pressure ____ the concentration of a gas is related to volume (pressure) ie) volume ____, concentration ______ the concentration of a gas is related to volume (pressure) Chemistry 30 EAB Notes 7 Jill Agnew an _______________________________caused by a ____________ in volume causes a shift towards the side of the equation with ______________________________ eg) N2(g) + 3 H2(g) ⇌ 2 NH3(g) 4 moles 2 moles if the number of moles are the ________ on both sides of the reaction, a change in volume (pressure) has _______________________ changes in volume and pressure have __________________ on the value of __________ 4. Colour Changes in many equilibrium systems, the reactants will have a different colour than the products predictions can be made about the equilibrium shift and the resulting change in colour Example Use the following reaction to predict the equilibrium shift and resulting colour change when the stresses are applied 2 CrO42(aq) + 2 H3O+(aq) ⇌ 2 Cr2O72(aq) + 3 H2O() yellow orange a) a crystal of Na2CrO4(s) is added b) a crystal of K2Cr2O7(s) is added c) a few drops of concentrated acid is added d) water is removed e) a few crystals of NaOH(s) are added Chemistry 30 EAB Notes 8 Jill Agnew Sample Diploma Question In blood, the enzyme carbonic anhydrase catalyzes the formation of carbonic acid from aqueous carbon dioxide and water. Carbonic acid and hydrogen carbonate form an important buffer in the blood. Two reactions that occur in the blood are represented by the equations below. Reactions in the Blood Equation I CO2(aq) + H2O(l) ⇌ H2CO3(aq) Equation II H2CO3(aq) + H2O(l) ⇌ HCO3(aq) + H3O+(aq) If the concentration of CO2(aq) in the blood increases, then the equilibria will shift to the _____i____, and the concentration of the HCO3(aq) in the blood will ____ii______. R ow A. i ii left increase B. left decrease C. right increase D. right decrease Your Assignment: pgs 3-4 “Le Chatelier’s Principle” Chemistry 30 EAB Notes 9 Jill Agnew all of the changes that can happen to systems in equilibrium can be shown graphically: 30-D1.3s interpret data from a graph to determine when equilibrium was established and to determine the cause of a stress on the system Example State what change to the equilibrium takes place at each of the labelled parts of the graph: Manipulations of An Equilibrium System N2(g) + 3 H2(g) ⇌ 2 NH3(g) + energy NH3(g) N2(g) Concentration (mol/L) H2(g) A B C D Time (min) Equilibrium Stress Time A B C D Your Assignment: pg 5 Chemistry 30 EAB Notes 10 Jill Agnew F. ICE Tables 30-D2.3k calculate equilibrium constants and concentrations for homogeneous systems and Bronsted-Lowry acids and bases (excluding buffers) when concentrations at equilibrium are known initial concentrations and one equilibrium concentration are known the equilibrium constant and one equilibrium concentration are known 30-D2.3s use experimental data to calculate equilibrium constants we can use a table set-up to calculate the equilibrium concentrations and/or Kc for any system you must be able to calculate all ______________________________ before you can use the equilibrium law Example 1 Hydrogen iodide gas decomposes into hydrogen gas and iodine gas. If 2.00 mol of HI(g) is place in a 1.00 L container and allowed to come to equilibrium at 35C, the final concentration of H2(g) is 0.214 mol/L. Find the value for Kc. Chemistry 30 EAB Notes 11 Jill Agnew Example 2 In a 500 mL stainless steel reaction vessel at 900C, carbon monoxide and water vapour react to produce carbon dioxide and hydrogen. Evidence indicates that this reaction establishes an equilibrium with only partial conversion of reactants to products. Initially, 2.00 mol of each reactant is placed in the vessel. Kc for this reaction is 4.20 at 900C. Calculate the concentration of each substance at equilibrium. Example 3 Gaseous phosphorus pentachloride decomposes into gaseous phosphorus trichloride and chlorine gas at a temperature where Keq = 1.00 103. Suppose 2.00 mol of PCl5(g) in a 2.00 L vessel is allowed to come to equilibrium. Calculate the equilibrium [ ] of each species. Chemistry 30 EAB Notes 12 Jill Agnew when the concentrations are greater than _______________________ the equilibrium constant, we can make an ______________________ that greatly simplifies our calculations if Kc is very small, the equilibrium doesn’t lie very far to the right and ________________________________________________ ***in this example, ___________ can be assumed to be ________ since x is really _________, so… Example 4 Gaseous NOCl decomposes to form gaseous NO and Cl2. At 35C the equilibrium constant is 1.6 105. Calculate the equilibrium [ ] of each species when 1.0 mol of NOCl is placed in a 2.0 L covered flask. Your Assignment: pg 6 #1-5 “ICE Tables” Chemistry 30 EAB Notes 13 Jill Agnew G. Ionization of Water the equilibrium of water can be written as follows: the equilibrium law is: 30-D2.2k define Kw, Ka and Kb and use these to determine pH, pOH, [H3O+] and [OH] of acidic and basic solutions the equilibrium constant for water is designated as _______________ at 25C, neutral water has [H+(aq)] = [OH(aq)] = 1.0 107 mol/L Kw = = (on pg 3 of Data Booklet) Kw is always constant and therefore can be used to determine the _________________ or the ________________ eg) if [H3O+(aq)] = 1.0 104 mol/L then [OH(aq)] = if [H3O+(aq)] = [OH(aq)], then solution is ________________ if [H3O+(aq)] > [OH(aq)], then solution is ________________ if [H3O+(aq)] < [OH(aq)], then solution is ________________ Try These: 1. [H3O+(aq)] = 1.0 109 mol/L [OH(aq)] = 2. [H3O+(aq)] = 1.0 101 mol/L [OH(aq)] = 3. [H3O+(aq)] = [OH(aq)] = 1.0 102 mol/L 4. [H3O+(aq)] = 6.3 109 mol/L [OH(aq)] = 5. [H3O+(aq)] = 8.1 103 mol/L [OH(aq)] = 6. [H3O+(aq)] = [OH(aq)] = 2.8 107 mol/L Chemistry 30 EAB Notes 14 Jill Agnew H. Review of pH and pOH 30-D2.1k recall the concepts of pH and hydronium ion concentration and pOH and hydroxide ion concentration, in relation to acids and bases the number of digits following the ____________________________ in the ______________________ is equal to the number of ______________________ in the ___________________ Example 1 Find the pH of a solution where the [H3O+(aq)] = 4.7 1011 mol/L. Example 2 Find the pH of a solution where the [OH(aq)] = 2.4 103 mol/L. Example 3 Calculate the [H3O+(aq)] if the pH of the solution is 5.25. Chemistry 30 EAB Notes 15 Jill Agnew Example 4 Calculate the pH of a solution where 10.3 g of Ca(OH)2(s) is dissolved in 500 mL of water. Sample Diploma Question A 100 mL sample of lactic acid has a pH of 3.38. The hydroxide ion concentration in this sample of lactic acid, expressed in scientific notation, is a.b 10cd mol/L. The values of a, b, c, and d are ______, ______, ______, _______. Sample Diploma Question When a solution with a pH of 3 is compared to a solution with a pH of 5, you could say that the solution with a pH of 3 has A. higher acidity and lower [H3O+(aq)] B. higher acidity and higher [H3O+(aq)] C. lower acidity and lower [H3O+(aq)] D. lower acidity and lower [H3O+(aq)] Your Assignment: pgs 6-7 #1-11 “pH and pOH” Chemistry 30 EAB Notes 16 Jill Agnew I. Brønsted-Lowry Definition of Acids & Bases (1923) 30-D1.3k describe Bronsted-Lowry acids as proton donors and bases as proton acceptors this theory looks at the role of the acid or base an acid is a ______________________________________________ __________________________________________________________________ ______________________________________________ a base is ________________________________________________ like in electrochemistry where e are transferred…now we transfer H+ H+ HCl(aq) + H2O(l) ⇌ H3O+(aq) + Cl(aq) acid H+ NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH(aq) base water does not have to be involved! H+ eg) HCl(g) + NH3(g) ⇌ NH4Cl(s) a Brønsted-Lowry acid doesn’t necessarily have to produce an acidic solution…it depends on what accepts the proton an acid/base reaction is a chemical reaction in which _____________ is transferred from an _________ to a ___________ forming a ________________________ and a _______________________ this theory explains how some chemical species can be used to neutralize both acids and bases eg) HCO3(aq) + H3O+(aq) ⇌ HCO3(aq) + OH(aq) ⇌ Chemistry 30 EAB Notes 17 Jill Agnew a substance that appears to act as a Brønsted-Lowry acid in some rxns and a Brønsted-Lowry base in other rxns is said to be _____________ _______________________________________________________ eg) Your Assignment: pgs 7-8 #1-2 “Brønsted-Lowry Acids and Bases” J. Conjugate Acids and Bases 30-D1.7k identify conjugate pairs and amphiprotic substances a pair of substances that differ only by a proton is called a ___________________________________…the ___________ is on one side of the rxn and the ___________ is on the other in general, the reaction can be shown as follows: HA(aq) + H2O(l) ⇌ H3O (aq) + A (aq) + Sample Diploma Question Lactic acid, HC3H5O3(aq), is produced in human muscle cells when not enough oxygen is supplied to the muscle during heavy physical activity. The equation below represents the Brønsted-Lowry reaction of lactic acid with water. HC3H5O3(aq) + H2O(l) ⇌ C3H5O3(aq) + H3O+(aq) Which of the following rows identifies the Brønsted-Lowry acids and a conjugate acidbase pair in the equation above? Row Brønsted-Lowry Acids Conjugate Acid-Base Pair A. HC3H5O3(aq) and C3H5O3(aq) H2O(l) and H3O+(aq) B. HC3H5O3(aq) and C3H5O3(aq) C3H5O3(aq) and H3O+(aq) C. HC3H5O3(aq) and H3O+(aq) H2O(l) and H3O+(aq) D. HC3H5O3(aq) and H3O+(aq) C3H5O3(aq) and H3O+(aq) Chemistry 30 EAB Notes 18 Jill Agnew the ____________ an acid, the _____________ its conjugate base the ____________ an acid, the _____________ its conjugate base Sample Diploma Question Weak Acids 1 HF(aq) 2 H2S(aq) 3 HOCl(aq) 4 H2SO3(aq) Numerical Response When the weak acids numbered above are ordered from the acid with the strongest conjugate base to the acid with the weakest conjugate base, the order is ___________, ___________, ___________, and ___________. Strongest Weakest Your Assignment: pg 8 #3 K. Strengths of Acids and Bases 30-D2.2k define Kw, Ka and Kb and use these to determine pH, pOH, [H3O+] and [OH] of acidic and basic solutions two different acids (or bases) can have the same [ ] but have different strengths eg) 1 M CH3COOH(aq) and 1 M HCl(aq) will react in the same way but not to the same degree the stronger the acid, the __________ electricity it conducts, the ___________ the pH and the __________ it reacts with other substances 1. Strong Acids acids that ionize _________________ in water to form H3O+(aq) percent rxn = ______________ the bigger the Ka (Kc for acids) the more the ______________ are favoured Chemistry 30 EAB Notes 19 Jill Agnew top 6 acids on the table (pg 11 in Data Book) have a very large Ka …note the H3O+ is the strongest acid on the chart (leveling effect)…all strong acids react to form H3O+(aq) so it is the strongest when calculating pH, the __________________________________ so use _________________________________________ Example What is the pH of a 0.500 mol/L solution of HNO3(aq)? 2. Weak Acids a weak acid is one that _____________________________________ _______________________________________________________ most ionize _________________ Ka value is __________________ to calculate pH, you need to use the ___________________…you cannot use just the ___________ because it is not ________________ the Ka law is an __________________________ is devised the same way we did _________ eg) HA(aq) + H2O(l) ⇌ H3O+(aq) + A(aq) you will be required to figure out the ____________ before you can calculate the pH you have the __________ and the __________ value but you don’t have the _____________ since the mole ratio for __________________ is __________, they have the same [ ] (this is a _________________!) Chemistry 30 EAB Notes 20 Jill Agnew now you can solve for [H3O+(aq)] Example 1 What is the pH of a 0.10 mol/L acetic acid? Example 2 What is the pH of 1.0 mol/L acetic acid? Example 3 A 0.25 mol/L solution of carbonic acid has a pH of 3.48. Calculate Ka. Chemistry 30 EAB Notes 21 Jill Agnew the _____________________________________________ can be written as a _______above the ______ in a chemical reaction: 1.3% eg) CH3COOH(aq) + H2O(l) ⇌ H3O+(aq) + CH3COO(aq) Ka = 1.8 x 105 mol/L the % reaction be calculated using [H3O+] and [HA] Example 1 Calculate the % ionization for a 0.500 mol/L solution of hydrosulphuric acid if the [H3O+(aq)] is 5.0 104 mol/L. Example 2 The pH of a 0.10 mol/L solution of methanoic acid is 2.38. Calculate the % ionization. Your Assignment: pg 8 #1-3 “Strengths of Acids” 3. Strong Bases according to Arrhenius, bases are substances that increase the ___________________________ of a solution all _________________________________ are strong bases eg) Chemistry 30 EAB Notes 22 Jill Agnew % reaction = _______________ strength depends on ____________________________________ …_______________ is a stronger base than _______________ at the same [ ] because it produces ________________ ______________________________ where x is the number of ____________ ions (think about the dissociation equation!) once you have the [OH(aq)], you can calculate the pH using pOH or KW Example Calculate the pH of a 0.0600 mol/L solution of Ca(OH)2(aq). 4. Weak Bases do not ________________________________ in water…just like weak acids Kb is the dissociation constant or equilibrium constant for bases B(aq) + HOH(l) ⇌ BH+(aq) + OH(aq) you can calculate Kb using _________ for the _____________ _________________________________________ eg) Calculate Kb for SO22(aq). Chemistry 30 EAB Notes 23 Jill Agnew Sample Diploma Question The Kb of OCl(aq)is ___i____, and OCl(aq) is a weaker base than ___ii______. Row i ii A. 2.5 107 PO43(aq) B. 2.5 107 CH3COO(aq) C. 4.0 108 PO43(aq) D. 4.0 108 CH3COO(aq) once you have Kb, you can then solve for [OH(aq)] using the equilibrium law (just like with weak acids!) now you can solve for [OH(aq)] Example Find the pH of a 15.0 mol/L NH3(aq) solution. Chemistry 30 EAB Notes 24 Jill Agnew Your Assignment: pg 9 #1-3 “Strengths of Bases” pg 9 #1-10 “Strengths of Acids and Bases – pH Calc” L. Predicting Acid-Base Equilibria 30-D1.6k write Bronsted-Lowry equations, including indicators, and predict whether reactants or products are favoured for acid-base equilibrium reactions for monoprotic and polyprotic acids and bases acids are listed in order of __________________ strength on the left side and bases are listed in order of ________________ strength on the right side when predicting reactions, the substance with ___________________ _____________________________ will react with the substance that ____________________________________________________ we will assume that only _________________ is transferred per reaction to predict the acid-base reaction, follow the following steps: Steps: 1. _______________________________________________________ Note: ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ 2. Identify all possible __________________________________. 3. Identify the ___________________ and _________________…like redox rxns the ____________________________ and the ______________________________. 4. To write the reaction, ______________________________________ ________________________________________________________ 5. Predict the position of the equilibrium. Note: ________________________________________________ ________________________________________________ Chemistry 30 EAB Notes 25 Jill Agnew Example 1 Predict the acid-base reaction that occurs when sodium hydroxide is mixed with vinegar. Example 2 Predict the acid-base reaction when ammonia is mixed with HCl(aq). Your Assignment: pg 10 #1-13 “Predicting Acid-Base Reactions” M. Monoprotic vs. Polyprotic Acids and Bases an acid capable of donating only one proton is called _____________ eg) __________________________________________ if an acid can transfer more than one proton, it is called ___________ (____________ if 2 protons, ___________ if 3 protons eg) Label each of the following acids as monoprotic or polyprotic: 1. H2SO4(aq) 2. HOOCCOOH(aq) 3. HCOOH(aq) 4. CH3COOH(aq) 5. H2PO4(aq) 6. NH4+(aq) a base that can accept only one proton is called _________________ a base that can accept more than one proton is called _____________ (_____________ or ____________) eg) _____________ can accept up to 3 H+ to form__________, ________________, and _______________ respectively Chemistry 30 EAB Notes 26 Jill Agnew eg) Label each of the following as monoprotic or polyprotic acids, bases or polybasic: 1. HSO4(aq) 2. H2PO4(aq) 3. HPO42(aq) 4. HCO3(aq) 5. H2O(l) reactions involving polyprotic acids or polybasic substances involve the same principles of reaction prediction only _____________________ is transferred at a time and always from strongest acid to strongest base Example 1 Potassium hydroxide is continuously added to oxalic acid until no more reaction occurs. Example 2 Sodium hydrogen phosphate is titrated with hydroiodic acid. If we assume all steps are quantitative, show all steps and give the net reaction. Your Assignment: pg 11 #1-5 “Polyprotic Acids and Bases” Chemistry 30 EAB Notes 27 Jill Agnew O. Titrations titrations are used to determine the pH of the ___________________ of acid-base reactions the information from the titration can be plotted on a graph, buffer regions can be analyzed and stoichiometric calculations can be performed 1. pH Curves 30-D1.3s interpret, qualitatively, titration curves of monoprotic and polyprotic acids and bases for strong acid-weak base and weak acid-strong base combinations, and identify buffering regions a ________________ is a graph showing the ____________________ ________________________________________________________ graph of __________________ vs ____________________________ the _________________ is the point (usually shown by a change in indicator colour) when the reaction has gone to completion the ________________________ is the ______________ of titrant required for the reaction to go to completion they contain a relatively flat region called the ___________________ all pH curves have 4 major features: o the _____________________________ of the curve must be the pH of the _____________________ o the co-ordinate of the ________________________________ must be correct in terms of _______ and __________________ o the ______________________________ must be _____________________ (approaches but never touches) with the pH of the __________________ o ___________________________________________________ must match the ______________________________________ _________________________________________ occurring titrant selection: o if the sample is an acid, titrant should be a _________________ such as _______________________________________ o if the sample is a base, titrant should be ___________________ ___________________________________________________ Chemistry 30 EAB Notes 28 Jill Agnew you need to be able to interpret pH curves: 1. Strong Monoprotic with Strong Monoprotic o pH of __________ at the equivalence point 14 pH 14 7 pH 0 7 0 volume volume 2. Weak Monoprotic with Strong Monoprotic o if weak acid, then pH of _______ at equivalence point o if weak base, then pH of _______ at equivalence point o bottom “flat” region is _________________________ ___________________________________________ 14 pH 14 7 pH 0 7 0 volume volume 3. Strong Polyprotic with Strong Monoprotic o ___________________________________________ 14 pH 14 7 0 pH 0 volume Chemistry 30 EAB Notes 7 29 volume Jill Agnew Sample Diploma Question Which of the following graphs represents the titration of a weak, polyprotic base with a strong monoprotic acid? A. B. pH pH volume volume C. D. pH pH volume volume 2. Indicators an indicator is a substance that ____________________________ when it reacts with an ______________________________ and are usually ____________________________ themselves they exist in one of two conjugate forms that are reversible and distinctly different in color Chemistry 30 EAB Notes 30 Jill Agnew recall that to show the equivalence point of an acid-base titration, choose an indicator: 1. whose ___________________________________________ includes the ______________________________________ of the titration 2. that will react _________________________________________ …this means the indicator is a weaker acid or base than the sample Your Assignment: pgs 11-12 #1-5 “pH Curves” 3. Buffers ________________ are chemicals that, when added to water, protect the solution from __________________________________________ _______________________________________________________ they are used to __________________________ and _____________ _________________________________________________ typical buffers are solutions containing relatively large amounts of __________________________________ such as a ______________ and the ____________________________________________ typical buffers are eg) _______________________________ the ___________ in the conjugate pair of the buffer protects against any _____________ added the ____________ in the conjugate pair of the buffer protects against any _____________ added buffers can be ___________________ by the addition of __________ ________________________________________________________ Example 1 Using an acetic acid – sodium acetate buffer system, show what happens when: a) a small amount of HCl(aq) is added b) a small amount of NaOH(aq) is added Chemistry 30 EAB Notes 31 Jill Agnew Sample Diploma Question Pairs of Solutions I HCl(aq) and NsOH(aq) II HClO4(aq) and KClO4(aq) III H2SO4(aq) and LiHSO4(aq) IV H3PO4(aq) and NaH2PO4(aq) If each pair of solutions listed above is mixed together in equal amounts, then the pair of solutions that would act as a buffer is A. I B. II C. III D. IV Your Assignment: pg 12 #1-2 “Buffers” Chemistry 30 EAB Notes 32 Jill Agnew