L07 Chem 151 Lecture Notes - Lecture 13: Titration Curve, Protonation, Equivalence Point

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limehorse889

23 Feb 2017

School

WUSTL

Department

University College - Chemistry

Course

L07 Chem 151

Professor

Redden

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Equilibrium: ha + h2o -> approx. x[a-]/[ha]0. Equilibrium shifted dramatically left due to the common ion. +]0 + x)/([nh3]0 x) -> approx. x[nh4+]0/[nh3]0. Equilibrium shifted left, poh is given by x. Buffer solutions weak acid at equilibrium with a weak base e. g. ha + a-, b- + hb+ can come from the dissociation of a salt. Henderson hasselbach equation ph = pka log([ha]eq/[a-]eq) When x is very small (in the case of buffers) equilibrium is shifted right. Works best when [ha] is very close to [a-] Further apart the concentrations are, the less accurate the equation is. 10:1 ratio of acid:base or base:acid is the limit. Titration curve of a strong base with a weak acid. Protonated and deprotonated forms are different colors ph = pka log([hin]eq/[in-]eq) To find the pkin -> look for max/min ph at which only first color/second color is visible and find midpoint.

Related Questions

Exp 25. pH Measurements- Buffers and Their Properties

I need help with finding kPa in the calculations part C for 1,2, and 3 Thanks!

Experiment 25 pH Measurements- Buffers and Their Properties ne of the more important propertics of an aqucous solution is its concentration of hydrogen ion. The H ion (or, more precisely, the HO ion) has a great effect on the solubility of many inorganic and organic species, on the nature of complex mctallic cations found in solutions, and on the rales of many chemical reac- tions. It is important that we know how to measure the concentration of hydrogen ion and understand its effect on solution properties. For convenience, the concentration of H' ion is frequendly expressed as the pH of the solution rather than as molarity. The pH of a solution is defined by the following equation: pH =-log where the logarithm is taken to the base 10. If [H] is I x 10-*moles per liter, the pH of the solution is, by the equation, 4. If the [H'1 is 5 x 10 M, the pH is 1.3, Basic solutions can also be described in terms of pH. In aqucous solutions the following equilibrium rela- tion will always be obeyed: In distilled water url equals [ OHÂ·], s, by Equation 2, [HÂ·l must be l x 10" M. Therefore, the pH of distilled water is 7. Solutions in which [H.] > 10é¨are sad to be acidic and will have a pH 7. A solution with a pH of 10 will have a [H"] of 1 x 10 0 M and a (OH] of I x 10M We measure the pH of a solution experimentally in two ways. In the first of these we use a chemical called an indicator, which is sensitive to pH. These substances have colors that change over a relatively short pH range (about two pH units) and can, when properly chosen, be used to delermine roughly the pH of a solu tion. Two very common indicators are litmus, usually used on paper, and phenolphthalein, the most common indicator in acid-base titrations. Litmus changes from red to blue as the pH of a solution goes from about 6 to about 8. Phenolphthalein changes from colorless to red as the pH goes from 8 to 10. A given indicator is useful for determining pH only in the region in which it changes color. Indicators are available for measure- ment of pH in all the important ranges of acidity and basicity. By matching the color of a suitable indicator in a solution of known pH with that in an unknown solution, one can determine the pH of the unknown to within about 0.3 pH units. The other method for finding pH is with a device called a pH meter. In this device two electrodes, one of which is sensitive to [H']. are immersed in a solution. The potential between the two electrodes is related to the pH. The pH meter is designed so that the scale will directly furnish the pH of the solution. A pH meter gives much more precise measurement of pH than does a typical indicator and is ordinarily used when an accurate determination of pH is needed Some acids and bases undergo substantial ionization in water, and are called strong because of their essentially complete ionization in reasonably dilute solutions. Other acids and bases, because of incomplete ionization (often far less than even 1% in 0.1 M solution), are called weak. Hydrochloric acid, HC, and sodium hydroxide, NaOH, are typical examples of a strong acid and a strong base. Acetic acid, HC,H,0, and ammonia, NH, are classic examples of a weak acid and a weak base. A weak acid will ionize according to the Law of Chemical Equilibrium: HBlaq)--H'(aq) + B-(aq)

Exp 25. pH Measurements-Buffers and Their Properties.

I need help in the calculations for part C finding the pKa in 1,2, and 3. Thanks!

Experiment 25 pH Measurements- Buffers and Their Properties ne of the is its concentration of hydrogen ion. The pecies, on they, the H,O ion) has a great effect on the solubility of many isorganic and ora tions. It is important H ion (or. more more important properties of an aqueous solution conplex metallic cations found in solutions, and on the rates of many chemical reac- of hydrogen ion and understand its effect on solution propertics that we know how to measure the concentration For convenience, the concentration of H" as molarity. The frequendly ex ãion is frequently expressed as the pH of the solution rather than pH of a solution is defined by the following equation: the equation, 4. If the [H to the base 10. If (H'l is 1 x 104 moles per liter, the pH of the solution is, by is 10-? M, the pH is 1.3. tion will always be obeyed: described in terms of pH. In aqueous solutions the following equilibrium rela- In distillecd water [H Soler t lequals IOH 1. so, by Equation 2, IH"] must be I X 10 M. Therefore,the pH of distilled will have a pH 7; if H 1 IOH1. the solution is basic and its pH >7. A solution with a pÅ of 10 will have or 1 Ã 10-4 M. We measure the pH of a solution experimentally in two ways. In the first of these we use a chemical an indicator, which is sensitive to pH. These substances have colors that change over a relatively short two pH units) and can, when properly chosen, be used to determine roughly the pH of a solu- called H range on. Two very common indicators are litmus, usually used on paper, and phenolphthalein, the most common indicator in acid-base titrations. Litmus changes from red to blue as the pH of a solution goes from about 6 to about 8. Phenolphthalein changes from colorless to red as the pH goes from 8 to 10. A given indicator is useful for determining pH only in the region in which it changes color. Indicators are available for measure- ment of pH in all the important ranges of acidity and basicity. By matching the color of a suitable indicator in a solution of known pH with that in an unknown solution, one can determine the pH of the unknown to within about 0.3 pH units. The other method for finding pH is with a device called a pH meter. In this device two electrodes, one of which is sensitive to [H'], are immersed in a solution. The potential between the two electrodes is related to the pH. The pH meter is designed so that the scale will directly furnish the pH of the solution. A pH meter gives much more precise measurement of pH than does a typical indicator and is ordinarily used when an accurate determination of pH is needed Some acids and bases undergo substantial ionization in water, and are called strong because of their essentially complete ionization in reasonably dilute solutions. Other acids and bases, because of incomplete ionization (often far less than even 1% in 0.1 M solution), are called weak Hydrochloric acid, HCl, and sodium hydroxide, NaOH, are typical examples of a strong acid and a strong base. Acetic acid, HCH,0, and ammonia, NH, are classic examples of a weak acid and a weak base. A weak acid will ionize according to the Law of Chemical Equilibrium HB(aq)H'(a) B (aq) 3)

HERE IS HOW THIS IS GOING TO WORK! IF YOU ANSWER THE QUESTIONS IWILL GIVE YOU THE 3K POINTS + MORE AFTER I REPOST IT.

2. The amount of heat involved in the synthesis of 1 mole of acompound from its elements, with all substances in their standardstates at 25*C, is called _________.

3. What is a valid unit for specific heat?

4. Use Hess's Law to find the heat of reaction in the examplebelow.

N2O4 (g) ----> 2NO2 (g)

Given that:

N2O4 (g) ----> N2 (g) + 2O2 (g) (Delta H =-9.7kJ)

2NO2 (g) ----> 2O2(g) + N2(g) ( Delta H= -67.7kJ)

5. Use Hess's Law to find the heat of reaction in the examplebelow. (Example doesn't exist btw.)

6. (Delta H) for the formation of rust (Fe2O3) is -826 kJ/mol. Howmuch energy is involved in the formation of 5 grams ofrust?

7. How many kilocalories of heat are required to raise thetemperature of 50g of aluminum from -5*C to 35*C? (Specific heat ofAluminum = 0.21 cal/g*C)

8.Calculate the (Delta H) for this reaction:

Zn(s) + Cu (2+ ion)(aq) ---> Zn(2+) + Cu(s)

(Delta H) for Cu(2+) = +64.4 kJ/Mol; (Delta H) for Zn(2+) = -152.4kJ/mol

9. The following equation shows the reaction that occurs whennitroglycerine explodes.

4C3H5O9N3 ----> 12CO2 + 6N2 + O2 +10H2O + 1725 Kcal

Is this reaction exothermic , endothermic, a combustion reaction ,or a combination reaction?

10. What does it mean for ammonia, (NH3) to have a (Delta H f) =-46 kJ/mol?

(for example: Define heat of formation. What does a negative heatof formation mean? what do the units of kJ/mol mean?)

11. What is the maximum amount of KCl that can dissolve in 500g ofwater?

(solubility of KCl is 34 g/ 100g of water at 20*C)

12.List the ways(operations) that can help make a substancedissolve faster in a solvent?

13. If a crystal added to an aqueous solution causes many particlesto come out of solution, the original solution was (saturate,unsaturated, supersaturated).

14. What is the number of moles of solute in 165 mL of a 0.82 Msolution?

15. What mass of NaCl is needed to make 350 mL of a 1.00 Msolution?

16. Colligative properties depend upon...

17. If one mole of each of these solutes in added to the sameamount of water, which solution has the highest boiling point?(glucose, aluminum sulfate, magnesium acetate, copper (I)chloride)

18. When an acid reacts with a base, what compounds areformed?

19. If the [H+] in a solution is 1x10^(-13) mol/L, what is the[OH-]?

20. If the [OH-] = 1x10^-6 mol/L, what is the pH of thesolution?

21. For a solution to be considered acidic what must be thehydrogen-ion concentration?

22. Which of the following represents a Bronsted-Lowry conjugateacid-base pair?

a) SO3(2-) and SO2 b) CO3(2-) and CO c) H3O and H2 d) NH4(+) and NH3

23. With solutions of "strong" acids and "strong" bases, the word"strong" refers to ...

24. What are the products of Al(OH)3 + H2CO3?

25.What is the concentration of hydrochloric acid if 5.0 mL of acidis neutralized by 30.0 mL of 2.00M sodium hydroxide.

26. At equilibrium, what is the rate of production of reactantscompared with the rate of production of products?

27. What is the equilibrium constant for the following reaction2SO3 ---> 2SO2 + O2

28. How does an increase in pressure affect the following reaction?2SO3 (g) --> 2SO2(g) +O2(g)

29.What stresses would shift the reaction to the right?

2SO3(g) ==> 2SO2(g) + O2(g)

30. The Keq of a reaction 4.9 x 10^(-7). Are products or reactantsfavored at equilibrium?

31. In which of these systems is the entropy decreasing?

a) air escaping from a tire b) snow melting c) a gas condensing d) salt dissolving inwater

32. If an atom is reduced in a redox reaction, what must occur toanother atom in the system?

33. Identify the oxidizing agent in the following reaction: 2Na + S---> Na2S

34. What are transferred in an oxidation -reductionreaction?

35. Give the oxidation number for each atom in KMnO4.

36. Which atom has a change in oxidation number of +4 in thefollowing reaction?

K2Cr2O7 + H2O + S ----> KOH + Cr2O3 +SO2

37. What is the oxidation number of sulfur in each of the following:

a. SO3 c.SO2(2-)

b. Na2SO4 d. S2O4 (2-)

38.Fe(3+) ----> Fe represents oxidation, reduction, orhydrolysis?

39. When the half reactions Br2+ 2e- -----> 2Br- and Na---->e- + Na(+) are combined the balanced redox equation is_____________________ ( WRITE the BALANCED REDOX eq)

40. To balance the oxygen and hydrogen for a redox reaction thattakes place in basic solution, it is necessary to use whichsubstance?

41. What particle completes this nuclear equation? 55/25 Mn + 2/1 H====> _____ +2 1/0 n

42. The half-life of tungsten-182 (182/74 W) is 1.1x10^(17) years.How long would it take for a 376.2 kg sample to decay until only123.0 grams remain?

43. After 3 days, the quantity of certain radioisotope is reducedfrom 13.6 grams to 1.9 grams. Calculate the half-life of theisotope.

44. What is the name of the compound having the formulaC8H18.

45. What is the name of the following compound:

CH3---CH2----CH---CH2--C

I \

CH3 OH

46. What is an isomer? Give an isomer of hexane (C6H14) and drawit's structure.

47. What is the name of the hydrocarbons with double covalentbonds?

48. Draw the stucture for 3-methylbutanoic acid.

49. Draw the structure for methylbenzene?

50. What is the name of the following compound:

CH3----C-----CH3

CH3

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L07 Chem 151 Lecture Notes - Lecture 13: Titration Curve, Protonation, Equivalence Point

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