# Chemistry 201. Practical aspects of buffers. NC State University. Lecture 15

Save this PDF as:

Size: px
Start display at page:

Download "Chemistry 201. Practical aspects of buffers. NC State University. Lecture 15"

## Transcription

1 Chemistry 201 Lecture 15 Practical aspects of buffers NC State University

2 The everyday ph scale To review what ph means in practice, we consider the ph of everyday substances that we know from experience. Remember that [H + ] = 10 -ph. ph + poh = 14 Therefore that [OH - ] = 10 ph-14.

3 Two ways to make a buffer Method 1 Method 2 Add the acid and conjugate base to the solution in a defined proportion. Add a strong acid to the weak base (or vice versa) until the desired proportion [A - ]/[HA] is obtained.

4 Buffer strength The ratio [A - ]/[HA] should be as close as possible 1:1, but the amounts may vary. To make a stronger buffer you simply need to increase the amount of each component. Let s investigate. Suppose we add 1 ml of 1 M HCl to 1 liter of solution. The final concentration of HCl is M.

5 Buffer strength The ratio [A - ]/[HA] should be as close as possible 1:1, but the amounts may vary. To make a stronger buffer you simply need to increase the amount of each component. Let s investigate. Suppose we add 1 ml of 1 M HCl to 1 liter of solution. The final concentration of HCl is M. ph = 3

6 Buffer strength The ratio [A - ]/[HA] should be as close as possible 1:1, but the amounts may vary. To make a stronger buffer you simply need to increase the amount of each component. Let s investigate. Suppose we add 1 ml of 1 M HCl to 1 liter of solution. The final concentration of HCl is M. ph = 3 Suppose we add 1 ml of 1 M HCl to 1 liter of 10 mm optimal phosphate buffer solution (pka = 7.2) solution. The final concentration of HCl is M. ph = pka + log10([a - ]/[HA])

7 Buffer strength Keeping in mind that the unbuffered solution in this example ([HCl] = M) would be ph = 3 Suppose we add 1 ml of 1 M HCl to 1 liter of 10 mm optimal phosphate buffer solution (pka = 7.2) solution. The final concentration of HCl is M. ph = pka + log 10 ([A - ]/[HA]) [A - ] = = [HA] = = ph = log10(0.004/0.006) = 7.02 If the target ph = 7.2 (i.e. ph = pka) then this buffer is too weak. An error of 0.2 ph units could be significant.

8 Buffer strength Keeping in mind that the unbuffered solution in this example ([HCl] = M) would be ph = 3 Suppose we add 1 ml of 1 M HCl to 1 liter of 100 mm optimal phosphate buffer solution (pka = 7.2) solution. The final concentration of HCl is M. ph = pka + log 10 ([A - ]/[HA]) [A - ] = = [HA] = = ph = log10(0.049/0.051) = 7.18 If the target ph = 7.2 (i.e. ph = pka) then this buffer is reasonable. The difference is only

9 Buffer strength Keeping in mind that the unbuffered solution in this example ([HCl] = M) would be ph = 3 Suppose we add 1 ml of 1 M HCl to 1 liter of 300 mm optimal phosphate buffer solution (pka = 7.2) solution. The final concentration of HCl is M. ph = pka + log 10 ([A - ]/[HA]) [A - ] = = [HA] = = ph = log10(0.149/0.151) = If the target ph = 7.2 (i.e. ph = pka) then we would say that this buffer is definitely strong enough, difference =

10 Titrating to make a buffer You can create a buffer either by adding the acid and Its conjugate base to a solution or by titrating in strong base to acid (or vice versa). Remember, regardless of the method used to prepare it: The buffering strength is maximum when [HA] = [A - ] The buffering range is considered to extend from [HA] / [A - ] = 0.1 to [HA] / [A - ] = 10. This is subjective. Wertz suggests 0.01 to 100 is an acceptable range.

11 Understanding the titration curve Suppose we want to make a buffer by titrating [OH - ]. We cannot use the H-H equation initially. We do not know the concentration of [A - ]. Instead at this initial point we will use the other form of the equilibrium constant and make an ICE table. Starting point [HA] = [HA] 0 Added [OH - ] = 0

12 Understanding the titration curve Suppose we want to make a buffer by titrating [OH - ]. We cannot use the H-H equation initially. We do not know the concentration of [A - ]. Instead at this initial point we will use the other form of the equilibrium constant and make an ICE table. Starting point [HA] = [HA] 0 Added [OH - ] = 0

13 Understanding the titration curve We can calculate x = [H+] and therefore the ph from the equilibrium constant. Starting point [HA] = [HA] 0 Added [OH - ] = 0

14 Understanding the titration curve When we have a buffer we can use the Hendersen-Hasselbach equation. This is nice since it is the simplest treatment of the acid-base equilibrium. In the case shown we have ph = pk a. Maximum buffer capacity [HA] = [A - ]. Added [OH - ] = 1/2 [HA] 0

15 Understanding the titration curve The buffer range is defined as approximately from: ph = pk a 1 R = [A - ]/[HA] = 0.1 [OH - ] ~ [HA] 0 to ph = pk a + 1 R = [A - ]/[HA] = 10 [OH - ] ~ 0.91 [HA] 0 Maximum buffer capacity [HA] = [A - ] when [OH - ] ~ 0.5 [HA] 0 Buffer region

16 Understanding the titration curve Once the solution moves outside the buffer range the ph shoots up. The equivalence point is reached when the added is equal to the original acid concentration, i.e. [OH - ] ~ [HA] 0 At this point one can no longer use the H-H equation. Instead, we assume that [A - ] ~ [HA] 0 Then we use the base equil- -ibrium: Buffer region Note that pk b = 14 - pk a

17 Types of buffers There are inorganic buffers, e.g. phosphate, but there are many more organic buffers. In fact, the number of buffers is staggering. Organic buffers: Tris, HEPES, MOPS, MES Biological buffers: citrate, acetate, carbonate, malonate, Proteins themselves are polyelectrolytes and therefore tend to the buffer the solution they are in. This can have important physiological impact (e.g. hemoglobin).

18 Tris buffer Tris(hydroxymethyl)aminomethane), is an organic buffer with the formula (HOCH 2 ) 3 CNH 2. Tris has a pka = The buffer range is It is is widely used as a component for solutions of nucleic acids, proteins and for any application in which phosphate is not a good choice. For example, calcium phosphate has a low solubility product, Which means that phosphate buffers are a poor choice in any application where calcium is present. Important point: Tris can react with aldehydes since it is a primary amine. Choice of buffer should done by consulation of the chemical interactions in your application.

19 Other organic buffers HEPES: pka = 7.5 MOPS: pka = 7.2

20 Citrate buffer Citric acid is found in abundance in citrus fruits. It is also part of the citric acid cycle in biochemistry. It is a triprotic acid, with three carboxylic acid groups as seen by its structure (on the right). pk a1 = 3.14 pk a2 = 4.75 pk a3 = 6.40 Citric acid crystals under polarized light

21 Citrate buffer: species in solution The middle H atom has the lowest pka. This is because the neighboring OH group has an electron withdrawing effect that stabilizes the negative charge created.

22 Amino acids are amphipathic All amino acids contain the carboxylic acid and amino group. These have very different pka values so the amino acids have a doubly charged form (zwitterion) at ph 7. In proteins only the N- and C-terminus have these pkas. Amino acids can be classified in part according to the pka of their side chains.

23 Amino acid side chain pk a Proteins are made of up of a number of titratable amino acids. At ph 7 the terminal carboxyl, aspartate and glutamate have a negative charge. Terminal amino, lysine and arginine are positively charged. Others are neutral, but can be charged due to interactions within the protein. The pka of any of these groups may be altered by the protein.

24 The isoelectric point of a protein pi Proteins have many titratable groups on their surface. It is not possible to define a single ph since all of the groups have different pka values. However, we can define the point at which protein is neutral in charge: the isoelectric point. At the isoelectric point the protein has 0 net charge, which means that there as many positive as negative groups on the surface. The isoelectric point concept applies to polymers, nanoparticles etc. Any macromolecule can be described in terms of its overall charge. IMPORTANT: When ph = pi a macromolecule has a neutral surface. This is the minimum stability point. Macromolecules tend to precipitate at this poin.

25 Hemoglobin as a buffer Hemoglobin is the most abundant protein inside of red blood cells and accounts for one-third of the mass of the cell. During the conversion of CO 2 into HCO 3-, H + liberated in the reaction are buffered by hemoglobin, which is reduced by the dissociation of oxygen. This buffering helps maintain normal ph. The process is reversed in the pulmonary capillaries to re-form CO 2, which then can diffuse into the air sacs to be exhaled into the atmosphere.

26 Bicarbonate (hydrogen carbonate): an important regulator in the body As with the phosphate buffer, a weak acid or weak base captures the free ions, and a significant change in ph is prevented. Bicarbonate ions and carbonic acid are present in the blood in a 20:1 ratio if the blood ph is within the normal range. With 20 times more bicarbonate than carbonic acid, this capture system is most efficient at buffering changes that would make the blood more acidic. This is useful because most of the body s metabolic wastes, such as lactic acid and ketones, are acids. Carbonic acid levels in the blood are controlled by the expiration of CO 2 through the lungs.

27 The role of carbonic anhydrase The enzyme does not change the equilibrium, but it accelerates the Rate of reaching the equilibrium on each side of a membrane.

28 Acid/Base Mixtures : Reactions How do you calculate ph after an acid/base reaction occurs? Text : Section 7.3

29 Examples: Strong acids and bases What is the ph when: a) 25 ml of 0.30 M HCl are added to 35 ml of 0.20 M NaOH? b) 15 ml of 0.25 M HClO 4 are added to 25 ml of 0.20 M NaOH?

30 Examples: Strong acids and bases What is the ph when 25 ml of 0.30 M HCl are added to 35 ml of 0.20 M NaOH?

31 Examples: Strong acids and bases What is the ph when 25 ml of 0.30 M HCl are added to 35 ml of 0.20 M NaOH? Step 1. Calculate dilutions. First add the volumes Total volume = 25 ml + 35 ml = 60 ml Calculate concentrations in the solution

32 Examples: Strong acids and bases What is the ph when 25 ml of 0.30 M HCl are added to 35 ml of 0.20 M NaOH? Step 2. Write a balanced chemical reaction for the limiting reaction and the excess reaction. Limiting reaction Species HCl NaOH Na + Cl - Initial Difference -x -x x x Final x x x x

33 Examples: Strong acids and bases What is the ph when 25 ml of 0.30 M HCl are added to 35 ml of 0.20 M NaOH? Step 2. Write a balanced chemical reaction for the limiting reaction and the excess reaction. Limiting reaction Species HCl NaOH Na + Cl - Initial Difference Final Excess reaction Species HCl H + Cl - Initial Final

34 Examples: Strong acids and bases What is the ph when 25 ml of 0.30 M HCl are added to 35 ml of 0.20 M NaOH? Recognize that both HCl and NaOH are strong acid/base, respectively. Therefore, rather than find the equilibrium constant, we assume that the reaction goes to completion. In this case we find the limiting reagent which is NaOH. In the general case we could include both H + and OH - on the right hand side. We may not know initially which one is going to dominate, since we must first calculate the limiting reagent.

35 Examples: Strong acids and bases What is the ph when 25 ml of 0.30 M HCl are added to 35 ml of 0.20 M NaOH?

36 Examples: Strong acids and bases What is the ph when 25 ml of 0.30 M HCl are added to 35 ml of 0.20 M NaOH? Short cut method: Step 1. calculate number of moles of each reagent

37 Examples: Strong acids and bases What is the ph when 25 ml of 0.30 M HCl are added to 35 ml of 0.20 M NaOH? Short cut method: Step 1. calculate number of moles of each reagent Step 2. calculate the total volume ( = L) Step 3. make a table considering only H + and OH - Species H + OH - H2O Initial Difference Final

38 Examples: Strong acids and bases What is the ph when 25 ml of 0.30 M HCl are added to 35 ml of 0.20 M NaOH? Short cut method: Step 4. calculate the final concentration of [H + ] Step 5. calculate the ph

39 Examples: Strong acids and bases 15 ml of 0.25 M HClO 4 are added to 25 ml of 0.20 M NaOH?

40 Examples: Strong acids and bases 15 ml of 0.25 M HClO 4 are added to 25 ml of 0.20 M NaOH? Step 1. Calculate dilutions. First add the volumes Total volume = 25 ml + 15 ml = 40 ml Calculate concentrations in the solution

41 Examples: Strong acids and bases 15 ml of 0.25 M HClO 4 are added to 25 ml of 0.20 M NaOH? Step 2. Write a balanced chemical reaction for the limiting rxn. Excess rxn is Species HClO 4 NaOH Na + ClO - 4 Initial Difference Final Species NaOH Na + OH - Initial Final

42 use rxn table goes 100% calc ph or poh Strong Acid Weak Acid Strong Base Weak Base

43 Examples: One strong and one weak What is the ph when 50. ml of 0.25 M NaOH are added to 40. ml of 0.20 M HF?

44 Examples: One strong and one weak What is the ph when 50.0 ml of 0.25 M NaOH are added to 40.0 ml of 0.20 M HF? Step 1. Calculate dilutions. First add the volumes Total volume = 50 ml + 40 ml = 90 ml Calculate concentrations in the solution

45 Examples: One strong and one weak What is the ph when 50.0 ml of 0.25 M NaOH are added to 40.0 ml of 0.20 M HF? Step 2. Write a balanced chemical reaction and determine the form of the equilibrium constant. Make a reaction table.

46 Examples: One strong and one weak What is the ph when 50.0 ml of 0.25 M NaOH are added to 40.0 ml of 0.20 M HF? Step 2. contd. We calculate 1/K b from the data in the tables K a = 6.6 x Step 3. Make a reaction table. Species HF OH - F - Initial Difference -x -x x Final x x x

47 Examples: One strong and one weak What is the ph when 50.0 ml of 0.25 M NaOH are added to 40.0 ml of 0.20 M HF? Step 4. Solve for x

48 Examples: One strong and one weak What is the ph when 50.0 ml of 0.25 M NaOH are added to 40.0 ml of 0.20 M HF? Step 5. Calculate OH - and poh. We see from the table that [OH - ] = x = BIG PICTURE: This example is very high on the titration Curve. We can get [OH-] approximately from [OH - ] = [OH - ] 0 [HF] 0 = = The additional information from the ICE is in the third decimal place.

49 Strong base exceeds weak acid The key point of the previous problem is that we are no longer in the buffer range. We cannot use H-H in this case. Since: [OH - ] 0 > [HA] 0 While K b still applies it is often unnecessary since [OH - ] is in excess. If you need to use K b then use: Buffer region

50 use rxn table goes 100% calc ph or poh use rxn table goes 100% buffer : H-H base : poh Strong Acid Weak Acid Strong Base Weak Base

51 Examples: One strong and one weak What is the ph when 25.0 ml of 0.40 M HCl are added to 40.0 ml of 0.30 M NH 3?

52 Examples: One strong and one weak What is the ph when 25.0 ml of 0.40 M HCl are added to 40.0 ml of 0.30 M NH 3? The total volume is 65 ml so the final concentrations are: [HCl] = 25/65(0.40 M) = M [NH 3 ] = 40/65(0.30 M) = M In this case the [HCl] < [NH 3 ] so this will make a buffer. Assume that the strong acid reacts completely then at equilibrium we have: [NH 3 ] = M = 0.03 M and [NH 4+ ] = M

53 Examples: One strong and one weak

54 use rxn table goes 100% calc ph or poh use rxn table goes 100% buffer : H-H base : poh Strong Acid Weak Acid Strong Base Weak Base use rxn table goes 100% buffer : H-H acid : ph

55 Examples: Weak acid and weak base For a reaction of a weak acid and a weak base we need to calculate the equilibrium constant from the known K a s. We take the example of ammonium acetate. We see that the overal reaction is composed of two acid-base equilibria for acetate for ammonia

56 Examples: Weak acid and weak base Therefore, the overall equilibrium constant for the reaction is Now, that we can see how to calculate the Equilibrium constant, we can solve any acid-base Reaction problem using the standard methods That we have used. Step. 1. determine dilutions Step. 2. set up the reaction table Step. 3. solve for the unknown and then calculate ph

57 Examples: Weak acid and weak base 20.0 ml of 0.30 M NaH 2 PO 4 was added to 20.0 ml of 0.30 M NaHS. What are the concs. of all species at equil.?

58 Examples: Weak acid and weak base 20.0 ml of 0.30 M NaH 2 PO 4 was added to 20.0 ml of 0.30 M NaHS. What are the concs. of all species at equil.? Solution: Look up the K a for each reaction involved in this acid-base equilibrium.

59 Examples: Weak acid and weak base Species Initial Difference -x -x x x Final 0.15-x 0.15-x x x

60 Strong Acid Weak Acid Strong Base Weak Base if conjugates use H-H calc ph if not conjugates calc. K calc concs.

61 Goals Calculate the ph of acid/base mixtures Calculate the ph at any point in a titration Calculate the concentration of all species in acid/base mixtures at equilibrium

### Chemical equilibria Buffer solutions

Chemical equilibria Buffer solutions Definition The buffer solutions have the ability to resist changes in ph when smaller amounts of acid or base is added. Importance They are applied in the chemical

### Chapter 17. The best buffer choice for ph 7 is NaH 2 PO 4 /Na 2 HPO 4. 19)

Chapter 17 2) a) HCl and CH 3 COOH are both acids. A buffer must have an acid/base conjugate pair. b) NaH 2 PO 4 and Na 2 HPO 4 are an acid/base conjugate pair. They will make an excellent buffer. c) H

### Chapter 9 Acids, Bases and Buffers in the Body Outline 9.1 Acids and Bases Definitions Acids

Lecture Presentation Chapter 9 Acids, Bases and Buffers in the Body Julie Klare Fortis College Smyrna, GA Outline 9.1 Acids and Bases Definitions 9.2 Strong Acids and Bases 9.3 Chemical Equilibrium 9.4

### Chapter 21 Buffers and the titration of Acids and Bases Shuffle order make 21-3 last!

Chapter 21 Buffers and the titration of Acids and Bases Shuffle order make 213 last! 211 The HendersonHasselbalch Equation What happens when you mix an acid and its own conjugate base? Using an acetic

### 9.5 ph and the ph Scale

9.5 ph and the ph Scale Living things prefer a constant ph. Normal blood ph is strictly regulated between 7.35 and 7.45. The ph of a solution is commonly measured either electronically by using an instrument

### Note: (H 3 O + = hydronium ion = H + = proton) Example: HS - + H 2 O H 3 O + + S 2-

AcidBase Chemistry Arrhenius acid: Substance that dissolves in water and provides H + ions Arrhenius base: Substance that dissolves in water and provides OH ions Examples: HCl H + and Cl Acid NaOH Na +

### AP Chemistry- Acids and Bases General Properties of Acids and Bases. Bases- originally defined as any substance that neutralized an acid

AP Chemistry Acids and Bases General Properties of Acids and Bases Acids Electrolyte Taste Litmus Phenolphthalein React with metals to give off H 2 gas H 2 SO 4 (aq) + Mg (s) MgSO 4 (aq) + H 2 (g) Ionize

### Write the acid-base equilibria connecting all components in the aqueous solution. Now list all of the species present.

Chapter 16 Acids and Bases Concept Check 16.1 Chemists in the seventeenth century discovered that the substance that gives red ants their irritating bite is an acid with the formula HCHO 2. They called

### An acid is a substance that produces H + (H 3 O + ) Ions in aqueous solution. A base is a substance that produces OH - ions in aqueous solution.

Chapter 8 Acids and Bases Definitions Arrhenius definitions: An acid is a substance that produces H + (H 3 O + ) Ions in aqueous solution. A base is a substance that produces OH - ions in aqueous solution.

### CHEM 10123/10125, Exam 2

CHEM 10123/10125, Exam 2 March 7, 2012 (50 minutes) Name (please print) Please box your answers, and remember that significant figures, phases (for chemical equations), and units do count! 1. (13 points)

### CHEM 102: Sample Test 5

CHEM 102: Sample Test 5 CHAPTER 17 1. When H 2 SO 4 is dissolved in water, which species would be found in the water at equilibrium in measurable amounts? a. H 2 SO 4 b. H 3 SO + 4 c. HSO 4 d. SO 2 4 e.

### 4. Acid Base Chemistry

4. Acid Base Chemistry 4.1. Terminology: 4.1.1. Bronsted / Lowry Acid: "An acid is a substance which can donate a hydrogen ion (H+) or a proton, while a base is a substance that accepts a proton. B + HA

### Q.1 Classify the following according to Lewis theory and Brønsted-Lowry theory.

Acid-base A4 1 Acid-base theories ACIDS & BASES - IONIC EQUILIBRIA 1. LEWIS acid electron pair acceptor H, AlCl 3 base electron pair donor NH 3, H 2 O, C 2 H 5 OH, OH e.g. H 3 N: -> BF 3 > H 3 N BF 3 see

### Chapter 17. How are acids different from bases? Acid Physical properties. Base. Explaining the difference in properties of acids and bases

Chapter 17 Acids and Bases How are acids different from bases? Acid Physical properties Base Physical properties Tastes sour Tastes bitter Feels slippery or slimy Chemical properties Chemical properties

### 1. For the equilibrium that exists in an aqueous solution of nitrous acid (HNO 2, a weak acid), the equilibrium constant expression is:

1. For the equilibrium that exists in an aqueous solution of nitrous acid (HNO 2, a weak acid), the equilibrium constant expression is: a) K = [H+ ][NO 2 ] [HNO 2 ] b) K = [H+ ][N][O] 2 [HNO 2 ] c) K =

### 1. Read P. 368-375, P. 382-387 & P. 429-436; P. 375 # 1-11 & P. 389 # 1,7,9,12,15; P. 436 #1, 7, 8, 11

SCH3U- R.H.KING ACADEMY SOLUTION & ACID/BASE WORKSHEET Name: The importance of water - MAKING CONNECTION READING 1. Read P. 368-375, P. 382-387 & P. 429-436; P. 375 # 1-11 & P. 389 # 1,7,9,12,15; P. 436

### CHAPTERS 15 FAKE TEST QUESTIONS. 1. According to the Brønsted Lowry definition, which species can function both as an acid and as a base?

You might need to know the following K values: CHAPTERS 15 FAKE TEST QUESTIONS CH 3 COOH K a = 1.8 x 10 5 Benzoic Acid K a = 6.5 x 10 5 HNO 2 K a = 4.5 x 10 4 NH 3 K b = 1.8 x 10 5 HF K a = 7.2 x 10 4

### We remember that molarity (M) times volume (V) is equal to moles so this relationship is the definition of the equivalence point.

Titrations Titration - a titration is defined as the determination of the amount of an unknown reagent (analyte) through the use of a known amount of another reagent (titrant) in an essentially irreversible

### Chapter 9 Lecture Notes: Acids, Bases and Equilibrium

Chapter 9 Lecture Notes: Acids, Bases and Equilibrium Educational Goals 1. Given a chemical equation, write the law of mass action. 2. Given the equilibrium constant (K eq ) for a reaction, predict whether

### Buffer Solutions. Buffer Solutions

Buffer Solutions ph of solution adding 0.10 M HCl to 100 ml water HCl added ph 0 ml 7.00 2 ml 2.71 5 ml 2.32 10 ml 2.04 20 ml 1.78 50 ml 1.48 7 6 5 4 3 2 1 0 10 20 30 40 50 ml of 0.10 M HCl added Buffer

### 3 The Preparation of Buffers at Desired ph

3 The Preparation of Buffers at Desired ph Objectives: To become familiar with operating a ph meter, and to learn how to use the Henderson-Hasselbalch equation to make buffer solutions at a desired ph

### Q.1 Classify the following according to Lewis theory and Brønsted-Lowry theory.

Acid-base 2816 1 Acid-base theories ACIDS & BASES - IONIC EQUILIBRIA LEWIS acid electron pair acceptor H +, AlCl 3 base electron pair donor NH 3, H 2 O, C 2 H 5 OH, OH e.g. H 3 N: -> BF 3 > H 3 N + BF

### Review for Solving ph Problems:

Review for Solving ph Problems: Acid Ionization: HA H 2 O A - H 3 O CH 3 COOH H 2 O CH 3 COO - H 3 O Base Ionization: B H 2 O BH OH - 1) Strong Acid complete dissociation [H ] is equal to original [HA]

### KEY. Practice Problems: Applications of Aqueous Equilibria

Practice Problems: Applications of Aqueous Equilibria KEY CHEM 1B 1. Ammonia (NH 3 ) is a weak base with a K b = 1.8 x 1 5. a) Write the balanced chemical equation for the reaction of ammonia with water.

### Acids and Bases. When an acid loses a proton, the resulting species is its conjugate base. For example, NH 3 + H +

Acids and Bases Definitions An acid is a proton donor, e.g. HCl. For example, consider the reaction between HCl and H 2 O. HCl + H 2 O H 3 O + + Cl - Acid In this reaction, HCl donates a proton to H 2

### WEAK ACIDS AND BASES

WEAK ACIDS AND BASES [MH5; Chapter 13] Recall that a strong acid or base is one which completely ionizes in water... In contrast a weak acid or base is only partially ionized in aqueous solution... The

### Titrations. Acid-Base Indicators and Titration Curves. Shapes of Titration Curves. A titration curve is a graphical history of a titration

Acid-Base Indicators and Titration Curves Titrations In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical

### 3. Which of the following describes a conjugate acid-base pair for the following equilibrium? CN - (aq) + CH 3 NH 3 + (aq) H 2 CO 3 (aq) + H 2 O (l)

Acids, Bases & Redox 1 Practice Problems for Assignment 8 1. A substance which produces OH ions in solution is a definition for which of the following? (a) an Arrhenius acid (b) an Arrhenius base (c) a

### Chapter 14 - Acids and Bases

Chapter 14 - Acids and Bases 14.1 The Nature of Acids and Bases A. Arrhenius Model 1. Acids produce hydrogen ions in aqueous solutions 2. Bases produce hydroxide ions in aqueous solutions B. Bronsted-Lowry

### ACID-BASE TITRATIONS: DETERMINATION OF CARBONATE BY TITRATION WITH HYDROCHLORIC ACID BACKGROUND

#3. Acid - Base Titrations 27 EXPERIMENT 3. ACID-BASE TITRATIONS: DETERMINATION OF CARBONATE BY TITRATION WITH HYDROCHLORIC ACID BACKGROUND Carbonate Equilibria In this experiment a solution of hydrochloric

### ph: Measurement and Uses

ph: Measurement and Uses One of the most important properties of aqueous solutions is the concentration of hydrogen ion. The concentration of H + (or H 3 O + ) affects the solubility of inorganic and organic

### 2. Write a balanced chemical equation which corresponds to the following equilibrium constant expression. 1/2 3/ 2

Practice Problems for Chem. 1B Exam 1 F2011 These represent the concepts covered for exam 1. There may be some additional net ionic equations from chem. 1A. This is not the exact exam! Sections 16.1-16.3

### CH302 Exam 4 Practice Problems (buffers, titrations, Ksp)

CH302 Exam 4 Practice Problems (buffers, titrations, Ksp) 1 Equilibrium Constants The following equilibrium constants will be useful for some of the problems. Substance Constant Substance Constant HCO

### Chapter 16: Acid-Base Equilibria

Chapter 16: Acid-Base Equilibria In the 1 st half of this chapter we will focus on the equilibria that exist in aqueous solutions containing: weak acids polyprotic acids weak bases salts use equilibrium

### Chem 116 POGIL Worksheet - Week 10 - Solutions Weak Acid and Base Equilibria

Chem 116 POGIL Worksheet - Week 10 - Solutions Weak Acid and Base Equilibria Key Questions 1. A 0.0100 M solution of a weak acid HA has a ph of 2.60. What is the value of K a for the acid? [Hint: What

### Chemical Reactions in Water Ron Robertson

Chemical Reactions in Water Ron Robertson r2 f:\files\courses\1110-20\2010 possible slides for web\waterchemtrans.doc Properties of Compounds in Water Electrolytes and nonelectrolytes Water soluble compounds

### Chemical Reactions in Water

Chemical Reactions in Water Ron Robertson r2 f:\files\courses\1110-20\2010 possible slides for web\waterchemtrans.doc Acids, Bases and Salts Acids dissolve in water to give H + ions. These ions attach

### UNIT 14 - Acids & Bases

COMMON ACIDS NOTES lactic acetic phosphoric citric malic PROPERTIES OF ACIDS 1. 1. PROPERTIES OF BASES 2. 2. 3. 3. 4. 4. 5. 5. NAMING ACIDS NOTES Binary acids (H + one element) Practice: 1. hydro- - HF

### Name period Unit 9: acid/base equilibrium

Name period Unit 9: acid/base equilibrium 1. What is the difference between the Arrhenius and the BronstedLowry definition of an acid? Arrhenious acids give H + in water BronstedLowry acids are proton

### CHAPTER 16: ACIDS AND BASES

CHAPTER 16: ACIDS AND BASES Active Learning: 4, 6, 14; End-of-Chapter Problems: 2-25, 27-58, 66-68, 70, 75-77, 83, 90-91, 93-104 Chapter 15 End-of-Chapter Problems: 69-74, 125, 129, 133 16.1 ACIDS AND

### Buffer Solutions. Buffer Solutions

Chapter 18 Common Ion Effect Buffers and Titration Curves A/B Titrations Salts and Solubility Product The Common Ion Effect and If a solution is made in which the same ion is produced by two different

### CHEM 101/105 Aqueous Solutions (continued) Lect-07

CHEM 101/105 Aqueous Solutions (continued) Lect-07 aqueous acid/base reactions a. a little bit more about water Water is a polar substance. This means water is able to "solvate" ions rather well. Another

### Spring 2009 CH302 Practice Exam 2 Answer Key

Spring 2009 CH302 Practice Exam 2 Answer Key 1. What would be the ph of a solution prepared by dissolving 120.1 g of CH 3 COOH and 82 g of NaCH 3 COO in 1 L of water? Acetic acid has a K a of 1.8 x 10

### ionic substances (separate) based on! Liquid Mixtures miscible two liquids that and form a immiscible two liquids that form a e.g.

Unit 7 Solutions, Acids & Bases Solution mixture + solvent - substance present in the amount solute - in the solvent solvent molecules solute particles ionic substances (separate) based on! Liquid Mixtures

### Worksheet 23 Strong Acid/Strong Base Titrations

Worksheet 2 Strong Acid/Strong Base Titrations A. Initial ph This is always determined based solely on the initial concentration of the acid or base being titrated. Every mole of acid or base will produce

### Ch Acids and Bases. Arrhenius Definition Acids produce hydrogen ions in aqueous solution. Bases produce hydroxide ions when dissolved in water.

Ch 15-16 Acids and Bases Arrhenius Definition Acids produce hydrogen ions in aqueous solution. Bases produce hydroxide ions when dissolved in water. Limits to aqueous solutions. Only one kind of base.

### Lecture 6. Classes of Chemical Reactions

Lecture 6 Classes of Chemical Reactions Lecture 6 Outline 6.1 The Role of Water as a Solvent 6.2 Precipitation Reactions 6.3 Acid-Base Reactions 1 Electron distribution in molecules of H 2 and H 2 O The

### Name: Per: Date: Unit 11 - Acids, Bases and Salts Chemistry Accelerated Chemistry I Define each of the following: 1. Acidic hydrogens.

Name: Per: Date: Unit 11 - Acids, Bases and Salts Chemistry Accelerated Chemistry I Define each of the following: 1. Acidic hydrogens 2. Binary acids 3. Oxyacids 4. Carboxylic acid 5. Amines Name the following

### Acids and Bases. Chapter 16

Acids and Bases Chapter 16 The Arrhenius Model An acid is any substance that produces hydrogen ions, H +, in an aqueous solution. Example: when hydrogen chloride gas is dissolved in water, the following

### Notes: Acids and Bases

Name Chemistry Pre-AP Notes: Acids and Bases Period I. Describing Acids and Bases A. Properties of Acids taste ph 7 Acids change color of an (e.g. blue litmus paper turns in the presence of an acid) React

### Chapter 19: Acids and Bases Homework Packet (50 pts) Name: Score: / 50

Chapter 19: Acids and Bases Homework Packet (50 pts) Topic pg Section 19.1 1-3 Section 19.2 3-6 Section 19.3 6-7 Section 19.4 8 Naming Acids 9 Properties of Acids/Bases 10-11 Conjugate Acid/Base Pairs

### Bronsted- Lowry Acid Base Chemistry

Bronsted Lowry Acid Base Chemistry Just a few reminders What makes an acid an acid? A BronstedLowry Acid is a compound that donates a proton (a hydrogen ion with a positive charge, H + ) o Think of the

### Solubility Equilibria

Chapter 17: Acid-Base Equilibria and Solubility Equilibria Key topics: Common ion effect Buffers Acid-base equilibria Solubility equilibria; complex ion formation The Common Ion Effect If we have two solutes

### Chapter 15 Acids and Bases reading guide.

Chapter 15 Acids and Bases reading guide. Be active while reading the text. Take notes, think about what you ve read, and ask yourself questions while reading. Use this document as a guide for making your

### Acids, Bases and Concentrations

61 Chapter 7 Acids, Bases and Concentrations Thoughts or pictures of a shark usually evoke fear. But most sharks are not harmful to humans and shark attacks while dangerous and sometimes fatal are extremely

### CHAPTER 9. ANS: a. ANS: d. ANS: c. ANS: a. ANS: c

CHAPTER 9 1. Which one of the following is the acid in vinegar? a. acetic acid b. citric acid c. muriatic acid d. ascorbic acid 2. Which is a basic or alkaline substance? a. gastric fluid b. black coffee

### Acid/Base Definition. Acid/Base Reactions. Major vs. Minor Species. Terms/Items you Need to Know. you need to memorize these!!

Acid/Base Reactions some covalent compounds have weakly bound H atoms and can lose them to water (acids) some compounds produce OH in water solutions when they dissolve (bases) acid/base reaction are very

### Buffer solutions. Division of Radiooncology, Deutsches Krebsforschungszentrum, 69120 Heidelberg, Germany

Buffer solutions WOLF D. KUHLMANN, M.D. Division of Radiooncology, Deutsches Krebsforschungszentrum, 69120 Heidelberg, Germany Aqueous buffer solutions and acid-base reactions Buffer solutions have the

### Titration Curve of a Weak Acid

Titration Curve of a Weak Acid Amina Khalifa El-Ashmawy, Ph.D. Collin College Department of Chemistry Introduction: Titration is an analytical process whereby two reactant solutions are carefully reacted

### 6) Which compound is manufactured in larger quantities in the U.S. than any other industrial chemical?

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) Which statement concerning Arrhenius acid-base theory is not correct? A) Acid-base reactions must

### Acids and Bases: A Brief Review

Acids and : A Brief Review Acids: taste sour and cause dyes to change color. : taste bitter and feel soapy. Arrhenius: acids increase [H ] bases increase [OH ] in solution. Arrhenius: acid base salt water.

### Topic 5. Acid and Bases

Topic 5 5-1 Acid and Bases Acid and Bases 5-2 There are a number definitions for aicd and bases, depending on what is convenient to use in a particular situation: Arrhenius and Ostwald: Theory of electrolyte

### Acids and Bases: Definitions. Brønsted-Lowry Acids and Bases. Brønsted-Lowry Acids and Bases CHEMISTRY THE CENTRAL SCIENCE

CHEMISTRY THE CENTRAL SCIENCE Professor Angelo R. Rossi Department of Chemistry Spring Semester Acids and Bases: Definitions Arrhenius Definition of Acids and Bases Acids are substances which increase

### 4.1 Stoichiometry. 3 Basic Steps. 4. Stoichiometry. Stoichiometry. Butane Lighter 2C 4 H 10 + 13O 2 10H 2 O + 8CO 2

4. Stoichiometry 1. Stoichiometric Equations 2. Limiting Reagent Problems 3. Percent Yield 4. Limiting Reagent Problems 5. Concentrations of Solutes 6. Solution Stoichiometry 7. ph and Acid Base Titrations

### Acid/base Definitions. Acid/Base Definitions. Acid / Base Chemistry. Acid/Base Definitions. Identifying Acids and Bases

Acids Identifying Acids and Bases Acid (anhydrides) contains H+ ions as the cation, with and other element as the anion Non-metal oxide H2SO4 HI P2O5 Bases Base (anhydrides) Contains OH- as the anion Combined

### Chem101: General Chemistry Lecture 9 Acids and Bases

: General Chemistry Lecture 9 Acids and Bases I. Introduction A. In chemistry, and particularly biochemistry, water is the most common solvent 1. In studying acids and bases we are going to see that water

### CHEMISTRY 101 EXAM 3 (FORM B) DR. SIMON NORTH

1. Is H 3 O + polar or non-polar? (1 point) a) Polar b) Non-polar CHEMISTRY 101 EXAM 3 (FORM B) DR. SIMON NORTH 2. The bond strength is considerably greater in HF than in the other three hydrogen halides

### We were able to use the RICE expression to determine the ph for the autodissociation of water H 2 O H + + OH - with [H + ] = K w 0.

1 Lecture 10: The Strong Acid/Strong Base Equilibrium Calculation After an entire lecture on water with nothing added, you must be pumped to know that in this lecture something will actually be added to

### This value, called the ionic product of water, Kw, is related to the equilibrium constant of water

HYDROGEN ION CONCENTRATION - ph VALUES AND BUFFER SOLUTIONS 1. INTRODUCTION Water has a small but definite tendency to ionise. H 2 0 H + + OH - If there is nothing but water (pure water) then the concentration

### Acids and Bases: A Brief Review, see also pp and pp Brønsted-Lowry Acids and Bases 143. The H + Ion in Water

Quiz number 5 will be given in recitation next week, Feb 26Mar 2 on the first part of Chapter 16, to be covered in lectures this week. 16.1 Acids and Bases: A Brief Review 16.2 BronstedLowry Acids and

### Chapter 4 Notes - Types of Chemical Reactions and Solution Chemistry

AP Chemistry A. Allan Chapter 4 Notes - Types of Chemical Reactions and Solution Chemistry 4.1 Water, the Common Solvent A. Structure of water 1. Oxygen's electronegativity is high (3.5) and hydrogen's

### 14-Jul-12 Chemsheets A

www.chemsheets.co.uk 14-Jul-12 Chemsheets A2 009 1 BRONSTED-LOWRY ACIDS & BASES Bronsted-Lowry acid = proton donor (H + = proton) Bronsted-Lowry base = proton acceptor (H + = proton) Bronsted-Lowry acid-base

### CHM1 Review for Exam 12

Topics Solutions 1. Arrhenius Acids and bases a. An acid increases the H + concentration in b. A base increases the OH - concentration in 2. Strong acids and bases completely dissociate 3. Weak acids and

### Equilibrium Constants The following equilibrium constants will be useful for some of the problems.

1 CH302 Exam 4 Practice Problems (buffers, titrations, Ksp) Equilibrium Constants The following equilibrium constants will be useful for some of the problems. Substance Constant Substance Constant HCO

### UNIT (6) ACIDS AND BASES

UNIT (6) ACIDS AND BASES 6.1 Arrhenius Definition of Acids and Bases Definitions for acids and bases were proposed by the Swedish chemist Savante Arrhenius in 1884. Acids were defined as compounds that

### Acid-Base 2/27/2012. Definitions of Acids/Bases. Acid-Base Behavior. Arrhenius Definition. Arrhenius Definition

Acids Taste sour Burn Skin Turn Litmus Red Dissolve metals Citrus fruit Vitamin C (Ascorbic Acid) Vinegar Battery Acid Bases Taste Bitter Behavior Burn Skin/Feel Slippery Turn Litmus Blue Soap Ammonia

### ph Measurement and its Applications

ph Measurement and its Applications Objectives: To measure the ph of various solutions using ph indicators and meter. To determine the value of K a for an unknown acid. To perform a ph titration (OPTIONAL,

### CHEM 101 HOUR EXAM II 13-OCT-98. Directions: show all work for each question only on its corresponding numbered blue book page.

CHEM 101 HOUR EXAM II 13-OCT-98 Directions: show all work for each question only on its corresponding numbered blue book page. 1. Write a balanced net ionic equation for each reaction or process shown:

### ACID-BASE REACTIONS/ THE PH CONCEPT.

Dr Mike Lyons School of Chemistry Trinity College Dublin. melyons@tcd.ie ACID-BASE REACTIONS/ THE PH CONCEPT. Chemistry Preliminary Course 2011 1 Lecture topics. 2 lectures dealing with some core chemistry

### What does pka tell you?

ph and pka What does pka tell you? pka tells you if a given molecule is going to either give a proton to water at a certain ph, or remove a proton A pka of 2 for substance X means that at a ph of 2, X

### Unit Two: Acids and Bases

Section One: Theoretical Stuff Unit Two: Acids and Bases The concept of acids and bases has existed for centuries. We can discuss them two ways, operational definitions and theoretical definitions. 1.

### QUESTION (2012:3) (a) (i) Complete the table below showing the conjugate acids and bases. CO 3 H 2 O OH HCN CN -

QUESTION (2012:3) (i) Complete the table below showing the conjugate acids and bases. Conjugate acid Conjugate base - HCO 3 2 CO 3 H 2 O OH HCN CN - (ii) HPO 4 2 (aq) Write equations for the reactions

### Atoms Atom smallest part of an element that has the characteristics of that element. Each element has a distinct atom based on structure.

Atoms Atom smallest part of an element that has the characteristics of that element. Each element has a distinct atom based on structure. Nucleus- positively charged contains protons (p+), neutrons(n0),

### If we write these equations in ionic form, in each case the net ionic equation is the same; H 3 O + (aq) + OH - (aq) H 2H 2 O(l)

CHEM 1105 ACIDS AND BASES 1. Early Definitions Taste: Effect on Indicators: Neutralization: acids - sour; bases - bitter acids turn blue litmus red; bases turn red litmus blue phenolphthalein is colourless

### ph of strong acid and base

ph of strong acid and base What does strong mean in terms of acids and bases? Solubility. Basically, if you say an acid or base is strong, then it dissociates 100% in water. These types of situations are

### Types of Reactions. What are Acids &Bases? Chapter 15. Acids & Bases. Definition? a) Arrhenius. b) Bronsted-Lowry. c) Lewis

Chapter 15. Acids & Bases Acid/Base Definitions Types of Acids/bases Polyprotic Acids The Ion Product for Water The ph and Other p Scales Aqueous Solutions of Acids and Bases Hydrolysis The Common Ion

### Similarities The ph of each of these solutions is the same; that is, the [H + ] is the same in both beakers (go ahead and count).

Compare 1 L of acetate buffer solution (0.50 mol of acetic acid and 0.50 mol sodium acetate) to 1 L of HCl solution AcO - AcO - H+ Cl - AcO - AcO - Cl - Cl - AcO - Cl - Cl - Cl - Cl - AcO - AcO - AcO -

### CHEMISTRY 101 EXAM 3 (FORM A) DR. SIMON NORTH

CHEMISTRY 101 EXAM 3 (FORM A) DR. SIMON NORTH 1. When considering conjugate acids and bases, (2 points) a) Strong acids have strong conjugate bases. b) Strong bases have strong conjugate acids. c) Weak

### WATER, ph, ACIDS, BASES, AND BUFFERS

COURSE READINESS ASSESSMENT FOR PHYSIOLOGY WATER, ph, ACIDS, BASES, AND BUFFERS Sections in this module I. Water is a polar molecule II. Properties of water III. ph IV. Acids and bases V. Buffers I. Water

### b. Calculate these values based on the given information and your calculations in (a). ph poh [H3O +1 ] [OH 1 ] [H3O +1 ] [OH 1 ]

Name Period Date Pre-AP Chemistry Review: Acids & Bases 1. 0.18 M phenol acid forms this equilibrium: C6H5OH (aq) + H2O(l) C6H5O -1 (aq) + H3O +1 (aq) + Energy ; (K=1.60 10-10 ) a. Complete the ICE chart

### Chapter 10 Acid-Base titrations Problems 1, 2, 5, 7, 13, 16, 18, 21, 25

Chapter 10 AcidBase titrations Problems 1, 2, 5, 7, 13, 16, 18, 21, 25 Up to now we have focused on calculations of ph or concentration at a few distinct points. In this chapter we will talk about titration

### Worksheet 4-2 Bronsted Acids and Equilibria

Worksheet 42 Bronsted Acids and Equilibria Worksheet 42 Bronsted Acids and Equilibria Name Date Due Hand In With Corrections by 1. Write the formula for a proton 2. Write the formula for a hydrated proton

### Chemical reactions. Classifications Reactions in solution Ionic equations

Chemical reactions Classifications Reactions in solution Ionic equations Learning objectives Distinguish between chemical and physical change Write and balance chemical equations Describe concepts of oxidation

### 1. Identify the Bronsted-Lowry acids and bases and the conjugate acid base pairs in the following reactions.

Exercise #1 Brønsted-Lowry s and Bases 1. Identify the Bronsted-Lowry acids and bases and the conjugate acid base pairs in the following reactions. (a) HCl(aq) + H 2 O(l) H 3 O + (aq) + Cl (aq) (b) H 2

### Lecture 6: Lec4a Chemical Reactions in solutions

Lecture 6: Lec4a Chemical Reactions in solutions Zumdahl 6 th Ed, Chapter 4 Sections 1-6. 4.1 Water, the Common Solvent 4.2 The Nature of Aqueous Solutions: Strong and Weak Electrolytes 4.3 The Composition

### Acids, Bases, Salts, and Buffers

Acids, Bases, Salts, and Buffers GOAL AND OVERVIEW Hydrolysis of salts will be used to study the acid-base properties of dissolved ions in aqueous solutions. The approximate ph of these solutions will

### p3 Recognizing Acid/Base Properties when p11 Recognizing Basic versus Nonbasic

General Chemistry II Jasperse Acid-Base Chemistry. Extra Practice Problems 1 General Types/Groups of problems: Conceptual Questions. Acids, Bases, and p1 K b and pk b, Base Strength, and using K b or p7-10