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Unit 10

WPHS

Acid-Base

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Chemistry Unit 10: Acids and Bases

Assignment Done In Class?Podcast 10.1 Acid-BaseWorksheet 10.1: Acid-Base Podcast 10.2 Acid-Base Hydrolysis Worksheet 10.2 Acid-Base Hydrolysis Small-Scale Acid-Base Lab Purple Cabbage Demo Take Home Lab: Purple Cabbage (optional)Podcast 10.3 pH/pOHWorksheet 10.3 pH/pOHPodcast 10.4 Neutralization ReactionsWorksheet 10.4 Neutralization ReactionsPodcast 10.5 Titration Worksheet 10.5 Titration Titration Lab Podcast 10.6 Salt HydrolysisWorksheet 10.6 Salt Hydrolysis

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Unit 10 VocabUnit 10 Exam

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Unit 10 Vocabulary

AcidBaseHydroxide ionHydronium ionSelf-ionizationNeutral solutionAcidic solutionBasic solutionAlkaline solutionpHmonoprotic aciddiprotic acidtriprotic acidArrhenius acidArrhenius baseBronsted-Lowry acidBronsted-Lowry baseLewis acidLewis baseAmphotericConjugate acidConjugate baseConjugate acid-base pairStrong acidWeak acidStrong baseWeak baseNeutralization reactionStandard solutionTitrationEnd pointEquivalence point

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Take Home Lab Name_____________________Parent/Student Experiment Date__________Period______

Red Cabbage Indicator

Subject/Concept: Chemistry/Acids-Bases, Indicators

Purpose: The purpose of this laboratory is to investigate the indicator properties of red cabbage and to classify household acids and bases.

Materials: 2 or 3 leaves of a red (purple) cabbage torn into small pieces. water blender 6 clear glasses or plastic cups 5 or more kitchen or food products (suggestions: baking soda, vinegar, soaps, lemon juice, cleansers with

ammonia, drain clog remover, milk, clear sodas, other food or drink liquids or powders, antacid tablets, ....)

Procedure:SAFETY PRECAUTIONS:

1. Treat all kitchen products used in this lab with extreme care as they may be very acidic or very basic and can therefore be toxic or corrosive.

2. Do NOT mix any of the household chemicals together as these chemicals may react with each other (especially the cleansers and soaps!).

3. The purple solution produced from the red cabbage leaves may stain clothing, counters, or floors. If spilled, wash surface promptly.

1. Read and then reread the above SAFETY PRECAUTIONS.2. In the blender, blend the cabbage and about 2 cups of water for about 30 seconds to make a purple solution. Fill

one glass at least one inch with the cabbage juice in a glass. This purple is the color of the cabbage juice in a neutral water solution, the control solution.

3. Place 1/3 of a cup of any of the five kitchen or food products which are clear liquids in the other five cups. If the product is a powder, use only a teaspoon of the powdered product dissolved in a 1/3 cup tap water. If the product to be used is a colored liquid (like milk), first dilute the liquid with water so that it is fairly transparent and use 1/3 cup of this solution.

4. Add approximately two tablespoons of the cabbage solution to each glass and observe the color of the resulting solution.

Questions:1. Knowing that baking soda and ammonia are basic and that vinegar and lemon juice are acidic, try to

classify all of the products you used as basic, acidic, or neutral. Give the reasoning each classification.2. As an extension, you may wish to repeat the above experiment using strong tea as an indicator. The

tea will change from a deep brown to a light yellow across the pH scale. (Which way does the color change as pH increases?)

For Credit:To receive credit, your parent or guardian must write a short note confirming that you performed the

experiment for them and explained the results to their satisfaction using the concept of acid/base indicators. Attach your note to the back of this sheet.

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Small-Scale Lab: Strong and weak acids and bases (SS31)Revised from:Waterman, E. L. (2002). Strong and weak acids and bases. In Small-scale chemistry laboratory

manual. Upper Saddle River, NJ: Prentice-Hall, Inc.

Objectives:1. Identify and distinguish between strong and weak acids and strong and weak bases.2. Identify acids and bases as hydrogen—ion acceptors and hydrogen-ion donors.3. Identify conjugate acid—base pairs in acid—base reactions.4. Describe acid—base reactions by using hydrogen—ion transfer equations.5. Explain the differences between strong and weak acids and bases by using equilibrium

principles.

Background:You have seen that acids are substances that react with water to produce H ions in

solutions. Similarly, bases are chemicals that react with water to produce 0H ions. For example, you have already seen that when an acid like HC1 dissolves in water, it reacts by transferring a hydrogen ion to water according to the following equation:

HCl + H2O H3O+ + Cl-

To what degree does this reaction proceed? Do all the molecules of HC1 react, or do only some of them transfer hydrogen ions while others remain intact?

Purpose:In this lab you will take a new look at acids and bases and classify them according to the Brønsted-Lowry theory. You have already acquired working definitions of acids and bases. Acids turn BTB yellow and produce hydrogen ions in solution. Bases turn BTB blue and produce hydroxide ions in solution. You will use BTB (bromthymol blue) and UI (universal indicator) as probes to classify solutions as acids and bases. You will review how to write net ionic equations to show how each substance transfers a hydrogen ion to or from water. You will learn to identify the acid-base conjugate pairs in hydrogen-ion transfer equations. You will then use the hydrogen carbonate ion, HCO3

-, to investigate acid-base reactions and group acid solutions according to relative strengths. You will use your data to formulate the concept that acids and bases can be classified as both strong and weak, depending on their behavior.

Materials and Equipment: NaHSO4 NaHCO3 NaH2PO4 Na2HPO4 CH3COONa Na3PO4 Ca(OH)2 HNO3 HCl H2SO4

NaOH KOH NaHSO3 CH3COOH Na2CO3

UI H3BO3 C6H8O7 NH4Cl NH3

BTB

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Experimental/Data Page:

Part A: Acids and IndicatorsMix 1 drop of each indicated solution. Look carefully for similarities and differences to distinguish strong acids from weak acids.

***************STRONG ACIDS***************** ----------------WEAK ACIDS----------------

1 drop eachhydrochloric

HClnitricHNO3

sulfuricH2SO4

2 drops HCl + 9 drops

H2Oethanoic

CH3COOHcitric

C6H8O7

boric H3BO3

BTB

Record the color

UIRecord the color and the matching pH

Part B: Acids, Bases, and IndicatorsMix 1 drop of the indicator (BTB or UI) with 5 drops of each indicated solutions. Record your results.

5 drops each NaHSO4 NaOH Na2HPO4 KOH NaHCO3 Na2CO3 NaH2PO4

BTB

Record the color

UIRecord the color and the matching pH

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Questions for Analysis:Use what you learned in this lab to answer the following questions.

1. What are

the limitations of using the color chart to identify the pH of each substance?

2. What does BTB indicate that all solutions in Part A can be classified as?

3. React each chemical with water and to show that the substance is either an acid or a base

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1 drop each NaHSO3Ca(OH)2 NaCH3COO Na3PO4 NH3

BTB

Record the color

UIRecord the color and the matching pH

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Determining the Concentration of Acetic Acid in Commercial VinegarIntroductionThe neutralization of an acid by a base can be done using titration. In titration, a solution of known acidity, or pH, is added gradually to a basic solution of unknown pH. When the unknown solution is exactly neutralized, as shown by the color of an acid-base indicator or by the reading of a pH meter, it is said that the number of hydronium ions equals the number of hydroxide ions.

moles H3O+ = moles OH-

In titration, the solutions are dispensed from burettes. The volume used of each solution is calculated by subtracting the volume read before the titration from the volume read after the titration. The volume in a buret can be read accurately to +/- 0.01 mL.

Before the titration of the unknown can be done the titrant (solution being used for the titration) must standardized (calculating the accurate concentration). A solution whose concentration is known to a high degree of accuracy is known as a standard solution. In this experiment you will use solid KHC8H4O4, potassium hydrogen phthalate, to prepare a very accurate solution. This solution will be used to titrate a solution of sodium hydroxide in order to standardize it. This standardized solution of sodium hydroxide will then be used to titrate vinegar to find the molarity of commercial vinegar.ProcedurePart A. Standardization of solution of Sodium Hydroxide

1. Make 250 mL of a 0.1 M solution of NaOH. You will be provided with a solution of NaOH of known concentration (approximate). Use distilled water, prepare, stopper, and store this in an Erlenmeyer flask.

2. Clean a 50 mL buret thoroughly with distilled water. Mount the buret vertically in a buret clamp attached to a ring stand. Place a white sheet of paper beneath the buret.

3. Rinse the buret with 5 mL of the NaOH solution, 3 times. Let each portion drain out of the buret before the next rinse. Dispose of the waste NaOH. (This step is done so that any water that might be in the buret prior to the experiment will not dilute your NaOH during the titration.) Fill the buret with NaOH.

4. Get approximately 0.5 grams of KHC8H4O4 into a 125 mL erlenmeyer flask. Make sure that you know the exact mass of your solid acid.

5. Dissolve the KHC8H4O4 into about 50 mL of water. Make sure that it is completely dissolved.

6. Now, slowly titrate the NaOH into the KHP, swirling at all times, until the solution turns the lightest shade of pink possible. The color needs to stay a pale pink for 15-30 seconds. This is the endpoint.

7. Do one "quick & dirty" titration to get an approximate amount. 8. Record all information so that you know exactly how much NaOH was added to the

flask.9. Do at least three trials, with usable data, to insure accurate results. Rinse out your buret

three times with tap water after completion of this experiment and then fill it with water.

10. Calculate the molarity of the NaOH solution using the mass of the KHC8H4O4. Use stoichiometry to do this.

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Part B: Determination of the Molarity of Acetic Acid in Vinegar1. Pipette 20 mL of commercial vinegar into a 200 mL volumetric flask (or 25 mL into a

250 mL volumetric) and dilute with DI water. Transfer this solution to an Erlenmeyer and label it 10% vinegar solution.

2. Pipette 25 mL of the 10% vinegar to a flask. Add 2 drops phenolphthalein indicator. Titrate the vinegar with your standardized NaOH.

3. Do one "quick & dirty" titration to get an approximate amount and then 3 trials. Rinse out your buret three times with tap water after completion of this Experiment and then fill it with water.

4. Calculate the molarity of the 10% solution of vinegar. 5. Multiply by 10 to get the concentration of commercial vinegar.

 Questions1. Why did you have to be careful to measure the precise amounts of acids and base used in

a titration but you could add as much water as you wanted to the flask while titrating the solution?

2. Discuss at least three sources of error.3. If a young child drank a large amount of vinegar or other acid, what might be a possible

way to help the child?ConclusionRestate the purpose of the lab. Summarize the procedure briefly explaining why each part (A, B) was performed in order to determine the molarity of acid in vinegar. Suggest how your results could be more accurate.

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Determining the concentration of acetic acid in commercial vinegar

Data:Part A: (Numbering corresponds to procedural steps)

1. Calculate volume of ___M NaOH needed to make 250ml of 0.1M NaOH. (The molarity will be given to you by your teacher)

M1V1=M2V2

Then dilute to V1 250ml in erlenmeyer flask. 6 – 9.

11. Calculate molarity of NaOH from mass of KHC8H4O4. (The equation is given below)

NaOH + KHC8H4O4 NaKC8H4O4 + HOH

Trial 1 =

Trial 2 =

Trial 3 =

Average of 3 trials =

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Trial 1 Trial 2 Trial 3Volume NaOH Endpoint (ml)Mass KHC8H4O4 (g)

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Worksheet 10.1: Acid-Base & pH Name

1. Listed below are some of the properties of acids and bases. Fill in the blanks with the appropriate word, acids or bases:

a) _______ produce hydrogen ions (H+) in solution e) _______ have a sour taste

b) _______ have a bitter taste f) _______ have a slippery, soapy feel

c) _______ produce hydroxide ions (OH-) ions g) ____ react with acids to form salts

d) _______ react with bases to form salts h) _______ react with many metals

2. List 3 strong acids and explain why these acids are considered strong acids.

3. List 3 weak acids and explain why these acids are considered weak acids.

4. List 2 strong bases and explain why these bases are considered strong bases.

5. List 1 weak base and explain why it is considered a weak base.

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Worksheet 10.2: Acid-Base HydrolysisWrite a balanced equation for the dissociation (ionization) of the following acids in water (For those acids that are strong use a single arrow, , and for those that are weak you need to use a double arrow, ↔)

a) HClO4 H+ + ClO4-

b) H2SO4

c) HC2H3O2

d) H2S

e) HCl

f) HNO3

6. Write an equation for the dissociation (ionization) of the following bases in water. (For those acids that are strong use a single arrow, , and for those that are weak you need to use a double arrow, ↔)

a) NaOH

b) Ca(OH)2

c) Ba(OH)2

d) KOH

e) LiOH

f) NH3 + HOH

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Worksheet 10.3: pH and pOH Calculate the appropriate values for pH, pOH, hydronium ion and hydroxide ions in this table.

[H+] (Mol/L) [OH-] (Mol/L) pH pOH Acid, Base, or neutral

1.34 10-6

2.54 10-10

2.6

5.9

2.76 10-1

9.25 E -2

12.5

2.89

3.45 E -7

2.75 E -6

5.55

4.67 E -8

2.55 x 10 -11

14

1

7

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Worksheet 10.4: Neutralization Name1. When an acid and base neutralize each other, what two substances are formed?

2. Write and balance the neutralization reactions for the followinga. HBr + KOH

b. HCl + LiOH

c. HF + Ba(OH)2

d. H2SO4 + LiOH

e. H3PO4 + NaOH

f. H2SO4 + Al(OH)3

g. H3PO4 + Mg(OH)2

h. Phosphoric acid + silver hydroxide

i. Nitric acid + Iron III hydroxide

j. Ammonia reacts with Sodium hydroxide

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Worksheet 10.5: Titration 1. When titrating an acid with a base, how do you see that you have reached the end of the

titration?

2. What indicator is clear in an acid and pink in a base?

3. A student pours exactly 26.9 mL of HCl acid of unknown molarity into a beaker. The student then adds 2 drops of the indicator spelled correctly in question #4 above and titrates the acid to neutrality using 43.7 mL of 0.13 M NaOH base.

a. Write and balance the neutralization reaction of the acid and base.

b. What is the molarity of the acid?

4. A student makes an acid by dissolving 34 grams of KHSO4 in 150 mL of water. a. Calculate the molarity of the KHSO4 acid

b. The student then uses 32.6 mL of the KHSO4 acid to titrate 12.1 mL of a KOH base of unknown molarity. Calculate the molarity of the KOH base solution

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5. In a laboratory, you make a base by adding 75 grams of NaOH to 380 mL of water. a. Calculate the molarity of the NaOH base

b. Then you titrate 15 mL of your base using a nitric acid (HNO3) that is 2.2 M. How many mL of the 2.2 M HNO3 acid will be required to titrate the 15-mL of base?

6. A student makes a standard acid by dissolving 4 grams of KHSO4 in 250 mL of water. a. What is the molarity of the standardized acid?

b. The student then uses 45 mL of the standard acid to titrate 20 mL of NaOH. What is the molarity of the base?

c. Using the base from part (b) to titrate 20 mL of an 0.32 M HCl would require how many mL of the base?

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Worksheet 10.6: Salt Hydrolysis

1. React each of the following ions with water and determine if it is an acid or a base. (Generally, those ions that have a negative charge gain a H+ and those that have a positive charge lose one H+)

a. C2H3O21-

b. NH4+

c. F-

d. CN-

e. CH3NH2+

f. NO2-

g. C5H5NH+

h. H2PO4- (this is the exception to the positive and negative rule)

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