Slide 1

Volume of Titrant

pHAcid-Base TitrationO12-10732 r1.041

The Snapshot button is used to capture the screen. The Journal is where snapshots are stored and viewed.The Share button is used to export or print your journal to turn in your work.

IntroductionJournals and SnapshotsNote: You may want to take asnapshot of the first page ofthis lab as a cover page for your Journal.Each page of this lab that contains the symbol

should be inserted into your journal. After completing a lab page with the snapshot symbol, tap (in the upper right hand corner) to insert the page into your journal.

Acid-Base Titration

2

Lab Challenge

Many foods and household products contain acids and bases. Knowing if a sample is acidic or basic is only part of the question. How do you determine the actual amount of acid or base dissolved in a solution? Acid-Base Titration

3

Background

Titration is a common quantitative laboratory method used to determine the concentration of a reactant. A reagent of known concentration, called the titrant, is used to react with a measured volume of another reactant, called the analyte. The point at which the number of moles of the titrant and the analyte are equal is called the equivalence point. On a titration curve, the equivalence point is the point where the slope is the steepest. TitrantAnalyteEquivalence pointAcid-Base Titration4

...Background

When a basic solution is added to an acidic solution of unknown concentration, hydroxide ions (OH-) from the basic solution react with hydronium ions (H3O+) from the acidic solution to form neutral water and a salt. The type of salt formed depends on the acid and base used. This is called a neutralization reaction.

Acidic solutionBasic solution

Neutral solution+Acid-Base Titration5

This image is a reminder that you need to tap to take a snapshot of this page after you have entered your response.

Self-CheckTitrations are used to determine the _____________ of a reactant. densitypHmassconcentration

Acid-Base Titration

L6 Text box[ The best choice is ]

6

Safety

Follow all common laboratory safety proceduresSodium hydroxide, hydrochloric acid, and acetic acid are corrosive irritants. Avoid contact with the eyes and wash hands after handling.When mixing acids with water, always add the acid to the water, not the other way around, as the solution can get hot enough to boil. Be sure that all acids and bases are neutralized before being disposed of down the drain. BE SAFEAlways wash hands to remove residue before leavingAcid-Base Titration

7Materials and Equipment

Collect all of these materials before beginning the lab.Drop counterpH sensorMagnetic stirrerMicro stir barBeakers (2), 50-mLBuffer solution pH 4, 25 mLBuffer solution pH 10, 25 mLFunnelGraduated cylinder, 100-mLAcid-Base Titration

8

...Materials and Equipment

Also collect these additional materials before beginning.Buret, 50-mLBuret clampRing standRight-angle clampBeakers (2), 250-mLTransfer pipetVolumetric pipet or graduated cylinder, 10-mLWash bottle filled with distilled (deionized) waterAcid-Base Titration

9...Materials and Equipment

Also collect these additional materials before beginning.Waste container deionized (distilled water), 200 mLStandardized sodium hydroxide solution, 100 mLHydrochloric acid solution, 10 mLAcetic acid solution, 10 mL wasteAcid-Base Titration

Distilled Water

waste10

Sequencing Challenge

A. Setup the titration equipment and calibrate the pH sensor. B. Measure and record the starting volumes of NaOH and HCl. Start collecting data and then release the titrant.

C. Thoroughly clean the equipment and then repeat the procedure using acetic acid. D. When the pH is 12, close the stopcock and then stop collecting data. Record the final volume of NaOH. The steps to the left are part of the procedure for this lab activity. They are not in the right order. Determine the correct sequence of the steps, then take a snapshot of this page.Acid-Base TitrationL6 Text box[ The correct sequence of steps is ]

11Connect the pH sensor to the data collection system.Calibrate the pH sensor: Pour approximately 25 mL of the pH 4 buffer solution in a 50-mL beaker.Pour approximately 25 mL of the pH 10 buffer solution in a second 50-mL beaker. Remove the pH sensor from its electrode storage bottle and rinse it with distilled water to thoroughly clean the sensor. Read the instructions on how to calibrate the pH sensor on the next page. Setup: HCl TitrationBuffer solutions and pH sensorAcid-Base Titration

12To Calibrate the pH Sensor: Note: During the calibration process you will not be able to return to this page. 1. Open the Calibrate Sensor screens: Tap Tap CALIBRATE SENSOR

2. Ensure that the correct measurements are selected: Sensor: (name of sensor) Measurement: pH Calibration Type: 2 pointb. Tap NEXT Calibration Point 1: Place the pH probe in a pH 4 buffer solution. Enter 4.0 as the pH in the Standard Value box under Calibration Point 1. Tap Read From Sensor underCalibration Point 1. Rinse the pH probe thoroughly using distilled water.

4. Calibration Point 2:Repeat the process used in calibration point 1 using a pH 10 buffer solution. Tap OK to exit the calibration screen and then tap OK again to return to the lab.

Acid-Base Titration

13

Setup: HCl TitrationConnect the drop counter to the data collection system.Assemble the titration apparatus.

Q1:Using the terms accuracy and precision, explain why it is necessary to calibrate the pH sensor. Acid-Base TitrationBuret clampRing standRight-angle clampDrop counterBeaker, 250-mLBuretpH sensorMicro stir barMagnetic stirrer

L6 Text box[ The pH sensor needs to be calibrated ]

14

Q2:Why is it necessary to rinse the buret with standardized NaOH solution? Setup: HCl TitrationUse a transfer pipet to rinse the inside of the buret with several milliliters of the standardized sodium hydroxide (NaOH) solution.Drain the NaOH from the buret into the waste container.Repeat this process two more times. Make sure the stopcock on the buret is in the "off" position and then use a funnel to fill the buret with ~50 mL of the standardized NaOH solution (titrant). Off positionOnpositionAcid-Base Titration

L6 Text box[ The buret needs to be rinsed with NaOH solution ]

15

Setup: HCl TitrationPractice adjusting the stopcock on the buret so that the titrant goes through the drop counter in distinguishable drops that fall at about 2 to 3 drops per second. Note: It is important that you have good control of adjusting the stopcock. If you accidently open the stopcock too far and the NaOH flows out (as opposed to drops out), then you will have to start over. Close the stopcock and then remove the waste container. Q3: Why is it be necessary to start your titration over again if you accidently allow the titrant to flow out of the stopcock instead of drop? Acid-Base TitrationL6- Text box[ If you accidently allow the titrant to flow out of the stopcock instead of drop ]

16

Setup: HCl TitrationQ4:Record the initial volume of NaOH and the concentration of the standardized NaOH solution in the text box below.Read the initial volume of the titrant in the buret to 0.01 mL.Using the 100-mL graduated cylinder measure 100 mL of distilled water and add it to a clean 250-mL beaker.Using the 10-mL graduated cylinder or volumetric pipet measure 10.0 mL of hydrochloric acid (HCl) and add it to the 100 mL of distilled water. Record the exact volume of HCl added in the text box on the next page. Caution: Always add acid to water.Acid-Base TitrationL6 Text box[ Initial volume of NaOH: ][ Concentration of NaOH: ]

17

Setup: HCl TitrationAdd the pH sensor, micro stir bar, and 250-mL beaker containing the acidic solution to the titration apparatus. Turn on the magnetic stirrer and begin stirring at a slow to medium speed.Q5:Record the volume of HCl added to the beaker in the text box below. Note: Make sure the bulb of the pH sensor is fully submerged.Acid-Base Titration

L6 text box[ Initial volume of HCl: ]

18Tap to start collecting data. Carefully open the stopcock on the buret so that 2 to 3 drops per second are released.

Continue to collect data until the pH of the solution is 12.Collect Data: Continue to the next page.Acid-Base Titration

Graph pH versus Drop Count (drops)19Q6:Why is it necessary to stir the solution during a titration?

Q7:What substances are being formed in the beaker? Acid-Base Titration

L3 Digits- pH

L4 Text box[ It is necessary to stir the solution ] L5 text box[ The products being formed in the beaker are ] L6 Digits drop count (drops)20Collect Data: When the pH of the solution is 12 close the stopcock.

Continue to the next page.Acid-Base TitrationGraph pH versus Drop count (drops)

L6 - Digits pH21

Collect Data:Tap to stop data collection. 6. Record the final volume of NaOH in the buret.Acid-Base Titration

Graph- pH versus Drop Count (drops)

L6 text box[ Final volume of NaOH: ]

22* To View a Page in the Journal: Tap to open the Journal screen. Tap or to scroll through the thumbnail size pages of the journal. Tap the thumbnail image of the page to view it. Data Analysis: HClDetermine the total volume of NaOH used in the titration by following steps a-c below.

Enter the final volume of NaOH in the text box on the right.Record the initial volume of NaOH in the text box on the rightSubtract the initial volume of NaOH from the final volume of NaOH and record the total volume in the text box on the right. Volume NaOH = Final Volume NaOH - Initial Volume of NaOHAcid-Base Titration

Note: Initial and final volumes of NaOH were recorded earlierin the journal. Refer to the journal to get these numbers.*

L6 text box[ a. Final volume NaOH: ][ b. Initial volume NaOH: ][ c. Total volume of NaOH used: ]

23*To Create a Calculation:Tap to open the Experiment Tools screen. Tap CALCULATED DATA to open the calculator. Enter the calculation in the space provided. Tap Measurements to insert collected data into the calculation.Note: [drop count] = collected datavolume of titrant = total volume of NaOH used (it is in your journal)final drop count = the total number of drops added (it is displayed on the right) Data Analysis: HCl2. Create a calculation to convert drop count to volume (mL). *CalcVolume1 = [drop count]*(volume of titrant/final drop count)Acid-Base Titration

L3 Digits drop count (drops)24Tap then to see the slope.Tap or buttons to move to nearby points. Tap .

Tap then to open the Graph Properties screen. Tap the Measurement box for the x-axis and tap CalcVolume1. Then tap OK. Tap to scale the axes. 3. Change the x-axis to display CalcVolume1 of NaOH. Acid-Base Titration

4. Display the volume of NaOH at the equivalence point. The equivalence point is the point on the curve with the greatest slope and is found using the slope tool.

25Data Analysis: HClCalculate the molar concentration of HCl. Follow the steps below:Determine the number of moles of NaOH added using the volume of NaOH at the equivalence point and the molarity of the standardized NaOH solution.Convert from moles of NaOH to moles of HCl using the balanced chemical equation.Use the moles of HCl and the starting volume of HCl to determine the molarity of the acid. Note: the values need for the calculations above can be found in your journal .Acid-Base Titration

L456 text box[ a. moles of NaOH: ][ b. moles of HCl: ] [ c. molarity of HCl: ]

26

Setup: Acetic Acid Titration Turn off the magnetic stirrer and then remove the beaker. Dispose of its contents according to your teacher's instructions.Place the waste container under the pH sensor and use the wash bottle to thoroughly clean the micro stir bar and the pH sensor. Re-fill the buret so that there is ~50 mL of the standardized NaOH solution.Read the initial volume of the titrant in the buret to 0.01 mL.Q1: Record the initial volume of NaOH, the concentration of the standardized NaOH solution in the text box below.Acid-Base TitrationL6 text box[ Initial volume of NaOH: ] [ Concentration of NaOH: ]

27

Setup: Acetic Acid Titration Using the 100-mL graduated cylinder measure 100 mL of distilled water and add it to a clean 250-mL beaker.Using a clean 10-mL graduated cylinder or volumetric pipet measure 10.0 mL of acetic acid and add it to the 100 mL of distilled water. Caution: Always add acid to water.Remove the waste container from the titration apparatus and replace it with the 250-mL beaker containing the acetic acid solution.Reposition the pH sensor and then turn on the magnetic stirrer and begin stirring at a slow to medium speed.Q2:Record the volume of the acetic acid solution that was added to the beaker in the text box below. Acid-Base TitrationL6 text box[ Initial volume of acetic acid: ]

28Tap to start collecting data. Carefully open the stopcock on the buret so that 2 to 3 drops per second are released.

Continue to collect data until the pH of the solution is 12. Collect Data: A.A. Continue to the next page.Acid-Base Titration

Graph- pH versus Drop Count (drops)29

Q4: What type of reaction is occurring?Q3: What substances are being formed in the beaker? Acetic Acid = HC2H3O2HC2H3O2 + NaOH ?Acid-Base Titration

L3 Digits - pHL4 text box[ The products being formed in the beaker are ] L5 text box[ The type of reaction ] L6- Digits Drop count (drops)

30Collect Data: A.A.When the pH of the solution is 12 close the stopcock.

Continue to the next page.Acid-Base TitrationGraph pH versus Drop Count (drops)

L6- Digits - pH31

Tap to stop data collection. Record the final volume of NaOH in the buret.Acid-Base TitrationCollect Data: A.A.

Graph pH versus Drop Count (drops)

L6 text box[ Final volume of NaOH: ]

32* To View a Page in the Journal: Tap to open the Journal screen. Tap or to scroll through the thumbnail size pages of the journal. Tap the thumbnail image of the page to view it. Data Analysis: Acetic Acid Determine the total volume of NaOH used in the titration. Follow steps a-c below.

Enter the final volume of NaOH in the text box on the right.Record the initial volume of NaOH in the text box on the rightSubtract the initial volume of NaOH from the final volume of NaOH and record the total volume in the text box on the right. Volume NaOH = Final Volume NaOH - Initial Volume of NaOHAcid-Base Titration

Note: Initial and final volumes of NaOH were recorded earlierin the journal. Refer to the journal to get these numbers.*

L6 text box[ a. Final volume NaOH: ][ b. Initial volume NaOH: ][ c. Total volume of NaOH used: ]

33*To Create a Calculation:Tap to open the Experiment Tools screen. Tap CALCULATED DATA to open the calculator. Enter the calculation in the space provided. Tap Measurements to insert collected data into the calculation.Note: [drop count] = the collected datavolume of titrant= total volume of NaOH used (it is in your journal)final drop count= the total number of drops added (it is displayed on the right) Data Analysis: Acetic Acid 2. Create a calculation to convert drop count to volume (mL). *CalcVolume2 = [drop count]*(volume of titrant/final drop count)Acid-Base Titration

L3 Digits Drop Count (drops)34Tap then to see the slope.Tap or buttons to move to nearby points. Tap .

Tap then to open the Graph Properties screen. Tap the Measurement box for the x-axis and tap CalcVolume1. Then tap OK. Tap to scale the axes. 3. Change the x-axis to display CalcVolume2 of NaOH. Acid-Base Titration

4. Display the volume of NaOH at the equivalence point. The equivalence point is the point on the curve with the greatest slope and is found using the slope tool.

35Data Analysis: Acetic AcidCalculate the molar concentration of acetic acid. Follow the steps below:Determine the number of moles of NaOH added using the volume of NaOH at the equivalence point and the molarity of the standardized the NaOH solution.Convert from moles of NaOH to moles of acetic acid using the balanced chemical equation.Use the moles of acetic acid and the starting volume of acetic acid to determine the molarity of the acid.Acid-Base Titration

Note: the values need for the calculations above can be found in your journal .

L456 text box[ a. moles of NaOH: ][ b. moles of HCl: ] [ c. molarity of HCl: ]

36AnalysisWhat is the significance of the point on the titration curve where the slope is the steepest?Acid-Base Titration

L456 = text box[The point on a titration curve where the slope is the steepest is ]

37Analysis2. What trend did you notice in the slope of the titration curve between the start of the titration and the equivalence point?Acid-Base Titration

Graph pH versus Drop Count (drops)

L6 text box[ The slope of the titration curve ]

38AnalysisWhat is the likelihood that the concentration of acid and base is exactly equal at the experimentally determined equivalence point? Explain your reasoning.Acid-Base Titration

L456 text box[ The experimentally determined equivalence point ]

39Analysis4. What difference do you notice between the start of the titration and the equivalence point in the appearance of the titration curve for the two different acids? Acid-Base Titration

L6 text box[ The start of the titration curve ]

40

Analysis5. What is the difference between pH at the equivalence points between the two titration curves for the different acids? Explain. Acid-Base TitrationL6 text box[ The pH at the equivalence point ]

41

SynthesisHow could you determine the concentration of an unknown sodium hydroxide solution? Acid-Base TitrationL456 text box[ To determine the concentration of a sodium hydroxide solution ]

42

Synthesis2. Use the Prediction Button to sketch the titration curve for an acid that is weaker than acetic acid. *To Draw a Prediction: Tap to open the tool palette.Tap then use your finger to draw your prediction.Tap when finished.If you make a mistake, tap to clear your prediction.Acid-Base Titration

Graph pH versus Drop Count (drops)43

SynthesisExplain the difference between the strength and the concentration of an acid solution. Acid-Base TitrationL456 text box[ The strength of an acid ]

44Multiple ChoiceFor the titration of an acid with a base, the pH will start _________ and finish ________.

low; lowhigh; lowlow; highhigh; highHint: the acid is the analyte in the beaker and the base is the titrant in the buret. BaseAcidAcid-Base Titration

L6 text box[ The best choice is ]

45

Multiple ChoiceOn a titration curve, the equivalence point is ____________________________. the point with the smallest slope. the point with the greatest slope. the point with a slope of zero. when the pH is equal to zero. Titration CurveAcid-Base Titration

L6 text box[ The best choice is ]

46

Multiple ChoiceAn ________ in the hydronium ion concentration in an aqueous solution causes the hydroxide ion concentration to ________ and the pH of the solution to _________. Increase; increase; increase Decrease; decrease; decrease Increase; decrease; decrease Increase; decrease; increase

Acidic solutionAcid-Base TitrationL6 text box[ The best choice is ]

47

Multiple ChoiceA reaction between an acid and a base is called a(n) ______________. pH reaction titration reactions-shaped curveneutralization reaction

Acid-Base TitrationL6 text box[ The best choice is ]

48

Multiple ChoiceTitrations are used to __________________. determine the concentration of known solutions determine the pH of known solutions determine the type of molecules in a solution differentiate an acid from a base Acid-Base Titration

L6 text box[ The best choice is ]

49

You have completed the lab.Congratulations!Please remember to follow your teacher's instructions for cleaning-up and submitting your lab.Acid-Base TitrationColor scheme (RGB values)biology 121, 173, 54chemistry 0 176, 216physics 0, 102, 204earth 204, 102, 0middle 153, 102, 153elementary 255, 51, 0

50All images were taken from PASCO documentation, public domain clip art, or Wikimedia Foundation Commons.

SODA http://freeclipartnow.com/food/beverages/soda/soda-can.jpg.htmlSALAD http://freeclipartnow.com/food/salad/salad_png-rl.jpg.htmlGLASS CLEANER http://freeclipartnow.com/household/chores/cleaners/glass-cleaner.jpg.htmlVINEGAR http://freeclipartnow.com/household/chores/cleaners/vinegar.jpg.htmlLEMONS http://freeclipartnow.com/food/fruits/grapefruits/grapefruit-4.jpg.htmlBURET http://commons.wikimedia.org/wiki/File:buret.svgBEAKER http://www.freeclipartnow.com/science/flasks-tubes/beaker-2.jpg.htmlBEAKER http://freeclipartnow.com/science/flasks-tubes/beaker.jpg.htmlCORROSIVE WARNING http://commons.wikimedia.org/wiki/Image:DIN_4844-2_Warnung_vor_Aetzenden_Stoffen_D-W004.svgBE SAFE http://freeclipartnow.com/signs-symbols/warnings/safety-hands.jpg.htmlACETIC ACID http://commons.wikimedia.org/wiki/File:Acetic_acid_structures.pngNAOH http://wikimediafoundation.org/wiki/File:NaOH.gifReferencesAcid-Base Titration51