volume of titrant ph acid-base titration o12-10732 r1.04
TRANSCRIPT
Volume of Titrant
pH
Acid-Base Titration O12-10732 r1.04
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IntroductionJournals and Snapshots
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Acid-Base Titration
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
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.
Titrant
Analyte
Equivalence point
Acid-Base Titration
...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 solution Basic solution Neutral solution
+
Acid-Base Titration
This image is a reminder that you need to tap to take a snapshot of this page after you have entered your response.
Self-Check
1. Titrations are used to determine the _____________ of a reactant.
a) density
b) pH
c) mass
d) concentration
Acid-Base Titration
Safety
• Follow all common laboratory safety procedures
• Sodium 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 leaving
Acid-Base Titration
Materials and EquipmentCollect all of these materials before beginning the lab.
• Drop counter• pH sensor• Magnetic stirrer• Micro stir bar• Beakers (2), 50-mL• Buffer solution pH 4, 25 mL• Buffer solution pH 10, 25 mL• Funnel• Graduated cylinder, 100-mL
Acid-Base Titration
...Materials and EquipmentAlso collect these additional materials before beginning.
• Buret, 50-mL• Buret clamp• Ring stand• Right-angle clamp• Beakers (2), 250-mL• Transfer pipet• Volumetric pipet or graduated
cylinder, 10-mL• Wash bottle filled with distilled
(deionized) water
Acid-Base Titration
...Materials and EquipmentAlso collect these additional materials before beginning.
• Waste container • deionized (distilled water), 200 mL• Standardized sodium hydroxide solution, 100 mL• Hydrochloric acid solution, 10 mL• Acetic acid solution, 10 mL
waste
Acid-Base Titration
Distilled Waterwaste
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 Titration
1. Connect the pH sensor to the data collection system.
2. Calibrate the pH sensor:
a. Pour approximately 25 mL of the pH 4 buffer solution in a 50-mL beaker.
b. Pour approximately 25 mL of the pH 10 buffer solution in a second 50-mL beaker.
c. Remove the pH sensor from its electrode storage bottle and rinse it with distilled water to thoroughly clean the sensor.
d. Read the instructions on how to calibrate the pH sensor on the next page.
Setup: HCl Titration
Buffer solutions and pH sensor
Acid-Base Titration
To 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: a. Tap b. Tap CALIBRATE SENSOR
2. Ensure that the correct measurements are selected:c. Sensor: (name of sensor)
Measurement: pH Calibration Type: 2 point
b. Tap NEXT
3. Calibration Point 1: a. Place the pH probe in a pH 4 buffer
solution. b. Enter 4.0 as the pH in the Standard
Value box under Calibration Point 1. c. Tap Read From Sensor under
Calibration Point 1. d. Rinse the pH probe thoroughly using
distilled water.
4. Calibration Point 2:e. Repeat the process used in calibration point
1 using a pH 10 buffer solution. f. Tap OK to exit the calibration screen and
then tap OK again to return to the lab.
Acid-Base Titration
Setup: HCl Titration3. Connect the drop counter to the data collection
system.
4. Assemble the titration apparatus.
Q1: Using the terms accuracy and precision, explain why it is necessary to calibrate the pH sensor.
Acid-Base Titration
Buret clamp
Ring stand
Right-angle clamp
Drop counter
Beaker, 250-mL
Buret
pH sensor
Micro stir bar
Magnetic stirrer
Q2: Why is it necessary to rinse the buret with standardized NaOH solution?
Setup: HCl Titration
5. Use a transfer pipet to rinse the inside of the buret with several milliliters of the standardized sodium hydroxide (NaOH) solution.
6. Drain the NaOH from the buret into the waste container.
7. Repeat this process two more times.
8. 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 position
Onposition
Acid-Base Titration
Setup: HCl Titration
9. Practice 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.
10.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 Titration
Setup: HCl Titration Q4:Record the initial volume of NaOH and the concentration of the standardized NaOH solution in the text box below.
11. Read the initial volume of the titrant in the buret to 0.01 mL.
12. Using the 100-mL graduated cylinder measure 100 mL of distilled water and add it to a clean 250-mL beaker.
13. 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 Titration
Setup: HCl Titration
14.Add the pH sensor, micro stir bar, and 250-mL beaker containing the acidic solution to the titration apparatus.
15.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
1. Tap to start collecting data.
2. Carefully open the stopcock on the buret so that 2 to 3 drops per second are released.
3. Continue to collect data until the pH of the solution is 12.
Collect Data:
Continue to the next page.
Acid-Base Titration
Q6: Why is it necessary to stir the solution during a titration?
Q7:What substances are being formed in the beaker?
Acid-Base Titration
Collect Data: 4. When the pH of the
solution is 12 close the stopcock.
Continue to the next page.
Acid-Base Titration
Collect Data:5. Tap to stop data
collection. 6. Record the final volume of
NaOH in the buret.
Acid-Base Titration
* To View a Page in the Journal: 1. Tap to open the Journal
screen. 2. Tap or to scroll through
the thumbnail size pages of the journal.
3. Tap the thumbnail image of the page to view it.
Data Analysis: HCl
1. Determine the total volume of NaOH used in the titration by following steps a-c below.
a. Enter the final volume of NaOH in the text box on the right.
b. Record the initial volume of NaOH in the text box on the right
c. Subtract 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 NaOH
Acid-Base Titration
Note: Initial and final volumes of NaOH were recorded earlierin the journal. Refer to the journal to get these numbers.*
*To Create a Calculation:1. Tap to open the
Experiment Tools screen. 2. Tap CALCULATED DATA to
open the calculator. 3. Enter the calculation in the
space provided. 4. 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: HCl
2. Create a calculation to convert drop count to volume (mL). *
CalcVolume1 = [drop count]*(volume of titrant/final drop count)
Acid-Base Titration
•Tap 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.
Data Analysis: HCl5. Calculate the molar concentration of HCl. Follow the steps below:
a. 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.
b. Convert from moles of NaOH to moles of HCl using the balanced chemical equation.c. 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
Setup: Acetic Acid Titration 1. Turn off the magnetic stirrer and then remove the
beaker. Dispose of its contents according to your teacher's instructions.
2. Place the waste container under the pH sensor and use the wash bottle to thoroughly clean the micro stir bar and the pH sensor.
3. Re-fill the buret so that there is ~50 mL of the standardized NaOH solution.
4. 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 Titration
Setup: Acetic Acid Titration 5. Using the 100-mL graduated cylinder measure 100 mL
of distilled water and add it to a clean 250-mL beaker.
6. 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.
7. Remove the waste container from the titration apparatus and replace it with the 250-mL beaker containing the acetic acid solution.
8. 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 Titration
1. Tap to start collecting data.
2. Carefully open the stopcock on the buret so that 2 to 3 drops per second are released.
3. Continue to collect data until the pH of the solution is 12.
Collect Data: A.A.
Continue to the next page.
Acid-Base Titration
Q4: What type of reaction is occurring?
Q3: What substances are being formed in the beaker?
Acetic Acid = HC2H3O2
HC2H3O2 + NaOH ?
Acid-Base Titration
Collect Data: A.A.4. When the pH of the
solution is 12 close the stopcock.
Continue to the next page.
Acid-Base Titration
5. Tap to stop data collection.
6. Record the final volume of NaOH in the buret.
Acid-Base Titration
Collect Data: A.A.
* To View a Page in the Journal: 1. Tap to open the Journal
screen. 2. Tap or to scroll through
the thumbnail size pages of the journal.
3. Tap the thumbnail image of the page to view it.
Data Analysis: Acetic Acid
1. Determine the total volume of NaOH used in the titration. Follow steps a-c below.
a. Enter the final volume of NaOH in the text box on the right.
b. Record the initial volume of NaOH in the text box on the right
c. Subtract 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 NaOH
Acid-Base Titration
Note: Initial and final volumes of NaOH were recorded earlierin the journal. Refer to the journal to get these numbers.*
*To Create a Calculation:1. Tap to open the
Experiment Tools screen. 2. Tap CALCULATED DATA to
open the calculator. 3. Enter the calculation in the
space provided. 4. 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
•Tap 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.
Data Analysis: Acetic Acid5. Calculate the molar concentration of acetic acid. Follow the steps below:
a. 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.
b. Convert from moles of NaOH to moles of acetic acid using the balanced chemical equation.c. 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 .
Analysis
1. What is the significance of the point on the titration curve where the slope is the steepest?
Acid-Base Titration
Analysis2. 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
Analysis
3. What 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
Analysis4. 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
Analysis5. What is the difference
between pH at the equivalence points between the two titration curves for the different acids? Explain.
Acid-Base Titration
Synthesis
1. How could you determine the concentration of an unknown sodium hydroxide solution?
Acid-Base Titration
Synthesis2. Use the Prediction Button
to sketch the titration curve for an acid that is weaker than acetic acid.
*To Draw a Prediction: 1. Tap to open the tool
palette.2. Tap then use your finger
to draw your prediction.3. Tap when finished.4. If you make a mistake, tap
to clear your prediction.
Acid-Base Titration
Synthesis3. Explain the difference between the strength and the concentration of an acid
solution.
Acid-Base Titration
Multiple Choice
1. For the titration of an acid with a base, the pH will start _________ and finish ________.
a) low; low
b) high; low
c) low; high
d) high; high
Hint: the acid is the analyte in the beaker and the base is the titrant in the buret.
Base
Acid
Acid-Base Titration
Multiple Choice
2. On a titration curve, the equivalence point is ____________________________.
a) the point with the smallest slope.
b) the point with the greatest slope.
c) the point with a slope of zero.
d) when the pH is equal to zero.
Titration Curve
Acid-Base Titration
Multiple Choice
3. An ________ in the hydronium ion concentration in an aqueous solution causes the hydroxide ion concentration to ________ and the pH of the solution to _________.
a) Increase; increase; increase
b) Decrease; decrease; decrease
c) Increase; decrease; decrease
d) Increase; decrease; increase
Acidic solution
Acid-Base Titration
Multiple Choice
4. A reaction between an acid and a base is called a(n) ______________.
a) pH reaction
b) titration reaction
c) s-shaped curve
d) neutralization reaction
Acid-Base Titration
Multiple Choice
5. Titrations are used to __________________.
a) determine the concentration of known solutions
b) determine the pH of known solutions
c) determine the type of molecules in a solution
d) differentiate an acid from a base
Acid-Base Titration
You have completed the lab.Congratulations!
Please remember to follow your teacher's instructions for cleaning-up and submitting your lab.
Acid-Base Titration
All images were taken from PASCO documentation, public domain clip art, or Wikimedia Foundation Commons.
1. SODA http://freeclipartnow.com/food/beverages/soda/soda-can.jpg.html2. SALAD http://freeclipartnow.com/food/salad/salad_png-rl.jpg.html3. GLASS CLEANER http://freeclipartnow.com/household/chores/cleaners/glass-cleaner.jpg.html4. VINEGAR http://freeclipartnow.com/household/chores/cleaners/vinegar.jpg.html5. LEMONS http://freeclipartnow.com/food/fruits/grapefruits/grapefruit-4.jpg.html6. BURET http://commons.wikimedia.org/wiki/File:buret.svg7. BEAKER http://www.freeclipartnow.com/science/flasks-tubes/beaker-2.jpg.html8. BEAKER http://freeclipartnow.com/science/flasks-tubes/beaker.jpg.html9. CORROSIVE WARNING http://commons.wikimedia.org/wiki/Image:DIN_4844-
2_Warnung_vor_Aetzenden_Stoffen_D-W004.svg10. BE SAFE http://freeclipartnow.com/signs-symbols/warnings/safety-hands.jpg.html11. ACETIC ACID http://commons.wikimedia.org/wiki/File:Acetic_acid_structures.png12. NAOH http://wikimediafoundation.org/wiki/File:NaOH.gif
ReferencesAcid-Base Titration