chem lab- neutralizationthe entire lab is attached in the file belowplease fill it out and return it as a PDF
Chemistry 151 Week 13 – Neutralization by Acid-Base TitrationCollege of the Canyons Fall 2020Page 1Name ______________________Date ________________ Section_________________________________INTRODUCTIONA neutralization reaction is a double-displacement reaction in which an acid and base are the reactants andliquid water and an ionic salt are the products:Acid(aq) + Base(aq) Æ Ionic Salt(aq) + H2O(l)Recall that an acid is a compound that will release H+ ions into solution, and a base is a compound that willrelease OH- ions into solution. Neutralization reactions can occur with a monoprotic acid (meaning one H+ion) such as HCl, or with a diprotic acid (meaning two H+ ions) such as H2CO3, or a polyprotic acid(meaning more than two H+ ions) such as H3PO4. The following examples demonstrate an example of eachof these reactions:HCl(aq) + KOH(aq) Æ KCl(aq) + H2O(l)H2CO3(aq) + 2 NaOH(aq) Æ Na2CO3(aq) + 2 H2O(l)2 H3PO4(aq) + 3 Ba(OH)2(aq) Æ Ba3(PO4)2(s) + 6 H2O(l)Often, the concentration of an acid or a base in solution is measured by titration. A titration is a commonlyused technique in which a solution with a known concentration is slowly added to a solution of unknownconcentration. In the acid-base titration being performed today, an H2SO4 sample of unknown concentrationwill be titrated with a NaOH solution of known concentration. Using the molarity of NaOH and amount ofbase added, along with the volume of the H2SO4 solution, the concentration of H2SO4 solution can bedetermined.Example Calculation – In an acid-base titration, 50.00 mL of 0.5000 M sodium hydroxide is needed toneutralize 32.26 mL of sulfuric acid. What is the molarity of the aqueous sulfuric acid solution?Write the neutralization reaction: H2SO4(aq) + 2 NaOH(aq) Æ Na2SO4(aq) + 2 H2O(l)Recall that molarity (M), is expressed as:�������� = ����� �� ������������ �� ���������� � = ������To determine the molarity of the sulfuric acid solution, first find the moles of sodium hydroxide added tothe solution:�� = ����� = 0.5000 ���� ∗ 0.05000 � = 0.02500 ����� ����Chemistry 151 Week 13 – Neutralization by Acid-Base TitrationCollege of the Canyons Fall 2020Page 2We will then use the stoichiometry of the reaction to calculate the moles of H2SO4 that reacted with theNaOH.����� �2��4 = 0.02500 ����� ���� ∗ 1 ��� �2��42 ����� ���� = 0.01250 ��� �2��4We can then calculate the molarity of the sulfuric acid by dividing the moles of H2SO4 by the originalvolume in liters:0.0125 ��� �2��40.03226� = �. ��� � �����We can also put all of these steps together for one calculation:0.05000 � ∗0.5000 ��� ����1 � ∗ 1 ��� �2��42 ��� ���� ∗ 10.03226� = �. ��� � �����In today’s experiment you will prepare a standard sodium hydroxide solution. You are going to standardizeyour NaOH solution by titrating a known mass of potassium hydrogen phthalate (KHP). NaOH and KHPreact in a 1:1 ratio. Note that KHP is just an abbreviation and its actual chemical formula is C8H5KO4. Youwill then slowly and carefully add the standardized NaOH solution to a sample of H2SO4 solution using aburette, a device used to precisely deliver a specific volume of solution. The NaOH will be added until allof the H2SO4 has been consumed. This point is called the equivalence point of the titration, the point wherethe moles of acid are equal to the moles of base. As both NaOH and H2SO4 are clear and colorless, anindicator must be used to indicate the equivalence point of the titration. An indicator is a chemical that willproduce an observable change when a chemical reaction occurs. The indicator used in this experiment isphenolphthalein, a pH sensitive dye that is colorless in acidic solutions and dark pink in basic solutions. Atthe equivalence point of the titration, adding even one additional drop of the NaOH solution will changethe color of the solution in the Erlenmeyer flask from colorless to a very pale pink. The color changes in atitration seen while using phenolphthalein as an indicator are shown in Figure 12.1 below. The indicatormust be added before the titration begins.Figure 12.1 – Titration Color Changes with Phenolphthalein as an IndicatorUnless otherwise noted, content of Santa Monica College is licensed under CC BY 4.0Chemistry 151 Week 13 – Neutralization by Acid-Base TitrationCollege of the Canyons Fall 2020Page 3PROCEDURE:Part A – Preparation and Standardization of NaOH(aq) (simulation)
Navigate to the following video that describes how to set up a buret.https://youtu.be/Lr1nLTCqZvMWatch this video for directions on reading a buret:https://youtu.be/qdmp4_Nwd-QThis last video shows the general steps in a titration:https://youtu.be/YqfvRBJ-iPg
Now navigate to the Standardization of NaOH with a KHP solution simulation available fromChemCollective at http://chemcollective.org/vlab/101.
From the stockroom, obtain:
0.1 L of the NaOH solution of unknown concentration
25 mL of a 0.500 M KHP solution
a solution of phenolphthalein
a 50 mL burette (located under ‘other’ glassware).The stockroom is located on the left side of the simulation. To choose glassware, solutions, or tools, clickon the appropriate tab. To add something to your lab bench, click on the ‘+’ icon for the item. To renameor remove something from the bench, right click on the item.
Fill the burette with the NaOH solution by dragging the Erlenmeyer flask containing NaOH on top ofthe burette. A dialog box will pop up. Choose precise mode. You will pour 52.00 mL into the box andclicking ‘pour’. This will enough volume to give a starting volume of 0.00 mL. Record the initial volumein the burette in Data Table 1.
Add 1.00 mL of phenolphthalein indicator to the flask containing 0.500 M KHP.
Drag the burette on top of, and literally into, the flask that contains 0.500 M KHP to start the titration.This is tricky. A dialogue box pop-up will indicate if you were successful. In the dialog box, select‘realistic’ and hold down the left mouse button to open the burette and titrate the KHP solution.
As you add the NaOH the color of the receiving solution (called the analyte) will eventually turn pink.To check your progress, slow the NaOH addition and visually inspect the color of the receiving solution.On the first trial, it’s very likely that you will overshoot the endpoint because you had no initial estimateof the volume of titrant needed. Rather than record this 1st volume, use it as a rough estimate of theendpoint volume.
Discard the flask containing the titrated KHP by right clicking on it and selecting ‘Remove’. From thestockroom, obtain another flask containing 25 mL of 0.500 M KHP. Add 1 mL of phenolphthalein to theflask.
Titrate the new analyte with the NaOH solution from the burette. This time slow the titration as youapproach the endpoint volume from Step 7. Record the endpoint volume for the titration when the analytesolution turns pale pink.Chemistry 151 Week 13 – Neutralization by Acid-Base TitrationCollege of the Canyons Fall 2020Page 4
Repeat steps 8-9 to obtain two more endpoint volumes.
Discard all solutions from the lab bench and complete the Data Analysis section for Part 1.
Calculate the molarity of the NaOH solution for each trial and then record the average molarity ofNaOH in Data Table 1.Data Table 1. Part A – Preparation and Standardization of NaOH(aq)Trial 1 Trial 2 Trial 3Volume of 0.500 M KHP used (mL) 25.00 mL 25.00 mL 25.00 mLInitial Burette Reading (mL)Final Burette Reading (mL)Volume of NaOH used (Vf – Vi) (mL)Part B – Concentration of H2SO4(aq) (‘dry’ lab data)
After standardizing the sodium hydroxide solution in Part A, you used it to titrate three H2SO4 (aq)samples. Each sample was prepared by using a 10.00 mL volumetric pipette to transfer exactly 10.00mL of H2SO4 (aq) to each of the volumetric flasks and 20 mL of distilled water was added to theErlenmeyer flask with 3-4 drops of phenolphthalein indicator.
Use the titration results in the Data Table 2 (below) to calculate the molarity of H2SO4 for each of thethree titrations and report the average molarity of H2SO4 in Data Table 2. Part B.Data Table 2. Part B – Concentration of H2SO4 (aq)Trial 1 Trial 2 Trial 3Volume of H2SO4 used (mL) 10.00 mL 10.00 mL 10.00 mLInitial Burette Reading (mL) 0.00 mL 7.80 mL 15.95 mLFinal Burette Reading (mL) 7.80 mL 15.95 mL 24.00 mLVolume of NaOH used (Vf – Vi) (mL)Chemistry 151 Week 13 – Neutralization by Acid-Base TitrationCollege of the Canyons Fall 2020Page 5DATA ANALYSIS
Determine the molarity of NaOH for each of the three trials. Remember that NaOH and KHP(C8H5KO4) react in a 1:1 ratio. Show all your work for full credit.
What is the average molarity of NaOH from the three trials?
Write a complete and balanced chemical equation for the reaction between NaOH and H2SO4.
Determine the molarity of the H2SO4 for each of the three trials using the average molarity of NaOHthat you calculated in #2. Show all your work for full credit.Chemistry 151 Week 13 – Neutralization by Acid-Base TitrationCollege of the Canyons Fall 2020Page 6
What is the average molarity of H2SO4 from the three trials?
Obtain the molarity of H2SO4 from your instructor. Find the percent error of your titrations.
Name two sources of error in this experiment. Explain how each of these errors could have affectedthe molarity of H2SO4.Chemistry 151 Week 13 – Neutralization by Acid-Base TitrationCollege of the Canyons Fall 2020Page 7POST-LABORATORY QUESTIONS
Write the balanced chemical equation for the neutralization of hydrobromic acid with a solution ofcalcium hydroxide.
A sample of solid sodium hydroxide, weighing 13.20 grams is dissolved in deionized water to make asolution. What volume in mL of 0.235 M H2SO4 will neutralize this solution? Write the balancedequation for the chemical reaction first.
What volume in milliliters of 0.250 M HNO2 is required to neutralize 36.0 milliliters of a 0.150 MNaOH solution?
How many grams of calcium hydroxide, Ca(OH)2 are required to neutralize 43.26 milliliters of 0.550M H2SO4 solution?Chemistry 151 Week 13 – Neutralization by Acid-Base TitrationCollege of the Canyons Fall 2020Page 8PRE-LABORATORY ASSIGNMENT
In the experiment for today, which is solution is added to the burette, and which solution is added tothe Erlenmeyer flask in Part A? What about in Part B? Label the solutions in the figure below for PartB.
Is the concentration of the base known or unknown in Part A? Is the concentration of the acidknown or unknown in Part A?
Is the concentration of the base known or unknown in Part B? Is the concentration of the acidknown or unknown in Part B?
What is the equivalence point? How will you know when you have reached it in today’s experiment?
What indicator are we using in today’s experiment? At what point in the experiment do you add theindicator? How much indicator is needed?Chemistry 151 Week 13 – Neutralization by Acid-Base TitrationCollege of the Canyons Fall 2020Page 9
If you start with a sample of solid potassium KOH, weighing 12.5 grams, what volume in mL of a0.500 M HCl solution will neutralize this solution? Write the balanced neutralization reaction first.
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