Zixuan Zhang
PART.1
I) Purpose:
Find the concentration of Monoprotic acid and the PH in various points of titration.
II) Material:
2 Burette、Stand、Baker、Cylinder、Flask
PART.2
III) Procedure
1、Add 15ml of 0.150M from the blue burette into the flask.
Performer can use
to get where the performer should stop adding base into the flask since not every single NaOH in the blue burette starts with 0ml.
2、Add 2 or 3 drops Phenolphthalein into the flask.
It works as an indicator to warn the Equivalence point has been reached by changing the solution to slightly pink.
3、Add 5ml of (Acid) from the red burette into the flask and record the volume.
Use for react with NaOH(Base) to reach the equivalence point. Because of performer did not know the So in order to prevent missing the Equivalent point, performers must record the volume they added into the flask,
4、 Swirl the flask after adding 5 ml of acid
Accelerate up the speed of Acetic Acid to complete react with the Hydroch Acid
5、Rinse Flask inner surface if there is an acid or base residue.
The acid or base adsorbed on the cup wall needs to fully participate in the chemical reaction, otherwise it will easily lead to miss equivalent point.
6、Repeat step3 and step6 until the pink color is hard to disappear.
A warning sign of an equivalent point is about to reach.
7、Start adding acid drop by drop since the pink color is hard to disappear, and then record volume every single time.
The purpose is to prevent missing the equivalent point, only need a slight amount of acid to reach the equivalence point.
8、Wash the flask 3 times with water
Guarantee that there is no residue of any substance
9、Change Acetic Acid to Hydroch Acid then Repeat step1— step8 for the second trial.
Recollect the data to calcula
10、Calculation
Use RBCA, RICE table and to calculate the pH of both trials
PART.3
IV) Observations and data collection:
Observations during reaction：
The empty flask with acid inside it at first.
The tube with the base in the stand.
The tube with the acid in the stand.
The entire stand itself with the flask at the bottom.
After the base is dropped into the acid, the solution changes color until it is swirled.
After added 9.94ml NaOH
Faintly pink solution, signifying that the solution has reached equivalence point.
Trial 1（HC2H3O2）
The average volume of added (mL)
15.16
The average volume of NaOH (mL)
9.90
The concentration of NaOH(M)
0.150
Trial 2（HCl）
The average volume of HCl added (mL)
15.13
The average volume of NaOH (mL)
9.94
The concentration of NaOH(M)
0.150
V) Data Analysis:
Trial 1 (Weak Acid)
a) Initial pH
b) pH When 2.5mL NaOH added
c）PH at the Half Equivalence point
d)PH at the Equivalence point
e)PH when 5.00mL NaOH added after EP reached
Trial 2 (Strong Acid)
PART.4
VI) Discussion:
Titration is an analytical technique that allows the quantitative determination of specific substances (analytes) that are soluble in a sample. By adding a precise concentration of reagent(titrant) dropwise to the analyte solution until the dropwise titrant reacts quantitatively with theanalyte in a stoichiometric relationship. Move the tap switch to control the amount of reagentadded. When the reaction reaches the end point, the color of the solution changes. When only themost primitive means are available at the beginning, only titrations with end-point color changescan be performed, and indicators can be artificially added for subsequent titrations. Therefore,titration experiments can be performed even for transparent solutions when the color does not change after the equivalence point is inverted. The accuracy of the results mainly depends on thetechnical ability of the chemist, especially his ability to distinguish between different colors.
Our experiment belongs to acid-base titration, which is a qualitative analysis method todetermine the concentration of an unknown acid-base solution by adding a known volume of aknown acid-base titrant that neutralizes the analyte. The reason to reach an equivalence point isbecause only at that point, the moles of both substances are the same. Therefore the equation ofna=nb=M1V1=M2V2 can be applied to calculate the ungiven concentration’s substance.
When performing an acid-base titration using one of the pH indicators, the change incolor is determined by taking the pH range of the indicator, rather than a fixed colonization. Thiscauses the actual results to be somewhat calculated differences, so using a different indicator foreach acid-base reaction can easily smooth out the differences.
Acids are those that are fully ionized in aqueous solution. A strong acid will always losea proton (H+) when dissolved in H. In other words, a strong acid is always in water and releasesprotons very efficiently. Weak acids are acids that are partially ionized in solution. It can onlyrelease a small amount of hydrogen atoms into solution. Because the pH volume is determinedby concentration of ,therefore it causes the calculation to be different between strong acid andweak acid.
Titration is not limited to just chemistry, but it can also be used in other fields of sciencesuch as biology and physics as well. Such as the food industry, where they can use titration to find out the exact amount of a substance, like salt, in a certain food. Or in the medical field,where titration can be used to find the amount of acid inside fluids like urine or blood todetermine what is wrong with it and to have more accurate diagnoses. For example, a doctorwould be able to use titration to figure out the glucose level in a possible-diabetic patient tofigure out if that person is actually diabetic or not, or a nurse could use titration to figure out theexact amount of dosage they should use to inject the patient with. Another example isengineering, where the mechanic can determine the amount of a certain substance in differenttypes of fuel. The application of titration is endless, and it can only be used to help advancehumanity further.
VII) Error Analysis
Error Percentage:
Error 1: Because solution residue on the inner surface of the flask while swirling the flask, butwe didn’t record the final volume, which causes the concentration of the 𝐻𝐶2𝐻3𝑂2 go down.
Propagation: The solution remaining on the surface of the flask means that the mole andvolume of the acid have decreased at the same time to maintain the identical concentration as before, but we did not remeasure the volume after loss, which mean mole goes down but thevolume stay constant, therefore the concentration of 𝐻𝐶2𝐻3𝑂2 goes down. In order to fix it, usewater to rinse the surface of the flask frequently while we are doing the lab.
Error 2: Because did not wait 30 second after the solution turning to faintly pink, which leadingthe less needs of NaOH’s amount,causing the concentration of 𝐻𝐶2𝐻3𝑂2 goes down.
Propagation: Did not wait 30 seconds after the solution turn to faintly pink while it’s areversible chemical reaction, which means the chemical have to possibility to turn back clear.Itcausing less amount of NaOH is needed, therefore the mole of NaOH also goes down, but thevolume of 𝐻𝐶2𝐻3𝑂2 (𝑉2)stay constant, therefore the concentration of 𝐻𝐶2𝐻3𝑂2 smaller than it issupposed to be. In order to fix it, wait for 30 second after the solution turns to light pink.
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