"Determination of K for a Weak Acida Hands-On Labs, Inc. Version 42-0151-00-02Lab Report AssistantThis document is not meant to be a substitute for a formal laboratory report. The Lab ReportAssistant is simply a summary of the experiment’s questions, diagrams if needed, and datatables that should be addressed in a formal lab report. The intent is to facilitate students’writing of lab reports by providing this information in an editable file which can be sent to aninstructor.Exercise 1: Determination of K aData Table 1. Determination of Equivalence Point. Trial 1 Trial 2Volume of Unknown Weak Acid 4 mL 4 mLTotal Number of Drops Required to Reach Equivalence Point 91 96Average Number of Drops 93.5Data Table 2. Titration Curve Values.+ -pH pH ValuepH ValuepH Value [H ]=10Drops NaOH Added Trial 1Trial 2(Average)Half-Equivalent Point = (46 Drops)Equivalent Point = (93 Drops)-4 0 4 4 4 10-6 10 6 5 5.5 3.16 x 10-6 20 6 6 6 10-6 30 6 6 6 10-6 40 6 6 6 10-6 50 6 6 6 10-6 60 6 6 6 10-6 70 6 6 6 10-7 80 6.5 6.5 6.5 3.162x10-7 90 6.5 6.5 6.5 3.162x10-7 100 7 7 7 1010 110 10 10 10 1012 120 12 12 12 10 Data Table 3. Determination of Unknown.pK of Unknown Weak Acid:a 6-6 K of Unknown Weak Acid: 10a Unknown Weak Acid Identity: Carbonic Acid% Error pK : 5.8%a % Error K :-0.0228%a QuestionsA. Using the data collected in Data Table2, create a graph of “Drops of NaOH added” vs “pH”where “drops of NaOH added” is on the x-axis and “pH” is on the y-axis. B. pH indicator strips work by changing color in the presence of solutions with varied pHvalues. Thinking about your procedure steps and results in Part 1, why do you think the pHof the unknown weak acid was not determined with pH indicator strips until Part 2?C. Discuss possible causes of error in the experimental procedure. Why do you think therewas a percent of error in the pK and K values of the unknown weak acid, in comparison toa a the values presented in Table 2?D. Do you think using a pH meter instead of pH indicator strips would have created a larger orsmaller percent error? Explain your answer.E. Why was phenolphthalein a good indicator to use for determining the equivalence pointbetween the unknown weak acid and strong base? Answers:A B. In the experiment above, the pH value is determined by the titration curve and not by a pHstrip. This is because the strip readily changes its color depending on acidic or basic medium.However, the strip does not determine the scale or the accurate value of pH at the equivalencepoint. From part two, we can analyze the required drops of NaOH for each value of pH.C. The possible cause of error kin the experimental setup could be as follows:? Optical error may cause a misjudging of the change in the color of the strip.? Conducting the experiment at a random temperature may also be a leading cause oferror.? Pipetting excess or less amount of reagent.? Incorrect measurement of indicator can lead to shifting of the end point.The error percentage in pK or K occurred due to the error in the measurement of the givena a concentration of base or acid or both.D. A pH meter would have created smaller error percentage as it shows the most accuratevalue of pH in comparison with a pH strip. A pH strip tends to change color depending on theacidic or basic medium, which determines the nature of the sample. However, a pH metermeasures the concentration of acidity or basicity of the given sample.E.It can be observed that when H+ is added to the sample shifts the equilibrium positontowards the left. In that case, the indicator is colorless. However, addition of OH- ions removesthe hydrogen ions and hence, it returns to its original color – pink. Thus, it’s easy to know whenthe end point is approaching, which is an approximation of the equivalence point. "