92 THE TITRATION OF VINEGAR: Design and Analysis This exercise presents you with
ID: 582251 • Letter: 9
Question
92 THE TITRATION OF VINEGAR: Design and Analysis This exercise presents you with a problem in experimental design. You have carried out all the procedures that are necessary to complete the exercise successfully; however, you must adapt your previous methods to the problem at hand and also assess whether you can tell a difference between a sample and a specification. Teams of three or four will standardize NaOH and use it to analyze the percent by mass acetic acid content of vinegar (which is approximately 5% acetic acid, CH,COOH. Acetic acid formula is also written as HC H,O). Your team will plan ahead to have a practical titration plan for a two-part procedure: standardization and analysis The NaOH will be given to you as a solution of about 0.1 M. You need to standardize the NaOH with potassium hydrogen phthalate "KHp, 204.2 g/mole). KHP is a dry powder that reacts with NaOH in a 1:1 mole ratio: NaOH(aq) + KHCsH,04 (aq) NaKC14Odaq) + H20(1) B) Analysis Acetic acid reacts with NaOH in a l : 1 mole ratio: CH3C00H + NaOH NaCHC00 + H20 Vinegar is about 5% CH,COOH by weight. You will use the NaOH to titrate enough samples of vinegar to establish precision. Prelaboratory assignment: Write plans for A) standardization of sodium hydroxide, and B) analysis of vinegar. Use the estimates (0.10 M NaOH and 5% CH COOH) to make a two-part plan. Your instructions should be written as if your group is communicating with another scientist who is not a member of this lab. The two-part plan must utilize at least three significant figures and include: Al) A clear statement of how you plan to prepare (make) your KHP solution. You may use no more than a total of 2.0 g. A2) How much KHP will you use per titration? (Which unit: Grams? Moles? mL?) A3) What volume of NaOH (approximately .10 M) will be needed to reach the end point? A4) Prove your proposal with a numerical example. A5) At minimum, how many titrations will you need? At maximum, how many can you perform? BI ) How much vinegar (ie., 5% CHCOOH) will you use per titration? B2) Will you measure your original vinegar sample by mass or by volume? B3) Will you need to do a dilution? Will you need to measure a density? B4) Write a clear statement of how you plan to prepare your vinegar sample. B5) How much NaOH (approximately .10 M) will be needed to reach the end point? B6) Prove your proposal with a numerical example. B7) At minimum, how many titrations will you need? At maximum, how many can you perform? Submit ONE Prelaboratory assignment for the team by the end of class. It will be assessed with the same point value for each student, 30% of the lab report grade. .Keep a copy for your team's use. The instructor must approve the plan before you start work. It will be disapproved if it is: o impractical o unclear After approval and prior to lab: Make the usual preliminary entries in your lab notebook and include both the KHP+NaOH reaction equation and the acetic acid+ NaOH reaction equation. Make an entry labeled "Plan" in your notebook giving a short version of the plan above (without calculations). (continues) CHEM&161 F17Explanation / Answer
A1-3) The KHP reacts with NaOH 1:1, if you have a solution of NaOH about 0.1M, then you need at least the same moles of KHP that NaOH. An option is to use a solution of KHP more concentrated than the NaOH.
You should choose how much volume you are going to use of NaOH in order to know the amount of KHP.
Also, you can choose arbitrarily some quantity of KHP and then calculate the volume approximately of NaOH for the titration:
moles of KHP= grams used/molecular weight
and moles of KHP=moles of NaOH
A5) To standardize the solution of NaOH you need at least three titrations, the maximum is limited by the quantity of reagents (2 g of KHP)
B1) You must calculate the molar concentration of acetic acid of the vinegar,
molar concentration= moles of acetic acid/volume
If we know that vinegar is 5% (by weight), this meaning that there are 5 g of acetic acid per 100 mL of the solution,
molar concentration= (weight/molecular weight)/volume
Knowing the molar concentration you can estimate how much vinegar you can use for titration. You should consider the volume of NaOH that you want to spend in each titration. The reaction of acetic acid with NaOH is 1:1.
B2) Titrations should be in volume because you measure the volume added of NaOH, not the weight.
B3) According to the molar concentration calculated in B1 if the concentration of acetic acid is higher than the NaOH you must dilute. The density is not measured because in titration we can obtain the mole number in a known volume, then we can calculate the concentration of the sample.
B4-6) These steps can be resolved when you choose the previous points.
B7) the same that in point A5.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.