Tjia 1Michelle TjiaKusumawatiChemistryMarch 8, 2013FINDING THE UNKNOWN MOLARITY OF ETHANOIC ACID IN VINEGAR.ObjectiveThe aim of this experiment is to determine the molarity of ethanoic acid in vinegar (CH3COOH) byadding a volume of sodium hydroxide (NaOH).HypothesisThe more volume of vinegar (CH3COOH) we put in, the more volume of sodium hydroxide(NaOH) we need.Variables- Independent Variables: Volume of acid (0.5 mL, 1 mL, 1.5 mL, 2 mL, 2.5 mL.)- Dependent Variable: The molarity of acid.- Controlled Variables: The molarity of sodium hydroxide (1M), the type of vinegar (CH3OOH),room temperature, pressure, the addition of phenolphthalein indicator (3 drops), the volume ofdistilled water into the acid (50 mL).Theoretical BackgroundVinegar is a versatile liquid that is created from the fermentation of ethanol. According tothe Merriam-Webster dictionary, Vinegar is, “A sour liquid obtained by fermentation of dilutealcoholic liquids and used as a condiment or preservative.” The main ingredient of vinegar is a typeof acid called the ethanoic acid (CH3COOH). Other acids such as the tartaric and citric acid is alsoa part of the ingredient. The pH range of a vinegar is usually from 3 to 3. 5. Vinegar can be used formany different things, one of them is in food. It can be used as an ingredient and condiments whilecooking. Other than using it as an ingredient in a meal, vinegar can be used for household cleaningand other uses too.One of the methods that can be used to analyze the content of a vinegar is titration. Titrationis a method used in chemistry to determine the molarity of an acid or a base. A chemical reaction ismade between a known volume of solution of an unknown concentration and a known volume of asolution with a known concentration. To conduct this method, you will need a burette to hold thereactant. Then a stopcock will be attached to the burette that can enable us to control the amount ofliquid that is coming through.Some acids and bases are polyprotic, which means that each mole can release more than oneacid or base equivalent. When the solution of known concentration and the solution of unknownconcentration equals, a chemical reaction happens. The equivalence point of a strong acid or astrong base will occur at pH 7. For weak acids and bases, the equivalence point will not be at pH 7.To estimate the equivalence point we can use the pH meter or use an indicator. While usingthe pH meter a graph will be made and will plot the pH of the solution. Using an indicator, we willobserve the change of color in the solution. However, this method is used in low concentration,which is why indicators cant really change the equivalence point of a titration. The point which theindicator changes color is called the end point. A common method to get the pH of solution is to use
Tjia 2an acid base indicator. An indicator is a large organic molecule that is similar like a color dye. Theseacid base indicators reacts when there is a change in the concentration of hydrogen ion.In any titration, end point is the point where the indicator changes its color. After this point,the reaction is complete. The equivalence point in a titration is the point when the chemical reactionis complete. Although the end point is when the color change, but it sometimes is not the end of thereaction. At this equivalence point, medium is neutral. Equivalence point happens right before theend point. The equivalence point is that point at which the moles of the titrant and analyte are equal.Materials/Tools- Burette (1)- 250 mL Erlenmeyer Flask (5)- 50 mL Measuring Cylinder (1)- 10 mL Measuring Cylinder (1)- 250 mL Beaker (3)- 150 mL beaker (2)- 10 mL beaker (1)- Retort Stand and Clamp (1)- 25 mL of Vinegar (CH3COOH)- 600 mL of Sodium Hydroxide Indicator- 20 mL of Phenolphthalein Indicator- 1 L of Distilled Water- Wash Bottle (1)- 5 mL Pipette (3)- Dropper (1)- Funnel (1)- Goggles- Gloves- Lab Coat- Sheet of White and Dark PaperMethod1.Rinse the tools (burette, flasks, and beakers).2.Make sure the burette stopcock is closed.3.Fill the burette with 25 mL of sodium hydroxide.4.Place a beaker under the burette.5.Open the stopcock to allow the liquid to drain out into the beaker and then close thestopcock. Make sure that there is no air bubbles remain in the stopcock.6.Remove the beaker.7.Using the 5 mL pipette, pour 0.5 mL of vinegar solution into the Erlenmeyer flask.8.Measure 50 mL of distilled water using the 50 mL measuring cylinder and add it to thevinegar solution.9.Add 3 drops of phenolphthalein into the vinegar solution in the Erlenmeyer flask. Thesolution should remain colorless at this point.10.Place the flask under the burette. Put a sheet of white paper under the flask to make theendpoint easier to see.11.Read the volume of the sodium hydroxide in the burette. This is your initial volume.Reading is made easier by holding a piece of dark paper behind the burette.
Tjia 3184.108.40.206.16.17.18.Slowly open the burette stopcock and add some sodium hydroxide into the flask, whiledoing so, swirl the flask. Observe the colour of the solution, you may notice a temporarycolour change in the solution.Continue adding the sodium hydroxide. The colour change will take longer to disappear.This is a signal that the endpoint is getting closer and the sodium hydroxide should beadded drop wise.Stop adding the sodium hydroxide when a permanent colour change is observed (a palepink; longer than 30 seconds). This indicatesthat the solution has reached its endpoint.Record the volume of sodium hydroxide inthe burette. This is your final volume.Subtract the initial volume from the finalvolume to determine the volume of sodiumhydroxide added.Repeat step 1 to 15 using different volumeof vinegar. 1 mL, 1.5 mL, 2 mL, and 2.5mL.Refill the burette with sodium hydroxidesolution if it was not enough but rememberto record the volume of sodium hydroxideused.Repeat step 1 to 17 three times to obtainaccurate results.Data Collection (Raw)Volume Of NaOH (mL)Volume ofVinegar (mL)1st TrialDistilled Water(mL)2nd Trial3rd 448.1582.550534442Data ProcessingAfter conducting this experiment, as a group, we found out that the chemical equation isCH3COOH NaOH CH3COONa H2O. Through this equation, we can say that the molarityof NaOH and the molarity of CH3OON is equal since their ration is 1:1. Since the NaOH is astandard solution, it reacts with the Acetic Acid (CH3COOH).The formula to find the moles and the molarity:This means that 1M of NaOH means thatthere is 1 mole in the NaOH/L.
Tjia 4Data PresentationVolume ofVinegar Used(mL)0.511.522.5Volume ofNaOH Used(mL)Moles ofNaOH (moles)Molarity ofCH3COOH (M)Moles ofCH3COOH41 x 0.04 40.04 / 0.0505 0.72920.0451 x 0.05 0.050.05 / 0.0505 0.990.0511.71 x 0.0117 0.01170.0117 / 0.0505 0.3610.011716.51 x 0.0165 0.01650.065 / 0.051 0.02320.016518.31 x 0.0183 0.01830.0183 / 0.051 0.3590.018317.31 x 0.0173 0.01730.0173 / 0.051 0.3390.017329.61 x 0.0296 0.03640.0296 / 0.0515 0.5750.029631.51 x 0.0315 0.03150.0315 / 0.0515 0. 6120.0315261 x 0.026 0.0260.026 / 0.0515 0.5040.026341 x 0.034 0.0340.034 / 0.052 0.6530.03448.11 x 0.0481 0.04810.0481 / 0.052 0.9250.0481581 x 0.04430.058 / 0.052 1.120.058531 x 0.058 0.0580.053 / 0.0525 1.010.053441 x 0.044 0.0440.044 / 0.0525 0.8380.044421 x 0.042 0.0420.042 / 0.0525 0.80.042From the table above, we can see that our experiment has succeed. The volumes for NaOH weresimilar with each other. We can also see that the more vinegar we used, the more NaOH we need topour.
Tjia 51st Trial2nd Trial3rd TrialAmount of Sodium Hydroxide Used for Each Titration.6058Amount of Sodium Hydroxide (mL)534548.1443031.529.61542342616.518.317.211.704 50.511.522.5Amount of Vinegar (mL)The graph above can help you visualize more about how our method was conducted. Before westarted to conduct this experiment, our science teacher showed us how to do it, but because I wasabsent at that time, I did not see it. Our teacher said that it is better if we can get a really pale pinkrather than really dark pink. From the pictures (you can see at the Appendix category), you can seethat most of our experiments’ color are very pale pink. However we do have some that has becomefull pink. Through the graph we can see that our last experiment was more accurate because out ofall the experiments, the one that has 2.5 mL of vinegar is the ones that has the most similar amountof Sodium Hydroxide.The table below will prove that we has conducted the experiment well. This table can also answerthe objective and also my hypothesis because as you can see, the more vinegar we put in, the moreNaOH we need to pour in to enable it to have a color reaction.Amount of0.5Vinegar (mL)Amount ofNaOH (mL)Averageamount ofNaOH (mL)456.811.711.5216. 18. 17.53229. 31. 26 34 48. 5865153 44 4217.329.146.346.72.5
Tjia 6DiscussionIn this experiment that my group and I have conducted, I can say that the results we got areaccurate. The results that we got also supports my hypothesis and the objective. Through the results,we can see that the more vinegar we add, the more sodium hydroxide we need to add. Also toanswer the objective, which is to determine the molarity of ethanoic acid in vinegar (CH3COOH)by adding a volume of sodium hydroxide (NaOH), we have made a few tables and graphs that canhelp to determine the molarity of ethanoic acid clearly. Since I have put the answers on the table, Ithink that I have already answered the objective too.The pattern that I have seen through this project is as I have repeated a few time, the more vinegaryou add the more sodium hydroxide we need to pour to make it turn to pink which refers back tomy hypothesis.EvaluationThe method that my group and I used to conduct this experiment was very accurate. Since wefollow the method very carefully, I believe that we have also gotten good answer from thisexperiment. I think the method that we followed was very clear, easy to understand and also has alot of details. So I don’t think that there is anything else we can improve. Also in my opinion I don’tthink that there is any weaknesses in my method. Although what could be improved from thismethod is, it is better if we do more than three trials for one experiment. If we have more trials, thenwe can get more precise and accurate information.Since we only did three trials for each experiment, I think that our data and results were prettyaccurate, however it is not 100% accurate. This experiment -with only three trials for eachexperiment- allows us to see the ‘big picture’ of the results and help us to understand more abouttitration. However it could not give us exact and very accurate answers.ConclusionIn conclusion, I have learned about the scientific concept through this experiment. It has also givenme a clear conclusion based on the results and data that I have gotten which is the more vinegar weused, the more sodium hydroxide we need to it to react. Throughout conducting this experiment, wedid not have any difficulties or problems. The experiment went very well without any problemsbecause we followed the method which was also written, read and followed carefully by my groupand I. As I have said before the only improvement that is needed in the method is to have more thanthree trials for each experiment.This experiment has also enabled me to find the molarity of CH3COOH, even if its not thataccurate. Through the result table I have also learned that there are various amounts, differentamounts of molarity because of the amount of sodium hydroxide that we use were different. Thishappens because sometimes, when we see just a tiny hint of pink, we stop the stopcock. However,sometimes, it turns that it has not reached the endpoint enough and dissolves back to pure color. Sowe had to add more sodium hydroxide again.Further InquiryFor further inquiry, we can try to substitute the vinegar with another chemical. This way, studentswould be able to learn about how different chemicals react to different things and also how theyreact in different situations. By substiting the vinegar with another chemical, it enables the studentto gain more insight on the topic that they are learning and will give them more knowlegde andunderstanding to go on throughout the semester.
Tjia 7Another thing that can be done is to do this experiment backwards. This way, students will also getmore understanding and insight. Students will also be able to see that chemicals affect whichchemical.Appendix0.5 mL of vinegar.1.5 mL of vinegar.2.5 ml of vinegar.1 mL of vinegar.2 mL of vinegar.
Tjia 8Bibliography" Equivalence Point." Chemistry Help Online, Online Chemistry Courses, Online Chemistry Helpby Expert Chemistry Tutors Web. 13 Feb. 2013. ry/equivalence-point.html# ." Vinegar - Definition and More from the Free Merriam-Webster Dictionary." Dictionary andThesaurus - Merriam-Webster Online. Web. 13 Feb. 2013. http://www.merriam-webster.com/dictionary/vinegar ." What Is Vinegar? ." wiseGEEK. Web. 13 Feb. 2013. http://www.wisegeek.com/what-is-vinegar.htm ." chemical indicator " Britannica Online Encyclopedia. Web. 13 Feb. 2013. 7/chemical-indicator .