A titration is a technique used to find the solution of known concentration in the concentration of another unknown solution. Typically, the known solution is added from a known quantity of unknown solution until the reaction is complete. Titrations are also often used to determine the pH of a solution. This is important because without knowing how acid or basic a solution is people could hurt themselves and others but mixing chemicals together that are lethal.
The objective of the is lab is to develop familiarity with the concepts and techniques of titration and to determine the concentration of an acidic acid solution. It was necessary to add Phenolphthalein because it acts as an indicator, that is a weak acid, so it is easier to tell when the acids and bases react together. Without the indicator one would not be able to see when the reactants had balanced each other out. The purpose of the is lab was to find out how acids and bases can neutralize the other when the right amount of drops of solution are added.
Materials -5 mL White Vinegar -Phenolphthalein -White Paper Towel -.5 M NaOH -Well Plate -50 mL Beaker Micro-tip Pipets
Methods and Procedure With a wax marker, mark the two micro pipets you will use in this experiment: V for vinegar and NaOH for Sodium Hydroxide. Place a 24-well reaction plate on a white piece of paper to help you see color changes. Pour about 5 mL of you r commercial white vinegar into a 50 mL beaker and fill the bulb of the “V” micro-tip pipet from this source. From the micro-tip pipet, dispense 10 drops of white vinegar into well A-1. Carefully hold the pipet vertically and make certain that the drops fall directly to the bottom of the well, not against the walls, or the tests may be impaired. Add 1 drop of phenolphthalein directly from its pipet into the vinegar in well A-1.
Squeeze the contents of you Sodium Hydroxide pipet into well D-6 and fill the bulb of the “NaOH” micro-tip pipet from this source. Next you will add 5 drops of Sodium Hydroxide from the micro-tip pipet to the vinegar in well A-1, but you will do this one drop at a time and stir with a clean toothpick between drops. Again, hold the pipet vertically and make certain the drops fall directly to the bottom of the well. Record your observations. Now, continue to add drops of NaOH to the vinegar in well A-1 until the “endpoint” is reached.
This occurs when the solution’s color turns to a light pink and remain that color for at least 30 seconds. Note: Just prior to reaching the endpoint, the solution may turn pink when a drop is added, but the color quickly disappears upon stirring. Record the total number of drops of Sodium Hydroxide used to reach the endpoint. Repeat the process two more times, using wells A-2 and A-3. Record your results for each trial. Note: All three titration results should agree within 1 drop of the others. If they do not, you have made a computation error and should repeat the titration.
Calculate the average number of drops of NaOh used for the 3 trials and record. Calculate the Normality of the vinegar using the previously given equation. Calculate the mass of the acetic acid in grams using the previously given equation. Calculate the percentage of acetic acid using the previously given equation. Thoroughly clean all your equipment and wash any left over acid or base down the sink with lots of water. Remember, acids and bases will neutralize each other when mixed.
Data and Results *Normality of vinegar (Na) = (Nb)(dropsb) / (dropsa) (.5)(22) / (10) = 1.1 N *Mass of Acetic Acid = (Na)(GMMa) (1.1)(60) = 66 g *% of Acetic Acid = Massa (g/L) / 1000 g/L x 100% 66 / 1000 x 100 = 6.6 g/L Balanced equation: HC2H3O2 + NaOH ——> NaC2H2O2 + H20 Discussion For the 1st trial it took 18 drops of Sodium Hydroxide to balance it out, for the 2nd trial 19 drops, 3rd trial 24 drops, 4th trial 25 drops, and for the 5th trial it took 24 drops.
The average amount of drops it took was twenty-two. The acid and base were so close in drops because while they are opposites, they are the exact opposite of each other, meaning that one drop of acid will neutralize one drop of a base and vice-versa. The normality of the base was .5 because there was only one equivalent of NaOH so the morality would be Nam. The equation that would be used to find Na is : *Na= (Nb)(average # drops of base) / drops of acid (10) The Nb is .5 N, the average number of drops of base is 22, and the drops of acid is 10. The answer is 1.1 and that is the normality of vinegar.
Some changes that took please were the change in color when the drops of base were added to the vinegar. Also, one could see that the more drops that were added made the solute a deeper pink, so much that it almost looked red. Some potential sources of error were that the plates had so left over water in them, the plates had al ready been used, and that the sizes of the drops of solution were either not big enough or to big which would mean that the data was not very accurate.
Conclusion Overall, this experiment yielded the information that equal amounts of bases and acids will neutralize each other perfectly. It showed that a titration is a way of finding out the concentration of an unknown solution by using one that you do need. The concentration of an acetic acid solution is the same amount of drops of an acid and base added together to neutralize the solution as a whole. Lastly, this lab explained how different amounts of drops of acids and bases can be used to change the pH os a solution.
