Full Lab Report
Experiment #2:
Acid-Base Titration
Lab Description: Acid-Base Titration
Introduction
In this lab exercise we will evaluate the effectiveness of several indicators for the determination of the point of completion of a specific acid-base neutralization reaction. We will also determine the unknown concentration of the strong base NaOH by its reaction with a known amount of the weak acid, potassium acid phtalate (HKC8H4O4, abbreviated KHP). This will be accomplished using the titration method. The KHP solution will be created and its volume and concentration recorded. The KHP solution will be poured in a flask along with a few drops of one of three indicators we will be evaluating. The NaOH solution will be poured into a
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The solution was then swirled carefully in order to dissolve the solute. Since our beakers were large we were able to stir the solution contents with the magnetic stirrer without the fear of spilling any solution. This method was more effective and less time consuming than swirling the beaker. This solution was then poured into a 250ml Erlenmeyer's flask and a magnetic stir bar and several drops of phenolphthalein indicator were added. The flask was then placed on the magnetic stirrer with a white paper under the flask to allow for more contrast and facilitate the detection of a color change.
Once the experimental setup was complete, a 50ml buret was rinsed twice with 10ml of the NaOH solution from the plastic bottle. The buret was then filled with the NaOH solution and the initial NaOH volume mark was recorded. With the magnetic stirrer still on, we then placed the buret directly above the opening of the flask and slowly add NaOH to the acidic solution in the flask by slightly turning the stopcock. (It is essential that the magnetic stirrer be mixing the solution continuously so that there is no delay due to the time it take for the hydronium ions to collide with the hydroxide ions.) The instant the color of the solution changes permanently from clear to pink the stopcock must be closed and the final NaOH volume mark must be recorded. The resultant solution was then poured into the designated waste beaker, eventually to be discarded in the waste container.
The color
pH was recorded every time 1.00 mL of NaOH was added to beaker. When the amount of NaOH added to the beaker was about 5.00 mL away from the expected end point, NaOH was added very slowly. Approximately 0.20 mL of NaOH was added until the pH made a jump. The pH was recorded until it reached ~12. This was repeated two more times. The pKa of each trial are determined using the graphs made on excel.
In 2 and 7 I added 50 mL of .1 M NaCl. I added sodium acetate to the rest of the beakers: 1 gram to 3 and 8, 5 grams to 4 and 9, and 10 grams to 5 and 10. I then filled the beakers that contained the solid sodium acetate with 50 ml of .10 M acetic acid. Specifics can be found on page 84 of the lab manual. Though the lab manual instructed to use a pipet, we did not have an accurate 1 mL pipet or a graduated pipet, so we instead prepared two graduated burets with 1 M Sodium Hydroxide and 1 M hydrochloric acid. Using a standardized pH probe with a Lab Pro to measure changes in pH, we added 1 mL of HCl at a time and recorded the changes. The same was done for the NaOH.
Three grams of a mixture containing Benzoic Acid and Naphthalene was obtained and placed in 100 ml beaker and added 30 ml of ethyl acetate for dissolving the mixture. A small amount (1-2 drops) of this mixture was separated into a test tube. This test tube was covered and labelled as “M” (mixture). This was set to the side and used the following week for the second part of lab. The content in the beaker was then transferred into separatory funnel. 10 ml of 1 M NaOH added to the content and placed the stopper in the funnel. In the hood separatory funnel was gently shaken for approximately one minute and vent the air out for five seconds. We repeated the same process in the same manner one more time by adding 10ml of 1M NaOH.
In order for the media to show the change in acidity the solutions are modified and include an indicator chemical. This indicator will change color depending on the ph level of the media it is in. For all the media used in this experiment, the indicator changes to a yellow color when in the presence of an acid and turns magenta/pink when in the presence of a base or alkali.
In Experiment 1, we used a trip balance and a weighing paper to weigh 15 g of NaCl. 50 mL of H2O was then poured into two 100 mL graduated cylinders. After doing that, a stirring bar was added to one of the 50 mL graduated cylinder of H2O. We then placed the graduated cylinder with the stirring bar onto the stirrer and started the stirrer. As the stirrer kept turning, NaCl was gradually added into the solution until all of the NaCl dissolved. After that, H2O from the 50 mL graduated cylinder was added to the NaCl solution until it reached the 100 mL mark. From this, you can get the concentration of the NaCl solution using the
ii. The second part of the titration series involves titration of NaOH with Hydrochloric acid (HCL). Again, three reps of titration and a blank titration have to be completed. A volumetric pipet is used to measure 10.00mL of HCL into three labeled conical flasks. Then the flasks are filled with deionized water until about the 50mL mark. A buret is
11. Recorded volume of water displaced in the 100 (+/- ?) mL graduated cylinder #1 and other necessary quantitative and qualitative observations of the process and the products of the reaction. Then, washed out the Erlenmeyer flask for 5 seconds and used the test tube brush to clean out any leftover solution. Afterwards, allowed the Erlenmeyer flask to air dry and used the second Erlenmeyer flask to perform trial 2.
Background A chemical equation that is in equilibrium will naturally balance itself out should either the products are the reactants be increased, or other stresses such as temperature and pressure are placed on it. However, as with a lever in physics, the fulcrum or balancing point is not always in the middle. In most cases, one side of the equation will be favored more. Ergo, the equation will try to balance to this point of equilibrium.
Observe and measure a weak acid neutralization and determine the unknown identity of an unknown acid by titration.
By using acid-base titration, we determined the suitability of phenolphthalein and methyl red as acid base indicators. We found that the equivalence point of the titration of hydrochloric acid with sodium hydroxide was not within the ph range of phenolphthalein's color range. The titration of acetic acid with sodium hydroxide resulted in an equivalence point out of the range of methyl red. And the titration of ammonia with hydrochloric acid had an equivalence point that was also out of the range of phenolphthalein.. The methyl red indicator and the phenolphthalein indicator were unsuitable because their pH ranges for their color changes did not cover the equivalence points of the trials in which they were used. However, the
Add 4 drops of phenolphthalein in to the prepared acetic acid, and check whether the color changes to dark pink.
First, three titration curves and three second derivative curves were created to determine the average pH at the half-equivalence point from the acetic acid titrations. Titration curves were used as visuals to portray buffer capacity. The graphs and a table, Table 1, that showcased the values collected were created and included below. The flat region, the middle part, of Figures 1, 2 and 3, showed the zone at which the addition of a base or acid did not cause changes in pH. Once surpassed, the pH increased rapidly when a small amount of base, NaOH, was added to the buffer solution. Using the figures below and
In this lab a acid-base indicator phenolphthalein was used to determine endpoint of a reaction HCl(aq) and KOH(aq). At the end point all of the HCl(aq) would have reacted with KOH(aq), and the pH becomes 7. The phenolphthalein would changed colours from colourless to pink indication when enough KOH(aq) was added. The purpose of numerous trials was to use the average volume of the 3 trials with similar measurements.
An acid-base titration is the determination of the concentration of an acid or base by exactly neutralizing the acid/base with an acid or base of known concentration. This allows for quantitative analysis of the concentration of an unknown acid
For this experiment, a pH meter was used so this part of the experiment began with the calibration of the pH meter with specified buffers. The buret was then filled with the standard HCl solution and a set-up for titration was prepared. 200g of the carbonate-bicarbonate solid sample was weighed and dissolved in 100 mL of distilled water. The sample solution was then transferred into a 250-ml volumetric flask and was diluted to the 250-mL mark. The flask was inverted several times for uniform mixing. A 50-mL aliquot of the sample solution was measured and placed unto a beaker. 3 drops of the phenolphthalein indicator was added to the solution in the beaker. The electrode of the pH meter was then immersed in the beaker and the solution containing the carbonate-bicarbonate mixture was titrated with the standard HCl solution to the phenolphthalein endpoint. Readings of the pH were taken at an interval of 0.5 mL addition of the titrant. After the first endpoint is obtained, 3 drops of the methyl orange was added to the same solution and was titrated with the standard acid until the formation of an orange-colored solution. Readings of the pH were also taken at 0.5 mL addition of the titrant.