This is a chemistry lab report on an Acid-Base Essay Example

unknown concentration of the Noah can then be calculated in the following manner: At the point of equivalence of a reaction of 1:1 psychometric ratio, An = N.B..

The number of moles of a solute is the concentration times the volume (N = PVC ). Thus Vacant = Bcc.

Knowing all other variables we can solve tort Cb by restructuring the previous equation as Cb = cave/Va. However, in order to determine the equivalence point the dissociation of the indicators being used must coincide with the pH at the equivalence point. The indicator, a weak organic acid, will dissociate at a certain PH. The dissociation of an indicator is concurrent with a color change or some other physical change which informs the observer of the solution's approximate PH.

A decreased amount of HUH+ a product of acid dissociation) makes it more probable for the dissociation reaction of the indicator to occur since equilibrium must be maintained. Depending on the specific dissociation constant of each indicator a different HUH+ concentration (and thus pH) will trigger the dissociation of each indicator.

Since we do not know the dissociation equilibrium of each indicator, we cannot calculate the exact range of pH at which a color change will appear. Thus we will must repeat the titration experiment with a pH-meter and record the pH of the acid- base solution per millimeter of Noah added.

The results of this part of the experiment ill be used as the correct reference in order to determine which indicators change color at a pH range that coincides with the approximate pH at the equivalence point of the given titration. The calculations of the concentration of

Noah must thus exclude the unsuitable indicator(s).

Method and Explanations ;Acid Base Titration with Different Indicators We first created a solution of Noah by adding ml of MM Noah to 500 ml of distilled water. This solution was poured into a plastic bottle with a lid and was shook vigorously for a few minutes.

It is essential that the solution be homogeneous for the titration experiment to be successful for in order to investigate and calculate the Noah concentration it must be constant throughout the solution. We then rinsed and dried four clean beakers and labeled them from one to four. We weighed precisely 0. 50 Goff KIP in each beaker, with an accuracy of + .

001 g. The mass of KIP added to each beaker was recorded. Ml of distilled water was then added to each beaker. 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 mall 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 Ml burette was rinsed twice with ml o t e An H solution trot the plastic bottle .

The burette was then tilled with solution and the initial Noah volume mark

was recorded. With the magnetic stirrer till on, we then placed the burette directly above the opening of the flask and slowly add Noah 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 hydration 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 Noah 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 of the solution should fluctuate for a few seconds from clear to pink and back again but this is simply because the equilibrium of the solution was temporarily thrown out of balance with the presence of more hydroxide ions (OH-).

The additional hydroxide ions neutralized the hydration ions (HUH+) in the solution. This causes a temporary lack of hydration and thus shifts the dissociation equilibrium of the indicator.

The indicator dissociates temporarily revealing an instance of pink coloration. However, as there was still some KIP present, the acid, having a stronger dissociation constant, dissociates and HUH+ is produced. The indicator's dissociation reaction is then forced backward and the solution once again appears clear. This experiment was then repeated using two other indicators: brotherly blue and methyl orange.

For the latter experiment, twice the amount of indicator drops was added. This makes it easier to detect the instant the color change occurs since the methyl orange indicator continually and gradually

changes its color.

It is thus difficult to determine exactly when the first permanent color change occurs. The gradual color changes of this indicator may be due to multiple steps of dissociation which may occur for example if the acid can release more than one H+ ion (this is simply a speculation, do you know why the color change is so gradual? . The experiment was then repeated once more. This time no indicator was used. Rather, a pH meter was used to devise a correct reference with which to determine which indicators are appropriate for the determination of the equivalence point for this specific reaction. The experimental setup is the same as previously however, we also inserted the probe of a pH meter in the flask.

The probe was rinsed with distilled water and dried. We then proceeded with the experiment recording the pH of the solution after every ml. Of added Noah.

With these results we then constructed a titration curve and determined which indicator(s) was inappropriate for this experiment so that we may calculate the experimental concentration of Noah excluding the unsuitable indicator(s).

Results and Calculations Method of Transubstantiation with Color Indicators meter Sample Number#1#2#3#4 Mass of Beaker, u 4. 91109. 86172. 13186. 25 Mass of Beaker and KIP sample, C)21 5.

41110. 36172. 63186. 75 Mass of the KIP sample, (g) WACKO. 50 Molecular weight of KIP, whom) MEMPHIS.

5 Number of KIP moles in the sample, KNAP 2. E-3 Indicator usedPhenolphthaleinBromothymol Blumenthal Orange/A Initial Noah volume reading, (ml) Vinous Final Noah volume reading at color change, (ml) Fifing. 521. 07. 023. 0 Noah volume used at equivalence point, (ml) Ivanhoe.

521. 07. 023. 0 Moles of

KIP sample= HAWK / MAKE = 0. 50 / 204. 15 = 2.

45+3 Venom = - ;Observations: Indicators colorless color methyl remorselessness's'. N. * PhenolphthaleinColorlessPink biorhythms bluebottles * As the solution becomes more basic the methyl orange indicator becomes more orange.

Data Table 2: Part 4 Burette Reading (ml)Ph reading 14.

56 24. 72 34. 85 44. 97 55. 07 65. 15 75.

24 85. 33 95. 42 105. 49 115.

58 125. 65 135. 74 145. 83 1 55.

92 166. 03 176. 15 186. 32 196. 57 206.

97 2110. 87 2211. 67 ;Titration Curve ;Data Table 3: Data Treatment Sample #MAKE (mol)Manna at equivalence (mol)Venom (L)Military of Noah iterant solution calculated from results (M)Calculated [OH-] value in Noah solution used for titration (M)pH of used Noah solution 12. 45+32.

45+30. 02050. 1 1950. 1 19513. 8 20. 02100.

11670. 116713. 07 3*0. 00700. 35000. 350013.

54 40. 02300. 10650. 106513. 03 Averages of Appropriate Samples.

11420. 114213. 6 *Indicator 3 is not suitable for the determination of the point of equivalence of this reaction as can be seen from the results of the pH meter experiment which we are using as our correct reference. Due to the 1:1 psychometric ratio of this reaction, Manna = MAKE at the point of equivalence.

The military of Noah iterant solution can be calculated using our experimental data.

The military is found with the following equation: Military of Noah iterant solution = Manna / Venom Since Noah is a strong acid it dissociates completely and thus [OH-] in the Noah iterant solution is equal to the military of iterant solution: Noah (aqua)] = [OH- (aqua)] The pH of the used Noah solution can be calculated in the

following manner: pH + POOH = 14 POOH = -log [OH. ] PH = 14 + log [OH. ] egg. Sample 1: pH = 4 log ( Sample Averages = Sum of Results of Appropriate Samples / # of Appropriate Samples Discussion, Conclusions and Errors following the Curve of Titration In this lab, four titration's were carried out.

The first three titration's were carried out with color indicators.

The fourth titration use a pH-meter and a titration curve was plotted for the results of the titration. The titration curve followed quite closely with the expected graph shape. From the graph, we see that the initial pH of the KIP solution is 4. 38. This means that KIP is a weak acid and, titrating it with the strong base Noah, the equivalence point should be greater than

The area in the beginning of the graph rose gradually.

After the buffer region there was a sharp rise in PH.

This steep rise coincides with the point of titration in which 20. 5 ml of Noah iterant had been added and the pH of the acid-base solution was about 9. 08.

The equivalence point was, as we expected for a weak acid-strong base titration, at a basic PH. Since the equivalence point of "chemically equivalent" reactants represents the point t which they have the same concentration in the solution, we know that there are 0. 00245 moles of Noah in 20. 5 ml of the iterant solution.

From this we calculated the unknown concentration of the Noah solution.

From the phenolphthalein results, we calculated the Noah iterant concentration to be 0. MM. From the brotherly blue we found the Noah iterant concentration to

be 0. MM.

Using methyl orange we calculated the Noah iterant concentration to be 0. 350. The pH-meter experiment revealed to us that the iterant Noah concentration was about 0. 1065. We used the results of the pH-meter experiment as the correct reference. Comparing the results found with the three indicators to the results from the pH meter it is evident that methyl orange is not an appropriate indicator for the given reaction.

Methyl orange has a greater dissociation constant and therefore dissociates (and changes color) in the presence of more hydration ions than the other indicators can dissociate in. Therefore color change of methyl orange does not signal the point of equivalence but rather a pH of approximately 4. 8. Other than the fact that methyl orange was an unsuitable indicator, it was difficult to determine when it first changed color permanently. The dissociation of methyl orange coincides with a rather gradual continuous color change.

As the pH decreases even more the indicator becomes more orange.

As I have speculated earlier, the gradual color changes of this indicator may be due to multiple steps of dissociation which may occur for example if the acid can release more than one H+ ion. It was also difficult to determine the exact point of a permanent color change with the other indicators as the new color appeared instantaneously and then disappeared. These fluctuating color changes are caused by the added Noah which temporarily throws the solution out to equilibrium.

In an attempt to regain equilibrium the indicator, a weak acid, dissociates.

However, since there is still some KIP present it dissociates when it detects the newly added hydroxide ions. This

forces the indicator dissociation reaction back. The reason this occurs is that KIP, while a weak acid, has a greater dissociation constant than the phenolphthalein and brotherly blue indicators and thus as long as it is present the indicators will not dissociate. These fluctuations in color change also occur with methyl orange but they are hard to recognize due to the pale yellow color of the indicator when it first starts to dissociate. Our average calculated concentration of the Noah iterant solution was 0.

MM. The actual concentration of the Noah iterant solution can actually be calculated exactly: Moles of Noah = MM (1 Orin/looms) Volume of solution = 500+ 10 ml = mall Military = Moles/ Liter = 6. MM (1 Orin/looms) / 0. 510 = 0. MM The experimental calculation of the concentration was actually quite close to the actual concentration. In fact the actual concentration may be slightly off due to minor inaccuracies in preparing the solutions and weighing.

The percentage difference of the actual and average experimental results is: 100(0. 176 - 0. 1142) / 0. 1176 = +2. 9%.

This is a very small percent error and indicates that our experiment was successful and that the chosen indicators, phenolphthalein and brotherly blue, are suitable for this experiment. Assuming the inaccuracies in preparation of the solutions was minor, the most suitable indicator for this experiment is actually brotherly blue with a percent error from the actual result of only +0. 77%. However, the pH-meter, which we can assume is quite accurate, had a percent error from the actual results of +9. 44%. Thus there must have been some error in repairing the solutions.

Nonetheless,

Brotherly blue is the best color indicator for this experiment as it is also the closest to the pH-meter results. Phenolphthalein is also a good indicator. While the percentage error of the Noah iterant concentration may be about +9% from the concentration calculated with the pH-meter results, the experimentally calculated pH of the solution is in all samples quite close to that found with the pH meter. In fact, the pH calculated from the results obtained from the Brotherly blue experiment displayed only +0. 307% error from the pH found with the pH meter.

There were several other sources of error or inaccuracies in this lab, however the errors of this lab were relatively minor. There is always error in weighing and measuring due to human and instrument limitations. It was hard to get an exact reading on the pH meter because the numbers fluctuated so much. The readings, however, should not have been significantly off. The pH meter had an error of +1- 0. 1 units This may nave caused some minor error in the titration curve.

Another source of inaccuracy is in the plotting of the titration curve. There is much estimation in the plotting of a graph without a computer.

Nonetheless, these inaccuracies are insignificant and do not affect our results greatly. There were also discrepancies in determining the point of equivalence and the half-equivalence point on the curve however this is merely the cause of the inevitable estimations made on the plotting of the curve. An obvious error in determining the end point is using an incorrect indicator. This is something we were aware of before the lab and we eliminated the

results of the unsuitable indicator, methyl orange, from any calculations.

It is important that the chosen indicator change color somewhere in the steepest part of the titration curve.

This makes it difficult to determine the actual end point because a small amount of solution can change the pH quite a bit. Ideally, the solution should have been added in very small increments. This would have allowed the end point determination to have been much more accurate.

These errors and inaccuracies are quite insignificant however and our experiment was successful in determining the Noah iterant concentration and its pH of 13. 03. We were also able to estimate the equivalence point of titration from the curve. We found the equivalence point occurs at a pH of approximated 9.08.