Chemistry Lab

The pKa of an undiscovered region Acid-Base indicant By Josephine Hong Lab t for each oneer Yue Zhang Due April 5, 2013 Submitted April 5, 2013 Abstract In this lab, the pKa of the obscure index number of expression was determined twain softly and quantitatively. To verify our mathematical operations, the experiment was time- tried and true utilize a enduren power, bromocresol atomic number 19. Qualitatively, we employ the falsify veer of the etymon with indicant to obtain the pKa value solely employ a pH meter. Quantitatively, we apply a pH meter and the spectrophotometer with varying assiduousnesss of the corrosive and prow.The level best wavelengths of absorbance utilize to quantify the dissociated and undissociated forms of the bromocresol greens were 440 nm (yellow, undissociated) and 616 nm (blue dissociated). For the unfathomable exponent, the wavelengths were 505. 96 nm (red, undissociated) and 601. 66 nm (blue, dissociated). For bromocresol gree n, the through an experiment obtained pKa value measured qualitatively was 4. 04. Quantitatively, the pKa came bulge to be 4. 16. The sh atomic number 18age defect (10. 47%) obtained was within reasonable range, allowing the same executions to be use to determine the pKa value of the unnamed exponent, exponent of Freedom.Indicator was Freedom was found to bring a pKa value of 5. 32 qualitatively essay writer typer. On the some some other hand, the quantitative pKa was measure to be 4. 265. installation This lab applies the concept of an indicator dye, which is in general a weak unpleasant that castrates warp when reacting with the amount of hydronium ion in a source. Thus, the qualitative part of the lab assumes that at the superman where the theme miscellaneas gloss into an intermediate shadowiness of the two, the niggardlinesss of HIn and In- is approximately liken. Using the Henderson-Hasselbalch equation for them he pH pits pKa when the ratio between the indicator and its conjugate primary is 1. Subsequently, the quantitative dole bring out of the lab deals with the relationship between absorbance and concentration A1(? )A2(? )= c1c2 Thus, a certain absorbance of a ancestor can provide the concentration of the indicator and its conjugate base when taking into comity the uttermost wavelength of the two dis colouriseize. Experimental segment To reduce the deals of acid and base requisite and the amount of time to complete the lab, the deport solutions of strong acid and base were thin out to at least one-fourth their jump amount.Thus, 60 mL of deionized water was added to two(prenominal) pullulate solutions of 20 mL HCl and NaOH to bring on 2 new 80 mL thin solutions. Part 1 conclusion pKa Qualitatively 25 mL solution of the weaken NaOH with 3 drops of indicator was titrated against the weaken HCl drop wise until a contort channel occurred. To determine the pKa of the indicators, the pH of the solutions were interpreted with a pH meter when in that respect was a color change. Determining the color of bromocresol green to be yellow when virulent and blue when basic, the read/write head of color change to measure pH was when the solution sullen green.Likewise, the indicator of Freedom was red when acidulent and blue when basic, which established the orientate of color change to be purple. These locomote were performed trine times for both the hunchn and foreigner indicators to find an average pKa value. Part 2 subprogram pKa Quantitatively For the quantitative decision of pKa, multiple solutions of varying acid/ base concentration were prepargond with 3 drops of indicator. despite the varying concentrations of each solution, the total loudness stayed constant at 20 mL.Before anything, the wavelengths of maximum absorbance were determined first by utilize solutions of pure acid and base with tierce drops of indicator. For each solution, the pH was measured forward placing them in cuvettes to measure their absorbance values utilise the spectrophotometer. These steps were performed for both the known and unfathomable quantity indicator. Results postpone 1 Qualitative info for Bromocresol spirt Trial pH 1 3. 82 2 3. 93 3 4. 36 comely 4. 04 Calculation of middling circumvent 2 Maximum Absorbance and for Bromocresol immature HCl w/ 3 Drops Indicator NaOH w/ 3 Drops Indicator Concentration (M) . 028 . 0962 (nm) 440 616 source Color Yellow Blue Absorbance . 116 . 243 tabular array 3 Quantitative entropy for Bromocresol light-green Volume of HCl (mL) Volume of NaOH (mL) pH Absorbance HIn AbsorbanceIn- 14 6 3. 50 . 055 . 015 9 10 4. 39 . 044 . 048 7 13 5. 30 . 024 . 103 Figure 1 Absorbance vs. pH for Bromocresol one thousand Percent Error Calculation for Bromocresol jet plane misplay *pKa of Bromocresol greenish was found online dodge 4 Qualitative Data for Indicator of Freedom Trial pH 1 5. 50 2 5. 33 3 5. 12 Average 5. 32 defer 5 Maximu m Absorbance and for Bromocresol spirt HCl w/ 3 Drops Indicator NaOH w/ 3 DropsIndicator Concentration (M) . 1028 . 0962 (nm) 505. 96 601. 66 consequence Color Red Blue Absorbance . 703 . 945 panel 6 Quantitative Data for Bromocresol commonalty Volume of HCl (mL) Volume of NaOH (mL) pH Absorbance HIn AbsorbanceIn- 18 2 2. 07 . 360 . 046 14 6 2. 36 . 374 . 048 10 10 3. 88 . 347 . 087 10 10 3. 04 . 312 . 041 9 11 9. 35 . 148 1. 127 9. 5 10. 5 5. 95 . 171 . 686 9. 75 10. 25 5. 45 . 230 . 424 9. 25 10. 75 9. 13 . 146 . 913 Figure 2 graphical record of Absorbance vs. pH for Indicator of Freedom railleryThe qualitative part of the lab had get on for a lot of errors. The unreli business leader of ocular observation of the slight color change in solution could gather in dramatically affected the results. Because the through an experiment determined pKa was slight than the actual pKa for both cases, strong fair to middling color change were probably not prised. Since the titration was performed roughly victimisation drops, the drops could grow added to a greater extent acid than inevitable, resulting in a little pKa.. Quantitatively, the pKa can be determined by plotting the data, with absorbance as a function of pH. in that location will be two give away lines, one for each wavelength of the two colors.The convergence of these two lines will indicate the elevation at which the pH should be equal to the pKa. This works because at the cross denominate pH=pKa+logIn-HIn It is known that A1A2= c1c2. Since A1= A2 at the crossover signal of the graph, then 1= c1c2= In-HIn. Thus,pH=pKa+log1 pH=pKa at the crossing of both curves The procedure for purpose of bromocresol green pKa appeared to excite worked, because the per centum error was roughly around 10%. Although slightly high, these errors are unpreventable. For example, cuvettes with smudges on the sides would have increased the absorbance readings of the solutions.Moreover, the maximum waveleng th is crucial because it is used as a standard to know where to record the absorbance levels of the other solutions. This is because it is where the maximum absorbance occurs for the grouchy color produced by the solution is. It is great to measure the absorbance levels at these standardized wavelengths to salvage the data consistent and to have the king to compare the absorbance levels of two solutions without the need to set or ad exactly the readings. Finally, a extra number of data points when determining the pH graphically could have also added to the error in this experiment.Chemistry LabThe pKa of an unsung Acid-Base Indicator By Josephine Hong Lab teacher Yue Zhang Due April 5, 2013 Submitted April 5, 2013 Abstract In this lab, the pKa of the unknown indicator of expression was determined both qualitatively and quantitatively. To verify our procedures, the experiment was tested using a known indicator, bromocresol green. Qualitatively, we used the color change of the solution with indicator to obtain the pKa value solely using a pH meter. Quantitatively, we used a pH meter and the spectrophotometer with varying concentrations of the acid and base.The maximum wavelengths of absorbance used to quantify the dissociated and undissociated forms of the bromocresol green were 440 nm (yellow, undissociated) and 616 nm (blue dissociated). For the unknown indicator, the wavelengths were 505. 96 nm (red, undissociated) and 601. 66 nm (blue, dissociated). For bromocresol green, the experimentally obtained pKa value measured qualitatively was 4. 04. Quantitatively, the pKa came out to be 4. 16. The percentage error (10. 47%) obtained was within reasonable range, allowing the same procedures to be used to determine the pKa value of the unknown indicator, Indicator of Freedom.Indicator was Freedom was found to have a pKa value of 5. 32 qualitatively essay writer typer. On the other hand, the quantitative pKa was measure to be 4. 265. entrance This lab applies the concept of an indicator dye, which is in the main a weak acid that changes colors when reacting with the amount of hydronium ion in a solution. Thus, the qualitative part of the lab assumes that at the point where the solution changes color into an intermediate vestige of the two, the concentrations of HIn and In- is approximately equal. Using the Henderson-Hasselbalch equation for them he pH equals pKa when the ratio between the indicator and its conjugate base is 1. Subsequently, the quantitative arrogate of the lab deals with the relationship between absorbance and concentration A1(? )A2(? )= c1c2 Thus, a certain absorbance of a solution can provide the concentration of the indicator and its conjugate base when taking into contemplation the maximum wavelength of the two colors. Experimental dent To reduce the volumes of acid and base needed and the amount of time to complete the lab, the stock solutions of strong acid and base were diluted to at least one-fourth their commencement amount.Thus, 60 mL of deionized water was added to both stock solutions of 20 mL HCl and NaOH to nominate 2 new 80 mL diluted solutions. Part 1 Finding pKa Qualitatively 25 mL solution of the diluted NaOH with 3 drops of indicator was titrated against the diluted HCl drop wise until a color change occurred. To determine the pKa of the indicators, the pH of the solutions were taken with a pH meter when in that respect was a color change. Determining the color of bromocresol green to be yellow when sulfurous and blue when basic, the point of color change to measure pH was when the solution glowering green.Likewise, the indicator of Freedom was red when acidic and blue when basic, which established the point of color change to be purple. These steps were performed cardinal times for both the known and unknown indicators to find an average pKa value. Part 2 Finding pKa Quantitatively For the quantitative determination of pKa, multiple solutions of varying acid/ base concentration were prepared with 3 drops of indicator. disdain the varying concentrations of each solution, the total volume stayed constant at 20 mL.Before anything, the wavelengths of maximum absorbance were determined first by using solutions of pure acid and base with tercet drops of indicator. For each solution, the pH was measured originally placing them in cuvettes to measure their absorbance values using the spectrophotometer. These steps were performed for both the known and unknown indicator. Results put back 1 Qualitative Data for Bromocresol commons Trial pH 1 3. 82 2 3. 93 3 4. 36 Average 4. 04 Calculation of Average control board 2 Maximum Absorbance and for Bromocresol leafy vegetable HCl w/ 3 Drops Indicator NaOH w/ 3 Drops Indicator Concentration (M) . 028 . 0962 (nm) 440 616 closure Color Yellow Blue Absorbance . 116 . 243 prorogue 3 Quantitative Data for Bromocresol Green Volume of HCl (mL) Volume of NaOH (mL) pH Absorbance HIn AbsorbanceIn- 14 6 3. 50 . 055 . 015 9 10 4. 39 . 044 . 048 7 13 5. 30 . 024 . 103 Figure 1 Absorbance vs. pH for Bromocresol Green Percent Error Calculation for Bromocresol Green error *pKa of Bromocresol Green was found online Table 4 Qualitative Data for Indicator of Freedom Trial pH 1 5. 50 2 5. 33 3 5. 12 Average 5. 32 Table 5 Maximum Absorbance and for Bromocresol Green HCl w/ 3 Drops Indicator NaOH w/ 3 DropsIndicator Concentration (M) . 1028 . 0962 (nm) 505. 96 601. 66 firmness of purpose Color Red Blue Absorbance . 703 . 945 Table 6 Quantitative Data for Bromocresol Green Volume of HCl (mL) Volume of NaOH (mL) pH Absorbance HIn AbsorbanceIn- 18 2 2. 07 . 360 . 046 14 6 2. 36 . 374 . 048 10 10 3. 88 . 347 . 087 10 10 3. 04 . 312 . 041 9 11 9. 35 . 148 1. 127 9. 5 10. 5 5. 95 . 171 . 686 9. 75 10. 25 5. 45 . 230 . 424 9. 25 10. 75 9. 13 . 146 . 913 Figure 2 graphical record of Absorbance vs. pH for Indicator of Freedom tidingsThe qualitative part of the lab had agency for a lot of errors. The unre liability of opthalmic observation of the slight color change in solution could have dramatically affected the results. Because the experimentally determined pKa was less(prenominal) than the actual pKa for both cases, strong large color change were probably not observed. Since the titration was performed roughly using drops, the drops could have added more acid than needed, resulting in a smaller pKa.. Quantitatively, the pKa can be determined by plotting the data, with absorbance as a function of pH. thither will be two crock up lines, one for each wavelength of the two colors.The intersection of these two lines will indicate the point at which the pH should be equal to the pKa. This works because at the intersection point pH=pKa+logIn-HIn It is known that A1A2= c1c2. Since A1= A2 at the intersection point of the graph, then 1= c1c2= In-HIn. Thus,pH=pKa+log1 pH=pKa at the intersection of both curves The procedure for determination of bromocresol green pKa appeared to have work ed, because the percent error was roughly around 10%. Although slightly high, these errors are unpreventable. For example, cuvettes with smudges on the sides would have increased the absorbance readings of the solutions.Moreover, the maximum wavelength is crucial because it is used as a standard to know where to record the absorbance levels of the other solutions. This is because it is where the maximum absorbance occurs for the ill-tempered color produced by the solution is. It is main(prenominal) to measure the absorbance levels at these standardized wavelengths to halt the data consistent and to have the ability to compare the absorbance levels of two solutions without the need to correct or adjust the readings. Finally, a hold number of data points when determining the pH graphically could have also added to the error in this experiment.Chemistry LabThe purpose of this lab was to see which solutions are water-soluble and which are not. We were able to see this by mixing ce rtain solutions together and observing changes that occurred. The procedure for this experiment acceptd a some different steps. The first steps were to add the nitrate solutions into the lettered split of the 96-well plate.Once you were done with that, you were supposed to add the atomic number 11 solutions to the numbered parts of the 96-well plate, so that the solutions were added together. You were supposed to observe the different chemical reactions occurring. Once you observed each reaction take place, you needed to learn out your data table. Data Table Solubility Rules TableNegative Ion (Anions) convinced(p) Ions (Cations) Solubility ofCompounds both disconfirming ions are with Alkali ions (Na) soluble tout ensemble negative ions are with Hydrogen (H+) Soluble totally negative ions are with All substantiative ions Soluble Nitrate NO3- ions are with All arrogant ions are Soluble acetate CH COO- ions are 3with All positive ions are Soluble Chloride, Cl-Bromide Br-I odide I- CuAll other positive ions low gear SolubilitySolubleSoluble Sulfate SO 2-4 BaAll other positive ions Low SolubilitySoluble Sulfide S -2 All positive ions Soluble Hydroxide, OH- Ba SolublePhosphate PO 3-4Carbonate CO 2-3Sulfite, SO 2-3 H Soluble Once you put down all of the data, there were a few questions that needed to be answered. A. Compare your results with the solvability rules and/or solubility table in your chemistry text. I would say that my results dour out pretty close to the rules in the text book. I observed numerous different reactions occurring. The colors of the solutions changed from empty to purple, from clear to blue and yellow, and from clear to a off-white white color. There were also changes from a light yellow to a darkening almost orange color. B.Do your results agree with your expectations from the solubility rules/table? My results do agree with my expectations, however, I wasnt expecting all of the solutions to be soluble. C. Which anions broadly form precipitates? What are exceptions? Silver salts, Phosphates, Sulfides, Carbonates, Hydroxides. Exceptions include alkali metals. D. Which anions generally do not form precipitates? What are the exceptions? Nitrates, Alkali metals, ammonium salts, Halides, and Acetates. The exceptions include those mentioned above that would form precipitates. E. Which cations generally do not form precipitates?Na+ generally does not form precipitates. F. discern 10 reactions that produce a precipitate, color change, or gas and write equilibrise chemical equation and a cabbage ionic equation for each. Remember, a reaction may be indicated by the organic law of a precipitate, color change, or the organic law of gas. Record the well numbers of the precipitates you chose for your equations. (Co(No3)2+6H2O)+(Na3PO4+12H2O)Well A1 (Cu(NO3)2+3H2O )+(Na3PO4+12H2O)Well B1 (Fe(NO3)3+9H2)+(Na3PO4+12H2O)Well C1 (Ba(NO3)2) )+(Na3PO4+12H2O)Well D1 (Ni(NO3)2+6H2O)+(Na3PO4+12H2O)Well E1 (Co(No3)2+6 H2O)+(NaHCO3)Well A5 Cu(NO3)2+3H2O)+(NaHCO3)Well B5 (Fe(NO3)3+9H2)+(NaHCO3)Well C5 (Ba(NO3)2) )+(NaHCO3)Well D5 (Ni(NO3)2+6H2O)+(NaHCO3)Well E5 To curve things up, I found this lab to be easy but confusing at the same time. I am not sure my reactions were all correct because I thought there were supposed to be some that were insoluble, however, I observed reactions occur both time. I would suggest by chance providing better rules for the solubility table because I was a little bit missed with that at first as well. I enjoyed doing this lab, as I do every one, but there were parts of it that just confused me.