XXXXXXXX Professor Tue Nguyen June 29, 2015 Titration of Commercial Bleach Introduction/Purpose: The strength of commercial laundry bleach is ultimately determined through the discovery of the amount of sodium hypochlorite, NaClO, since it’s the main component in bleach. Depending on the brand of bleach, the concentration of NaClO can vary drastically. In this experiment, titration is used to determine the concentration of NaClO in a giving sample of commercial bleach. However, NaClO can not be measured directly and thus, a two-step method was used. The two-step reaction first required ClO- to be converted to I2, and then I2 being titrated with S2O3-2 resulting in the production of iodide ions. The disappearance of I2 is detected via starch indicator as the solution is blue when I2 is present and clear in its absence. Preparation step : OCl- + 2 I- + 2 H3O+ → I2 + Cl- + 3 H2O Titration step: I2 + 2 S2O32- → 2 I- + S4O62- Overall, the investigation provided the lab group with the appropriate findings in order to calculate the percentage of sodium hypochlorite in bleach to determine its strength. Procedures: The lab group participated in the following steps in order to complete the experiment regarding the strength of laundry bleach. First, the Na2S2O3 solution(0.1M) was poured into a 50mL buret in order to begin titrating the prepared bleach solution, which contained 10mL of 10% I-1 (aq) solution, 10Ml of HCl (1M) solution, and 25mL of diluted bleach solution. A stirring bar was placed into the beaker, full of the reaction solution, and was put on the stirring plate so the solution could be stirred. The Na2S2O3 solution was added into the prepared bleach solution until a light yellow color appeared. Afterwards, 5mL of 0.1% starch indicator was added into the beaker until the solution transitioned into a dark blue color. Lastly, the Na2S2O3 solution was leisurely added into XXXXXXXX Professor Tue Nguyen June 29, 2015 the beaker until the solution was completely clear indicating the endpoint. The lab group recorded the volume of the Na2S2O3 solution added, and then these steps were repeated for a total of three trials. Data: The data gathered during the experiment included the volume of S2O3-2 at the equivalence point over the span of three trials. 29.6 milliliters of S2O3 was recorded as the volume at equivalence point for trials one and two. 30.4 milliliters of S2O3 was noted as the volume at equivalence point in trial three. Calculations: -Formula: (M)(V)= mol -Sample calculation: (0.1 M)(.0296 L)= 2.96E-3 mol S2O3 -Final values: 2.96E-3 mol S2O3, 2.96E-3 mol S2O3, and 3.04E-3 mol S2O3 -Formula: (1/2)(mol S2O3)= mol ClO -Sample calculation: (1/2)(2.96E-3 mol S2O3)= 1.48E-3 -Final values: 1.48E-3 mol ClO, 1.48E-3 mol ClO, and 1.52E-3 mol ClO -Formula: (MW)(mol)= grams -Sample calculation: (74.44 MW NaClO)(1.48E-3 mol ClO)= 0.110172 g NaClO -Final values: 0.110172 g NaClO, 0.110172 g NaClO, and 0.1131488 g NaClO -Formula: (mL)(g/mL)= grams XXXXXXXX Professor Tue Nguyen June 29, 2015 -Sample Calculation/Final Value: (2.5 mL)(1.08 g/mL)= 2.7 gramsbleach -Formula: (gramsNaClO/gramsbleach) x 100= mass percentage NaClO in bleach -Sample calculation: (0.110172)/(2.7)= 0.041 g x 100= 4.1% NaClO -Final values: 4.1% NaClO, 4.1% NaClO, and 4.2% NaClO Results: Table 1: Mass % Trial # Mass % of NaClO in Bleach 1 4.1% 2 4.1% 3 4.2% Discussion: We determined the percentage of sodium hypochlorite to be about 4.1% by mass in commercial bleach. The results of the experiment also indicates the overall strength of commercial laundry bleach. In table 1, the mass percentage of NaClO in bleach didn’t fluctuate enormously so the values documented were highly precise. Therefore, the lab group did the technique used to obtain these results properly. Errors may have occurred during the process of determining the end point by color changing indicators as we allowed the titration to continue slightly after the color change. Overall the results were fairly accurate being that household bleach, in general, contains 3 to 8 percent sodium hypochlorite. XXXXXXXX Professor Tue Nguyen June 29, 2015 Conclusion: A reducing agent, S2O3-2, was used for the experiment in order to find the percentage of NaClO in bleach indirectly. The volume of the Na2S2O3 solution was noted to ultimately find the mass percentage of the NaClO in bleach, which was 4.1% for trial 1 and 2 and 4.2% for trial 3. Overall, the experiment revealed the amount of sodium hypochlorite in commercial laundry bleach through the findings collected during the experiment. Antacid Comparison Pre-Lab questions 1. List 5 different antacids in the market and their active ingredients. Gaviscon: sodium alginate; sodium bicarbonate (sodium hydrogencarbonate); and. calcium carbonate. Gelusil: aluminum hydroxide and magnesium hydroxide. Maalox: aluminum hydroxide, magnesium hydroxide and simethicone Mylanta: aluminum hydroxide and magnesium hydroxide. Rolaids: calcium carbonate (550 mg) and magnesium hydroxide (110 mg) 2. Identify most common anions in antacids calcium carbonate, magnesium hydroxide, aluminum hydroxide and/or sodium bicarbonate. 3. a. What is neutralization reaction? A neutralization reaction is when an acid and a base react to form water and a salt and involves the combination of H+ ions and OH- ions to generate water. b. Write balance chemical equation for neutralization reaction. H+(aq) + OH−(aq)⟶H2O(l) 2H+(aq) + CO32- (aq)⟶H2O(l) +CO2(g) 4. Calculate the maximum volume in mL of 0.15 M HCl that each of the following antacid formulations would be expected to neutralize. Assume complete neutralization. (Show your work.) a. A tablet containing 150 mg Mg(OH)2 Mole of 𝑶𝑯− in 𝑴𝒈(𝑶𝑯)𝟐 = 150x2 : 58 = 5.17 moles Mole of 𝑯+ = Mole of HCl = Mole of OH- = 5.17 moles Cm= n/V => V = n/Cm = 5.17 : 0.15 = 34.3 1 b. A tablet containing 850 mg of CaCO3 Mole of 𝑪𝑶𝟑 𝟐− = 850 : 100 = 8.5 moles Mole of 𝑯+ = 2 Mole Of 𝑪𝑶𝟑 𝟐− = mole of HCL = 17 moles V = n/Cm = 17/ 0.15 = 113.33ml Introduction Antacids are bases that react stoichiometrically with acid. The number of moles of acid that can be neutralized by a single tablet of a commercial antacid will be determined by back titration. To do the experiment, an antacid tablet will be dissolved in a known excess amount of acid. The resulting solution will be acidic because the tablet did not provide enough moles of base to completely neutralize the acid. The solution will be titrated with base of known concentration to determine the amount of acid not neutralized by the tablet. To find the number of moles of acid neutralized by the tablet, the number of moles of acid neutralized in the titration is subtracted from the moles of acid in the initial solution. Acid-base reactions and the acidity (or basicity) of solutions are extremely important in a number of different contexts — industrial, environmental, biological, etc. The quantitative analysis of acidic or basic solutions can be performed by titration. In a titration, one solution of known concentration is used to determine the concentration of another solution by monitoring their reaction. Concentration is reported in molarity, M. For example, a 1.019 M HCl solution means 1.019 moles of HCl have been dissolved in 1 L solution. A common way of representing molarity is to write 1.019 mol/L HCl, or [HCl] = 1.019 M. An acid is a source of aqueous H+(aq). For example, HCl(aq) is the acid in your stomach: HCl(aq) → H+(aq) + Cl–(aq). The parietal cells in the stomach secrete hydrochloric acid (HCl) at a concentration of roughly 0.16 M. The flow of HCl increases when food enters the stomach. In a healthy stomach, pH is regulated naturally and digestion functions properly when the pH is around 3 (recall neutral is pH = 7). If you eat or drink too much, you may develop heartburn or indigestion. Antacids, are bases and are used to neutralize this excess acid. Bases are H+(aq) acceptors; in water, they provide species that can react with H+(aq). Common ingredients in antacids are metal hydroxide and metal carbonate salts. The hydroxides provide hydroxide ion, OH–, which can react with H+(aq) to form H2O. 2 Carbonates provide the carbonate ion, CO32–, which can react with H+(aq) to form H2O and CO2. H+(aq) + OH−(aq)⟶H2O(l) 2H+(aq) + CO32- (aq)⟶H2O(l) +CO2(g) In this exercise, the method of titration will be used to determine the number of moles of H+ reacted per gram of antacid. In the “back-titration,” a portion of antacid will be mixed with an excess of HCl. The H+ that has not reacted with the antacid is then titrated with standardized NaOH in the presence of the indicator bromophenol blue to a blue end point. The end point, is defined as the volume of OH- needed to see a color change. Because only the tiniest excess of OH- over H+ can cause the color change of an indicator, the end point is a close approximation of the equivalence point. (The difference between the end point and the equivalence point is known as the titration error.) At the equivalence point, the number of moles of OH- added is equal to the number of moles of excess H+ that had not been neutralized by the antacid. By knowing the total moles of HCl added, one can then calculate the number of moles of H+ neutralized by the antacid. Total moles of H+ = moles of H+ reacted with antacid + moles of H+ neutralized by NaOH Because the antacid includes both OH− and CO32−, it is not possible to calculate the number of moles of each of these ion species independently. Instead, the number of H+ reacted with the antacid is found. The more cost effective antacid is the one that reacts with the most HCl. moles of H+ reacted with antacid = Total moles of H+ - moles of H+ neutralized by NaOH Materials 3 – 250 mL Erlenmeyer Flasks Powder funnel (stemless) 4 different brands of antacids 10 mL graduated cylinder stirring plate and magnetic stir bar 100 mL graduated cylinder DI water 50 mL buret 3 mortar and pestle safety goggles 25mL volumetric pipette 0.5 M HCl 0.5 M NaOH Procedure: 1. Grind up 1 tablet with the pestle and mortar. 2. Place a weigh boat on the scale and tare the machine. Carefully transfer the powder from the mortar to the weigh boat and record the weight of the powder. 3. Using a graduated cylinder, carefully measure out 50 mL of 1.0 M HCl. 4. Add the powder to a 250 mL Erlenmeyer and pour in the HCl. After the solution is done foaming, gently slide a stir bar into the Erlenmeyer and place it on the hotplate. 6. Heat and stir the solution on the lowest setting for three minutes to drive off any CO2 still dissolved in solution. Do not let the solution boil. 7. Remove the Erlenmeyer from the hotplate and allow the hotplate and Erlenmeyer to cool. 8. Add five drops of phenolphthalein to the mixture. 9. Attach the burette to the ring stand using the clamp. 10.Place the Erlenmeyer back on the stir plate and position the burette over the Erlenmeyer. 4 11.Begin stirring the solution on the lowest setting. 12.Using a funnel, add 1.0M NaOH to the burette until it is filled to the 0 mL line. 13.Titrate the NaOH into the HCl. Look for a red streak starting to appear in solution, this means the mixture nearing the endpoint of the titration. At this point add the NaOH carefully. 14.Once the solution has completely turned red/pink, record the final volume of NaOH needed to neutralize the acid. 15.Empty the solution down the drain. 16. Repeat the procedure for each type of antacid tablet provided and find the volume of NaOH needed to neutralize the acid. 5 Data and results Data table Brand name Mass of the tablet Molarity of HCl Volume of HCl Molarity of NaOH Volume of NaOH Antacid 1 Tums 1.10g Antacid 2 Rolaid 1.41g Antacid 3 Gelusil 1.17g Antacid 4 Gaviscom 1.61g 1M 50ml 1M 1M 50ml 1M 1M 50ml 1M 1M 50ml 1M 40ml 23.5ml 32.5ml 38.5ml Antacid tablet 1 0.05 Antacid tablet 2 0.05 Antacid tablet 3 0.05 Antacid tablet 4 0.05 0.04 0.0235 0.0325 0.0385 0.01 0.0265 0.0175 0.0115 Results table Initial moles of HCl HCl moles react with NaOH HCl moles react with antacid Post Lab Questions: 1. Using stoichiometry, determine how many moles of acid each type of antacid neutralized. Then convert this to grams. Which antacid neutralized more acid? How do you know? Results table Antacid tablet 1 Antacid tablet 2 Antacid tablet 3 Antacid tablet 4 HCl moles react 0.01 moles 0.0265moles 0.0175moles 0.0115moles with antacid Mass of HCl 0.365g 0.967g 0.63875g 0.41975g react with antacid The rolaid will neutralize more acid. We determine this from the table above, with the following equations. 6 2. The mass of each antacid tested is different. Which antacid had the most effectiveness per weight of the entire tablet? Rolaid because it reacts with antacid most. 3. Look up the prices of each antacid at an online pharmacy. Which one is more cost efficient? By looking up the prices at an online pharmacy, Rolaid is more cost efficient. 4. Why do you think the solution had to be heated to drive off the remaining CO2? Because this was an equilibrium-restricted reaction. The reaction is reversible, and carbonic acid will form if the CO2 is not driven off by heating the solution. Gas is less soluble in hot solutions. If there is carbonic acid left in the solution, it will take more NaOH to titrate to a neutral pH, so the results of the experiment will be skewed. 5. Consider the table below: 7 How accurate of an indicator do you think the phenolphthalein was? I think the phenolphthalein’s accurate is one of the best one because we can easily and clearly see the color change (colorless to pink). 6) Based on your answer above, how reliable are the results of this lab? The results of this lab are quite reliable because NaOH is base, So PH is above 7. Since the HCL completely react with NaOH when the phenolphthalein will turn to pink color. 8 Your name Instructor’s name Date submitted Title: Formal Lab Report Introduction/Purpose: Introduce the experiment by providing some background information along with the purpose. The purpose must be written in your own words; do not plagiarize from the lab handout/manual. The purpose is the goal of the experiment. It is not simply what was done in the experiment, but more importantly, why the experiment was performed. Background information typically describes scientific concepts or techniques that are relevant to the experiment with related mathematical or chemical equations, similar to the coverage of a topic in a textbook. Procedures: Briefly summarize the procedural steps performed in the experiment. Use complete sentences in paragraph form to state what was done in the experiment. It should be comprehensive enough for someone else with experience to reproduce the experiment, but do not provide a list of detailed instructions like the lab handout/manual. Include information about amounts used (masses, volumes, concentrations etc.), but do not include routine steps like washing glassware or taring balances. Data: Please be aware that the tables in your lab manual often include data, calculation, and result section all-in-one. Therefore, you CAN NOT copy the tables in your manual as they are. You must split this information into their appropriate section! Organize your data further if needed. Be sure to include correct units and labels for tables Present all data observed and collected during the experiment. Insert tables to display the data in an organized fashion. Use captions to label the tables numerically and provide a descriptive title. Use a header row to identify the contents of each column and their relevant units. Write some text to go along with the data tables that discusses the data (e.g. number of trials performed, type of measurements made, etc.) and refers readers to the data tables (e.g. “See Table 1”). Include data for invalid trials as well and explain the error that occurred during the experiment. For example, “Trial 2: Too much titrant was added; the endpoint was exceeded.” Your name Instructor’s name Date submitted Calculations: Show all calculations used to analyze the observed data. Any values not directly observed should be represented by a calculation here. You are encouraged to learn how to insert equations using word processing software. Include any error/statistical analysis calculations, such as determining averages, standard deviations, etc. One sample set of calculations is sufficient for experiments involving multiple trials. For multi-step calculations, carry one to two extra digits throughout the intermediate steps and then only round at last step. If an experiment did not require calculations, omit this section. -Provide the general formula you used -Provide at least 1 sample calculation using your general formula -Thereafter, you can just provide the final values. Results: Analyze the collected data and summarize the results. Report the results of any calculations performed on the data, including error/statistical analysis. Summarize the results by listing the average and standard deviation of multiple trials, list the ranges of values obtained and comment on outliers, state the identity of the unknown, report percent yields, use calibration plot equations to solve for unknown values, etc. Determine whether tables or graphs would help present the results. Tables can be inserted in the document to display the results. Always label the contents of the rows/columns clearly using headings. If the presentation remains clear and concise, calculated results can be included along with raw data in tables in the Data section, just refer readers to the table (e.g. “See Table 1”). Graphs are useful for experiments that involve variables controlled over a range of values, such as calibration plots. Remember that the controlled variable is always plotted on the x-axis. Label graph axes with descriptive names and relevant units (e.g. “Mass (g)”). Give the graph a number and descriptive title by inserting a figure caption. If using the axes labels for the graph title, the format should be ’y-axis’ vs. ‘x-axis’. Write text that states the results and refers the reader to any included summary tables or graphs Discussion: Your name Instructor’s name Date submitted Explain the meaning of the results of the experiment and answer any postlab questions. What do the results mean? Interpret the results for your reading audience and discuss what you learned from the experiment. Comment on accuracy (% error) and precision (standard deviation), make comparisons, or discuss results obtained from graphs, etc. Discuss reasons for any errors that might have occurred. Here are some brief examples of discussion topics: “All samples involving X did not produce Y.” “Three out of five trials indicated a positive result.” “The calculated standard deviation indicates low precision likely caused by...” “The graph implies a directly proportional relationship between the variables.” “The calculated average is different than the accepted value; the percent error is …” “These values are higher than...” “The results indicate that X is not effected by Y.” Do not just list the postlab questions and your answers; instead, make it a discussion by incorporating the postlab questions into your answers, thereby giving context to your reading audience. Logically connect concepts and be thorough with your answers. For example, instead of “No, it does not affect the result”, a better answer might take the form of “If extra X was added, the measured amount of Y would not be affected because X is not part of the chemical reaction; only the amounts of the reactants A and B are relevant to the stoichiometry of the reaction used to produce Y”. Conclusion: A brief summary of what was done, how, the results and your conclusions of the experiment. Restate the major results of the experiment and connect back to the original purpose of the experiment. Think of this like reporting your final answer to the problem you originally set out to solve with the experiment. A couple of sentences should be sufficient. Writing Style Your name Instructor’s name Date submitted 1) Use the third person, passive voice. Do not use the first person, active voice. For example, instead of “I mixed the two solutions”, use “The two solutions were mixed”. This choice of impersonal writing voice is used to take the focus away from the scientist and place it on the experiment itself, implying that people do not cause an experiment to turn out a certain way. A good habit is to go through your report to find and replace every use of “I”, “she”, “he”, “we”, or “they”. Also, avoid using the phrase “the student”; keep the emphasis on the experiment! 2) Use past tense for everything completed in the past. This includes procedure and data sections especially, as these sections refer to procedures already performed or data that has been collected. For example in a procedure, “The two solutions were mixed” is preferred over “Mix the two solutions”. The other sections that state facts or draw conclusions from the data, like the discussion, can be written in thepresent tense. 
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