BLEACH AND BROMOCRESOL GREENI. Data Collection: Concentration EffectsA. Obtain about 100 mL of pH 7 buffer in a 250 mL beaker about 20 mL of pH 4buffer in a 50 mL beaker and 50 mL of bromocresol green (BCG) solution. All ofthese are aqueous solutions.B. Into a 100 mL beaker measure 20 mL of a pH 4 buffer 30 mL of distilled water and 2 mL of BCGsolution. Swirl the beaker to mix. Your solution should be yellow with a hint of greenin it. If not see your laboratory instructor for help. This solution is to be used as astandard for the followingexperiments.C. Measure 7 mL of 5.25% NaOCI (liquid bleach) with a 10 mL graduated cylinder.Combine this with 413 mL of distilled water (measured with a 50 mL graduatedcylinder) in a 600 mL beaker.Mix well. Label this beaker as “Bleach Solution” and use it in any future steps thatrequire bleach.D. Into a 100 mL beaker measure 10 mL of a pH 7 buffer 10 mL of bleach solution(made in part I. C) and 30 mL of distilled water. Into a 10 mL graduated cylindermeasure exactly 3 mL of BCG solution. Arrange the 100 mL beaker and the standardsolution next to each other on a piece of white paper. With a stopwatch begin timingat the same time that the BCG is added to the 100mL beaker. Swirl the solution tomix and observe the color of the solution. Stop timing as soon as the colors of thesolution and the standard match. The match should be one of color not of brightnessor intensity. Repeat this procedure. If the amount of time for the color change isconstant (or almost constant) there is no need to repeat a third time; otherwiserepeat until two readings are consistent. Record your data in the table on the nextpage.E. Using the procedure in section I.D measure the amount of time for solutions tomatch for eachof the combinations in the table and any other combinations you want to try.Exp #BCG(mL)Water Tim(mL) (sec)Tim(sec)Time(sec)1Bleach Phsoln7buffer(ml)(mL101033020.65s20.75s2101062719.23s20.20s19.75s320103208.20s9.75s8.50s430103105.69s5.76s54010304.11s4.19s 620532511.0811.8774010358.19s24.40sII. Data Analysis: Concentration EffectsA. What role did water play in the mixtures? Why was water added and whatdetermined the amount of water needed?B. One way of reporting concentration is as a volume/volume percentage. In thisformat the volume of the reagent being referred to as a solute is divided by the totalvolume of the solution. A formula for volume/volume percent concentration is:Volume of solute x 100Volume of solutionConstruct a table to show the volume/volume percent concentration of eachreactant (bleach buffer and BCG) and the average time of reaction (based onreliable data) for each trial.C. Examine two experiments where the concentration of the buffer varied. To whatextent did thebuffer concentration affect the rate of the reaction? What is the effect of doubling theconcentration? State the experiments compared and quantitatively show the effect. D. Examine two experiments where the concentration of bromocresol green varied.To whatextent did the BCG concentration affect the rate of the reaction? What is the effect ofdoubling the concentration? State the experiments compared and quantitativelyshow the effect.E. Examine experiments where the concentration of bleach varied. To what extentdid the bleach concentration affect the rate of the reaction? What is the effect ofdoubling the concentration? State the experiments compared and quantitativelyshow the effect.F. What experiment numbers would be useful in a graph demonstrating the effect ofConcentration of bleach on the rate of the reaction? If you eliminated anyexperiments explain why.G. Write a rate law for the reaction you have studied in this lab.III. Data Collection: Temperature EffectsA. Using the same procedure as part I above make a solution of 10 mL of bleachsolution (made in part I.C) 10 mL of pH 7 buffer and 30 mL of water in a 100mL beaker.B. Place a 250 mL beaker ¼ filled with water on a ring stand over a piece ofgauze and heat the water with a Bunsen burner. Place the 100 mL beakerwith the test solution in the hot water bath. With a thermometer measure thetemperature of the test solution. When the temperature is approximately10°C higher than room temperature remove the beaker from the water bathwith tongs.C. Place the beaker next to the standard solution and add 3 mL of BCG whilebeginning timing. When the reaction has finished measure the temperatureof the solution. Record all data in the table on the next page.D. Using the procedure outlined above measure the amount of time for thesolution to match the standard for six different temperatures (20 °C± roomtemp). Temperatures below room temperature can be obtained by using anice bath. Time (sec)Initial TemperatureFinal Temperature12345623.3C8.94.7C38.1C30.9C26.8CAverageTemperature23.6C13.1C10.0C36.0C29.1C26.1CIV. Data Analysis: Temperature EffectsHow did the temperature of the solution affect the rate of the reaction? Graph yourdata and find a best fit (consider non-linear fits also). What temperature change(s)resulted in doubling the rate?
