4 3 2 We Acid base titration is used quite frequently in
Last updated: 5/11/2023
4 3 2 We Acid base titration is used quite frequently in research labs to titrate buffers or cell culture media to a desired pH This is accomplished by adding acids such as HCI or bases such as NaOH to shift the pH of the solution either to be more acidic or more basic respectively The changes in pH achieved by the addition of the acid or base can be monitored in two ways First the pH shifts can be monitored chemically by adding an acid base indicator such as phenol red Phenol red is a chemical which is normally red at around pH 7 but turns yellow at the lower pH of acidic environments This is a quick way to check the health of cells normally grown at around pH 7 in culture as cellular waste products or contamination will turn the cell culture media yellow The second way to monitor pH is by measuring the conductivity or ability of solution to conduct electricity A student conducted the following titration experiment at room temperature 25 C The solutions used were 0 1 M NaOH 0 1 M NH nd 0 2 M HCI The acid base indicator used was enol red which is purple at pH above 8 2 yellow pH 6 8 and below and red between 8 2 and 6 8 Deriment 1 First several drops of phenol red were added 30 mL of NaOH solution in an Erlenmeyer flask solution was then titrated with HCI while the uctivity was monitored When adding a strong to a solution it is important to add the acid because the heat of hydration for H ions is migh The conductivity of the titrated solution monitored continuously Figure 1 shows the ctivity titration curve conductivity umho cm conductivity umho cm 8642086420 18 16 14 12 10 0 18 16 14 12 10 8 6 4 Lat 2 0 0 Experiment 2 The first experiment was repeated with a weak base NH instead of the NaOH solution while every other condition remained the same Figure 2 shows this conductivity titration curve purple 10 10 purple red 20 30 volume of HCI mL Figure 1 red yellow 20 30 volume of HCI mL Figure 2 40 yellow 40 50 50 1 Lesson 4 Support of Hypotheses Part 2 4 3 2 Weakening the Hypothesis Another student claimed that the pH of the NH solution required a greater volume of HCI to become acidic than the NaOH solution Comparing Figures 1 and 2 is this claim accurate A Yes because the yellow portion of the graphs start at different volumes of HCI B Yes because the conductivity is different in both experiments after 30 mL No because the yellow portion of the graphs both start at the same point near C 30 mL D No because the conductivity is the same in both experiments after 30 mL 2 Is the hypothesis that conductivity always increases as the concentration of acid increases supported by the results of Experiment 1 Yes because the experiment showed that the heat of hydration for H ions increased over time along with the conductivity of the solution G Yes because the slope of the graph is positive as volume of HCI increases over time H No because the conductivity of the solution initially decreased with the addition of acid J No because the conductivity of the solution increased and decreased independently from the concentration of acid in the solution F 3 Suppose a scientist comes up with a theory that the conductivity of a solution is highest before any acid is added to it Which of the experiments results would most strongly contradict this theory JEFTENE A Experiment 1 B Experiment 2 C Both Experiment 1 and Experiment 2 Neither Experiment 1 nor Experiment 2 D Science Tip 50 50 Lifeline You can use the process of elimination to narrow down the answer choices to two gettin rid of two answer choices with the wrong yes no or two answer choices with the wrong supporting deta