SC CHEM 321 - Measuring pH (8 pages)

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Measuring pH



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Measuring pH

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Pages:
8
School:
University Of South Carolina-Columbia
Course:
Chem 321 - Quantitative Analysis

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Cameron Kahn TA Muditha Dias Post lab Write up 3 March 2014 Experiment 3 Measuring pH 1 Indicate the make and model number for the pH meter and probe you used in this study pH electrode information Make OakTon Model 2082158 Salts used 1 1 Salt NaCl 1 2 Salt Na2SO4 2 Indicate the lot numbers for each of the NIST certified pH buffers and their pH Calibration of Unaltered Buffers Buffer pH mV Lot 7 20 135109 4 156 133274 10 197 132388 Figure 1 3 Show the calculations used to solve for how much salt you needed to add to your buffers Indicate the amount used for the other buffers also In general the way you calculate how much salt you have to add to the buffers is the same process for both salts NaCl and Na2SO4 The only noticeable difference beyond the values you re plugging into each step is the stoichiometry molecular weight of the salts and that NaCl is a 1 1 salt and Na2SO4 is a 1 2 salt It is because of these similarities that I have provided the steps to find the amount added to the buffers for NaCl only These steps are repeated to find the amount added of Na2SO4 to the buffers ci zi 2 1 2 Where ci is the ions concentration and zi is the ions charge Calculating amount of NaCl to add to adjust the ionic strength of the pH buffers Kahn 1 P a g e 99889 55661 2 778 M 1 2 778 M 01 L 00778 moles NaCl 58 44 g 00778 mol 455 g added of NaCl 1 mol Just repeat these simple steps for calculating how much Na2SO4 is needed to be added into the buffers Buffers adjusted with NaCl pH mV pH 7 Buffer 6 23 17 pH 4 Buffer 3 39 184 pH 10 Buffer 9 18 155 Figure 2 Once you do the steps for Na2SO4 the readings from the pH meter were as follows Buffers adjusted with Na2SO4 pH mV pH 7 Buffer 6 7 9 pH 4 Buffer 3 91 151 pH 10 Buffer 9 64 182 Figure 3 4 Plot pH vs mV for all 3 calibrations There will be 3 graphs for the 3 calibrations which the data tables for each are denoted by figure 1 2 and 3 and can be found from the last few questions Kahn 2 P a g e Calibration for Unaltered Buffers 15 pH



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