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Chemistry
Calculate the HCl concentration in H2O from the conductivity
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[QUOTE="gpsimms, post: 6320127, member: 470375"] Thank you all for the help so far. I have tried to take my data and calculate #moles HCl by using both pH and conductance. The answers disagree significantly, so I think I must be doing something wrong, and would like to check. For one case, my final pH is 1.66, and my final conductance is 21.47 mS/cm. I started with 2 L of H2O, but did not measure the final volume (it sounds like maybe this should be done in future experiments...). Using pH: $$10^{-1.66}=0.02188$$ $$0.02188 \frac{moles}{L} \cdot 2L = 0.04376$$ So 0.04 moles HCl. Now, using conductivity my final measurement is 21.47 mS/cm. Also, the water's temperature was being held constant at ##15^{o}##C. Now, it looks like on the table I posted that there is also a pretty strong temperature dependence on conductivity (see below): [ATTACH type="full" alt="1585777330827.png"]259808[/ATTACH] Now, our concentration is off this chart. So using the first chart, and the trend in this chart I *guessed* that the conductivity might be 330000 mS*cm^2/mol @ 0.1 moles @ 15 degrees C. *If you are wondering why I used 0.1 moles instead of 0.01 moles like the pH calculation suggests I should, I'll come back to this...* Which gives this calculation: (measured conductance [mS/cm]) ##\div## (molar conductivity [mS cm^2/mol]) = (concentration [mol/cm^3]) so... $$21.47 \frac{ms}{cm} \times \frac{1 mol}{330000 mS \cdot cm^{2}} = 6.51\cdot 10^{-5} \frac{mol}{cm^{3}}$$ And we have approx 2000 cm^3, so ##6.51\cdot10^{-5}\cdot 2000=.13## moles. *This is why I used 0.1 moles to calc the molar conductivity.* Which disagrees with my pH calculation by a factor of 3. Which of the two measurements/calculations would you mistrust? Or did I screw something up in either of the calculations? Finally, if anyone knows of a better table or a polynomial for HCl conductance, so I am not guessing the number there, please let me know. Thanks! [/QUOTE]
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Calculate the HCl concentration in H2O from the conductivity
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