Resistance versus temperature in weak acids, strong acids, and water

In summary: Please provide a summary of the content.In summary, the question is whether or not the resistance of acids decreases as a function of temperature. The data suggests that it does, but the reason for this is unknown.
  • #1
inutard
93
0
The question below is a rather theoretical one and does not concern any actual calculations. So I have decided to abandon the traditional format.

In the past few weeks, I have designed and carried out a lab in which I would test the resistance of a strong acid (0.5 M HCl), a weak acid (0.5 M vinegar) and water at varying temperatures (10 - 50 deg Celcius to avoid error caused by evaporation). The same volume of solutions put into the same type of beaker (i.e. geometric proportions of the solutions are conserved) with resistance measured across the same two points in the solution every time were used as controls.

I had assumed that the resistances would go down as a function of temperature because:
1) The Keq/dissociation constant of the acid equilibriums increase, thus producing more H3O+ ions and conjugate base ions.
2) The increased temperature increases the kinetic energy of the solutions and the ions therein, thus increasing conductivity and decreasing resistance.
3) Water tends to auto-ionize more at greater temperatures (this relates to point 1 and is also shown to be true in the experiment as the trials show lower resistances versus higher temperatures)

The lab turned out to be a success and a general trend of high temperature / lower resistance was shown. At the onset, this trend looks to be a logarithmic one. However, when I plot conductance (1/R) versus temperature (celcius), the trend becomes linear. In other words, temperature is directly proportional to (1/R).

My question is: Why does this happen?

The lab data is contained in an attachment below.
 

Attachments

  • Lab Data.xls
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  • #2
Review the Nernst Equation, eg... E = Eo - (RT/nF)lnQ
 
  • #3
Interesting equation. However, the sample of acids I am testing are not really electrochemical cells in any way. They are just simple solutions of vinegar and HCl at 0.5 M.
 
  • #4
Did you notice the temperature term in the equation? Notice how it's first order?
 
  • #5
Yes.. but i was under the equation that the Nernst equation only applied to working chemical cells
 
  • #7
Ok. But reading the contents of the link you've sent, I see that the final equation derived relates molar conductivity or conductivity to the equation:
http://tannerm.com/images/difcond12.gif
However, as you can see, the conductivity is proportional to T^-1 where my experiment seemed to indicate that conductivity is proportional to T
 
  • #8
My bad. I thought you had plotted resistance vs temp. Take another look at your data. It isn't linear at all. It looks like a typical y = a(1/x) graph.
 
Last edited:
  • #9
I did plot resistance versus temperature. That was the graph that looked like the 1.x graph. Take a look at the third graph from the left. That is a conductance versus temperature graph and it seems to be linear.
 
  • #10
inutard said:
I did plot resistance versus temperature. That was the graph that looked like the 1.x graph. Take a look at the third graph from the left. That is a conductance versus temperature graph and it seems to be linear.

Are you asking if you plot conductance vs temperature you should get something nonlinear if you already know that the resistance vs temperature looks like it varies inversely with temperature?
 
  • #11
No i did plot conductance vs temperature. According to the site you linked, the conductivity should be inversely proportional. However, i found in my experiment that it was proportional to temperature.
 
  • #12
What is the surface area of the electrodes your using?
 
  • #13
Ah, there is nothing like to post in an abandoned, year and half old thread.

Locked.
 

1. How does the resistance change with temperature in weak acids?

In weak acids, the resistance decreases with increasing temperature. This is because the ions in the acid are more mobile at higher temperatures, allowing for easier flow of electric current.

2. What is the relationship between resistance and temperature in strong acids?

In strong acids, the resistance also decreases with increasing temperature. This is due to the high concentration of ions in strong acids, which leads to a more conductive solution at higher temperatures.

3. Does water behave differently from acids in terms of resistance and temperature?

Yes, water behaves differently from acids in terms of resistance and temperature. Unlike acids, the resistance of pure water increases with increasing temperature. This is because at higher temperatures, water molecules become more mobile and can disrupt the formation of hydrogen bonds, leading to a decrease in conductivity.

4. How does the strength of an acid affect its resistance-temperature relationship?

The strength of an acid does not significantly impact its resistance-temperature relationship. Both weak and strong acids exhibit a decrease in resistance with increasing temperature, although the extent of the decrease may vary depending on the concentration of ions in the solution.

5. Can the resistance-temperature relationship in acids be used for practical applications?

Yes, the resistance-temperature relationship in acids can be used for various practical applications, such as in temperature sensors and thermometers. By measuring the change in resistance with temperature, the temperature of a solution can be determined. This is particularly useful in industries where accurate temperature control is crucial.

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