New (to me) toy- conductivity meter

[Randy Holmes-Farley Verified Community Expert]

I bought a scale that reads done to 0.001 g and some calibration weights. I made two back to back standards with 12.400g salt and 364.00g water. They are within 0.2% of each other so I mixed them together and calibrated the unit.

I am now mixing a saturated kalkwasser standard. I have a magnetic stirrer and I’m measuring periodically to see how long it takes to saturate. I have a feeling I have not been mixing kalk long enough for 30 years. I may start a separate thread on this.

Sounds good. :)

 

[KStatefan]

I bought a scale that reads done to 0.001 g and some calibration weights. I made two back to back standards with 12.400g salt and 364.00g water. They are within 0.2% of each other so I mixed them together and calibrated the unit.

I am now mixing a saturated kalkwasser standard. I have a magnetic stirrer and I’m measuring periodically to see how long it takes to saturate. I have a feeling I have not been mixing kalk long enough for 30 years. I may start a separate thread on this.

That was my experience with my kalk when I was mixing by hand and testing conductivity with a lower end conductivity meter. I did not like the inconsistencies I was getting.
Nice meter purchase some day I will add something like that to my gear collection.

 

[rishma]

This level of precision is very satisfying

Freshly mixed saltwater!

 

[Randy Holmes-Farley Verified Community Expert]

This level of precision is very satisfying

Freshly mixed saltwater!

lol

Now you should strive for calcium at 420.0 ppm. Then the tank will really take off!

 

[rishma]

that would require me to test calcium, which I refused to do

 

[rishma]

@Randy Holmes-Farley

My meter can have up to 5 calibration points. I only have one at 53.0 mS/cm which works well for salinity. Another lower point would be useful, but making the 3.29 weight percent sodium chloride solution was the limit of my scale accuracy. Is there anything I can mix to saturation that has a known standard conductivity that is much lower around 10 mS/cm? I can buy one but they aren’t cheap.

 

[Randy Holmes-Farley Verified Community Expert]

@Randy Holmes-Farley

My meter can have up to 5 calibration points. I only have one at 53.0 mS/cm which works well for salinity. Another lower point would be useful, but making the 3.29 weight percent sodium chloride solution was the limit of my scale accuracy. Is there anything I can mix to saturation that has a known standard conductivity that is much lower around 10 mS/cm? I can buy one but they aren’t cheap.

In general, I’m not sure a lower point is needed because the 0,0 point is a true fixed calibration point.

That said, I think serial dilution of sodium or potassium chloride solutions to known concentration is a better way to go than is trying to use a saturated solution.

 

[rishma]

@Randy Holmes-Farley

My meter can have up to 5 calibration points. I only have one at 53.0 mS/cm which works well for salinity. Another lower point would be useful, but making the 3.29 weight percent sodium chloride solution was the limit of my scale accuracy. Is there anything I can mix to saturation that has a known standard conductivity that is much lower around 10 mS/cm? I can buy one but they aren’t cheap.

In general, I’m not sure a lower point is needed because the 0,0 point is a true fixed calibration point.

That said, I think serial dilution of sodium or potassium chloride solutions to known concentration is a better way to go than is trying to use a saturated solution.

Oh that makes sense! I could have just diluted my 53.0 mS/cm solution. Duh.

 

[Randy Holmes-Farley Verified Community Expert]

Oh that makes sense! I could have just diluted my 53.0 mS/cm solution. Duh.

Note that conductivity is not exactly concentration linear. It drops off a bit less than linear.

If you look at NaCl in this linked table you can see that effect. Thus, you’d need a table of conductivity vs concentration that someone made if you want to be very accurate. The reason for the effect is that more ions in the water start to interact with each other more, retarding their response to an applied electric field.

That effect gets much bigger at very high concentration. It’s not so big at seawater or lower concentrations,.

https://diverdi.colostate.edu/all_c...ctrical conductivity of aqueous solutions.pdf

 

[rishma]

Note that conductivity is not exactly concentration linear. It drops off a bit less than linear.

If you look at NaCl in this linked table you can see that effect. Thus, you’d need a table of conductivity vs concentration that someone made if you want to be very accurate. The reason for the effect is that more ions in the water start to interact with each other more, retarding their response to an applied electric field.

That effect gets much bigger at very high concentration. It’s not so big at seawater or lower concentrations,.

https://diverdi.colostate.edu/all_c...ctrical conductivity of aqueous solutions.pdf

Learning a lot! Thank you. I have some math to do.

 

[rishma]

Note that conductivity is not exactly concentration linear. It drops off a bit less than linear.

If you look at NaCl in this linked table you can see that effect. Thus, you’d need a table of conductivity vs concentration that someone made if you want to be very accurate. The reason for the effect is that more ions in the water start to interact with each other more, retarding their response to an applied electric field.

That effect gets much bigger at very high concentration. It’s not so big at seawater or lower concentrations,.

https://diverdi.colostate.edu/all_c...ctrical conductivity of aqueous solutions.pdf

Based on the data it doesn’t match the 3.29 wt% 53.0 mS/cm from the diy standard. Is this because the data is at 20C and the DIY solution is 25C? Or did I mess something up?

 

[Randy Holmes-Farley Verified Community Expert]

Based on the data it doesn’t match the 3.29 wt% 53.0 mS/cm from the diy standard. Is this because the data is at 20C and the DIY solution is 25C? Or did I mess something up?

Yes, I expect that is why.

 

[rishma]

Yes, I expect that is why.

For huge crowd filling this thread

Red 25C data from Washburn, E.W. (Ed.). International Critical Tables of Numerical Data, Physics, Chemistry and Technology. Vol. VI. McGraw-Hill.