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Percipitate while pH setting of insect ringer


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#1 Flo

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Posted 29 April 2015 - 05:00 AM

Hi,

I have a big problem: I´m preparing an insect ringer solution (pH 7,4; total volume 100 ml) with those ingredients

 

15.75g NaCl

2.35ml 2M KCl

3.7ml 2M KH2PO4

0.05g NA2HPO4

0.37g MgCl2

 

All ingredients dissolve excellently. The starting value of pH is app. 4,4. When I was trying to set up 7,4 by NaOH or KOH everything was working fine. But at the point of 7,0 - 7,1 there was percipitation.

Has anybody an idea what could be the reason for that percipitation or what substance I could use to set up the pH instead of NaOH/KOH?

 

Thanks in advance!

 



#2 mdfenko

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Posted 29 April 2015 - 08:27 AM

probably magnesium hydroxide.

 

you should adjust the pH prior to addition of mgcl2.


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#3 El Crazy Xabi

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Posted 30 April 2015 - 06:43 PM

I did some fast calculation in Minteq and the precipitate might be MgHPO4*3H2O and Mg(OH)2, although the calculations are not completely reliable due to the extremely high ionic strength. I guess you tried to prepare a stock rather than the working solution because ~16% of salts is a lot






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