[mmayer171]

How can I calculate the % weight concentration of a solution x % HCl and a fluid with density y given the density of the final mixture?  For example, I have a final fluid density of 1.14 g/mL and the density of the initial fluid is 1.08 g/mL.  What is the effective % weight HCl?

Thanks,

[Borek]

Not sure what you are trying to do. If the density went up (initial 1.08, final 1.14) you somehow concentrated the acid - care to elaborate how it was done?

But in general the short answer is: you can't easily convert density to concentration. Best approach is to read the answer from density tables.

[mmayer171]

Thank you for your response.  My apologies, I should have made that more clear.  The density of the fluid that the acid is being added to is 1.08 due to salt content.  The density of the acid depends on the concentration (we usually get 20 or 15%).  When the acid is added, the density of the fluid increases to 1.14. 

Basically, we have a coriolis meter measuring the density of the incoming fluid, acid of an unverified concentration is added, and another coriolis meter measures the density again.  I want to be able to use the measurements from the two coriolis meters to calculate the final acid concentration.

My first approach was to take 1.14 - 1.08 = .06 and use a curve fit from this lookup table http://www.starch.dk/isi/tables/hcl.htm to interpolate the concentration.  This method gives "reasonable" results but my gut tells me I'm missing something. 

[Borek]

I am afraid this is not trivial. Volumes are not additive (volume of the mixture is not sum of the volumes) which makes such calculations impossible in the general case.

If the ratio of added acid and incoming fluid is always the same you can try to use some other analytical methods of determining HCl concentration (simple titration will do) to prepare an experimental curve/data table which can be used to easily read the answer later. If the ratio is not guaranteed to be constant there are too many unknowns to do even that.

[mmayer171]

We also have conductivity and pH measurements before and after the acid is added.  Could these be utilized to calculate the effective HCl concentration?  Can I subtract the initial conductivity from the final conductivity and use a look-up table? 

[Borek]

Judging from the density your solution is far from being diluted - that means none of the parameters you measure is simply additive. Every parameter you are measuring depends not only on one factor, but also on concentration of all other species present (if not for other reasons ionic strength of the solution is enough). With the information you have determining acid concentration could be possible - but I can't think of a better way of calibrating the system than by experimental (separate) measurements of the acid concentration in addition to all other parameters. Once you have enough data points you can be able to fit some function that will nicely extrapolate data between.