Carried out conductometric titrations today with 0.1N HCl and 1N NaOH , the HCl used came with a composition of 1.18 g/ml at 20'C, I prepared the solution at 35'C , data from two sets of titration resulted in a normality estimate of 0.04N , less than half the expected concentration, what could have gone wrong?

GenesForLife wrote:Carried out conductometric titrations today with 0.1N HCl and 1N NaOH , the HCl used came with a composition of 1.18 g/ml at 20'C, I prepared the solution at 35'C , data from two sets of titration resulted in a normality estimate of 0.04N , less than half the expected concentration, what could have gone wrong?

What did you use to dilute the acid?

Distilled water, rainbow.

GenesForLife wrote:the HCl used came with a composition of 1.18 g/ml at 20'C

That's a density, not a composition, starshine. But presumably, HCl has a density-composition curve at 20°C and 1 bar. If that yields 0.1 N, then that's what it yields. But you would know better than I would, especially if you prepared the solution at 35°C.

How did you calibrate the conductimetry?

Yup, but I think it can still be used to deduce required volume for desired mass when working with normalities.
Density = mass / volume reduces to mass/unit volume, therefore required mass can be calculated as a function of the volume.

1.18 g ---> 1 ml
required weight ---> volume

the required weight being calculated from w=N x E / (1000/V)

Sorry for the error, in any case.

Cito di Pense wrote:

GenesForLife wrote:the HCl used came with a composition of 1.18 g/ml at 20'C

That's a density, not a composition, starshine. But presumably, HCl has a density-composition curve at 20°C and 1 bar. If that yields 0.1 N, then that's what it yields. But you would know better than I would, especially if you prepared the solution at 35°C.

How did you calibrate the conductimetry?

Conductometer has built in calibration.

GenesForLife wrote:

Cito di Pense wrote:

GenesForLife wrote:the HCl used came with a composition of 1.18 g/ml at 20'C

That's a density, not a composition, starshine. But presumably, HCl has a density-composition curve at 20°C and 1 bar. If that yields 0.1 N, then that's what it yields. But you would know better than I would, especially if you prepared the solution at 35°C.

How did you calibrate the conductimetry?

Conductometer has built in calibration.

That's great G4L. What I am left asking you, since I am a little rusty on this shit, is what a 20°C normality has to do with a 35° C normality. All I know is that they do not have to be the same, given the expected behavior of activities of ions in solutions. It's not as if I cannot learn something from you (or recall something on your prompt from this).

I think it can still be used to deduce required volume for desired mass when working with normalities.
Density = mass / volume reduces to mass/unit volume, therefore required mass can be calculated as a function of the volume.

It's not as if volume does not change with temperature. I just can't map it onto your titration problem. Sorry. Normality is volumetric, isn't it? Stupid me.

Precisely, which is why we had results at half the expected value, never mind, I've solved the problem now, I found what I was looking for, a standardized table for temperature-density relationships.

http://www.handymath.com/cgi-bin/hcltbl ... bmit=Entry ,

GenesForLife wrote:Precisely, which is why we had results at half the expected value, never mind, I've solved the problem now, I found what I was looking for, a standardized table for temperature-density relationships.

http://www.handymath.com/cgi-bin/hcltbl ... bmit=Entry ,

I am so glad to hear that. I was sort of on the trail of temperature-density stuff, was I not? EOS is king!

Nope, you are actually correct in noticing that temperature can cause changes in density,and therefore affect the normality of any solutions prepared on that basis, when using liquid solutions, the norm is to convert normalities to volumes ( If at 20' C, I needed 1.18 grams of HCl to make my solution, I'd take 1ml of the stock solution because it contains that much mass, and so on) , if the density differs, I'd get a different quantity of HCl in the same volume of solution, thus resulting in a different (and wrong) value for normality.

But on second look, things don't add up, the density (and therefore resulting normality) increases with temperature (according to that calculator) , in which case our lab temperature should have resulted in stronger HCl and not weaker HCl, I need to look elsewhere.

GenesForLife wrote:But on second look, things don't add up, the density (and therefore resulting normality) increases with temperature (according to that calculator) , in which case our lab temperature should have resulted in stronger HCl and not weaker HCl, I need to look elsewhere.

Well, you should be able to figure out what mass of HCl you need at any temperature. I guess the trick is to translate that into the volumes you want for solutions prepared at any particular temperature. It's the mass that is eventually going to titrate, isn't it, since titrations are more or less atom by atom...

yup, but the variation of the density doesn't account for the bizarre result we got.

GenesForLife wrote:Nope, you are actually correct in noticing that temperature can cause changes in density,and therefore affect the normality of any solutions prepared on that basis, when using liquid solutions, the norm is to convert normalities to volumes ( If at 20' C, I needed 1.18 grams of HCl to make my solution, I'd take 1ml of the stock solution because it contains that much mass, and so on) , if the density differs, I'd get a different quantity of HCl in the same volume of solution, thus resulting in a different (and wrong) value for normality.

OK the change in density is very small, but the change in specific conductance will vary much more with temperature. I think it is most likely a calibration error due to temperature variation.

Our protocols don't account for temperature variations during calibration, do you know of any that do?

GenesForLife wrote:Our protocols don't account for temperature variations during calibration, do you know of any that do?

Sorry no.
Please take a look here, this might help:

http://www.wileywater.com/Contributor/Sample_2.htm

I think I can help here. HCl is a gas. Hydrochloric acid is a solution of hydrogen chloride in water. Hydrochloric acid with a specific gravity of 1.18 corresponds to a solution of approximately 35% HCl by weight. This probably accounts for the result you obtained.

Yup, that is correct, but the solution I prepared took that into account as I took a volume that contained the weight/mass of HCl I needed.

GenesForLife wrote:Yup, that is correct, but the solution I prepared took that into account as I took a volume that contained the weight/mass of HCl I needed.

OK, Here is my calculation for the volume you need so you can compare it to your calculation:

the molecular mass of HCl is 36.5 so to make 1 litre of 0.1N (0.1M) HCl is 3.65 g

1 ml of 1.18 SG HCl (36% by weight HCl) contains 1.18 x 0.36 g of HCl = 0.4248 g

So required volume of HCl to make 1 litre of 0.1 N HCl = 3.65/0.428 = 8.6 ml

Was this the volume you used to make up your solution?

Well no, I got a different value, seems to be due to not factoring in the 35% purity (as I was led to believe that the original solution contained 1.18 g of HCl / ml )

My calculations are as follows.

wHCl = N x E / (1000/V)
= 0.1 x 36.5 / 10 (I was preparing 100 ml of the solution)
= 0.356 g

1 ml HCl = 1.18 g (this is where things seem to have gone wrong)
x ml HCl = 0.356 g

x = 1 x 0.356 / 1.18 = 0.30932.

My value is lower than yours by 2.7 times, which approximately fits the error in my experiment.

Thanks a lot, cheers.