[p1qret]

I have been asked to work out the hardness of water in German degrees and this is what I did:

I got a sample of water I didn’t measure how much I put into my volumetric flask perhaps it was 8.5ml but I don’t think I need it, but I do use it which made me believe I was wrong.

The sample was made up to 100ml 10ml of this dilution was used as the anaylte along with buffer and the indicator

I Titrated 9.07ml of EDTA with a concentration of 0.0185moldm3

So the calculation i did was

Moles of edta= (9.07x0.0185)/1000= 0.000167795 Moles of Ca2+ is the same So then I find the mass of Ca = 40x0.000167795= 0.0067188g

Now my issue

So 0.0067188g of Ca in the 10ml therefore in the 100ml there will be 10 times that, as it was a dilution. So 0.067188g which is 67.118mg

So there is 67.118mg of Ca in my 8.5ml sample
Now a 1 German degree is 10mg of Ca per 1000ml So is there 7896.2mg in 1000ml of sample Therefore having 789.6 German degree of hardness?

[Borek]

You definitely need to know the initial volume.

German degree is an equivalent of 10 mg of CaO, not Ca, per one liter of water, so your result is seriously off (not that far from being off by a factor of two).

Other than that the logic behind your calculations looks OK, although the final result - 800 - already looks suspicious, as it is a VERY hard water, typical values are an order of magnitude lower.