[aeothoin]

Hi guys,

I used a 10 ml milk sample diluted with 4 ml naoh, 40 ml distilled water with indicator.
I'm particularly stuck with this calculation.

I have already calculated the concentration of the standardised EDTA.

And then I've found out the moles of EDTA needed to form a complex with Ca2+. and as there is a 1:1 ratio between Ca2+ and edta, it's also the same number of moles for Ca2+.

So here's the bit where I am stuck.

My tutor said to take into consideration the dilution factor. which is 10 ml milk sample/ total volume of solution
 and we need to find the mass of calcium per 100 ml.

I've got the answer needed but there's a big gap in my calculation method.

so i did was divide the number of moles of Ca2+ by the dilution factor and then multiply 40g (RFM for Ca2+).

but how can i prove that the amount i got is per 100 ml? It just doesn't make sense.

Help please!!!
Thanks very much.

[Borek]

I can't see where dilution factor comes into play. If you know volume and concentration of EDTA you can calculate number of moles of calcium in the sample - and knowing your sample was 10 mL you can easily calculate mass of calcium per 100 mL. Volume of the sample after NaOH and water were added is irrelevant.