Dear All,
I'm doing a dilution calculation based on the following information.
Initial concentration of HMD (aq) 90% (wt). Final concentration of HMD 40% wt.
I've followed the following steps to calculate the volume of water required for dilution.
1. Calculate the molarity of HMD at 90% wt concentration
Molarity = (10*conc%(wt)*density) / molar mass
HMD molar mass 116.207 g / mol
HMD density 860 kg / m3 @ 90% and 60 degC
HMD 90 % conc wt
Molarity = 6.66 M (mol / litre)
2. Calculate the amount of HMD required to make 90% conc wt.
HMD required = molarity * molar mass * volume (litre) = 774 g
3. Calculate the molarity of HMD at 40% wt concentration
Using the same density as step 1
Molarity = 2.96 M (mol / litre)
4. Calculate volume of water required
C1*V1 = C2*V2
V1 = 1 litre
C1 = 90%
C2 = 40%
V2 = 2.25 litres
Volume of water required 1.25 litres
Different approach, repeat step 3 and 4.
3a. Calculate the molarity of HMD at 40% wt concentration
Now using HMD density 923.6 kg / m3 @ 40% wt conc and 60 degC
Molarity = 3.18 M (mol / litre)
4a. Calculate volume of water required
M1*V1 = M2*V2
M1 = 6.66 M
M2 = 3.18 M
V1 = 1 litre
V2 = 2.1 litres
Volume of water required 1.1 litres
If I use the density of HMD at 860 kg /m3 in step 4a and the molarity of step 3 i.e 2.96 M, the calculated volume of water required is 1.25 litres, i.e. the same as step 4.
I'm not sure why the answers are different for working out the amount of water required. Obviously i'm doing something wrong.
Can someone shed some light on this?
Thanks,
Imran
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