The final concentration assuming the volumes are additive when a 71.0 ml portion of a 1.50 m solution is diluted to a total volume of 258 ml. a 129 ml portion of that solution is diluted by adding 149 ml of water is 0.191 M
This can be solved by using the dilution factor.
So the dilution factor for the first dilution is 71.0 ml to 258 ml
DF1=258/71=3.63
For the first solution, the dilution factor is
3.163, refers that the concentration is decreased by a factor of 3.163.
The concentration of diluted solution is
c(diluted)=1.50/3.63=0.413
Now, you take a sample of 129 mL of this diluted solution and add another 165 mL of water. So,
V(final)=129ml +149 ml=278 mL
The concentration of the 129 mL sample is equal to the concentration of the first diluted solution, i.e. 0.413 M
So,
DF2=278/129=2.155
So, the final concentration is
c(final)=0.413/2.155=0.191 M
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