Given :
On a shelf sits a bottle of NaCl solutions with a molar concentration of 2.50 M and a total volume of 300 mL. If 15.0 mL of the solution is added to 985 mL of pure water .
To Find :
The molar concentration of NaCl in the new solution.
Solution :
Molarity M is given by :
[tex]M=\dfrac{\text{Total number of moles}}{\text{Volume in liters}}[/tex]
Now , 1000 ml of NaCl contains 2.5 moles of NaCl .
So , 15 ml of NaCl contains :
[tex]n=\dfrac{15\times 2.5}{1000}\\\\n=3.75\times 10^{-2}\ moles[/tex]
New , volume V = 15 + 985 = 1000 ml = 1 L .
So , putting value of n and V in above equation :
[tex]M=\dfrac{3.75\times 10^{-2}}{1}\ M\\\\M=0.0375\ M[/tex]
Therefore , the molar concentration of NaCl in the new solution is 0.0375 M .
Hence , this is the required solution .
