Question

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, what is the molar concentration of NaCl in the new solution

Answer 1

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 :

$M=\dfrac{\text{Total number of moles}}{\text{Volume in liters}}$

Now , 1000 ml of NaCl contains 2.5 moles of NaCl .

So , 15 ml of NaCl contains :

$n=\dfrac{15\times 2.5}{1000}\\\\n=3.75\times 10^{-2}\ moles$

New , volume V = 15 + 985 = 1000 ml = 1 L .

So , putting value of n and V in above equation :

$M=\dfrac{3.75\times 10^{-2}}{1}\ M\\\\M=0.0375\ M$

Therefore ,  the molar concentration of NaCl in the new solution is 0.0375 M .

Hence , this is the required solution .