A chemist makes 460 mL of magnesium fluoride (MgF2) working solution by adding distilled water to 20.0 mL of a 18.8 umol/L stock solution of magnesium chloride in water. Calculate the concentration of the chemist’s working solution in umol/L. Round your answer to the 3 significant digits
To solve this problem, we need to first calculate the number of moles of magnesium chloride in the stock solution, and then calculate the concentration of the working solution.
Step 1: Calculate the number of moles of magnesium chloride in the stock solution.
We can use the formula:
moles = concentration (mol/L) x volume (L)
The concentration of the stock solution is given as 18.8 umol/L. However, we need to convert this to moles per liter by dividing by 1000:
concentration (mol/L) = 18.8 umol/L / 1000 = 0.0188 mol/L
The volume of the stock solution is given as 20.0 mL. However, we need to convert this to liters by dividing by 1000:
volume (L) = 20.0 mL / 1000 = 0.0200 L
Now we can calculate the number of moles of magnesium chloride:
moles = 0.0188 mol/L x 0.0200 L = 0.000376 mol
Step 2: Calculate the concentration of the working solution.
The volume of the working solution is given as 460 mL. However, we need to convert this to liters by dividing by 1000:
volume (L) = 460 mL / 1000 = 0.460 L
Now we can calculate the concentration using the formula:
concentration (mol/L) = moles / volume (L)
concentration = 0.000376 mol / 0.460 L = 0.000817 mol/L
Finally, we need to convert this to umol/L by multiplying by 1000:
concentration (umol/L) = 0.000817 mol/L x 1000 = 0.817 umol/L
Rounded to three significant digits, the concentration of the chemist's working solution is 0.817 umol/L.