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

Answer 1

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.