Question

please help and explain. Thank you

A chemist prepares a solution of potassium permanganate (KMnO4) by measuring out 21. umol of potassium permanganate into a 400. mL volumetric flask and filling the flask to the mark with water. Calculate the concentration in mol/L of the chemist's potassium permanganate solution. Be sure your answer has the correct number of significant digits. xs ?

Answer 1

Answer:

Step 1:  Explanation:

Molarity / concentration is defined to be the number of moles of solute divided by the volume (in  liters ) of solution.

i.e Molarity = number of moles of solute / volume of solution in liters

Step 2: Conversion

The conversion factor for µmol and mol units is: 1 µmol = 10^-6 mol

Hence, 21 µmol = 21 × 10^-6 mol = 21 × 10^-6 mol

The conversion factor for mL and L units is: 1 mL = 10^-3 L

Hence, 400 mL = 400 × 10^-3 L

                          = 0.4 L

Step 3: Calculation

By using the formula

Molarity = number of moles of solute / volume of solution in liters

Molarity = ( 21 × 10^-6 mol ) / (0.4 L ) = 5.25 × 10^-5 mol / L

Hence, the concentration is 5.25 × 10^-5 mol / L