Potassium permanganate (KMnO4) solutions are used for the determination of iron in samples of unknown concentration. As a laboratory assistant, you are supposed to prepare 700. mL of a 0.200 M KMnO4 solution. What mass of KMnO4, in grams, do you need?

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To calculate the mass of KMnO4 needed, we can use the formula:

Mass (g) = molarity (mol/L) × volume (L) × molar mass (g/mol)

First, let's calculate the volume of the solution in liters:

Volume (L) = 700 mL × (1 L / 1000 mL) = 0.7 L

Next, we can substitute the values into the formula and calculate the mass:

Mass (g) = 0.200 mol/L × 0.7 L × molar mass of KMnO4

The molar mass of KMnO4 can be calculated using the periodic table:

Molar mass of KMnO4 = (1 × atomic mass of K) + (1 × atomic mass of Mn) + (4 × atomic mass of O)

Atomic mass of K = 39.10 g/mol
Atomic mass of Mn = 54.94 g/mol
Atomic mass of O = 16.00 g/mol

Molar mass of KMnO4 = (1 × 39.10 g/mol) + (1 × 54.94 g/mol) + (4 × 16.00 g/mol) = 158.04 g/mol

Now, we can substitute this value into the formula:

Mass (g) = 0.200 mol/L × 0.7 L × 158.04 g/mol

Calculating this expression gives us the mass of KMnO4 needed in grams.