In a similar experiment, a student needs a 0.50 M KOH solution (MM = 56.11 g/mol). The student only has a 50.00 mL volumetric flask. How much KOH should be added before the flask is filled with water?

0.50M KOH = mols KOH/L solution

0.50 M KOH x 0.050 L = ? mols.
Then mols = grams/molar mass. You know mols and molar mass, solve for grams.

28.055

To determine how much KOH should be added to the volumetric flask, we need to use the concept of molarity.

Molarity (M) is defined as the number of moles of solute (KOH) per liter of solution. Given that the desired molarity is 0.50 M, we can use the following formula to calculate the moles of KOH needed:

Moles of KOH = Molarity (M) × Volume of solution (L)

First, we need to convert the given volume of the volumetric flask (50.00 mL) to liters:

Volume of solution (L) = Volume of flask (mL) ÷ 1000

Plugging in the values:

Volume of solution (L) = 50.00 mL ÷ 1000 = 0.0500 L

Now we can calculate the moles of KOH needed:

Moles of KOH = 0.50 M × 0.0500 L = 0.025 mol

The molar mass of KOH is given as 56.11 g/mol, so we can convert the moles of KOH to grams using the formula:

Mass (g) = Moles × Molar mass

Plugging in the values:

Mass (g) = 0.025 mol × 56.11 g/mol = 1.40 g

Therefore, the student should add 1.40 grams of KOH to the volumetric flask before filling it with water to obtain a 0.50 M KOH solution.