What mass of KNO3 (MW=101) is needed to prepare 45omL of 0.250 M KNO3 in water?

How many moles do you want? That;s M x L = ?

Then mol = grams/molar mass.

Thank you

I get:

37g/200g x 100 = 18.5%

To find the mass of KNO3 needed to prepare a certain volume and concentration of a solution, you can follow these steps:

Step 1: Determine the number of moles of KNO3 needed.
The volume of the solution is given as 450 mL or 0.45 L.
The concentration is given as 0.250 M, which means there are 0.250 moles of KNO3 in one liter (or 1000 mL) of solution.
Therefore, the number of moles of KNO3 needed can be calculated using the following equation:
moles = concentration × volume
moles = 0.250 mol/L × 0.45 L
moles = 0.1125 moles

Step 2: Convert moles to grams.
The molar mass of KNO3 is given as 101 g/mol. To convert moles to grams, multiply the number of moles by the molar mass:
grams = moles × molar mass
grams = 0.1125 moles × 101 g/mol
grams = 11.3625 grams

Therefore, approximately 11.36 grams of KNO3 is needed to prepare 450 mL of a 0.250 M KNO3 solution in water.