Question

You need to make 150 mL of a .25 M solution of potassium chloride, KCl. How many grams of KCl do you need to dissolve in the 150 mL of solution

a.) 18.6 g
b.) 37.5 g
c.) 7.9 g
d.) 2.8 g

Answer 1

To make a 150 mL solution of 0.25 M potassium chloride (KCl), you would need approximately 2.8 g of KCl.

Step-by-step explanation:

To calculate the number of grams of KCl needed, we can start by using the formula:

Molarity (M) = moles of solute / liters of solution

Given that the molarity (M) is 0.25 M and the volume of the solution is 150 mL (which is 0.15 L), we can rearrange the equation to solve for moles of solute:

moles of solute = Molarity (M) * volume (L)

Substituting the values into the equation:

moles of solute = 0.25 M * 0.15 L = 0.0375 mol KCl

To find the grams of KCl needed, we can use the formula:

grams of solute = moles of solute * molar mass

The molar mass of KCl is the sum of the atomic masses of potassium (K) and chloride (Cl), which is 39.10 g/mol + 35.45 g/mol = 74.55 g/mol.

Substituting the values into the equation:

grams of KCl = 0.0375 mol * 74.55 g/mol = 2.79 g

Therefore, you would need approximately 2.8 g of KCl to dissolve in the 150 mL of solution.