The problem asks to find the mass of NaOH (with molar mass BM = 40 g/mol) dissolved in 250 mL of a 0.4 M NaOH solution.

To solve this, we will use the following formula:

$Molarity (M) = \frac{{\text{{moles of solute}}}}{{\text{{volume of solution (in liters)}}}}$

Rearranging this to solve for moles of NaOH:

$\text{{moles of NaOH}} = M \times \text{{volume in liters}}$

Then, to find the mass, we use:

$\text{{mass of NaOH}} = \text{{moles of NaOH}} \times \text{{molar mass of NaOH}}$

Let's proceed with the calculations:

1. Molarity $M = 0.4 \, \text{mol/L}$
2. Volume = 250 mL = 0.25 L
3. Molar mass of NaOH $BM = 40 \, \text{g/mol}$

Now, calculate the moles of NaOH and then find the mass.

Let me calculate this for you. Given values Molarity = 0.4 # M (mol/L) Volume_Liters = 0.25 # L (250 mL = 0.25 L) Molar_Mass_NaOH = 40 # g/mol

Calculate moles of NaOH

moles_NaOH = Molarity * Volume_Liters

Calculate mass of NaOH

mass_NaOH = moles_NaOH * Molar_Mass_NaOH mass_NaOHThe mass of NaOH required to prepare 250 mL of a 0.4 M NaOH solution is 4.0 grams.

Would you like further explanation or have any questions about this solution? Here are some related questions you might find helpful:

1. How does the molarity of a solution relate to the number of moles of solute?
2. What happens when you change the volume of a solution in a molarity calculation?
3. How do you convert between grams and moles in a chemical calculation?
4. What is the role of molar mass in determining the amount of a substance in a solution?
5. How do you calculate the volume needed to prepare a solution of a given molarity?

Tip: When preparing solutions, always ensure to convert volumes into liters and use the correct units for molarity and molar mass.