Calculate the mass of sodium hydroxide needed to prepare 500 mL of a 0.10 M solution. I'm pretty sure the answer is 2 grams, but how do I get to that?

mols NaOH = L x M = 0.500 L x 0.10 M = 0.05 mols NaOH.

Remember mols = grams/molar mass
Rearrange to obtain
grams = mols x molar mass = 0.05 mols x (40.0 g/1 mol) = 0.0500 x 40.0 = 2.0 g

To calculate the mass of sodium hydroxide (NaOH) needed to prepare 500 mL of a 0.10 M solution, we can follow these steps:

Step 1: Determine the molar mass of NaOH.
The molar mass of NaOH can be calculated by adding up the atomic masses of its constituent elements: sodium (Na), oxygen (O), and hydrogen (H).
- The atomic mass of sodium (Na) is approximately 22.99 g/mol.
- The atomic mass of oxygen (O) is approximately 16.00 g/mol.
- The atomic mass of hydrogen (H) is approximately 1.01 g/mol.

So, the molar mass of NaOH can be calculated as follows:
Molar mass (NaOH) = (1 * Na) + (1 * O) + (1 * H) = 22.99 g/mol + 16.00 g/mol + 1.01 g/mol = 40.00 g/mol.

Step 2: Convert the volume of the solution from mL to L.
Since we have 500 mL, we need to convert it to liters by dividing by 1000.
500 mL ÷ 1000 = 0.500 L.

Step 3: Calculate the number of moles needed.
We have a solution with a concentration of 0.10 M (moles per liter), and we want to calculate the number of moles needed for 0.500 L of the solution.
Number of moles = concentration (M) × volume (L)
Number of moles = 0.10 mol/L × 0.500 L = 0.050 mol.

Step 4: Calculate the mass of NaOH using the number of moles and molar mass.
Mass = number of moles × molar mass
Mass = 0.050 mol × 40.00 g/mol = 2.00 grams.

Therefore, the mass of sodium hydroxide needed to prepare 500 mL of a 0.10 M solution is 2.00 grams, which confirms your initial guess.