A solution contains 0.400 g of NaOH in 20.0 mL of solution.
What is its molarity
mols NaOH = grams/molar mass
M = mols/L soln.
To find the molarity (M) of a solution, you need to know the moles of solute and the volume of the solution.
The moles of solute can be calculated using the formula:
Moles = Mass / Molar mass
Given that the mass of NaOH is 0.400 g and its molar mass is 40.00 g/mol (sodium: 22.99 g/mol, oxygen: 15.99 g/mol, hydrogen: 1.01 g/mol):
Moles = 0.400 g / 40.00 g/mol
= 0.010 mol
The volume of the solution is given as 20.0 mL. However, molarity is expressed in liters (L), so we need to convert the volume to liters:
Volume = 20.0 mL = 20.0 mL * 1 L / 1000 mL
= 0.020 L
Now that we have the moles and volume, we can calculate the molarity:
Molarity (M) = Moles / Volume
= 0.010 mol / 0.020 L
= 0.500 M
Therefore, the molarity of the solution is 0.500 M.