Why does 40.0 g of NaOH added to 1.00 L of water not make a 1.00 M NaOH solution

First weigh 40g NaOH in breaker and dissolve with 400 to 500 mL with purified water. Then allow to cool the solution and volume upto 1000 mL with purified water. Then standardization your Solution.

Explanation:

molarity = no. of moles of solute / 1 liter.

* one moles of sodium hydroxide = 40 gm of sodium hydroxide.

so we can said; if want prepare 1 molar NaOH solution then we need 40 gm NaOH dissolve in one liter of water so it became one 1 molar NaOH solution.