We need to prepare 500 cm³ of 2.5 mol/L of NaOH
First, lets transform cm³ into Liters:
1 cm³ ---- 0.001 liters
500 cm³ ----- x
x = 0.5 L
So, let's use the formula:
Molarity = Moles of solute /Volume of solution
Molarity = 2.5 mol/L
Volume of solution : 0.5 L
Moles of solute = x
2.5 = x/0.5
x = 2.5 x 0.5
x = 1.25 moles of NaOH
We need to find how many grams of NaOH. For this we need to know the molar mass of NaOH: 40 g/mol
So:
40 g of NaOH ---- 1 mol of NaOH
x g of NaOH ----- 1.25 moles of NaOH
x = 50 g of NaOH
Answer: It's required 50 g of NaOH to prepare 500 cm³ of 2.5 mol/L NaOH solution.