The volume of the solution is 500‌ml The molarity of the solution is 0.2M, that is 0.2molL−1 Step 1 Molar mass: Molarity =‌
‌ Amount of solute ‌
‌ Molecular mass of solute ‌
×‌
1000
‌ volume of solution(ml) ‌
The atomic mass of Na is 23g The atomic mass of O is 16g The atomic mass of H is 1g The molecular mass of NaOH is 23+16+1=40g Step 2 Amount of Sodium hydroxide present: Let the amount of solute be 'w' Therefore, Molarity =‌
‌ Amount of solute ‌
‌ Molecular mass of solute ‌
×‌
1000
‌ volume of solution(ml) ‌
That is, 0.2=‌
w
40
×‌
1000
500
0.2=‌
w
40
×2 0.2=‌
w
20
w=0.2×20 w=4g Therefore, in order to prepare 500‌ml of 0.2M‌NaOH, the mass of NaOH required is 4g.