Question

prepare 200mL of a 6% w/v NaOH solution from stock NaOH (FW 40)

Answer 1

formula weight(FW) of NaOH is 40 gm/mole

6% w/v NaOH solution means 6 gm NaOH remains in 100 ml soltion.

so 200 ml solution contains = 6 * 2 = 12 gm NaOH.

6 gm NaOH = mass / molar mass = 6.00/40 = 0.15 mole

concetration of NaOH in 6% solution = 0.15*1000 / 100 = 1.5 M

If stock solution of NaOH concentration is 2.0 M

then using simple dilution law,

V1*S1 (stock soltion)= V2S2 (after dilution)

V1 * 2.0 = 200 * 1.5

V1 = 150 ml.

so volume of stock solution take 150 ml and mixed with adding (200-150) = 50 ml water.

otherwise,

200 ml water take in which 6*2 = 12 gm NaOH solid is added to prepare 200 ml 6% NaOH solution.