Question

Experiment "preparation and standardization of NaOH solution"

What is the purpose of an indicator soltion?

What does standardization mean? why does the NaOH solution have to be standardized???

Calculae ho many grams of solid NaOH are needed to prepare 500mL NaOH solution with a concentration of 0.4M (show work)

Answer 1

purpose of an indicator

to know the end point of the reaction little amount of substance is added it is called indicator . indicator having different colors in different conditions . in acidic medium one color and basic medium another color. so from the change in color of indicator we can know exact end point of the reaction

standardization mean

while preparing solution the concentration may be changed based on the compound is taken. suppose if you want to prepare 1 M NaOH solution we need to dissolve 40 g of NaOH in 1 litre of water.   after solution prepared we thought that it is 1M. but in reality the concetration may not be 1 M. in that case we have to check out whether it is 1M or not . this solution is titrating with another compound we get exact value of molarity . this process is called standardization.

NaOH is not prmary standard . NaOH is hygroscopic in nature it catches water vapur from atmopshere . mass is not correct value of NaOH and volume chanege molarity also chaneg. so the concentration is not correct . so we need to standardized NaOH before using NaOH for titration.

problem :

molarity = 0.4 M

volume = 500 ml = 0.5L

molarity = moles / volume

0.4 = moles / 0.5

moles = 0.4 x 0.5 = 0.2

moles = mass / molar mass

0.2 = mass / 40

mass = 8 g

NaOH mass = 8 g needed