A solution of NaOH has a molality of 107 molkg and a density

A solution of NaOH has a molality of 10.7 mol/kg and a density of 1.33 g/mL. Find

a) molality of solute particles
b) mass fraction OH-
c) %(w/v) of NAOH

Solution

1) a solution containg x moles of solute per kg of solvent , it is called x molal solution.

the given solution contain 10.7 moles of NaOH per kg solvent. so mole number is 10.7 and the molality of solute particles is 10.7.

2) MOLE NUMBER OF NaOH IS 10.7

mole number of Na⁺ is 10.7

mole number of OH^- is 10.7

mole fraction of OH^- = 10.7/(10.7+10.7)

=1/2

=0.5

or another way is  

mass of OH^- = 10.7*GMW

=10.7*17

=181.9

MASS OF Na⁺ IS =10.7*GMW

=10.7*23

=246.1

MASS FRACTION OF OH^- = 181.9/428

=0.425

3) molality = [W/GME] *1000/V

10.7 = W/40

W = 428 grams

428 gr present in kg slovent, similarly 4.28 gr present in 100gr of solvent

%(w/v) is 4.28 i.e 4.28 gr in 100 ml of water.