Question

Q3.It is desired to prepare 3 molal solution of NaOH. How much mass of it must be dissolved in 1500gm water?
​

Answer 1

Answer:

Molality=number of moles of solute/mass of solvent(kg)

3=  

massofsolvent

n

​  

 

mass of solvent =  

3

1000n

​  

 g

Also, number of moles=mass/molar mass

For NaOH solution, n=  

40

m

​  

 

Density of solution,ρ=1.110g/mL

Mass of 1 mL solution =1.11g=m  

solute

​  

+m  

solvent

​  

 

3

n×40+1000n

​  

=1.11

n=2.97×10  

−3

 mol

Molarity = number of moles of solute/ volume of solution(L)

M=  

0.001

2.97×10  

−3

 

​  

=2.97M

Explanation: