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I need help to approach these problems

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In this question, osmotic pressure and pH is given.
This information is used in two ways
First using osmotic  pressure (in atm) and R value and temperature (K) we will calculate molarity(M) of weak base (B)
pi(osmotic pressure) = MRT
so M = pi /RT
Now this can be taken as initial concentration of weak base.
pH of solution can be used to calculate pOH
pH +pOH = 14
pOH = 14-pH
Use this information to get [OH-]
[OH-] = 10^-pOH
Now we can make equilibrium system of this weak B
RICE table
R   B + H2O <----->   BH⁺ + OH^-
I     M Calculated above)     0                           0
C    - X                                 +X                        +X
E     M-X                               X                          X
K_b  =  [BH⁺] . [OH^-]/
K_b =   X²/  (M-X)

You know X = [OH-] and you now M so you can calculate K_b

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In this question, you want to calculate amount of Cl₂ in 1L of water.You can calculate molarity(M) of solution by using K_a value and RICE table.
pH = 1.19
[H⁺] = 10 ^-1.19



RICE table
R   Cl₂(aq) + H₂O (l)<----->   H⁺(aq) + Cl^- (aq) + HOCl(aq)
I     M Calculated above)     0                                  0              0              0
C    - X                                 +X                                 +X            +X              +X   
E     M-X                               X                                    X               X                 X

K_a =   X³/  (M-X)

You know X = [H⁺] and you now K_a so you can calculate M

Convert M into moles and moles into grams.
You know M = moles/Volume in L

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pH of solution can be used to calculate pOH
pH +pOH = 14
pOH = 14-pH
Use this information to get [OH-]
[OH-] = 10^-pOH
Now we can make equilibrium system of this weakNH₃
RICE table
R  NH₃ + H₂O <----->  NH₄⁺ + OH-
I     M Calculated above)     0                           0
C    - X                                 +X                        +X
E     M-X                               X                          X
K_b  =  1.8 * 10^-5
K_b =   X2/  (M-X)

You know X = [OH-] and you now calculate  M
From molarity calculate moles of NH₃ in 4L
Use ideal gas law
V = nRT/P to calculate volume of NH₃ bubbled in 4L of water.