Question

the density of 3M NaOH solution is 1.25g/ml . calculate i) amount of NaOH present in 100g of solution ii) molality of the solution iii)mole fraction of NaOH​

Answer 1

3 Molar solution means there are 3 moles of NaCl salt in 1 Liter. Molecular weight of NaCl = 58.44

Hence, there are 3×58.44 gms in 1 Litre of water.

Density =volume

mass

Mass of 1 litre of solution = 1.25 gms/ml * 1000 ml = 1, 250 gms

V = volume of water added to make the solution

175.32 gms + 1 gm /ml * V = 1, 250 gm

⟹V=1,074.68ml

So 1,074.68 ml or 1, 074.68 gms of water is mixed with 3 moles of Na Cl to make the 3 M solution.

Molality = mass of solute in number of moles / mass of solvent in kg

= 3 kg

1.07468

=2.7915 Molal

(i) Hear this out loud

100g NaOH solution has 20g NaOH

(ii) Molality of NaOH

(iii) Molarity of NaOH (atomic weight of sodium = 23, oxygen =16, density of NaOH solution =1.038g/cm3).

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