Question

In the laboratory you are asked to make a 0.264 m sodium sulfide solution using 525 grams of water.

How many grams of sodium sulfide should you add?
grams.

I'm having a hard understanding which formula to uses in this question.

molality vs Molarity

I known that the molar mass of Na2S= 78.05

and that H20= 18.02

We are given 0.0264 mol of Na2s which is the concentration, which is what I am guessing in a mixed solution of 525 grams of H2O.

Answer 1

here 0.264m of Na₂S is used. Here, " m" is unit of molality , so we have to use equation of molality and not molarity.

molality=0 .264m

molar mass of solute( Na₂S)=78.05

mass of solvent in kg = 0.525kg

we have to find mass of solute Na2S added

we know ;

molality=(moles of solute)÷(kg of solvent)

moles of solute=( mass of solute)÷( molar mass solute) so;molality= ( mass of solute)÷ ( molar mass of solute× kg of solvent)

  mass of solute(Na₂S)=molality× molar mass of solute× kg of solvent

mass of Na₂S added= 0.264×78.05×0.525

=10.81773