Respuesta :
17.7 g of potassium sulfite ([tex]K_2SO_3[/tex]) are required to dissolve in 872 g of water to make a 0.128M solution.
What is molality?
It is a measure of the concentration of a solute in a solution in terms of the amount of substance in a specified amount of mass of the solvent
You're looking for the mass of potassium sulfite, [tex]K_2SO_3[/tex], needed to make a 0.128 m, or 0.128 molal, solution.
Now, molality is used to express the concentration of a solution in terms of how many moles of solute it contains per kilogram of solvent.
This means that in order to find a solution's molality, you need to know
the number of moles of solute and the mass of the solvent expressed in kilograms.
In your case, you already know the mass of the solvent in grams, so the very first thing to do here is to convert it to kilograms.
872 g = 0. 872 Kg.
Now, a 0.128 m solution contains 0.128 moles of solute per kilogram of solvent. Since your sample contains 0.872 kg of solvent, it follows that it will contain 0.1116 moles [tex]K_2SO_3[/tex].
All you have to do now is use the molar mass of potassium sulfite to figure out how many grams would contain that many moles:
0.1116 moles x 158.26 g =17.7 g
Hence, 17.7 g of potassium sulfite ([tex]K_2SO_3[/tex]) are required to dissolve in 872 g of water to make a 0.128M solution.
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