Concentration of Solutions

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Homework Statement


You are given a 77.0% solution of sulfuric acid, H2SO4. What is the molality of this solution? The density of the H2SO4 solution is 1.303 g/mL.


Homework Equations





The Attempt at a Solution


I know I divide 77.0 by 100, and then I have no idea from there.
 

Answers and Replies

  • #2
symbolipoint
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Molality means the number of moles of solute in one kilogram of SOLVENT.

Express your percentage concentration as a fraction or ratio, using a numerator and a denominator. You are given the density of solution, and you may need the the molecular weight of H2SO4. Your targe result is to be in moles of H2SO4 per kilogram of water. You should obviously understand that 77.0% means [tex]\frac{77}{100}[/tex].
 
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Molality means moles solute over kg solvent but it did not say the solution was aqueous, so do not assume the solvent is water. Assume 77g in 100g solution. 100g-77g=23g solvent. Convert to kg solvent. Last step would be to convert the 77g sulfuric acid to moles using the molecular weight from the periodic table. If you need to convert to Molarity also, that's where the density conversion factor will be needed.
 

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