What Is the Mass Percent Concentration of CaCl₂ in the Solution?

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Discussion Overview

The discussion revolves around calculating the mass percent concentration of CaCl₂ in an aqueous solution, using vapor pressure data and Raoult's law. The context is primarily homework-related, focusing on the application of theoretical concepts to a specific problem.

Discussion Character

  • Homework-related, Mathematical reasoning, Technical explanation

Main Points Raised

  • One participant presents a homework problem involving the vapor pressure of a CaCl₂ solution and pure water, seeking to find the mass percent concentration.
  • Another participant introduces Raoult's law as a relevant concept for solving the problem.
  • Participants discuss the equation for vapor pressure, indicating a need to solve for mole fractions.
  • There is mention of the relationship between the vapor pressures and the need to account for the dissociation of CaCl₂ in solution.
  • One participant expresses uncertainty about how to proceed with the calculations involving molecular weights and total mass of the solution.

Areas of Agreement / Disagreement

Participants generally agree on the relevance of Raoult's law and the need to consider the dissociation of CaCl₂, but there is no consensus on the specific steps to solve the problem or the calculations involved.

Contextual Notes

Participants have not fully resolved the mathematical steps necessary to calculate the mass percent concentration, and there are dependencies on definitions and assumptions regarding vapor pressures and molecular weights.

blueskadoo42
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% by mass concentration

Homework Statement



An aqueous CaCL2 solution has a vapor pressure of 80.8mmHG at 50 degree C . The vapor pressure of pure water at this temperature is 92.6 mmHG .

What is the concentration of CaCl2 in mass percent?

Homework Equations



% by mass = mass solute/mass solution.

The Attempt at a Solution



I tried converting the pressure into moles then dividing the moles of CaCl2 by the total moles. I am pretty stuck..

Thanks
Skadoo!
 
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Do you know Raoult's law?
 


yeah i do. p = pa*xa+pb*xb correct? not sure how to solve for the x's...
 


xa+xb=1
 


alright knowing this, i use 'a' as the vap press for cacl2 and 'b' for vap press of water? then use molecular weights to to solve for total mass of solution..?
 


Sounds OK. Don't forget CaCl2 is dissociated.
 


ah right, almost forgot. Ill give this a run thanks.
 

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