How to Adjust KNO3 Solution Preparation for Temperature Variations?

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Discussion Overview

The discussion revolves around the preparation of a 1 M KNO3 solution at a specified temperature, addressing the effects of temperature on solution volume and density. Participants explore the implications of temperature variations on molarity and the necessary adjustments for accurate solution preparation in a laboratory setting.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses uncertainty about how to approach the problem, particularly regarding the impact of temperature on the preparation of the KNO3 solution.
  • Another participant questions whether the target concentration is 1 M or 1.000 M, highlighting the importance of precision in the problem statement.
  • Concerns are raised about the volume changes of both the solvent and the volumetric flask due to temperature differences, suggesting that these factors complicate the calculation.
  • A participant claims to have solved the problem using a specific formula relating concentrations and densities at different temperatures, indicating a buoyancy correction is also necessary.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the clarity of the question or the necessary adjustments for temperature variations. There is disagreement regarding the interpretation of the target concentration and the implications of temperature on the solution preparation process.

Contextual Notes

Participants note the lack of information regarding the volume changes of the solvent and the vessel at different temperatures, which could affect the accuracy of the solution preparation.

Who May Find This Useful

This discussion may be useful for students in analytical chemistry, particularly those dealing with solution preparation and the effects of temperature on molarity and density.

tigerlili
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Homework Statement



you want to prepare 500 ml of 1 M KNO3 at 20 C, but your lab and water are 24 C. How many grams of solid KNO3 (density= 2.109 g/ml) should be dissolved in a volume of 500 ml at 24 C so that the concentration will be 1 M at 20 C? what apparent mass of KNO3 weighed in air is required?

Homework Equations



Molarity = moles solute/liters solvent

and dimensional analysis


The Attempt at a Solution



i'm really not sure what to do with this..typically i am good with this kind of question but it was kind of thrown at us, and I've never seen the temperature issue before. please help!
 
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Is that really the question? 1 M KNO3? Not 1.000 M?

Your solvent at 24C will occupy a larger volume than at 20C so there is one source of error. That said, your vessel (volumetric flask) will also change its dimensions at 24C vs at 20C that will counteract this tendency. Unless you know both the dV of the vessel and the dV of the solution over the 4C range, you don't know how to solve it analytically. But I digress...

Did the question really ask for 1 M KNO3 or 1.000 M KNO3?

And... will you use the solution at 20C or 24C?
 
it said 1.000 M KNO3. sorry for not specifying.. i was really tired when i typed it out.

i don't know either of these things that you mention. This is only my 2nd day in analytical chem, and this question was given to me as an assignment.

i also think the question is unclear.. but, obviously, there's nothing we can do about it

thanks for your help anyway!
 
i actually solved this problem

the key lies in a formula that was quite difficult to find at first, but quite simple to use afterwards

c1/d1 = c2/d2, where the different concentrations and densities are due to the temperature difference

after that, the buoyancy correction equation is used

thanks for your help anyway
 

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