Calculating the Formula of a Hydrated Compound

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Discussion Overview

The discussion revolves around calculating the formula of a hydrated compound, specifically sodium carbonate in its hydrated form, Na2CO3.xH2O. Participants are addressing a homework problem involving titration data to determine the value of x in the hydrated compound.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • The initial post outlines a method for calculating the number of moles of sodium carbonate based on titration results with hydrochloric acid.
  • One participant questions the calculated molar mass of Na2CO3.xH2O, asking for the molar mass of anhydrous Na2CO3 and the implications of the difference in values.
  • Another participant confirms the molar mass of anhydrous Na2CO3 as 106 g/mol and seeks clarification on the correctness of the initial method used.
  • A later reply suggests that the initial calculations were performed correctly but encourages further exploration of the questions posed about the molar mass.

Areas of Agreement / Disagreement

Participants generally agree that the calculations have been performed correctly up to a point, but there is no consensus on the implications of the molar mass difference or the next steps in the calculation process.

Contextual Notes

There are unresolved questions regarding the significance of the calculated molar mass and how it relates to the hydrated compound. The discussion does not clarify the assumptions made in the calculations or the definitions of the terms used.

Who May Find This Useful

This discussion may be useful for students working on similar chemistry problems involving hydrated compounds and titration calculations, as well as those interested in the nuances of molar mass calculations.

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Homework Statement



Sodium carbonate exists in hydrated form, Na2CO3.xH2O, in the solid state. 3.5 g of a sodium carbonate sample was dissolved in water and the volume made up to 250 cm3. 25.0 cm3 of this solution was titrated against 0.1 moldm-3 HCl and 24.5 cm3 of the acid were required. Calculate the value of x given the equation:

Na2CO3 + 2HCl --> 2NaCl + CO2 + H2O

Homework Equations



NO. of Moles = Conc. x volume/1000

The Attempt at a Solution


I have attempted this question in this way,
Moles of HCI = 0.1 x 24.5 / 1000 = 0.00245
Then looking at the molar ratio, I see 1:2 ratio of Sodium carbonate and HCI.
So, Moles of Na2CO3, is 0.00245/2 = 0.001225 moles in 25 cm3
Then I did the NO. of moles for Na2CO3 in 250cm3 so 250cm3/25cm3 = 10 which is the multiplier, then i did 10 x 0.001225 = 0.01225 mol
I did the Molar Mass of Na2CO3 which is 3.5/0.01225 = 285.7142.. which rounds to 286.
I assumed the Mr of Na2CO3.xH2O is 286, as the mark scheme assumed that
I don't know what to do after this, can someone please help me, as this is Homework!
Thank you!
 
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Many ways to skin that cat, but if you got to the molar mass... What is the molar mass of anhydrous Na2CO3? Why is your number larger? By how much? What does the difference man?
 
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Borek said:
Many ways to skin that cat, but if you got to the molar mass... What is the molar mass of anhydrous Na2CO3? Why is your number larger? By how much? What does the difference man?
The molar mass of Na2CO3 is 106..
Is my method right, or have I done it differently/wrong?
 
Try to answer my other questions. You did everything OK so far.
 

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