Calculating the Formula of a Hydrated Compound

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SUMMARY

The discussion centers on calculating the value of x in the hydrated compound sodium carbonate (Na2CO3.xH2O) using titration data. A sample of 3.5 g of sodium carbonate was dissolved and titrated with 0.1 mol/dm³ hydrochloric acid (HCl), requiring 24.5 cm³ of acid for neutralization. The moles of Na2CO3 were calculated to be 0.01225 mol, leading to a calculated molar mass of 286 g/mol for Na2CO3.xH2O. The established molar mass of anhydrous Na2CO3 is 106 g/mol, indicating that the difference in mass corresponds to the water of hydration, which is essential for determining the value of x.

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  • Understanding of titration techniques and calculations
  • Knowledge of molar mass and its significance in chemical compounds
  • Familiarity with stoichiometry and mole ratios in chemical reactions
  • Basic skills in solving algebraic equations related to chemistry
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  • Calculate the molar mass of water (H2O) to determine the value of x
  • Review stoichiometric calculations in acid-base reactions
  • Explore the concept of hydration in ionic compounds
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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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