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Reading a Mass Loss Record for a Hydrate 4 questions

Reading a Mass Loss Record for a Hydrate

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A class compares two labels for a model sodium carbonate crystal. The labels are Na2CO3·H2O and Na2CO3·10H2O. On warming in the model, water leaves the crystal structure. The remaining solid is Na2CO3. Assume the carbonate stays in the container and only water leaves.

Material or measurementValue
Initial hydrate mass14.3 g
Final dry solid mass5.30 g
Molar mass of Na2CO3106 g/mol
Molar mass of H2O18.0 g/mol

Question 1

Calculate the mass of water that left the hydrate. Show your setup.

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Question 2

Find the mole ratio of water removed to sodium carbonate remaining. Show how you used both molar masses.

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Question 3

Which conclusion about the labels is supported by that ratio?

  1. The result supports Na₂CO₃·H₂O.
  2. The result supports Na₂CO₃·10H₂O.
  3. The result supports both labels equally.
  4. The result shows no water was in the initial crystal.

Another sample is tested, but the student stops while some water is still in the crystal structure. The student treats all the final solid mass as dry Na2CO3.

Question 4

Would that procedure tend to make the estimated water-to-carbonate mole ratio too high or too low? Explain using both the water lost and final solid mass.

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