   # Two general chemistry students working together in the lab weigh out 0.832 g of CaCl 2 · 2 H 2 O into a crucible. After heating the sample for a short time and allowing the crucible to cool, the students determine that the sample has a mass of 0.739 g. They then do a quick calculation. On the basis of this calculation, what should they do next? (a) Congratulate themselves on a job well done. (b) Assume the bottle of CaCl 2 · 2 H 2 O was mislabeled; it actually contained something different. (c) Heat the crucible again, and then reweigh it. ### Chemistry & Chemical Reactivity

9th Edition
John C. Kotz + 3 others
Publisher: Cengage Learning
ISBN: 9781133949640

#### Solutions

Chapter
Section ### Chemistry & Chemical Reactivity

9th Edition
John C. Kotz + 3 others
Publisher: Cengage Learning
ISBN: 9781133949640
Chapter 2, Problem 161IL
Textbook Problem
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## Two general chemistry students working together in the lab weigh out 0.832 g of CaCl2 · 2 H2O into a crucible. After heating the sample for a short time and allowing the crucible to cool, the students determine that the sample has a mass of 0.739 g. They then do a quick calculation. On the basis of this calculation, what should they do next?(a) Congratulate themselves on a job well done.(b) Assume the bottle of CaCl2 · 2 H2O was mislabeled; it actually contained something different.(c) Heat the crucible again, and then reweigh it.

Interpretation Introduction

Interpretation: The procedure has to be done for the given experiment from the given data’s of CaCl2.2H2O has to be identified from the given options.

Concept introduction:

• Conversion formula for mass of a molecule and number moles,

Numberofmoles=MassingramsMolarmass

• Molar mass of a molecule can be calculated from its molecular formula by taking the sum of atomic masses of all the elements present in it.

### Explanation of Solution

Given,

The mass of hydrated sample CaCl2.2H2O is 0.832g.

The mass of sample after heating is 0.739g.

Therefore,

The mass of water molecules driven off in the sample is 0.832g0.739g=0.093g

Equation for finding number moles from mass of a molecule and molar mass is,

Numberofmoles=MassingramsMolarmass

Therefore,

The number of moles of water molecule driven off from the sample is,

Numberofmoles=0.093g18g=0.00516mol

The number of moles of CaCl2.2H2O in sample is,

Numberofmoles=0.832g147

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