Question on Hydrates and Reactions

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Discussion Overview

The discussion centers on the appropriate representation of copper (II) chloride dihydrate in a chemical reaction involving aluminum. Participants explore whether to include the dihydrate in the formula when it is dissolved in water, considering implications for writing the reaction equation and ionic equation.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions whether to write copper (II) chloride as CuCl2.2H2O or simply as CuCl2 when it is dissolved in water, expressing confusion over varying conventions found in different sources.
  • Another participant suggests that the water of hydration adds mass to the molecule and should be included if measuring dry weight, but acknowledges that it can be ignored in certain contexts.
  • A third participant clarifies that their focus is on weighing the copper retrieved from the reaction to find the concentration of the original solution, raising further questions about how to represent the dihydrate in the reaction equation.
  • A participant shares a link to a webpage that discusses the reaction of aluminum with cupric chloride, although its relevance is uncertain.
  • One participant concludes that there is no simple answer to the question, indicating that the representation of the reaction depends on the specific context and what one aims to demonstrate.

Areas of Agreement / Disagreement

Participants express differing views on whether to include the dihydrate in the chemical formula when writing the reaction. There is no consensus on a definitive approach, as opinions vary based on context and intended application.

Contextual Notes

The discussion highlights the ambiguity surrounding the representation of hydrates in chemical equations, with participants noting that different contexts may warrant different approaches. The implications of including or excluding the dihydrate in the formula are not fully resolved.

rosyposy
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Hey! I am currently working on a project where I have to react copper (II) chloride dihydrate (dissolved in water) and aluminum. When writing the equation and the ionic equation for this, would you include the dihydrate in the formula since it’s dissolved in water and no longer in its crystalline form or would you still write it as CuCl2.2H2O, can you also provide an explanation for the correct way to write since I am really confused as some sites write it with the H2O and some don’t. Thank you!
 
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The water of hydration - .2H20 - adds mass to the molecule. So, if are going to get a dry weight to assay some reaction in a solution you have to include it. Is that what you are asking? You can write the reaction ignoring the extra mass but I do not see any immediate benefit other than teaching an introduction.
Practical aspect is what you have dictates what you do:
Copper chloride appears as a yellowish-brown powder (the anhydrous form) or a green crystalline solid (the dihydrate). The green stuff is usually what you have. If have the brown stuff you would measure the mass of copper chloride with no water to worry about.
 
Last edited:
Hey, so I am only weighing the copper retrieved from the reaction to find the concentration of the original solution using stoichiometry, but I also need to write the formula for the whole reaction with states so I was just asking if I would write the copper (II) chloride dihydrate as a dihydrate since it is dissolved in water and I’m not sure if you are supposed to write dihydrates as aqueous since they exist in crystalline form.
 
There is no simple yes/no answer to your question.

A lot depends and what you want to show. Every way of writing the reaction has its own applications and makes sense in different contexts.
 

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