Writing Ionic Formulas, Given the ions

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Discussion Overview

The discussion revolves around writing the ionic formula for potassium chromate, specifically focusing on the relationship between the charges of the ions involved (K+ and CrO42-). Participants explore different methods for determining the correct formula, including charge balancing and ratio analysis.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant attempts to find the formula by establishing a ratio based on the charges of the ions, suggesting that it takes 8 K+ ions to balance the charge of one CrO42- ion, leading to a proposed ratio of K8:CrO4.
  • Another participant corrects this approach by clarifying that the total charge of CrO42- is -2, not implying that each oxygen carries a double negative charge.
  • A third participant rephrases the notation of CrO42- to emphasize its total charge, suggesting it can be interpreted as (CrO4)2-.
  • The initial poster expresses understanding after receiving clarification on the charge balancing method.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial method proposed for determining the formula, but there is agreement on the correct interpretation of the charge of CrO42-.

Contextual Notes

The discussion highlights a misunderstanding regarding the charge distribution within the chromate ion, which may affect the approach to finding the correct ionic formula.

BrainMan
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Homework Statement


Potassium chromate is an important compound of chromium. It is composed of K+
and CrO42-. Write the formula of the compound.

Homework Equations


positive charge + negative charge = 0


The Attempt at a Solution


I know how to do this problem by cross switching the charges but I want to know how to do it by finding the ratio. So what I tried to do was say that it takes 8 K to equal the negative charge of the CrO4 so the ration is 8:4. That means K8 = CrO4. Then I reduced and got K2 = CrO. The correct answer is K2 = CrO4.
 
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You seem to think that each oxygen has a double negative charge. This is not true. The TOTAL charge on CrO42- is -2. So, consider K+ as A and CrO42- as B and now try to balance the charges assuming charge on B is -2.

Hope this helps! :)
-Adithyan
 
In other words: CrO42- means (CrO4)2-.
 
OK I get it now. Thanks!
 

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