Writing Ionic Formulas, Given the ions

  • Thread starter BrainMan
  • Start date
  • #1
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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.
 

Answers and Replies

  • #2
113
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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
 
  • #3
Borek
Mentor
28,530
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In other words: CrO42- means (CrO4)2-.
 
  • #4
279
2
OK I get it now. Thanks!
 

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