AP Chemistry Test FRQ: Balancing Equations

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SUMMARY

The discussion focuses on the challenges faced by students in balancing chemical equations for the AP Chemistry test, specifically regarding the reaction of sodium with water. The correct balanced equation is 2Na + 2H2O --> 2Na+ + 2OH- + H2, highlighting the importance of balancing both atoms and charges. The initial response incorrectly included H+ instead of H2, demonstrating a common misunderstanding in distinguishing between diatomic hydrogen and hydrogen ions. Additionally, the discussion touches on the relevance of solubility rules in determining whether to combine species or keep them as separate ions.

PREREQUISITES
  • Understanding of stoichiometric coefficients in chemical reactions
  • Knowledge of balancing chemical equations, including charge balance
  • Familiarity with diatomic molecules, specifically hydrogen (H2)
  • Basic principles of solubility rules in aqueous solutions
NEXT STEPS
  • Study the principles of balancing redox reactions in aqueous solutions
  • Learn about solubility rules and their application in chemical reactions
  • Practice with AP Chemistry exam questions focusing on balancing equations
  • Review the concept of ionic versus molecular compounds in chemical reactions
USEFUL FOR

High school students preparing for the AP Chemistry exam, educators teaching chemical reaction balancing, and anyone looking to improve their understanding of stoichiometry and reaction types.

cadillac
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I have no idea how to do the balanced equations portion of the FR. I know how to balance equations using stoichiometric coefficients, but not the particular type of "balanced equations" on the AP test.

For example: "a small piece of sodium is placed in distilled water"

my initial thinking:
Na + H2O --> NaOH + H+

but they have as the right answer:
2Na + 2H2O --> 2Na+ + 2OH- + H2

Why is my answer wrong? (I have the right species and my answer is balanced...)
Also, I have no idea when to combine certain species, or keep them separate as ions--do solubility rules account for this?


Any ideas?
 
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Nevermind, I asked a friend of mine, and got it resolved... But if anyone has any tips for these unique reaction questions, I would really appreciate it!
 
You didn't have a orrect species and your reaction was not balanced. H+ is not the same as H2 and not only atoms must be balanced - charge must be balanced too.

And free hydrogen is diatomic. You were close.
 

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