AP Chemistry Test FRQ: Balancing Equations

In summary, the conversation was about balancing equations for the FR portion of the AP test. The person was unsure how to balance equations using stoichiometric coefficients, and had a specific example of placing sodium in distilled water. They initially thought the equation was Na + H2O --> NaOH + H+, but the correct answer was 2Na + 2H2O --> 2Na+ + 2OH- + H2. They were confused as to why their answer was wrong and asked for tips on balancing unique reaction questions. The other person explained that not only atoms, but also charges must be balanced and pointed out that H+ is not the same as H2. The conversation was resolved when the person asked a friend
  • #1
cadillac
10
0
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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  • #2
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!
 
  • #3
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.
 

Related to AP Chemistry Test FRQ: Balancing Equations

1. What is the purpose of balancing equations in AP Chemistry?

Balancing equations is a fundamental skill in chemistry that ensures the conservation of matter in a chemical reaction. It allows us to accurately determine the amount of reactants needed and the amount of products produced in a reaction. In AP Chemistry, balancing equations is necessary to answer free response questions and to demonstrate understanding of chemical reactions.

2. How do you balance chemical equations?

To balance a chemical equation, you must ensure that the same number of atoms of each element are present on both sides of the equation. This can be achieved by adjusting the coefficients in front of each molecule. Start by balancing the most complex molecule, then move on to the other molecules. Remember to never change the subscripts as they represent the number of atoms in a molecule.

3. What are some common mistakes to avoid when balancing equations?

One common mistake is not considering the polyatomic ions when balancing ionic compounds. Remember to treat the polyatomic ion as a single unit and balance it as such. Another mistake is changing the subscripts in a molecule, which changes the chemical formula and therefore, the identity of the substance. Only coefficients should be changed when balancing equations.

4. Is there a specific order in which elements should be balanced?

There is no specific order in which elements should be balanced. However, it is helpful to start with elements that appear in only one reactant and one product, then move on to elements that appear in multiple reactants and products. Additionally, it is important to balance elements that appear in compounds before balancing elements that appear in their elemental form.

5. Are there any tips for balancing equations more efficiently?

One tip is to use the lowest possible whole numbers for coefficients. This can often be achieved by dividing all coefficients by their greatest common factor. It is also helpful to double-check your work by counting the number of atoms of each element on both sides of the equation. Lastly, practicing balancing equations regularly will improve your speed and accuracy.

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