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LilyRaines
Contributor

USNCO Exam Annotations: Comments and corrections

Here you can share with our editor and volunteers any comments, suggestions, or corrections you have after reviewing the annotated solutions shared on the USNCO Exams Page.

Please start your comment with the exam and year you are referencing - i.e. Local 2020, National 2019.

4 Replies
AndrewYe
New Contributor

Re: USNCO Exam Annotations: Comments and corrections

For question 50 on the 2017 national Part I exam, the exam annotations indicate that for part (B) the molecule whose Lewis structure is shown is C2H4, when the problem states that the comparison is between C2H6 and B2H6. The annotations give the correct answer, it's just that the different Lewis structure compared to the test answer might confuse some people. 

Dr_Chen
New Contributor

Re: USNCO Exam Annotations: Comments and corrections

Well received, thank you for pointing it out!

 

Dr. Chen

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Dr_Chen
New Contributor

Re: USNCO Exam Annotations: Comments and corrections

A few typos were found in national 2020 annotation by a reader as follows, thanks!

I noticed a couple of minor mistakes in the annotated solutions for National 2020.
 
Q24: It could just be that the author didn't balance the equation, but the dissociation equation for Ag2SO4 is missing a coefficient of 2 in front of Ag+. 
 
Q28: The solution says that ka = 0.00411, but 0.0114/2.79 = 0.00409.
 
Q29: This is very minor, but this equation is missing an open bracket around the second A.
 
Q30: Just a wording thing. The word should be "consistent"/"inconsistent" not "constant"/"inconstant" with regards to which of I and II are inconsistent with the mechanism. 

 

 
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Dr_Chen
New Contributor

Re: USNCO Exam Annotations: Comments and corrections

typo in 2019 national from reader, thank you!

Hi Dr. Chen, I see a typo in 2019 National #6. The volume of acid should be 45 + 50 + 55 = 150 so the molarity should be .0967 M. The solutions had 45 + 50 + 55 = 145, which isn't a big deal but it is a typo

 

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