Pearson Practice Test- Chemistry Question

[gabbybpm]

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Hi guys,

As some of you realized, Pearson Practice Tests have updated to included the new 2014-2015 standards. One of the questions that I took on a less recent update of the chem section now has a different answer.

Pearson 2: Chem #43

What compound is formed by the reaction of n-propyl bromide (CH3 CH2 CH2 Br) with aqueous sodium hydroxide (NaOH)?

Previously the answer was noted as B. (CH3 CH2 CH2 O- Na+). Reaction proceeds via Sn2, blah blah blah. I wrote it down in my notebooks and was certain I didn't misread it

Now the answer is A. (CH3 CH2 CH2 OH), with the same explanation: proceeds via Sn2 but now adding on the hydroxide ion.

Could someone explain? Or are they both correct? Thanks!

 

[jcpull850]

Leaving Group Leaves and -Nucl comes in to replace it, the carbocation accepts the electrons from the -Nucl

 

[Minokim2512]

You might have been mistaken this with a carboxylic acid rxn where one of the byproducts is too basic therefore pull an electron off the product. Eg:
CH3COOCH3 + NaOH --> CH3COO- +Na + CH3OH

CH3O- is a basic anion and cannot coexist with the acidic product (CH3COOH) therefore it "pulls" off the proton.
In the case of question 43, Na+Br-, the byproduct, is not an acid or a base so the answer is A. Br- won't pull off the proton.

I think the Pearsons made a mistake before the update cause I remember that question giving me headaches.

Orgo is my favourite subject 🙂 However, you could confirm this with your prof or tutor.

 

[Shiloh1990]

i would say that is a substitution reaction , and you would end up with alcohol and a salt

 

[gabbybpm]

thanks all!

good luck to everyone taking the pcat next week (myself included) !!!

 

[moneyman244]

Pearson Practice Test 4(third one).... Thought I did decent on it, but I missed over 20 questions, by far the most I've ever missed-also the toughest of the 3 practice tests in my opinion. Hoping someone will tell me that the 3rd practice test just asks more in-depth, tougher questions opposed to the actual pcat. Please tell me so..

 

[Minokim2512]

Pearson Practice Test 4(third one).... Thought I did decent on it, but I missed over 20 questions, by far the most I've ever missed-also the toughest of the 3 practice tests in my opinion. Hoping someone will tell me that the 3rd practice test just asks more in-depth, tougher questions opposed to the actual pcat. Please tell me so..

You missed >20 items for the whole test or just one subtest? I thought the bio section was very trivial and in depth to the point that it was obscure. That could be due to my lack of bio background, the chem section was ok, maths wasn't so bad but I tanked the RC portion 10-30% 🙁 For VA, I pray and hope for the best, haha. My composite comes out to be 65-85 for test 4 but 80-90 for the other 2.
Upon doing some reading, I've found that most people say that it is by far the hardest out of the three tests and is either at the same level or a bit tougher than the real thing.

 

[moneyman244]

You missed >20 items for the whole test or just one subtest? I thought the bio section was very trivial and in depth to the point that it was obscure. That could be due to my lack of bio background, the chem section was ok, maths wasn't so bad but I tanked the RC portion 10-30% 🙁 For VA, I pray and hope for the best, haha. My composite comes out to be 65-85 for test 4 but 80-90 for the other 2.
Upon doing some reading, I've found that most people say that it is by far the hardest out of the three tests and is either at the same level or a bit tougher than the real thing.

Biology subtest, I feel unprepared if that's the same difficulty as the actual PCAT.

 

[Minokim2512]

Me too, I don't have any bio courses under my belt so I've been self studying really hard and hope for the best next week. 🙂