FL#1 in Chem/Phy Q1

jumpinfeet
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FL#1 in Chem/Phy Q1

Postby jumpinfeet » Tue Aug 01, 2017 1:15 pm

On this first question, I am a little confused by Figure 1. I feel like it is giving me NaCl at 35 g per 100 g of H2O at 60 C. I use it to calculate and I get the wrong answer. I know that the first paragraph states that it is 3.5%, which calculates to the right answer. What is the clue to tell me to not use Figure 1? Thanks for the help!
NS_Tutor_Andrew
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Re: FL#1 in Chem/Phy Q1

Postby NS_Tutor_Andrew » Tue Aug 01, 2017 3:09 pm

Hi jumpinfeet,

Thanks for the question! Figure 1 gives you information about solubility, which corresponds to the maximum possible amount of the solute that could be dissolved before creating a saturated solution. However, the question is not asking about what the molarity of a saturated solution of NaCl and water would be, it's asking about what the actual molarity of ocean water is. This requires you to combine the density info given in the question with the info from paragraph one saying that ocean water is 3.5% NaCl by mass.

Hope this was helpful! The bigger-picture lesson here, I think, is to be super careful about whether the information you're pulling from a figure or table is precisely what you need to answer the question. This is a pretty common danger in MCAT questions, which is why my #1 piece of advice to students about figure/data interpretation is to carefully read the figure/table legends and axes in order to be absolutely sure of what the quantitative data means.
Andrew D.
Content Manager, Next Step Test Prep.
heatfan
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Re: FL#1 in Chem/Phy Q1

Postby heatfan » Sat Jun 09, 2018 4:13 pm

Hello, I just wanted to know what the significance of the 3.5 % to figure out the calculation? I missed that detail when I was trying figure out the calculation on the exam. Thanks.
NS_Tutor_Katelyn
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Re: FL#1 in Chem/Phy Q1

Postby NS_Tutor_Katelyn » Mon Jun 11, 2018 2:31 pm

heatfan wrote:Hello, I just wanted to know what the significance of the 3.5 % to figure out the calculation? I missed that detail when I was trying figure out the calculation on the exam. Thanks.


The 3.5% is necessary to determine what relative amount of the mass/density of salt water is actually due to NaCl.
Katelyn Sawyer
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