Help with 2 gen chem questions please

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This discussion focuses on two chemistry problems related to isotopes and weight percent calculations. The first problem involves determining the second isotope of a mythical element Z, given that 48.16% exists as 109Z with an atomic mass of 108.971 u. The solution reveals that the other isotope is 107Z with an atomic mass of 106.9 u. The second problem requires calculating the weight percent of fluorine in a soluble metal fluoride sample, using the reaction of calcium nitrate to precipitate fluorine as CaF2. The discussion emphasizes the importance of understanding equivalents and average atomic mass calculations.

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amar314
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Hello everyone, first time poster here.
I'm hoping someone can help me with these two questions, they're part of a study guide for my upcoming chem 1 exam.

Mythical element Z has an avg atomic mass of 107.9 u and is known to have only two naturally occurring isotopes. If 48.16% of Z exists as 109Z (108.971 u) what's the other isotope and its atomic mass?

a) 107 Z ; 106.9 u
b) 108 Z ; 107.9 u
c) 110 Z ; 109.9 u
d) 111 Z ; 111.1 u
e) 110 Z ; 110.2 u


and this one:

Fluorine can be precipitated out of solution with the use of calcium to create CaF2 (s). The use of 85.75mL of 0.3510 M Ca(NO3)2 precipitated out all of the fluorine present in a 4.585g sample of a soluble metal fluoride dissolved in water. Calculate the weight percent of fluorine in the sample.

a) 24.95%
b) 11.44%
c) 56.48%
d) 10.10%
e) 12.58%

I attempted both a few times but with no success, I'm just not sure how to start for either, especially the wording in the second problem is very confusing for me.

Any help is super appreciated, thank you so much!
 
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Hello Amar314,

The questions are actually simple. For the first one, the questions says that Z's average atomic mass is 107.9u and 48.16% of Z exists as 109Z (108.971 u); which means, 100-48.16 = 51.84% is made up of the other one.

So, going by the formula for Mean/Average, we get

Average Mass = (P')*[Mass of one] + (P'')*[Mass of the other]



2) For the second question,

Ca(NO3)2 + MFx (x=unknown) ------> CaF2

(Hint:No. of equivalents of Ca+2 = Number of equivalents of F- )

Try to find out the N factor.

Equivalents = Moles*Nfactor

NB: If you are not aware of equivalent weight and stuff, I suggest you to read :

http://www4.ncsu.edu/~franzen/public_html/CH201/lecture/Lecture_19.pdf

Hope this helps!

ADI.
 
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Adithyan said:
Hello Amar314,

The questions are actually simple. For the first one, the questions says that Z's average atomic mass is 107.9u and 48.16% of Z exists as 109Z (108.971 u); which means, 100-48.16 = 51.84% is made up of the other one.

So, going by the formula for Mean/Average, we get

Average Mass = (P')*[Mass of one] + (P'')*[Mass of the other]



2) For the second question,

Ca(NO3)2 + MFx (x=unknown) ------> CaF2

(Hint:No. of equivalents of Ca+2 = Number of equivalents of F- )

Try to find out the N factor.

Equivalents = Moles*Nfactor

NB: If you are not aware of equivalent weight and stuff, I suggest you to read :

http://www4.ncsu.edu/~franzen/public_html/CH201/lecture/Lecture_19.pdf

Hope this helps!

ADI.

Thank you so much! I really appreciate your help!

:)
 
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