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aniked [119]
2 years ago
11

A hypothetical element consists of two isotopes of masses 86.95amu and 88.95amu with abundances of 35.5% and 64.5% respectively.

What iis the average atomic mass of this element
Chemistry
1 answer:
Art [367]2 years ago
5 0

Answer: The average atomic mass of the element = 88.242amu

Explanation:

The abundance of the first isotope is =35.5%

 Atomic mass of first isotope = 68.9257

The average atomic mass of the first isotope =86.95amu X 35.5%  =86.95amu X 0.355 =30.8725 amu

The abundance of the second isotope =64.5%

Atomic mass of the second isotope =88.95amu

The average atomic mass of second isotope =88.95amu x 64.5% = 88.95amu x 0.645= 57.37275 amu

Now the average atomic mass =30.8725 +57.37275 = 88.242amu

OR using the formulae

Average atomic mass = [mass of isotope× its abundance] + [mass of isotope× its abundance] +...[ ] / 100

{(86.95amu X 35.5 )+(88.95amu x 64.5)}/100

8,824/100

=88.24amu

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If acetic acid is the only acid that vinegar contains (ka=1.8×10−5), calculate the concentration of acetic acid in the vinegar.
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CH_{3}COOH \ \textless \ ---\ \textgreater \   H^{+} + CH_{3}COO^{-}

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                                  CH3COOH          H+           CH3COOH    
Initial  moldm^{-3}                      x           0                     0
                                                                                                                       
Change moldm^{-3}        -0.001            +0.001           +0.001
                                                                                                       
Equilibrium moldm^{-3}      x- 0.001      0.001             0.001
                                                                              

Since the k_{a} value is so small, the assumption 
[CH_{3}COOH]_{initial} = [CH_{3}COOH]_{equilibrium} can be made.

k_{a} = [tex]= 1.8*10^{-5}  =  \frac{[H^{+}][CH_{3}COO^{-}]}{[CH_{3}COOH]} =  \frac{0.001^{2}}{x}

Solve for x to get the required concentration.

note: 1.)Since you need the answer in 2SF don&t round up values in the middle of the calculation like I've done here.

         2.) The ICE (Initial, Change, Equilibrium) table may come in handy if you are new to problems of this kind

Hope this helps! 



8 0
3 years ago
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