1. A naturally occuring element consists of two isotopes. Calculate the percent

Question

1. A naturally occuring element consists of two isotopes. Calculate the percent abundances for the two isotopes, if it's average atomic mass is 107.87. Isotope 1: 106.91amu; Isotope 2: 108.90amu

2. Write the balanced chemical equation for the following unbalanced chemical reaction: C3H8 + O2 ---> CO2 + H2O. How do I figure this out?

3. Acceleration die to gravity of a free-falling object is 9.8 m/s2. Express this in mm/ms2. Answer is 9.8 x 10^-3, but not sure how to get that.

4. Specific gravity of concentrated sulfuric at 25 °C is 1.84. If density of water at 25 °C is 0.995g/mL, what is the density of concentrated sulfuric acid at the same temperature? I thought the answer was 1.85g/mL but that is incorrect. The correct answer is 1.83g/mL but I'm not sure how to get this answer.

Explanation / Answer

1) Given that average atomic mass is 107.87. Isotope 1: 106.91amu; Isotope 2: 108.90amu

        Let x = % abundance of Isotope 1

             100-x = % abundance of Isotope 2

         Then,

                  [(x) (106.91) + (100-x) (108.9)] / 100 = 107.87

                   106.91 x - 108.9 x + 10890 = 10787

                  On solving,

                          x = 51.75

                       Then,

                      100-x = 48.25

         Therfore, % abundance of Isotope 1 = 51.75 %

                    % abundance of Isotope 2 = 48.25 %

2)            CxHy +   (x+y/2) O2 ----------> x CO2 + (y/2) H2O

Then,

        C3H8 + 5O2 ---> 3CO2 + 4H2O

           3 C atoms = 3 CO2

          8 H atoms = (8/2) H2O = 4 H2O

3)   Given that

       Acceleration due to gravity of a free-falling object = 9.8 m/s2

                    1 m = 10^3 mm

Hence,

      Acceleration due to gravity of a free-falling object = 9.8 x 10^3 mm/s2

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