Suppose you have 173.00 g of naturally occurring Uranium (a) How many moles of u
ID: 557828 • Letter: S
Question
Suppose you have 173.00 g of naturally occurring Uranium (a) How many moles of uranium do you have? The fraction of these atoms of each isotope is also listed. How many moles of 238U and 235U do you have? Ignore 234u n(U)= 0.7268 n(235) = 0.0052 n(238)= 0.7268 (b) Find the decay rate for each of the two isotopes, in inverse Gyr Gyr Gyr1 235 = 0.989 238 = 0.155 (c) The Earth is approximately 4.54 Gyr old. Based on this number, determine the number of moles of 235U and 238U in your sample when the Earth was born no(235) = no(238) = 0.4456 1.45 (d) Determine the fractional abundance of 235U and 238U at this time. Continue to ignore 234u f(235) = Your response differs from the correct answer by more than 10%. Double check your calculations, 96 f(238) =1 Your res Enter a number the correct answer by more than 10%. Double check your calculations. %Explanation / Answer
Ans. From #a, moles of 235U at present time = 0.0052 mol
moles of 238U at present time = 0.7268 mol
# Now,
Mass of 235U at present time = moles x molar mass
= 0.0052 mol x (235.044 / mol)
= 1.2222288 g
Mass of 238U at present time = 0.7268 mol x (238.0298 / mol)
= 173.00005864 g
Total mass of isotopes = Mass of 235U + Mass of 238U
= 1.2222288 g + 173.00005864 g
= 174.22228744 g
# Fractional abundance of 235U = (Mass of 235U / Total mass of isotopes
= (1.2222288 g / 174.22228744 g) x 100
= 0.70153 %
Fractional abundance of 238U = (Mass of 238U / Total mass of isotopes
= (173.00005864 g / 174.22228744 g) x 100
= 99.29847 %
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