i have two questions about stoichiometry. i don\'t know how to solve them. pleas

Question

i have two questions about stoichiometry. i don't know how to solve them. please be my angel :] (i do need to see how you solve the questions.(theprocess)) 1) what is the mass(grams) of hygrogen in 50.0g ofglucose? 2) oxygen has 3 naturally occurring isotopes. use the info.given to determine the average atomic mass     of oxygen.          16       O 99.759%    15.995amu
            17                O 0.037%      16.995amu
          18      O      ?                 ? i have two questions about stoichiometry. i don't know how to solve them. please be my angel :] (i do need to see how you solve the questions.(theprocess)) 1) what is the mass(grams) of hygrogen in 50.0g ofglucose? 2) oxygen has 3 naturally occurring isotopes. use the info.given to determine the average atomic mass     of oxygen.          16       O 99.759%    15.995amu
            17                O 0.037%      16.995amu
          18      O      ?                 ?

Explanation / Answer

for glucose. C6H12O6. You need to findthe percent mass. the molar mass of glucose is 180.16 g/mol. the molar mass of the 12 hydrogens is 1.00794*12=12.0953g/mol. divide and times by one hundred to get the percentmass. 12.0953/180.16 *100=6.71% times that by the weight of the same to find the mas in gramsof hydrogen .0671*50=3.36g. For the second one, are you trying to find the value of thelasst oxygen or the average atomic mass. I will assume thatit is the second. the value of O18 is .204% and 17.999amu To find the average times the percent by the weight in amu andadd them together. 15.995*.99759+16.995*.00037+.00204*17.999=15.999 amu Which is the same value on the periodic table.

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