The law of multiple proportions predates the concept of a mole or molar mass. Th

Question

The law of multiple proportions predates the concept of a mole or molar mass. Thus, scientists like John Dalton could only determine the relative amounts of each type of atom in a formula, and not the exact formula. For example, Dalton could determine that there were two carbon-oxygen compounds, one with twice as much oxygen as the other. However, he did not know for sure that the formulas were CO and CO_2. Other possibilities (given what they knew at the time) could have been C_2O and C_2O_2, or CO_2 and CO_4, etc. Samples of three different compounds were analyzed and the masses of each element were determined. If you were John Dalton and had never heard of a mole, which of the following would you think were possible sets of formulas for the compounds A, B, and C, respectively? Check all that apply. NO_2, NO_8, NO_10 NO, NO_2, NO_4 NO_4, NO_10, NO_5 N_2O, N_2O_4, N_2O_5

Explanation / Answer

For compound A

number of moles of N2 = 5.6/28 = 0.2

number of moles of O2 = 3.2/32 = 0.1

Since number of moles of N2 is twice the number of moles of O2

Hence the compound will be N2O

For compound B

number of moles of N2 = 3.5/28 = 0.125

number of moles of O2 = 8/32 = 0.25

Since number of moles of N2 is half the number of moles of O2

Hence the compound will be NO2

For compound C

number of moles of N2 = 1.4/28 = 0.05

number of moles of O2 = 4/32 = 0.125

Since number of moles of O2 is 2.5 times the number of moles of N2

Hence the compound will be N2O5

Correct answer is Option D

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