The Nature and Conceptual Basis
Of Modern Chemistry
1. Iodine (I) and flourine (F) form a series of binary compounds with the following compositions:
Compound Mass % I Mass % F
1 86.979 13.021
2 69.007 30.993
3 57.191 42.809
4 48.829 51.171
(a) Compute in each case the mass of flourine that combines with 1.000 g of iodine.
To find the mass of flourine that reacts with 1.000 g of ioding, the percentage mass of iodine for each compound is divided by the percentage mass of flourine for that compound.
Compound Mass of Flourine (mI/mF)
1 86.979 / 13.021 = 0.1497 g
2 69.007 / 30.993 = 0.449 g
3 57.191 / 42.809 = 0.7495 g
4 48.829 / 51.171 = 1.048 g
(b) By figuring out small whole-number ratios among the four answers in part (a), show that these compounds satisfy the law of multiple proportions.
The ratio of mass percentage of flourine with respect to iodine was found to be 0.1497, 0.449, 0.7495, and 1.048, for compounds 1, 2, 3, and 4, respectfully. The small whole-number ratios were then found by dividing all of the calculated ratios by the smallest one.
Cmpd whole-number ratios Compound Formula
1 0.1497 / 0.1497 = 1.00 IF
2 0.449 / 0.1497 = 3.00 IF3
3 0.7495 / 0.1497 = 5.00 IF5
4 1.048 / 0.1497 = 7.00 IF7
These satisfy the law of multiple proportions by the fact that all of the whole-number ratios are are actually whole numbers.
16. The last "missing" element from the first six periods was promethium, which was finally discovered in 1947 among the fission products of uranium. Determine (a) the ratio of number of neutrons in a 145Pm nucleus to the number of protons and (b) the number of electrons in a single Pm atom.
(a) The number of protons and neutrons in the promethium atom is 145. Promethiums's atomic number is 61. To find the number of neutrons we would have to find the difference of the atomic mass and the atomic number. That is found to be 145 - 61 = 84. The ratio would then be the number of neutrons over the number of protons.
ratio = 84
(b) The number of electrons in a single atom of promethium would be equivalent to the number of protons. Therefore there are 61 electrons in a single promethium atom.