Chia-Ching S. answered • 10/14/15

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New York University STEM Specialist

1. Refer to the periodic table. The mass of 1 Mole of any element is the same as the atomic mass in grams. For example, the mass of 1 mole of Br would be 79.904 and the mass of 1 mole of H

_{2}would be 1.008 * 2 = 2.016. Try the other two by yourself!2. This problem is about dissociation. Let's recall that cations are have positive charge and anions have negative charge.

When KCl dissociates, it forms K

^{+}and Cl^{-}. So when 1 mole of KCl dissociates, it will produce 1 mole of cation and 1 mole of anion.When Na

_{2}SO_{4}dissociates, it will produce 2Na^{+}and SO4^{-2}. 1 Mole of Na_{2}SO_{4}would produce 2 moles of Na^{+}^{ }and 1 mole of SO_{4}. So when you have 2 moles of Na_{2}SO_{4}you'd get 4 moles of Na^{+}and 2 moles of SO_{4}. Which is 4 moles of cations and 2 moles of anions. Again, give the other two a shot yourself.23. The atomic weight of an element is the sum of the the mass of each isotope multiplied by the naturally occurring frequency.

Since there are only two naturally occurring isotopes. If one isotope occurs x of the time, then the other must occur (1 - x) of the time.

When you put it into the equation, it becomes 63.546 = 62.9298x + (1 - x) * 64.9278. Now you just solve for x to find the percentage.