E 27 Sixth Edition

[Dustin Shin 2I]

For the first portion of E 25, they ask for formula units? How would you find this and will this concept be in future tests?

[megansardina2G]

"Formula units" is simply a term, similar to molecules or atoms. It references to the ions in an ionic compound, whereas "molecule" refers to two or more elements that are covalently bonded. Whether the problem asks for formula units, molecules, or atoms, you will multiply the number of moles given with Avogadro's constant, 6.022 x 10^23. In this problem (E25):
0.750 mol KNO3 x 6.022 x 10^23 formula units/mol = 4.52 x 10^23 formula units

[Jonathan Pai 2I]

Formula units mean atoms for an element or molecules for a compound. Use Avocado's number to get atom units from mols. For tests, the work function in the electric photoelectric effect can be given in joules/mol, which needs to be converted to joules/atom.