How do you determine the formula weight of "Na"_2"CO"_3" and "Ca"_3("PO"_4)_2"?

1 Answer
Meave60
Jun 30, 2017

See the explanation.

Explanation:

To determine the formula weight of a substance, multiply each element's subscript by its atomic weight on the periodic table, then add the result. Reminder: no subscript is understood to be 1.

Formula weight of "Na"_2"CO"_3":

(2xx22.990 "u Na")+(1xx12.011 "u C")+(3xx15.999 "u O")="105.998 u Na"_2"CO"_3",

where "u" is the symbol for unified mass unit.

Formula weight of "Ca"_3"(PO"_4)"_2:

(3xx40.078 "u Ca")+(2xx30.974 "u P")+(8xx15.999 "u O")="310.174 u Ca"_3"(PO"_4)"_2

If you need molar masses, replace "u" with grams/mole, or g/mol.

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