Question

What is the formula of potassium phosphate in $\dfrac{{grams}}{{mole}}$

Answer 1

Hint: The formula mass of a substance is the sum of the average atomic masses of each atom represented in the chemical formula and is expressed in atomic mass units. The formula mass of a covalent compound is also called the molecular mass.

Complete answer:
To write the chemical formula of any compound we must follow these following steps:
Write the symbols of all the elements which form the compound.
Write valency of each element below its symbol.
Now crisscross the valencies of the elements.
Write valency of second atom as subscript of first and Write valency of first atom as subscript of second.
The molecular formula of potassium phosphate is ${K_3}P{O_4}$
The formula mass for an ionic compound is calculated in the same way as the formula mass for covalent compounds: by summing the average atomic masses of all the atoms in the compound's formula. To calculate formula mass, multiply the subscript of each element in the formula by the element's atomic weight (relative atomic mass) found on the periodic table. The unit for formula mass is either $u$ or $Da$ (Daltons).
$3(39.0983) + 30.9738 + 4(15.999) = 212.2663gmo{l^{ - 1}}$
So, the formula mass of potassium phosphate in $\dfrac{{grams}}{{mole}}$is $212.2663gmo{l^{ - 1}}$

Note:
The difference between molar mass and formula mass is that formula mass is the sum of all the atomic weights of the atoms in its empirical formula while molar mass is just the mass of one mol of a substance. Molar mass also uses the units $\dfrac{{grams}}{{mole}}$ while formula mass uses atomic mass units.