Question

Write the formula of Aluminum sulfate? Calculate its formula unit mass.

Answer 1

To write the chemical formula of a compound , follow the given steps:

1. Write the symbols of elements followed by their valency below them.
2. Enclose the polyatomic ions in bracket with valency in their subscript.
3. Using the criss-cross method, assign the second valency to the first element and first valency to the second element.
4. Simplify the formula by dividing valencies with common factor.
5. Write the complete formula with valency in their subscript.

To write the formula of Aluminum sulfate-

Element - Aluminum Sulfate

Symbol- Al ${\mathrm{SO}}_2$

Valency- +3 -2

Formula- ${\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3$

To calculate the formula unit mass

$$\begin{gathered} =2\times massofAl+3\times massofsulfate \\ =2\times 27+3\times 96 \\ =342g/mol \end{gathered}$$