Question

What is the mass percent of oxygen in $A{l}_2(S{O}_4{)}_3\cdot 18H_{2}O?$

[The molar mass of this substance is 666.43 g/mol]

• A. 9.6
• B. 128.8
• C. 143.2
• D. 72

Answer 1

The correct option is D 72

There are 30 oxygen atoms present in 1 mol of $A{l}_2(S{O}_4{)}_3.18H_{2}O$

Mass of oxygen in the compound = $30\times 16=480$

Mass % of oxygen $=\frac{480}{666.43}\times 100$ $=72\%$

Hence, option $D$ is correct.