Question

The arsenic content of an agricultural insecticide was reported as $28\%$ $A{s}_2{O}_5$ . What is the percentage of arsenic in this preparation ?

• A. $16\%$
• B. $18\%$
• C. $15\%$
• D. $20\%$

Answer 1

Answer: (B)

There is $28\%$ $A{s}_2{O}_5$ in an insecticide. It means $28g$
$A{s}_2{O}_5$ in $100g$ insecticide.
Molar mass of $A{s}_2{O}_5=(2\times 75)+(5\times 16)=230g$
$230gA{s}_2{O}_5$ contains $=150gAs$
$28gA{s}_2{O}_6$ contains
$=\frac{150\times 28}{230}$
$=1826gAs$
$18.26gAs$ is present in $100g$ insecticide so it is
$18.26\%\approx 18\%$