Question

When a certain amount of octane is burnt completely, $7.04 g$ of $CO _{2}$ is formed. What mass of $H _{2} O$ is formed simultaneously?

• A. 3.24 g
• B. 6.68 g
• C. 6.48 g
• D. 6.16 g

Answer 1

Answer: (A)

$C _{8} H _{18}+\frac{25}{2} O _{2} \rightarrow 8 CO _{2}+9 H _{2} O$

Moles of $CO _{2}$ formed $=\frac{7.04}{44}$ moles

now, from equation

Moles of $H _{2} O$ formed when 8 moles of $CO _{2}$ react $=9$

Moles of $H _{2} O$ formed when $\frac{7.04}{44}$ moles of $CO _{2}$ react

$=\frac{9}{8} \times \frac{7.04}{44}$

$=\frac{63.36}{8 \times 44}=0.18$ moles

wt. of $H_{2}O$ formed $= 0.18 \times 18$

$=3.24\,g$