Question

When a certain amount of octane is burnt completely, $7.04g$ of $C{O}_2$ 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)

$C_8{H}_{18}+\frac{25}{2}{O}_2\to 8C{O}_2+9H_{2}O$

Moles of $C{O}_2$ formed $=\frac{7.04}{44}$ moles

now, from equation

Moles of $H_{2}O$ formed when 8 moles of $C{O}_2$ react $=9$

Moles of $H_{2}O$ formed when $\frac{7.04}{44}$ moles of $C{O}_2$ react

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

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

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

$=3.24g$