Question

The equation for the burning of octane is:

$2{\mathrm{C}}_8{\mathrm{H}}_{18}+25{\mathrm{O}}_2\to 16{\mathrm{CO}}_2+18{\mathrm{H}}_2\mathrm{O}$

(a) How many moles of carbon dioxide are produced when one mole of octane burns?

(b) What volume, at STP, is occupied by the number of moles determined in (a)?

(c) If the relative molecular mass of carbon dioxide is 44, what is the mass of carbon dioxide produced by burning two moles of octane?

(d) What is the empirical formula of octane?

Answer 1

(a)

Step 1: Write the chemical equation of the reaction:

$2{\mathrm{C}}_8{\mathrm{H}}_{18}+25{\mathrm{O}}_2\to 16{\mathrm{CO}}_2+18{\mathrm{H}}_2\mathrm{O}$

According to the given equation,

Step 2: Find the number of moles

When 2 moles of octane burns in a sufficient amount of oxygen gas then 16 moles of ${\mathrm{CO}}_2$ are produced.

Therefore, 1 mole of octane burns gives = 16/2 = 8 mole of ${\mathrm{CO}}_2$

Step 3:

Hence, 8 moles of ${\mathrm{CO}}_2$ will be produced.

(b)

1 mole of ${\mathrm{CO}}_2$ occupies volume= 22.4L

So, 8 moles will occupy volume= 8 x 22.4 = 179.2 L

Hence, 179.2 L volume is occupied by the 8 moles of ${\mathrm{CO}}_2$.

(c)

Step 1: 1 mole of ${\mathrm{CO}}_2$ has mass = 44 g

So, 16 moles will have mass = 44 x 16 = 704 g

Hence, the mass of carbon dioxide is 704 g.

(d) What is the empirical formula of octane?

Sol. The empirical formula of ethane is ${\mathrm{C}}_4{\mathrm{H}}_9$.