Myrcene is a naturally occurring compound found in the leaves of bay trees - VCE - SSCE Chemistry - Question 4 - 2009 - Paper 1

To calculate the amount of hydrogen gas reacting, we can use the ideal gas law. The formula is:

$n = \frac{PV}{RT}$

Where:

• $P$ = pressure in kPa = 105.0 kPa
• $V$ = volume in liters = 510 mL = 0.510 L
• $R$ = ideal gas constant = 8.31 L·kPa/(K·mol)
• $T$ = temperature in Kelvin = 20.0°C + 273 = 293 K

Substituting the values:

$n = \frac{105.0 \times 0.510}{8.31 \times 293} = 0.0220 \text{ mol}$

The molar mass of C₁₀H₂₂ can be calculated as follows:

• Carbon (C): 12.01 g/mol
• Hydrogen (H): 1.008 g/mol

Thus, the molar mass of C₁₀H₂₂ is:

$10 \times 12.01 + 22 \times 1.008 = 142.28 \text{ g/mol}$

Now, to find the mass produced, we use the number of moles of C₁₀H₂₂ produced:

Mass = Moles × Molar Mass

Given that 0.0220 moles of C₁₀H₂₂ were produced:

$\text{Mass} = 0.0220 \times 142.28 = 3.14 \text{ g}$

Each molecule of myrcene has three double bonds. This is because when myrcene undergoes hydrogenation, three molecules of H₂ are added, saturating its three double bonds to convert it into C₁₀H₂₂.