3 (a) Carbon dioxide is one of the gases in the Earth's atmosphere - Edexcel - GCSE Chemistry Combined Science - Question 3 - 2019 - Paper 1

Factor 1: Natural processes such as photosynthesis and respiration impact carbon dioxide levels. Plants absorb CO₂ during photosynthesis, reducing its concentration, while respiration from animals returns CO₂ to the atmosphere.

Factor 2: Human activities, including the burning of fossil fuels and deforestation, increase carbon dioxide concentrations. These activities release significant amounts of CO₂, contributing to variations in atmospheric levels.

Carbon dioxide has a low boiling point due to the weak intermolecular forces between its molecules. As a simple molecular compound, CO₂ experiences only van der Waals forces, which are easily overcome with relatively low energy, resulting in its low boiling point of -78.5°C.

First, we find the number of moles of CO₂ in 0.11 g:

$ext{Number of moles} = \frac{0.11 ext{ g}}{44 ext{ g/mol}} = 0.0025 ext{ moles}$

Next, using Avogadro's number to find the number of molecules:

$ext{Number of molecules} = 0.0025 ext{ moles} \times 6.02 \times 10^{23} ext{ molecules/mole} = 1.51 \times 10^{21} ext{ molecules}$

Rounding to two significant figures, the answer is 1.5 × 10²¹ molecules.