Fig. 27.1 shows three sealed containers, A, B and C, each holding the same substance (water) in a different state. In container A the molecules are arranged...

(a) Identify the state of matter in each container. [3]

• A is solid (ice): particles in a regular pattern, vibrating in fixed positions. [1]
• B is liquid (water): particles close together but free to move past each other. [1]
• C is gas (steam / water vapour): particles far apart, moving rapidly in all directions. [1]

(b) Describe the arrangement and movement of particles in container B. [2]

The particles are close together but not arranged in a regular pattern (they are disordered). [1]

They move randomly and can slide past each other, which is why liquids flow and take the shape of their container. [1]

(c) Calculate the density of the substance in container A. [2]

\(\rho = \frac{m}{V} = \frac{460}{500}\) [1]

\(\rho = 0.92 \text{ g/cm}^3\) [1]

This is the density of ice, which is less than that of liquid water (1.0 g/cm³). Ice is one of the rare substances whose solid form is less dense than its liquid form.

(d) Calculate the density of the substance in container C. [2]

\(\rho = \frac{m}{V} = \frac{0.46}{760}\) [1]

\(\rho = 6.1 \times 10^{-4} \text{ g/cm}^3\) (or 0.00061 g/cm³) [1]

This is about 1600 times less dense than liquid water, reflecting the very large spacing between gas particles.

(e) Explain why the density in container B is greater than the density in container A, even though both hold the same mass. [2]

In ice (A), the water molecules form an open crystalline structure with relatively large gaps between molecules. In liquid water (B), the molecules are closer together because the regular open structure has collapsed. [1]

Since both containers hold the same mass (460 g) but the liquid occupies a smaller volume (460 cm³ at 1.0 g/cm³) than the ice (500 cm³), the liquid has a higher density: the same mass in a smaller volume gives a higher density. [1]