The difference in the rates of reaction of large lumps and of small lumps of magnesium depends on the surface area to volume ratios of the lumps.
Figure 1 shows a cube of magnesium.
a.[3]
Calculate the surface area to volume ratio of the cube in Figure 1. Give your answer as the simplest whole number ratio in the form surface area:volume\text{surface area} : \text{volume}surface area:volume.
b.[2]
A larger cube of magnesium has side lengths of 1.8 cm.
Describe how the surface area to volume ratio of this larger cube differs from that of the cube shown in Figure 1.