Question

We know that liquid form of water is denser than the solid form because of hydrogen bonds (if I'm not mistaken). Also HF has hydrogen bonds and I try to find the density of solid and liquid form of it but couldn't find the solid form density. Could you please explain the reason of this density difference if I'm wrong about thinking that H bonds cause this. Please also explain it for HF whether that density difference valid or not for it. Thanks?

Answer 1

Yes, you are absolutely right!

The density of water (liquid at 25 ^oC) = 1 g/mL, whereas the density of ice (solid at 0 ^oC) = 0.9167 g/mL

i.e. The liquid form of water (water) is denser than the solid form (ice). This is due to the greater no. of hydrogen bonds that exist in water than in ice.

The density of HF (gas at 25 ^oC) = 1.15 g/mL

The density of HF (liquid at 19.5 ^oC) = 0.99 g/mL

The density of HF (solid at -125 ^oC) = 1.663 g/mL

Here, the opposite is the case, i.e. the solid form of HF is denser than the liquid form. This is due to the fact that the HF molecules will come closer, as a result, they form more no. of hydrogen bonds in the solid form at -125 ^oC; whereas the liquid water molecules are more separated, as a result, they form less no. of hydrogen bonds in the solid form at 0 ^oC.