Does a liquid with a pH level of 5 or below always boil under 100 degrees celsius?

Answer 1

Not True.
If the liquid is an aqueous solution with some non-volatile solute/s, the boiling point is usually raised to be more than 100C.
If the liquid is of different solvent or material, than it really depends on the material concerned.

Answer 2

Vapor pressure and boiling point have an intimate relationship. The boiling point is the temperature at which the vapor pressure of the liquid equals the external pressure. For example, because the air pressure is lower in a city far above sea level such as Denver, the boiling point of water is lower than in a sea level city such as New York. The most common unit for vapor pressure is the torr. 1 torr = 1 mm Hg (one millimeter of mercury). Most materials have very low vapor pressures. For example, water has a vapor pressure of approximately 15 torr at room temperature. But remember that vapor pressures increase with temperature; water will have a vapor pressure of 760 torr = 1 atm at its boiling point of 100 oC (212 oF). In general, the higher the vapor pressure of a material at a given temperature, the lower the boiling point. In other words, compounds with high vapor pressures are volatile, forming a high concentration of vapor above the liquid; this can sometimes pose a fire hazard.