The partial pressure of water vapor in air at 19 ° C was 1.1 kPa. Find the relative humidity.

The relative humidity is:
φ = (P / P0) * 100%, where, P – water vapor pressure at t = 19 ºС (Р = 1.1 kPa = 1100 Pa), Р – saturated steam pressure at t = 19 ºС (according to the saturated pressure table steam of water, at t = 19 ºС the pressure of saturated steam will be Р = 2198 Pa).
Let’s calculate the relative humidity:
φ = (P / P0) * 100% = (1100/2198) * 100% = 0.5 * 100% = 50%.
Answer. The relative humidity is 50%.