A 1000 cm3 container of ammonia (NH3) has a mass of 20.7g, it is stored at room temperature (298 K). When empty the container has a mass of 20.0 g, calculate the pressure inside the container in kPa to an appropriate number of significant figures.

A Level
  1. Using PV = nRT, make a note of the information you have, what you can calculate and what you need to find. P <-- need to find thisV = 1000 cm3n <-- can be calculated from mass = mr X mol since we know massR = 8.314 J K-1 mol-1 (from data book)T = 298 K2) convert 1000 cm3 to m3 (SI units)1000/ (100)3 divide by 100 for cm --> m conversionneed to do this 3x since volume has 3 dimensions1000/ (100)3 = 10-3 m3
    3) n (number of moles) = mass/ mr = (20.7g-20.0g)/14 g mol-1 = 0.05 mol4) now we have everything we need in SI unitsP <-- need to find thisV = 10-3 m3n = 0.05 molR = 8.314 J K-1 mol-1 (from data book)T = 298K
    5) P = nRT/V (rearrange equation to make P the subject)P = (0.05 mol x 8.314 J K-1 mol-1 x 298 K)/ 10-3 m3P = 123,879 Pa or 124 kPa

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