Question

Bromine gas reacts with fluorine gas to give a low boiling liquid. A sample of this liquid is vaporized at 42.0 °C into a flask with a volume of 0.2525 L. The atmospheric pressure is 0.9557 atm. Upon cooling to room temperature, the flask contains 1.632 g of the compound. Calculate the formula weight of the compound. (12 pts.) b. Based on the above answer is the compound bromine trifluoride, bromine pentafluoride or bromine heptafluoride? Show some work. (3 pts.)

Answer 1

a) Bra gas reacts with F₂ gas giving a low boiling liquid. This liquid is vaporized at 42.000 = (273+42)K= 315 K P producing Vapour. for the sake of simplicity, we can assume that the Vapour behaves ideally at 315k. A The volume of the flosk containing the vapour is also the volume of the vapour (v) = 0.2525L The pressure exerted by the vapour (P) = 0.9557atm. 'upon cooling to room temperature, the flask contains 1.632 g of liquid. From the mass conversation Law, we can say that 1.632 g of vapour is consensed to 1.632 g of liquid upon cooling. & weight of the vapour present in the flask at 315k temperature (W)= 1.632 g. ideal gas equation for nain more of gas. PV = nRT or PV = W.RT :IM= formula I weight of -, putting the values of (molecule. . PV ? ".. Pv, w, R,T., R20,0822-atmmoral - 1.632 gx 0.0824-atm.moik'* 3156 on, M2- 0.9557 atm x 0.2525 • NOW, M. WRT

M= 174.69 g molt Formula weight of the compound is 174. 69 g moi! (6). The molecular weight of bromine trifluoride - (atomic wt. of Br) + (3x atomic wt. of F) : 79. 9 + (3x19) gmot = 136.9 g mot similarly elecular weight of bromine pentafluoride (Br. Fs). = 79.9+(5x19) gmot = 174.9 gmail The molecular weight of bromine heptafluoride (.Br Fq). = 79.9+(7x19) gmail = 212.9 gmoi! Here, the molecular wt. of Br FG resembles to the formula Wto of the liquid produced. - The liquid (produced is Br F5, (Bromine pentafluoride).