What mass of f2 is needed to produce 120. g of pf3 if the reaction has a 78.1% yield?

write the equation for the reaction

that is 6 F2 +P4 =4 PF3

find the theoretical mass that is

let the theoretical yield be represented by y

theoretical yield = 78.1/100 = 120/y

y= 153.6 grams

find the number of moles of  PF3

moles = mass/molar mass

= 153.6/87.97 =1.746 moles

by use of mole ratio between  F2 :PF3 which is 6:4 the moles of F2 is therefore= 1.746 x 6/4 = 2.62 moles

mass = moles x molar mass

= 1.746 moles x38 g/mol = 99.6 grams

law of conservation of matter

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).