Chemistry

1. What is the molefraction of MgCl2 in a solution that is 11.04% by massMgCl2(aq)?The molar mass of MgCl2 is 95.21 g/mol.

In 100 g of the solution:
No. of moles of MgCl2 = 100 x 11.04% / 95.21 = 0.1160 mol
No. of moles of H2O = 100 x (1 - 11.04%) / (1.008x2 + 16.00) =4.9378 mol

Mole fraction of MgCl2 = 0.1160/(0.1160 + 4.9378) = 0.02295


2. When 27.0 g of an unknown metal at 88.4 °C isplaced in 115 g H2O at 21.0 °C, the final temperature of the wateris 23.7 °C. What is the specific heat capacity of the metal? The specific heatcapacity of water is 4.184 J/g•K.

Let c = Specific heat capacity of the metal

Heat released by the metal = Heat absorbed by water
27.0 x c x (88.4 - 23.7) = 115 x 4.184 x (23.7 - 21.0)
Specific heat capacity of the metal, c = 0.7437 J/g•K


3.Bromine has two naturally occurring isotopes. Theaverage mass of bromine is 79.904 u. If 50.54% ofbromine is found as bromine-79 (78.9183 u), what is the mass of the otherisotope?

Let m = Mass of the other isotope

78.9138 x 50.54% + m x (1 - 50.54%) = 79.904
Mass of the other isotope, m = 80.9158