A 1.59-g sample of a metal chloride, #MCl_2#, is dissolved in water and treated with excess aqueous silver nitrate. The silver chloride that formed weighed 3.60 g. How do you calculate the molar mass of M?

Question

15863 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2016-12-12T15:53:20

#"Molar mass of metal chloride"# #=# #126.2*g*mol^-1#

We need a stoichiometric equation:

#MCl_2(aq) + 2AgNO_3(aq) rarr M(NO_3)_2(aq) + 2AgCl(s)darr#

#"Moles of silver chloride:"#
#=# #(3.60*g)/(143.32*g*mol^-1)=2.51xx10^-2*mol.#

Given the stoichiometry of the precipitation reaction, there were #(2.51xx10^-2*mol)/2# #=# #1.26xx10^-2*mol# #MCl_2#.

So we have a molar quantity, and a given mass, and the #"molecular mass"# is the #"quotient"#, #"mass"/"molar quantity"#

#=(1.59*g)/(1.26xx10^-2*mol)# #=# #126.2*g*mol^-1#.