A salt crystal has a mass of 0.15mg. How many NaCl formula units does it contains?

1 Answer
anor277
Nov 4, 2016

We need (i) the molar quantity of #"sodium chloride"#........

Explanation:

#"Number of moles"# #=# #"Mass"/"Molar mass"#

#=# #(0.15xx10^-3*g)/(58.44*g*mol^-1)# #=# #"?? moles"#

And (ii) we need the number of sodium chloride units. Now it is a fact that #"Avogadro's number, "N_A# #-=# #6.022xx10^23*mol^-1#

And thus we mulitply the number of moles by #"Avogadro's number"# to give the number of sodium chloride formula units:

#(0.15xx10^-3*g)/(58.44*g*mol^-1)xx6.022xx10^23*mol^-1#, and we get the answer as a number, as required.

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