A salt crystal has a mass of 0.12 mg. How many NaCl formula units does it contain?

1 Answer
Trevor Ryan. · Stefan V.
Dec 22, 2015

#1.2xx10^(18)#

Explanation:

First, find the number of moles of sodium chloride in the #"0.12 mg"# by using the formula moles = mass/molar mass.

#therefore n=m/(Mr)=(0.12/1000"g")/((23+35.5)"g/mol")=2.051 * 10^(-6)# #"moles"#

But, #"1 mol"# contains an Avagadro number of particles, ie #6.022xx10^23# particles.

Therefore by ratio and proportion, #2.051 * 10^(-6)# #"mol"# will contain #1.2xx10^18# particles of #"NaCl"#.

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